diff --git "a/all_data/AR5/AR5.yaml" "b/all_data/AR5/AR5.yaml" new file mode 100644--- /dev/null +++ "b/all_data/AR5/AR5.yaml" @@ -0,0 +1,7897 @@ +full_paragraphs: + 1.1a: + - Atmosphere Each of the last three decades has been successively warmer at the + Earth’s surface than any preceding decade since 1850. The period from 1983 to + 2012 was very likely the warmest 30-year period of the last 800 years in the Northern + Hemisphere, where such assessment is possible and likely the warmest 30-year period + of the last 1400 years. The globally averaged combined land and ocean surface + temperature data as calculated by a linear trend show a warming of 0.85 [0.65 + to 1.06] °C20 over the period 1880 to 2012, for which multiple independently produced + datasets exist. The total increase between the average of the 1850–1900 period + and the 2003–2012 period is 0.78 [0.72 to 0.85] °C, based on the single longest + dataset available. For the longest period when calculation of regional trends + is sufficiently complete, almost the entire globe has experienced surface warming. In + addition to robust multi-decadal warming, the globally averaged surface temperature + exhibits substantial decadal and interannual variability. Due to this natural + variability, trends based on short records are very sensitive to the beginning + and end dates and do not in general reflect long-term climate trends. As one example, + the rate of warming over the past 15 years , which begins with a strong El Niño, + is smaller than the rate calculated since 1951 . Based on multiple independent + analyses of measurements, it is virtually certain that globally the troposphere + has warmed and the lower stratosphere has cooled since the mid-20th century. There + is medium confidence in the rate of change and its vertical structure in the Northern + Hemisphere extratropical troposphere. Confidence in precipitation change averaged + over global land areas since 1901 is low prior to 1951 and medium afterwards. + Averaged over the mid-latitude land areas of the Northern Hemisphere, precipitation + has likely increased since 1901 . For other latitudes area-averaged long-term + positive or negative trends have low confidence. + 1.1b: + - Ocean Ocean warming dominates the increase in energy stored in the climate system, + accounting for more than 90% of the energy accumulated between 1971 and 2010 with + only about 1% stored in the atmosphere. On a global scale, the ocean warming is + largest near the surface, and the upper 75 m warmed by 0.11 [0.09 to 0.13] °C + per decade over the period 1971 to 2010. It is virtually certain that the upper + ocean warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971. + It is likely that the ocean warmed from 700 to 2000 m from 1957 to 2009 and from + 3000 m to the bottom for the period 1992 to 2005. It is very likely that regions + of high surface salinity, where evaporation dominates, have become more saline, + while regions of low salinity, where precipitation dominates, have become fresher + since the 1950s. These regional trends in ocean salinity provide indirect evidence + for changes in evaporation and precipitation over the oceans and thus for changes + in the global water cycle. There is no observational evidence of a long-term trend + in the Atlantic Meridional Overturning Circulation. Since the beginning of the + industrial era, oceanic uptake of CO2 has resulted in acidification of the ocean; + the pH of ocean surface water has decreased by 0.1, corresponding to a 26% increase + in acidity, measured as hydrogen ion concentration. There is medium confidence + that, in parallel to warming, oxygen concentrations have decreased in coastal + waters and in the open ocean thermocline in many ocean regions since the 1960s, + with a likely expansion of tropical oxygen minimum zones in recent decades. + 1.1c: + - Atmosphere Each of the last three decades has been successively warmer at the + Earth’s surface than any preceding decade since 1850. The period from 1983 to + 2012 was very likely the warmest 30-year period of the last 800 years in the Northern + Hemisphere, where such assessment is possible and likely the warmest 30-year period + of the last 1400 years. The globally averaged combined land and ocean surface + temperature data as calculated by a linear trend show a warming of 0.85 [0.65 + to 1.06] °C20 over the period 1880 to 2012, for which multiple independently produced + datasets exist. The total increase between the average of the 1850–1900 period + and the 2003–2012 period is 0.78 [0.72 to 0.85] °C, based on the single longest + dataset available. For the longest period when calculation of regional trends + is sufficiently complete, almost the entire globe has experienced surface warming. In + addition to robust multi-decadal warming, the globally averaged surface temperature + exhibits substantial decadal and interannual variability. Due to this natural + variability, trends based on short records are very sensitive to the beginning + and end dates and do not in general reflect long-term climate trends. As one example, + the rate of warming over the past 15 years , which begins with a strong El Niño, + is smaller than the rate calculated since 1951 . Based on multiple independent + analyses of measurements, it is virtually certain that globally the troposphere + has warmed and the lower stratosphere has cooled since the mid-20th century. There + is medium confidence in the rate of change and its vertical structure in the Northern + Hemisphere extratropical troposphere. Confidence in precipitation change averaged + over global land areas since 1901 is low prior to 1951 and medium afterwards. + Averaged over the mid-latitude land areas of the Northern Hemisphere, precipitation + has likely increased since 1901 . For other latitudes area-averaged long-term + positive or negative trends have low confidence. + - Ocean Ocean warming dominates the increase in energy stored in the climate system, + accounting for more than 90% of the energy accumulated between 1971 and 2010 with + only about 1% stored in the atmosphere. On a global scale, the ocean warming is + largest near the surface, and the upper 75 m warmed by 0.11 [0.09 to 0.13] °C + per decade over the period 1971 to 2010. It is virtually certain that the upper + ocean warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971. + It is likely that the ocean warmed from 700 to 2000 m from 1957 to 2009 and from + 3000 m to the bottom for the period 1992 to 2005. It is very likely that regions + of high surface salinity, where evaporation dominates, have become more saline, + while regions of low salinity, where precipitation dominates, have become fresher + since the 1950s. These regional trends in ocean salinity provide indirect evidence + for changes in evaporation and precipitation over the oceans and thus for changes + in the global water cycle. There is no observational evidence of a long-term trend + in the Atlantic Meridional Overturning Circulation. Since the beginning of the + industrial era, oceanic uptake of CO2 has resulted in acidification of the ocean; + the pH of ocean surface water has decreased by 0.1, corresponding to a 26% increase + in acidity, measured as hydrogen ion concentration. There is medium confidence + that, in parallel to warming, oxygen concentrations have decreased in coastal + waters and in the open ocean thermocline in many ocean regions since the 1960s, + with a likely expansion of tropical oxygen minimum zones in recent decades. + 1.1d: + - Ocean Ocean warming dominates the increase in energy stored in the climate system, + accounting for more than 90% of the energy accumulated between 1971 and 2010 with + only about 1% stored in the atmosphere. On a global scale, the ocean warming is + largest near the surface, and the upper 75 m warmed by 0.11 [0.09 to 0.13] °C + per decade over the period 1971 to 2010. It is virtually certain that the upper + ocean warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971. + It is likely that the ocean warmed from 700 to 2000 m from 1957 to 2009 and from + 3000 m to the bottom for the period 1992 to 2005. It is very likely that regions + of high surface salinity, where evaporation dominates, have become more saline, + while regions of low salinity, where precipitation dominates, have become fresher + since the 1950s. These regional trends in ocean salinity provide indirect evidence + for changes in evaporation and precipitation over the oceans and thus for changes + in the global water cycle. There is no observational evidence of a long-term trend + in the Atlantic Meridional Overturning Circulation. Since the beginning of the + industrial era, oceanic uptake of CO2 has resulted in acidification of the ocean; + the pH of ocean surface water has decreased by 0.1, corresponding to a 26% increase + in acidity, measured as hydrogen ion concentration. There is medium confidence + that, in parallel to warming, oxygen concentrations have decreased in coastal + waters and in the open ocean thermocline in many ocean regions since the 1960s, + with a likely expansion of tropical oxygen minimum zones in recent decades. + 1.1e: + - Cryosphere Over the last two decades, the Greenland and Antarctic ice sheets + have been losing mass. Glaciers have continued to shrink almost worldwide. Northern + Hemisphere spring snow cover has continued to decrease in extent. There is high + confidence that there are strong regional differences in the trend in Antarctic + sea ice extent, with a very likely increase in total extent. Glaciers have lost + mass and contributed to sea level rise throughout the 20th century. The rate of + ice mass loss from the Greenland ice sheet has very likely substantially increased + over the period 1992 to 2011, resulting in a larger mass loss over 2002 to 2011 + than over 1992 to 2011. The rate of ice mass loss from the Antarctic ice sheet, + mainly from the northern Antarctic Peninsula and the Amundsen Sea sector of West + Antarctica, is also likely larger over 2002 to 2011. The annual mean Arctic sea + ice extent decreased over the period 1979 to 2012. The rate of decrease was very + likely in the range 3.5 to 4.1% per decade. Arctic sea ice extent has decreased + in every season and in every successive decade since 1979, with the most rapid + decrease in decadal mean extent in summer . For the summer sea ice minimum, the + decrease was very likely in the range of 9.4 to 13.6% per decade . It is very + likely that the annual mean Antarctic sea ice extent increased in the range of + 1.2 to 1.8% per decade between 1979 and 2012. However, there is high confidence + that there are strong regional differences in Antarctica, with extent increasing + in some regions and decreasing in others. There is very high confidence that + the extent of Northern Hemisphere snow cover has decreased since the mid-20th + century by 1.6 [0.8 to 2.4] % per decade for March and April, and 11.7% per decade + for June, over the 1967 to 2012 period. There is high confidence that permafrost + temperatures have increased in most regions of the Northern Hemisphere since the + early 1980s, with reductions in thickness and areal extent in some regions. The + increase in permafrost temperatures has occurred in response to increased surface + temperature and changing snow cover. + 1.1g: + - Sea level Over the period 1901–2010, global mean sea level rose by 0.19 [0.17 + to 0.21] m. The rate of sea level rise since the mid-19th century has been larger + than the mean rate during the previous two millennia. It is very likely that + the mean rate of global averaged sea level rise was 1.7 [1.5 to 1.9] mm/yr between + 1901 and 2010 and 3.2 [2.8 to 3.6] mm/yr between 1993 and 2010. Tide gauge and + satellite altimeter data are consistent regarding the higher rate during the latter + period. It is likely that similarly high rates occurred between 1920 and 1950. Since + the early 1970s, glacier mass loss and ocean thermal expansion from warming together + explain about 75% of the observed global mean sea level rise. Over the period + 1993–2010, global mean sea level rise is, with high confidence, consistent with + the sum of the observed contributions from ocean thermal expansion, due to warming, + from changes in glaciers, the Greenland ice sheet, the Antarctic ice sheet and + land water storage. Rates of sea level rise over broad regions can be several + times larger or smaller than the global mean sea level rise for periods of several + decades, due to fluctuations in ocean circulation. Since 1993, the regional rates + for the Western Pacific are up to three times larger than the global mean, while + those for much of the Eastern Pacific are near zero or negative. There is very + high confidence that maximum global mean sea level during the last interglacial + period was, for several thousand years, at least 5 m higher than present and high + confidence that it did not exceed 10 m above present. During the last interglacial + period, the Greenland ice sheet very likely contributed between 1.4 and 4.3 m + to the higher global mean sea level, implying with medium confidence an additional + contribution from the Antarctic ice sheet. This change in sea level occurred in + the context of different orbital forcing and with high-latitude surface temperature, + averaged over several thousand years, at least 2°C warmer than present . + 1.2a: + - 'Natural and anthropogenic radiative forcings Atmospheric concentrations of GHGs + are at levels that are unprecedented in at least 800, years. Concentrations of + carbon dioxide, methane and nitrous oxide have all shown large increases since + 1750 . CO2 concentrations are increasing at the fastest observed decadal rate + of change for 2002– 2011. After almost one decade of stable CH4 concentrations + since the late 1990s, atmospheric measurements have shown renewed increases since + 2007. N2O concentrations have steadily increased at a rate of 0.73 ± 0.03 ppb/yr + over the last three decades. The total anthropogenic radiative forcing over 1750–2011 + is calculated to be a warming effect of 2.3 [1.1 to 3.3] W/m , and it has increased + more rapidly since 1970 than during prior decades. Carbon dioxide is the largest + single contributor to radiative forcing over 1750–2011 and its trend since 1970. + The total anthropogenic radiative forcing estimate for 2011 is substantially higher + than the estimate reported in the IPCC Fourth Assessment Report for the year 2005. + This is caused by a combination of continued growth in most GHG concentrations + and an improved estimate of radiative forcing from aerosols. The radiative forcing + from aerosols, which includes cloud adjustments, is better understood and indicates + a weaker cooling effect than in AR4. The aerosol radiative forcing over 1750–2011 + is estimated as –0.9 [–1.9 to −0.1] W/m . Radiative forcing from aerosols has + two competing components: a dominant cooling effect from most aerosols and their + cloud adjustments and a partially offsetting warming contribution from black carbon + absorption of solar radiation. There is high confidence that the global mean total + aerosol radiative forcing has counteracted a substantial portion of radiative + forcing from wellmixed GHGs. Aerosols continue to contribute the largest uncertainty + to the total radiative forcing estimate. Changes in solar irradiance and volcanic + aerosols cause natural radiative forcing. The radiative forcing from stratospheric + volcanic aerosols can have a large cooling effect on the climate system for some + years after major volcanic eruptions. Changes in total solar irradiance are calculated + to have contributed only around 2% of the total radiative forcing in 2011, relative + to 1750.' + - Human activities affecting emission drivers About half of the cumulative anthropogenic + CO2 emissions between 1750 and 2011 have occurred in the last 40 years . Cumulative + anthropogenic CO2 emissions of 2040 ± 310 GtCO2 were added to the atmosphere between + 1750 and 2011. Since 1970, cumulative CO2 emissions from fossil fuel combustion, + cement production and flaring have tripled, and cumulative CO2 emissions from + forestry and other land use22 have increased by about 40% 23. In 2011, annual + CO2 emissions from fossil fuel combustion, cement production and flaring were + 34.8 ± 2.9 GtCO2/yr. For 2002–2011, average annual emissions from FOLU were 3.3 + ± 2.9 GtCO2/yr. About 40% of these anthropogenic CO2 emissions have remained + in the atmosphere since 1750. The rest was removed from the atmosphere by sinks, + and stored in natural carbon cycle reservoirs. Sinks from ocean uptake and vegetation + with soils account, in roughly equal measures, for the remainder of the cumulative + CO2 emissions. The ocean has absorbed about 30% of the emitted anthropogenic CO2, + causing ocean acidification. Total annual anthropogenic GHG emissions have continued + to increase over 1970 to 2010 with larger absolute increases between 2000 and + 2010. Despite a growing number of climate change mitigation policies, annual GHG + emissions grew on average by 1.0 GtCO2-eq per year, from 2000 to 2010, compared + to 0.4 GtCO2-eq per year, from 1970 to 2000 24. Total anthropogenic GHG emissions + from 2000 to 2010 were the highest in human history and reached 49 GtCO2-eq/yr + in 2010. The global economic crisis of 2007/2008 reduced emissions only temporarily. CO2 + emissions from fossil fuel combustion and industrial processes contributed about + 78% to the total GHG emission increase between 1970 and 2010, with a contribution + of similar percentage over the 2000–2010 period. Fossil-fuel-related CO2 emissions + reached 32 GtCO2/yr, in 2010, and grew further by about 3% between 2010 and 2011, + and by about 1 to 2% between 2011 and 2012. CO2 remains the major anthropogenic + GHG, accounting for 76% of total anthropogenic GHG emissions in 2010. Of the total, + 16% comes from CH4, 6.2% from N2O, and 2.0% from fluorinated gases 25. Annually, + since 1970, about 25% of anthropogenic GHG emissions have been in the form of + non-CO2 gases. Total annual anthropogenic GHG emissions have increased by about + 10 GtCO2-eq between 2000 and 2010. This increase directly came from the energy, + industry, transport and building sectors. Accounting for indirect emissions raises + the contributions by the building and industry sectors. Since 2000, GHG emissions + have been growing in all sectors, except in agriculture, forestry and other land + use 22. In 2010, 35% of GHG emissions were released by the energy sector, 24% + from AFOLU, 21% by industry, 14% by transport and 6.4% by the building sector. + When emissions from electricity and heat production are attributed to the sectors + that use the final energy, the shares of the industry and building sectors in + global GHG emissions are increased to 31% and 19%, respectively. See also Box + 3.2 for contributions from various sectors, based on metrics other than 100-year + Global Warming Potential. Globally, economic and population growth continue to + be the most important drivers of increases in CO2 emissions from fossil fuel combustion. + The contribution of population growth between 2000 and 2010 remained roughly identical + to that of the previous three decades, while the contribution of economic growth + has risen sharply. Between 2000 and 2010, both drivers outpaced emission reductions + from improvements in energy intensity of gross domestic product. Increased use + of coal relative to other energy sources has reversed the long-standing trend + in gradual decarbonization of the world’s energy supply. + 1.2c: + - Attribution of climate changes and impacts The evidence for human influence on + the climate system has grown since AR4. Human influence has been detected in warming + of the atmosphere and the ocean, in changes in the global water cycle, in reductions + in snow and ice, and in global mean sea level rise; and it is extremely likely + to have been the dominant cause of the observed warming since the mid20th century. + In recent decades, changes in climate have caused impacts on natural and human + systems on all continents and across the oceans. Impacts are due to observed climate + change, irrespective of its cause, indicating the sensitivity of natural and human + systems to changing climate. The causes of observed changes in the climate system, + as well as in any natural or human system impacted by climate, are established + following a consistent set of methods. Detection addresses the question of whether + climate or a natural or human system affected by climate has actually changed + in a statistical sense, while attribution evaluates the relative contributions + of multiple causal factors to an observed change or event with an assignment of + statistical confidence. Attribution of climate change to causes quantifies the + links between observed climate change and human activity, as well as other, natural, + climate drivers. In contrast, attribution of observed impacts to climate change + considers the links between observed changes in natural or human systems and observed + climate change, regardless of its cause. Results from studies attributing climate + change to causes provide estimates of the magnitude of warming in response to + changes in radiative forcing and hence support projections of future climate change. + Results from studies attributing impacts to climate change provide strong indications + for the sensitivity of natural or human systems to future climate change. + 1.3a: + - Observed impacts attributed to climate change In recent decades, changes in climate + have caused impacts on natural and human systems on all continents and across + the oceans. Impacts are due to observed climate change, irrespective of its cause, + indicating the sensitivity of natural and human systems to changing climate. Evidence + of observed climate change impacts is strongest and most comprehensive for natural + systems. Some impacts on human systems have also been attributed to climate change, + with a major or minor contribution of climate change distinguishable from other + influences. Impacts on human systems are often geographically heterogeneous because + they depend not only on changes in climate variables but also on social and economic + factors. Hence, the changes are more easily observed at local levels, while attribution + can remain difficult. In many regions, changing precipitation or melting snow + and ice are altering hydrological systems, affecting water resources in terms + of quantity and quality. Glaciers continue to shrink almost worldwide due to climate + change , affecting runoff and water resources downstream . Climate change is causing + permafrost warming and thawing in high-latitude regions and in high-elevation + regions . Many terrestrial, freshwater and marine species have shifted their + geographic ranges, seasonal activities, migration patterns, abundances and species + interactions in response to ongoing climate change. While only a few recent species + extinctions have been attributed as yet to climate change , natural global climate + change at rates slower than current anthropogenic climate change caused significant + ecosystem shifts and species extinctions during the past millions of years. Increased + tree mortality, observed in many places worldwide, has been attributed to climate + change in some regions. Increases in the frequency or intensity of ecosystem disturbances + such as droughts, windstorms, fires and pest outbreaks have been detected in many + parts of the world and in some cases are attributed to climate change . Numerous + observations over the last decades in all ocean basins show changes in abundance, + distribution shifts poleward and/ or to deeper, cooler waters for marine fishes, + invertebrates and phytoplankton, and altered ecosystem composition , tracking + climate trends. Some warm-water corals and their reefs have responded to warming + with species replacement, bleaching, and decreased coral cover causing habitat + loss . Some impacts of ocean acidification on marine organisms have been attributed + to human influence, from the thinning of pteropod and foraminiferan shells to + the declining growth rates of corals. Oxygen minimum zones are progressively expanding + in the tropical Pacific, Atlantic and Indian Oceans, due to reduced ventilation + and O2 solubility in warmer, more stratified oceans, and are constraining fish + habitat. Assessment of many studies covering a wide range of regions and crops + shows that negative impacts of climate change on crop yields have been more common + than positive impacts . The smaller number of studies showing positive impacts + relate mainly to high-latitude regions, though it is not yet clear whether the + balance of impacts has been negative or positive in these regions. Climate change + has negatively affected wheat and maize yields for many regions and in the global + aggregate. Effects on rice and soybean yield have been smaller in major production + regions and globally, with a median change of zero across all available data which + are fewer for soy compared to the other crops. Observed impacts relate mainly + to production aspects of food security rather than access or other components + of food security. Since AR4, several periods of rapid food and cereal price increases + following climate extremes in key producing regions indicate a sensitivity of + current markets to climate extremes among other factors . At present the worldwide + burden of human ill-health from climate change is relatively small compared with + effects of other stressors and is not well quantified. However, there has been + increased heat-related mortality and decreased cold-related mortality in some + regions as a result of warming. Local changes in temperature and rainfall have + altered the distribution of some water-borne illnesses and disease vectors. ‘Cascading’ + impacts of climate change can now be attributed along chains of evidence from + physical climate through to intermediate systems and then to people. The changes + in climate feeding into the cascade, in some cases, are linked to human drivers + , while, in other cases, assessments of the causes of observed climate change + leading into the cascade are not available. In all cases, confidence in detection + and attribution to observed climate change decreases for effects further down + each impact chain. + 1.4a: + - Extreme events Changes in many extreme weather and climate events have been observed + since about 1950. Some of these changes have been linked to human influences, + including a decrease in cold temperature extremes, an increase in warm temperature + extremes, an increase in extreme high sea levels and an increase in the number + of heavy precipitation events in a number of regions. It is very likely that the + number of cold days and nights has decreased and the number of warm days and nights + has increased on the global scale. It is likely that the frequency of heat waves + has increased in large parts of Europe, Asia and Australia. It is very likely + that human influence has contributed to the observed global scale changes in the + frequency and intensity of daily temperature extremes since the mid-20th century. + It is likely that human influence has more than doubled the probability of occurrence + of heat waves in some locations. There is medium confidence that the observed + warming has increased heat-related human mortality and decreased coldrelated human + mortality in some regions. Extreme heat events currently result in increases in + mortality and morbidity in North America , and in Europe with impacts that vary + according to people’s age, location and socio-economic factors. There are likely + more land regions where the number of heavy precipitation events has increased + than where it has decreased. The frequency and intensity of heavy precipitation + events has likely increased in North America and Europe. In other continents, + confidence in trends is at most medium. It is very likely that global near-surface + and tropospheric air specific humidity has increased since the 1970s. In land + regions where observational coverage is sufficient for assessment, there is medium + confidence that anthropogenic forcing has contributed to a global-scale intensification + of heavy precipitation over the second half of the 20th century. There is low + confidence that anthropogenic climate change has affected the frequency and magnitude + of fluvial floods on a global scale. The strength of the evidence is limited mainly + by a lack of long-term records from unmanaged catchments. Moreover, floods are + strongly influenced by many human activities impacting catchments, making the + attribution of detected changes to climate change difficult. However, recent detection + of increasing trends in extreme precipitation and discharges in some catchments + implies greater risks of flooding on a regional scale. Costs related to flood + damage, worldwide, have been increasing since the 1970s, although this is partly + due to the increasing exposure of people and assets. There is low confidence + in observed global-scale trends in droughts, due to lack of direct observations, + dependencies of inferred trends on the choice of the definition for drought, and + due to geographical inconsistencies in drought trends. There is also low confidence + in the attribution of changes in drought over global land areas since the mid-20th + century, due to the same observational uncertainties and difficulties in distinguishing + decadal scale variability in drought from long-term trends. There is low confidence + that long-term changes in tropical cyclone activity are robust, and there is low + confidence in the attribution of global changes to any particular cause. However, + it is virtually certain that intense tropical cyclone activity has increased in + the North Atlantic since 1970. It is likely that extreme sea levels have increased + since 1970, being mainly the result of mean sea level rise. Due to a shortage + of studies and the difficulty of distinguishing any such impacts from other modifications + to coastal systems, limited evidence is available on the impacts of sea level + rise. Impacts from recent climate-related extremes, such as heat waves, droughts, + floods, cyclones and wildfires, reveal significant vulnerability and exposure + of some ecosystems and many human systems to current climate variability . Impacts + of such climate-related extremes include alteration of ecosystems, disruption + of food production and water supply, damage to infrastructure and settlements, + human morbidity and mortality and consequences for mental health and human well-being. + For countries at all levels of development, these impacts are consistent with + a significant lack of preparedness for current climate variability in some sectors. Direct + and insured losses from weather-related disasters have increased substantially + in recent decades, both globally and regionally. Increasing exposure of people + and economic assets has been the major cause of long-term increases in economic + losses from weather- and climate-related disasters. + 2.1b: + - Key drivers of future climate and the basis on which projections are made Cumulative + emissions of CO 2 largely determine global mean surface warming by the late 21st + century and beyond. Projections of greenhouse gas emissions vary over a wide range, + depending on both socio-economic development and climate policy. Climate models + are mathematical representations of processes important in the Earth’s climate + system. Results from a hierarchy of climate models are considered in this report; + ranging from simple idealized models, to models of intermediate complexity, to + comprehensive General Circulation Models, including Earth System Models that also + simulate the carbon cycle. The GCMs simulate many climate aspects, including the + temperature of the atmosphere and the oceans, precipitation, winds, clouds, ocean + currents and sea-ice extent. The models are extensively tested against historical + observations. In order to obtain climate change projections, the climate models + use information described in scenarios of GHG and air pollutant emissions and + land use patterns. Scenarios are generated by a range of approaches, from simple + idealised experiments to Integrated Assessment Models. Key factors driving changes + in anthropogenic GHG emissions are economic and population growth, lifestyle and + behavioural changes, associated changes in energy use and land use, technology + and climate policy, which are fundamentally uncertain. The standard set of scenarios + used in the AR5 is called Representative Concentration Pathways. The methods + used to estimate future impacts and risks resulting from climate change are described + in Box 2.3. Modelled future impacts assessed in this report are generally based + on climate-model projections using the RCPs, and in some cases, the older Special + Report on Emissions Scenarios. Risk of climate-related impacts results from the + interaction between climate-related hazards and the vulnerability and exposure + of human and natural systems. Alternative development paths influence risk by + changing the likelihood of climatic events and trends, through their effects on + GHGs, pollutants and land use, and by altering vulnerability and exposure. Experiments, + observations and models used to estimate future impacts and risks have improved + since the AR4, with increasing understanding across sectors and regions. For example, + an improved knowledge base has enabled expanded assessment of risks for human + security and livelihoods and for the oceans. For some aspects of climate change + and climate change impacts, uncertainty about future outcomes has narrowed. For + others, uncertainty will persist. Some of the persistent uncertainties are grounded + in the mechanisms that control the magnitude and pace of climate change. Others + emerge from potentially complex interactions between the changing climate and + the underlying vulnerability and exposure of people, societies and ecosystems. + The combination of persistent uncertainty in key mechanisms plus the prospect + of complex interactions motivates a focus on risk in this report. Because risk + involves both probability and consequence, it is important to consider the full + range of possible outcomes, including low-probability, high-consequence impacts + that are difficult to simulate. + - Response options for mitigation Mitigation options are available in every major + sector. Mitigation can be more cost-effective if using an integrated approach + that combines measures to reduce energy use and the greenhouse gas intensity of + end-use sectors, decarbonize energy supply, reduce net emissions and enhance carbon + sinks in land-based sectors. A broad range of sectoral mitigation options is available + that can reduce GHG emission intensity, improve energy intensity through enhancements + of technology, behaviour, production and resource efficiency and enable structural + changes or changes in activity. In addition, direct options in agriculture, forestry + and other land use involve reducing CO2 emissions by reducing deforestation, forest + degradation and forest fires; storing carbon in terrestrial systems; and providing + bioenergy feedstocks. Options to reduce non-CO2 emissions exist across all sectors + but most notably in agriculture, energy supply and industry. An overview of sectoral + mitigation options and potentials is provided in Table 4.4. Well-designed systemic + and cross-sectoral mitigation strategies are more cost-effective in cutting emissions + than a focus on individual technologies and sectors with efforts in one sector + affecting the need for mitigation in others . In baseline scenarios without new + mitigation policies, GHG emissions are projected to grow in all sectors, except + for net CO2 emissions in the AFOLU sector. Mitigation scenarios reaching around + 450 ppm CO2-eq concentration by 21004328 show largescale global changes in the + energy supply sector . While rapid decarbonization of energy supply generally + entails more flexibility for end-use and AFOLU sectors, stronger demand reductions + lessen the mitigation challenge for the supply side of the energy system. There + are thus strong interdependencies across sectors and the resulting distribution + of the mitigation effort is strongly influenced by the availability and performance + of future technologies, particularly BECCS and large scale afforestation . The + next two decades present a window of opportunity for mitigation in urban areas, + as a large portion of the world’s urban areas will be developed during this period. Decarbonizing + electricity generation is a key component of cost-effective mitigation strategies + in achieving low stabilization levels . In most integrated modelling scenarios, + decarbonization happens more rapidly in electricity generation than in the industry, + buildings and transport sectors. In scenarios reaching 450 ppm CO2-eq concentrations + by 2100, global CO2 emissions from the energy supply sector are projected to decline + over the next decade and are characterized by reductions of 90% or more below + 2010 levels between 2040 and 2070. Efficiency enhancements and behavioural changes, + in order to reduce energy demand compared to baseline scenarios without compromising + development, are a key mitigation strategy in scenarios reaching atmospheric CO2-eq + concentrations of about 450 to about 500 ppm by 2100 . Near-term reductions in + energy demand are an important element of cost-effective mitigation strategies, + provide more flexibility for reducing carbon intensity in the energy supply sector, + hedge against related supply-side risks, avoid lock-in to carbon-intensive infrastructures + and are associated with important co-benefits . Emissions can be substantially + lowered through changes in consumption patterns and dietary change and reduction + in food wastes. A number of options including monetary and non-monetary incentives + as well as information measures may facilitate behavioural changes. Decarbonization + of the energy supply sector requires upscaling of low- and zero-carbon electricity + generation technologies. In the majority of low-concentration stabilization scenarios + , the share of low-carbon electricity supply, nuclear and CCS, including BECCS) + increases from the current share of approximately 30% to more than 80% by 2050 + and 90% by 2100, and fossil fuel power generation without CCS is phased out almost + entirely by 2100. Among these low-carbon technologies, a growing number of RE + technologies have achieved a level of maturity to enable deployment at significant + scale since AR4 and nuclear energy is a mature low-GHG emission source of baseload + power, but its share of global electricity generation has been declining. GHG + emissions from energy supply can be reduced significantly by replacing current + world average coal-fired power plants with modern, highly efficient natural gas + combined-cycle power plants or combined heat and power plants, provided that natural + gas is available and the fugitive emissions associated with extraction and supply + are low or mitigated. Behaviour, lifestyle and culture have a considerable influence + on energy use and associated emissions, with high mitigation potential in some + sectors, in particular when complementing technological and structural change + . In the transport sector, technical and behavioural mitigation measures for all + modes, plus new infrastructure and urban redevelopment investments, could reduce + final energy demand significantly below baseline levels. While opportunities for + switching to low-carbon fuels exist, the rate of decarbonization in the transport + sector might be constrained by challenges associated with energy storage and the + relatively low energy density of low-carbon transport fuels. In the building sector, + recent advances in technologies, know-how and policies provide opportunities to + stabilize or reduce global energy use to about current levels by mid-century. + In addition, recent improvements in performance and costs make very low energy + construction and retrofits of buildings economically attractive, sometimes even + at net negative costs. In the industry sector, improvements in GHG emission efficiency + and in the efficiency of material use, recycling and reuse of materials and products, + and overall reductions in product demand and service demand could, in addition + to energy efficiency, help reduce GHG emissions below the baseline level. Prevalent + approaches for promoting energy efficiency in industry include information programmes + followed by economic instruments, regulatory approaches and voluntary actions. + Important options for mitigation in waste management are waste reduction, followed + by re-use, recycling and energy recovery. The most cost-effective mitigation + options in forestry are afforestation, sustainable forest management and reducing + deforestation, with large differences in their relative importance across regions. + In agriculture, the most cost-effective mitigation options are cropland management, + grazing land management and restoration of organic soils . About a third of mitigation + potential in forestry can be achieved at a cost <20 USD/tCO2-eq emission. Demand-side + measures, such as changes in diet and reductions of losses in the food supply + chain, have a significant, but uncertain, potential to reduce GHG emissions from + food production . Bioenergy can play a critical role for mitigation, but there + are issues to consider, such as the sustainability of practices and the efficiency + of bioenergy systems . Evidence suggests that bioenergy options with low lifecycle + emissions, some already available, can reduce GHG emissions; outcomes are site-specific + and rely on efficient integrated ‘biomassto-bioenergy systems’, and sustainable + land use management and governance. Barriers to large-scale deployment of bioenergy + include concerns about GHG emissions from land, food security, water resources, + biodiversity conservation and livelihoods. Mitigation measures intersect with + other societal goals, creating the possibility of co-benefits or adverse side-effects. + These intersections, if well-managed, can strengthen the basis for undertaking + climate mitigation actions . Mitigation can positively or negatively influence + the achievement of other societal goals, such as those related to human health, + food security, biodiversity, local environmental quality, energy access, livelihoods + and equitable sustainable development . On the other hand, policies towards other + societal goals can influence the achievement of mitigation and adaptation objectives. + These influences can be substantial, although sometimes difficult to quantify, + especially in welfare terms. This multi-objective perspective is important in + part because it helps to identify areas where support for policies that advance + multiple goals will be robust. Potential co-benefits and adverse side effects + of the main sectoral mitigation measures are summarized in Table 4.5. Overall, + the potential for co-benefits for energy end-use measures outweigh the potential + for adverse side effects, whereas the evidence suggests this may not be the case + for all energy supply and AFOLU measures. + 2.1c: + - Climate system responses Climate system properties that determine the response + to external forcing have been estimated both from climate models and from analysis + of past and recent climate change. The equilibrium climate sensitivity 3325is + likely in the range 1.5°C to 4.5°C, extremely unlikely less than 1°C, and very + unlikely greater than 6°C. Cumulative emissions of CO2 largely determine global + mean surface warming by the late 21st century and beyond. Multiple lines of evidence + indicate a strong and consistent near-linear relationship across all scenarios + considered between net cumulative CO2 emissions and projected global temperature + change to the year 2100. Past emissions and observed warming support this relationship + within uncertainties. Any given level of warming is associated with a range of + cumulative CO2 emissions , and therefore, for example, higher emissions in earlier + decades imply lower emissions later. The global mean peak surface temperature + change per trillion tonnes of carbon emitted as CO2 is likely in the range of + 0.8°C to 2.5°C. This quantity, called the transient climate response to cumulative + carbon emissions, is supported by both modelling and observational evidence and + applies to cumulative emissions up to about 2000 GtC. Warming caused by CO2 emissions + is effectively irreversible over multi-century timescales unless measures are + taken to remove CO2 from the atmosphere. Ensuring CO2-induced warming remains + likely less than 2°C requires cumulative CO2 emissions from all anthropogenic + sources to remain below about 3650 GtCO2, over half of which were already emitted + by 2011. Multi-model results show that limiting total human-induced warming to + less than 2°C relative to the period 1861–1880 with a probability of >66% would + require total CO2 emissions from all anthropogenic sources since 1870 to be limited + to about 2900 GtCO2 when accounting for non-CO2 forcing as in the RCP2.6 scenario, + with a range of 2550 to 3150 GtCO2 arising from variations in non-CO2 climate + drivers across the scenarios considered by WGIII. About 1900 [1650 to 2150] GtCO2 + were emitted by 2011, leaving about 1000 GtCO2 to be consistent with this temperature + goal. Estimated total fossil carbon reserves exceed this remaining amount by a + factor of 4 to 7, with resources much larger still. + 2.1d: + - Climate system responses Climate system properties that determine the response + to external forcing have been estimated both from climate models and from analysis + of past and recent climate change. The equilibrium climate sensitivity 3325is + likely in the range 1.5°C to 4.5°C, extremely unlikely less than 1°C, and very + unlikely greater than 6°C. Cumulative emissions of CO2 largely determine global + mean surface warming by the late 21st century and beyond. Multiple lines of evidence + indicate a strong and consistent near-linear relationship across all scenarios + considered between net cumulative CO2 emissions and projected global temperature + change to the year 2100. Past emissions and observed warming support this relationship + within uncertainties. Any given level of warming is associated with a range of + cumulative CO2 emissions , and therefore, for example, higher emissions in earlier + decades imply lower emissions later. The global mean peak surface temperature + change per trillion tonnes of carbon emitted as CO2 is likely in the range of + 0.8°C to 2.5°C. This quantity, called the transient climate response to cumulative + carbon emissions, is supported by both modelling and observational evidence and + applies to cumulative emissions up to about 2000 GtC. Warming caused by CO2 emissions + is effectively irreversible over multi-century timescales unless measures are + taken to remove CO2 from the atmosphere. Ensuring CO2-induced warming remains + likely less than 2°C requires cumulative CO2 emissions from all anthropogenic + sources to remain below about 3650 GtCO2, over half of which were already emitted + by 2011. Multi-model results show that limiting total human-induced warming to + less than 2°C relative to the period 1861–1880 with a probability of >66% would + require total CO2 emissions from all anthropogenic sources since 1870 to be limited + to about 2900 GtCO2 when accounting for non-CO2 forcing as in the RCP2.6 scenario, + with a range of 2550 to 3150 GtCO2 arising from variations in non-CO2 climate + drivers across the scenarios considered by WGIII. About 1900 [1650 to 2150] GtCO2 + were emitted by 2011, leaving about 1000 GtCO2 to be consistent with this temperature + goal. Estimated total fossil carbon reserves exceed this remaining amount by a + factor of 4 to 7, with resources much larger still. + 2.2e: + - Water cycle Changes in precipitation in a warming world will not be uniform. + The high latitudes and the equatorial Pacific are likely to experience an increase + in annual mean precipitation by the end of this century under the RCP8.5 scenario. + In many mid-latitude and subtropical dry regions, mean precipitation will likely + decrease, while in many mid-latitude wet regions, mean precipitation will likely + increase under the RCP8.5 scenario. Extreme precipitation events over most mid-latitude + land masses and over wet tropical regions will very likely become more intense + and more frequent as global mean surface temperature increases. Globally, in + all RCPs, it is likely that the area encompassed by monsoon systems will increase + and monsoon precipitation is likely to intensify and El Niño-Southern Oscillation + related precipitation variability on regional scales will likely intensify. + 2.2f: + - Ocean, cryosphere and sea level The global ocean will continue to warm during + the 21st century. The strongest ocean warming is projected for the surface in + tropical and Northern Hemisphere subtropical regions. At greater depth the warming + will be most pronounced in the Southern Ocean . It is very likely that the Atlantic + Meridional Overturning Circulation will weaken over the 21st century, with best + estimates and model ranges for the reduction of 11% for the RCP2.6 scenario, 34% + for the RCP8.5. Nevertheless, it is very unlikely that the AMOC will undergo an + abrupt transition or collapse in the 21st century. Year-round reductions in Arctic + sea ice are projected for all RCP scenarios. The subset of models that most closely + reproduce the observationsproject that a nearly ice-free Arctic Oceanin September + is likely for RCP8.5 before mid-century. In the Antarctic, a decrease in sea ice + extent and volume is projected with low confidence. The area of Northern Hemisphere + spring snow cover is likely to decrease by 7% for RCP2.6 and by 25% in RCP8.5 + by the end of the 21st century for the multi-model average. It is virtually certain + that near-surface permafrost extent at high northern latitudes will be reduced + as global mean surface temperature increases. The area of permafrost near the + surface is likely to decrease by 37% to 81% for the multi-model average. The + global glacier volume, excluding glaciers on the periphery of Antarctica, is projected + to decrease by 15 to 55% for RCP2.6 and by 35 to 85% for RCP8.5. Global mean + sea level will continue to rise during the 21st century. There has been significant + improvement in understanding and projection of sea level change since the AR4. + Under all RCP scenarios, the rate of sea level rise will very likely exceed the + observed rate of 2.0 [1.7–2.3] mm/yr during 1971–2010, with the rate of rise for + RCP8.5 during 2081–2100 of 8 to 16 mm/yr . Sea level rise will not be uniform + across regions. By the end of the 21st century, it is very likely that sea level + will rise in more than about 95% of the ocean area. Sea level rise depends on + the pathway of CO2 emissions, not only on the cumulative total; reducing emissions + earlier rather than later, for the same cumulative total, leads to a larger mitigation + of sea level rise. About 70% of the coastlines worldwide are projected to experience + sea level change within ±20% of the global mean. It is very likely that there + will be a significant increase in the occurrence of future sea level extremes + in some regions by 2100. + 2.2g: + - Carbon cycle and biogeochemistry Ocean uptake of anthropogenic CO2 will continue + under all four RCPs through to 2100, with higher uptake for higher concentration + pathways. The future evolution of the land carbon uptake is less certain. A majority + of models projects a continued land carbon uptake under all RCPs, but some models + simulate a land carbon loss due to the combined effect of climate change and land + use change. Based on Earth System Models, there is high confidence that the feedback + between climate change and the carbon cycle will amplify global warming. Climate + change will partially offset increases in land and ocean carbon sinks caused by + rising atmospheric CO2. As a result more of the emitted anthropogenic CO2 will + remain in the atmosphere, reinforcing the warming. Earth System Models project + a global increase in ocean acidification for all RCP scenarios by the end of the + 21st century, with a slow recovery after mid-century under RCP2.6. The decrease + in surface ocean pH is in the range of 0.06 to 0.07 for RCP2.6, 0.14 to 0.15 + for RCP4.5, 0.20 to 0.21 for RCP6.0, and 0.30 to 0.32 for RCP8.5 . It is very + likely that the dissolved oxygen content of the ocean will decrease by a few percent + during the 21st century in response to surface warming, predominantly in the subsurface + mid-latitude oceans. There is no consensus on the future volume of low oxygen + waters in the open ocean because of large uncertainties in potential biogeochemical + effects and in the evolution of tropical ocean dynamics. + 2.2h: + - Ocean, cryosphere and sea level The global ocean will continue to warm during + the 21st century. The strongest ocean warming is projected for the surface in + tropical and Northern Hemisphere subtropical regions. At greater depth the warming + will be most pronounced in the Southern Ocean . It is very likely that the Atlantic + Meridional Overturning Circulation will weaken over the 21st century, with best + estimates and model ranges for the reduction of 11% for the RCP2.6 scenario, 34% + for the RCP8.5. Nevertheless, it is very unlikely that the AMOC will undergo an + abrupt transition or collapse in the 21st century. Year-round reductions in Arctic + sea ice are projected for all RCP scenarios. The subset of models that most closely + reproduce the observationsproject that a nearly ice-free Arctic Oceanin September + is likely for RCP8.5 before mid-century. In the Antarctic, a decrease in sea ice + extent and volume is projected with low confidence. The area of Northern Hemisphere + spring snow cover is likely to decrease by 7% for RCP2.6 and by 25% in RCP8.5 + by the end of the 21st century for the multi-model average. It is virtually certain + that near-surface permafrost extent at high northern latitudes will be reduced + as global mean surface temperature increases. The area of permafrost near the + surface is likely to decrease by 37% to 81% for the multi-model average. The + global glacier volume, excluding glaciers on the periphery of Antarctica, is projected + to decrease by 15 to 55% for RCP2.6 and by 35 to 85% for RCP8.5. Global mean + sea level will continue to rise during the 21st century. There has been significant + improvement in understanding and projection of sea level change since the AR4. + Under all RCP scenarios, the rate of sea level rise will very likely exceed the + observed rate of 2.0 [1.7–2.3] mm/yr during 1971–2010, with the rate of rise for + RCP8.5 during 2081–2100 of 8 to 16 mm/yr . Sea level rise will not be uniform + across regions. By the end of the 21st century, it is very likely that sea level + will rise in more than about 95% of the ocean area. Sea level rise depends on + the pathway of CO2 emissions, not only on the cumulative total; reducing emissions + earlier rather than later, for the same cumulative total, leads to a larger mitigation + of sea level rise. About 70% of the coastlines worldwide are projected to experience + sea level change within ±20% of the global mean. It is very likely that there + will be a significant increase in the occurrence of future sea level extremes + in some regions by 2100. + 2.2m: + - Ocean, cryosphere and sea level The global ocean will continue to warm during + the 21st century. The strongest ocean warming is projected for the surface in + tropical and Northern Hemisphere subtropical regions. At greater depth the warming + will be most pronounced in the Southern Ocean . It is very likely that the Atlantic + Meridional Overturning Circulation will weaken over the 21st century, with best + estimates and model ranges for the reduction of 11% for the RCP2.6 scenario, 34% + for the RCP8.5. Nevertheless, it is very unlikely that the AMOC will undergo an + abrupt transition or collapse in the 21st century. Year-round reductions in Arctic + sea ice are projected for all RCP scenarios. The subset of models that most closely + reproduce the observationsproject that a nearly ice-free Arctic Oceanin September + is likely for RCP8.5 before mid-century. In the Antarctic, a decrease in sea ice + extent and volume is projected with low confidence. The area of Northern Hemisphere + spring snow cover is likely to decrease by 7% for RCP2.6 and by 25% in RCP8.5 + by the end of the 21st century for the multi-model average. It is virtually certain + that near-surface permafrost extent at high northern latitudes will be reduced + as global mean surface temperature increases. The area of permafrost near the + surface is likely to decrease by 37% to 81% for the multi-model average. The + global glacier volume, excluding glaciers on the periphery of Antarctica, is projected + to decrease by 15 to 55% for RCP2.6 and by 35 to 85% for RCP8.5. Global mean + sea level will continue to rise during the 21st century. There has been significant + improvement in understanding and projection of sea level change since the AR4. + Under all RCP scenarios, the rate of sea level rise will very likely exceed the + observed rate of 2.0 [1.7–2.3] mm/yr during 1971–2010, with the rate of rise for + RCP8.5 during 2081–2100 of 8 to 16 mm/yr . Sea level rise will not be uniform + across regions. By the end of the 21st century, it is very likely that sea level + will rise in more than about 95% of the ocean area. Sea level rise depends on + the pathway of CO2 emissions, not only on the cumulative total; reducing emissions + earlier rather than later, for the same cumulative total, leads to a larger mitigation + of sea level rise. About 70% of the coastlines worldwide are projected to experience + sea level change within ±20% of the global mean. It is very likely that there + will be a significant increase in the occurrence of future sea level extremes + in some regions by 2100. + 2.3a: + - Exposure and vulnerability The character and severity of impacts from climate + change and extreme events emerge from risk that depends not only on climate-related + hazards but also on exposure and vulnerability of human and natural systems. Exposure + and vulnerability are influenced by a wide range of social, economic and cultural + factors and processes that have been incompletely considered to date and that + make quantitative assessments of their future trends difficult . These factors + include wealth and its distribution across society, demographics, migration, access + to technology and information, employment patterns, the quality of adaptive responses, + societal values, governance structures and institutions to resolve conflict. Differences + in vulnerability and exposure arise from non-climatic factors and from multidimensional + inequalities often produced by uneven development processes. These differences + shape differential risks from climate change. People who are socially, economically, + culturally, politically, institutionally or otherwise marginalized are especially + vulnerable to climate change and also to some adaptation and mitigation responses + . This heightened vulnerability is rarely due to a single cause. Rather, it is + the product of intersecting social processes that result in inequalities in socio-economic + status and income, as well as in exposure. Such social processes include, for + example, discrimination on the basis of gender, class, ethnicity, age and ability. Climate-related + hazards exacerbate other stressors, often with negative outcomes for livelihoods, + especially for people living in poverty. Climate-related hazards affect poor people’s + lives directly through impacts on livelihoods, reductions in crop yields or the + destruction of homes, and indirectly through, for example, increased food prices + and food insecurity. Observed positive effects for poor and marginalized people, + which are limited and often indirect, include examples such as diversification + of social networks and of agricultural practices. Violent conflict increases + vulnerability to climate change . Large-scale violent conflict harms assets that + facilitate adaptation, including infrastructure, institutions, natural resources, + social capital and livelihood opportunities. + - 'Future risks and impacts caused by a changing climate Climate change will amplify + existing risks and create new risks for natural and human systems. Risks are unevenly + distributed and are generally greater for disadvantaged people and communities + in countries at all levels of development. Increasing magnitudes of warming increase + the likelihood of severe, pervasive and irreversible impacts for people, species + and ecosystems. Continued high emissions would lead to mostly negative impacts + for biodiversity, ecosystem services and economic development and amplify risks + for livelihoods and for food and human security. Risk of climate-related impacts + results from the interaction of climate-related hazards with the vulnerability + and exposure of human and natural systems, including their ability to adapt. Rising + rates and magnitudes of warming and other changes in the climate system, accompanied + by ocean acidification, increase the risk of severe, pervasive, and in some cases, + irreversible detrimental impacts. Future climate change will amplify existing + climate-related risks and create new risks. Key risks are potentially severe + impacts relevant to understanding dangerous anthropogenic interference with the + climate system. Risks are considered key due to high hazard or high vulnerability + of societies and systems exposed, or both. Their identification is based on large + magnitude or high probability of impacts; irreversibility or timing of impacts; + persistent vulnerability or exposure; or limited potential to reduce risks. Some + risks are particularly relevant for individual regions, while others are global. + For risk assessment it is important to evaluate the widest possible range of impacts, + including low-probability outcomes with large consequences. Risk levels often + increase with temperature and are sometimes more directly linked to other dimensions + of climate change, such as the rate of warming, as well as the magnitudes and + rates of ocean acidification and sea level rise . Key risks that span sectors + and regions include the following : 1. Risk of severe ill-health and disrupted + livelihoods resulting from storm surges, sea level rise and coastal flooding; + inland flooding in some urban regions; and periods of extreme heat. 2. Systemic + risks due to extreme weather events leading to breakdown of infrastructure networks + and critical services. 3. Risk of food and water insecurity and loss of rural + livelihoods and income, particularly for poorer populations. 4. Risk of loss of + ecosystems, biodiversity and ecosystem goods, functions and services. The overall + risks of future climate change impacts can be reduced by limiting the rate and + magnitude of climate change, including ocean acidification. Some risks are considerable + even at 1°C global mean temperature increase above pre-industrial levels. Many + global risks are high to very high for global temperature increases of 4°C or + more. These risks include severe and widespread impacts on unique and threatened + systems, the extinction of many species, large risks to food security and compromised + normal human activities, including growing food or working outdoors in some areas + for parts of the year, due to the combination of high temperature and humidity. + The precise levels of climate change sufficient to trigger abrupt and irreversible + change remain uncertain, but the risk associated with crossing such thresholds + in the earth system or in interlinked human and natural systems increases with + rising temperature. Adaptation can substantially reduce the risks of climate + change impacts, but greater rates and magnitude of climate change increase the + likelihood of exceeding adaptation limits . The potential for adaptation, as well + as constraints and limits to adaptation, varies among sectors, regions, communities + and ecosystems. The scope for adaptation changes over time and is closely linked + to socio-economic development pathways and circumstances. See Figure 2.4 and Table + 2.3, along with Topics 3 and 4.' + - Climate change beyond 2100, irreversibility and abrupt changes Many aspects of + climate change and its associated impacts will continue for centuries, even if + anthropogenic emissions of greenhouse gases are stopped. The risks of abrupt or + irreversible changes increase as the magnitude of the warming increases. Warming + will continue beyond 2100 under all RCP scenarios except RCP2.6. Surface temperatures + will remain approximately constant at elevated levels for many centuries after + a complete cessation of net anthropogenic CO2 emissions . A large fraction of + anthropogenic climate change resulting from CO2 emissions is irreversible on a + multi-century to millennial timescale, except in the case of a large net removal + of CO2 from the atmosphere over a sustained period. Stabilization of global average + surface temperature does not imply stabilization for all aspects of the climate + system. Shifting biomes, re-equilibrating soil carbon, ice sheets, ocean temperatures + and associated sea level rise all have their own intrinsic long timescales that + will result in ongoing changes for hundreds to thousands of years after global + surface temperature has been stabilized. Ocean acidification will continue for + centuries if CO2 emissions continue, it will strongly affect marine ecosystems + , and the impact will be exacerbated by rising temperature extremes. Global mean + sea level rise will continue for many centuries beyond 2100. The few available + analyses that go beyond 2100 indicate sea level rise to be less than 1 m above + the pre-industrial level by 2300 for GHG concentrations that peak and decline + and remain below 500 ppm CO2-eq, as in scenario RCP2.6. For a radiative forcing + that corresponds to a CO2-eq concentration in 2100 that is above 700 ppm but below + 1500 ppm, as in scenario RCP8.5, the projected rise is 1 m to more than 3 m by + 2300 . There is low confidence in the available models’ ability to project solid + ice discharge from the Antarctic ice sheet. Hence, these models likely underestimate + the Antarctica ice sheet contribution, resulting in an underestimation of projected + sea level rise beyond 2100. There is little evidence in global climate models + of a tipping point or critical threshold in the transition from a perennially + ice-covered to a seasonally ice-free Arctic Ocean, beyond which further sea-ice + loss is unstoppable and irreversible. There is low confidence in assessing the + evolution of the Atlantic Meridional Overturning Circulation beyond the 21st century + because of the limited number of analyses and equivocal results. However, a collapse + beyond the 21st century for large sustained warming cannot be excluded. Sustained + mass loss by ice sheets would cause larger sea level rise, and part of the mass + loss might be irreversible. There is high confidence that sustained global mean + warming greater than a threshold would lead to the near-complete loss of the Greenland + ice sheet over a millennium or more, causing a sea level rise of up to 7 m. Current + estimates indicate that the threshold is greater than about 1°C but less than + about 4°C of global warming with respect to pre-industrial temperatures. Abrupt + and irreversible ice loss from a potential instability of marine-based sectors + of the Antarctic ice sheet in response to climate forcing is possible, but current + evidence and understanding is insufficient to make a quantitative assessment. Within + the 21st century, magnitudes and rates of climate change associated with medium + to high emission scenarios pose a high risk of abrupt and irreversible regional-scale + change in the composition, structure and function of marine, terrestrial and freshwater + ecosystems, including wetlands, as well as warm water coral reefs . Examples that + could substantially amplify climate change are the boreal-tundra Arctic system + and the Amazon forest. A reduction in permafrost extent is virtually certain + with continued rise in global temperatures. Current permafrost areas are projected + to become a net emitter of carbon with a loss of 180 to 920 GtCO2 under RCP8.5 + over the 21st century . + - 'Characteristics of adaptation pathways Adaptation can reduce the risks of climate + change impacts, but there are limits to its effectiveness, especially with greater + magnitudes and rates of climate change. Taking a longer-term perspective, in the + context of sustainable development, increases the likelihood that more immediate + adaptation actions will also enhance future options and preparedness. Adaptation + can contribute to the well-being of current and future populations, the security + of assets and the maintenance of ecosystem goods, functions and services now and + in the future. Adaptation is place- and context-specific, with no single approach + for reducing risks appropriate across all settings . Effective risk reduction + and adaptation strategies consider vulnerability and exposure and their linkages + with socio-economic processes, sustainable development, and climate change. Adaptation + research since the IPCC Fourth Assessment Report has evolved from a dominant consideration + of engineering and technological adaptation pathways to include more ecosystem-based, + institutional and social measures. A previous focus on cost–benefit analysis, + optimization and efficiency approaches has broadened with the development of multi-metric + evaluations that include risk and uncertainty dimensions integrated within wider + policy and ethical frameworks to assess tradeoffs and constraints. The range of + specific adaptation measures has also expanded, as have the links to sustainable + development. There are many studies on local and sectoral adaptation costs and + benefits, but few global analyses and very low confidence in their results. Adaptation + planning and implementation at all levels of governance are contingent on societal + values, objectives and risk perceptions. Recognition of diverse interests, circumstances, + social-cultural contexts and expectations can benefit decision-making processes. + Indigenous, local and traditional knowledge systems and practices, including indigenous + peoples’ holistic view of community and environment, are a major resource for + adapting to climate change, but these have not been used consistently in existing + adaptation efforts. Integrating such forms of knowledge into practices increases + the effectiveness of adaptation as do effective decision support, engagement and + policy processes. Adaptation planning and implementation can be enhanced through + complementary actions across levels, from individuals to governments. National + governments can coordinate adaptation efforts of local and sub-national governments, + for example by protecting vulnerable groups, by supporting economic diversification + and by providing information, policy and legal frameworks and financial support. + Local government and the private sector are increasingly recognized as critical + to progress in adaptation, given their roles in scaling up adaptation of communities, + households and civil society and in managing risk information and financing. A + first step towards adaptation to future climate change is reducing vulnerability + and exposure to present climate variability, but some near-term responses to climate + change may also limit future choices. Integration of adaptation into planning, + including policy design, and decision-making can promote synergies with development + and disaster risk reduction. However, poor planning or implementation, overemphasizing + short-term outcomes or failing to sufficiently anticipate consequences can result + in maladaptation, increasing the vulnerability or exposure of the target group + in the future or the vulnerability of other people, places or sectors. For example, + enhanced protection of exposed assets can lock in dependence on further protection + measures. Appropriate adaptation options can be better assessed by including co-benefits + and mitigation implications. Numerous interacting constraints can impede adaptation + planning and implementation. Common constraints on implementation arise from the + following: limited financial and human resources; limited integration or coordination + of governance; uncertainties about projected impacts; different perceptions of + risks; competing values; absence of key adaptation leaders and advocates; and + limited tools to monitor adaptation effectiveness. Other constraints include insufficient + research, monitoring and observation and the financial and other resources to + maintain them. Underestimating the complexity of adaptation as a social process + can create unrealistic expectations about achieving intended adaptation outcomes + . Greater rates and magnitude of climate change increase the likelihood of exceeding + adaptation limits. Limits to adaptation occur when adaptive actions to avoid intolerable + risks for an actor’s objectives or for the needs of a system are not possible + or are not currently available. Value-based judgments of what constitutes an intolerable + risk may differ. Limits to adaptation emerge from the interaction among climate + change and biophysical and/or socio-economic constraints. Opportunities to take + advantage of positive synergies between adaptation and mitigation may decrease + with time, particularly if limits to adaptation are exceeded. In some parts of + the world, insufficient responses to emerging impacts are already eroding the + basis for sustainable development. For most regions and sectors, empirical evidence + is not sufficient to quantify magnitudes of climate change that would constitute + a future adaptation limit. Furthermore, economic development, technology and cultural + norms and values can change over time to enhance or reduce the capacity of systems + to avoid limits. As a consequence, some limits are ‘soft’ in that they may be + alleviated over time. Other limits are ‘hard’ in that there are no reasonable + prospects for avoiding intolerable risks. Transformations in economic, social, + technological and political decisions and actions can enhance adaptation and promote + sustainable development. Restricting adaptation responses to incremental changes + to existing systems and structures without considering transformational change + may increase costs and losses and miss opportunities. For example, enhancing infrastructure + to protect other built assets can be expensive and ultimately not defray increasing + costs and risks, whereas options such as relocation or using ecosystem services + to adapt may provide a range of benefits now and in the future. Transformational + adaptation can include introduction of new technologies or practices, formation + of new financial structures or systems of governance, adaptation at greater scales + or magnitudes and shifts in the location of activities. Planning and implementation + of transformational adaptation could reflect strengthened, altered or aligned + paradigms and consequently may place new and increased demands on governance structures + to reconcile different goals and visions for the future and to address possible + equity and ethical implications: transformational adaptation pathways are enhanced + by iterative learning, deliberative processes, and innovation. At the national + level, transformation is considered most effective when it reflects a country’s + own visions and approaches to achieving sustainable development in accordance + with its national circumstances and priorities. Building adaptive capacity is + crucial for effective selection and implementation of adaptation options . Successful + adaptation requires not only identifying adaptation options and assessing their + costs and benefits, but also increasing the adaptive capacity of human and natural + systems . This can involve complex governance challenges and new institutions + and institutional arrangements. Significant co-benefits, synergies and trade-offs + exist between mitigation and adaptation and among different adaptation responses; + interactions occur both within and across regions . Increasing efforts to mitigate + and adapt to climate change imply an increasing complexity of interactions, particularly + at the intersections among water, energy, land use and biodiversity, but tools + to understand and manage these interactions remain limited. Examples of actions + with co-benefits include improved energy efficiency and cleaner energy sources, + leading to reduced emissions of health-damaging, climate-altering air pollutants; + reduced energy and water consumption in urban areas through greening cities and + recycling water; sustainable agriculture and forestry; and protection of ecosystems + for carbon storage and other ecosystem services.' + 2.3b: + - 'Future risks and impacts caused by a changing climate Climate change will amplify + existing risks and create new risks for natural and human systems. Risks are unevenly + distributed and are generally greater for disadvantaged people and communities + in countries at all levels of development. Increasing magnitudes of warming increase + the likelihood of severe, pervasive and irreversible impacts for people, species + and ecosystems. Continued high emissions would lead to mostly negative impacts + for biodiversity, ecosystem services and economic development and amplify risks + for livelihoods and for food and human security. Risk of climate-related impacts + results from the interaction of climate-related hazards with the vulnerability + and exposure of human and natural systems, including their ability to adapt. Rising + rates and magnitudes of warming and other changes in the climate system, accompanied + by ocean acidification, increase the risk of severe, pervasive, and in some cases, + irreversible detrimental impacts. Future climate change will amplify existing + climate-related risks and create new risks. Key risks are potentially severe + impacts relevant to understanding dangerous anthropogenic interference with the + climate system. Risks are considered key due to high hazard or high vulnerability + of societies and systems exposed, or both. Their identification is based on large + magnitude or high probability of impacts; irreversibility or timing of impacts; + persistent vulnerability or exposure; or limited potential to reduce risks. Some + risks are particularly relevant for individual regions, while others are global. + For risk assessment it is important to evaluate the widest possible range of impacts, + including low-probability outcomes with large consequences. Risk levels often + increase with temperature and are sometimes more directly linked to other dimensions + of climate change, such as the rate of warming, as well as the magnitudes and + rates of ocean acidification and sea level rise . Key risks that span sectors + and regions include the following : 1. Risk of severe ill-health and disrupted + livelihoods resulting from storm surges, sea level rise and coastal flooding; + inland flooding in some urban regions; and periods of extreme heat. 2. Systemic + risks due to extreme weather events leading to breakdown of infrastructure networks + and critical services. 3. Risk of food and water insecurity and loss of rural + livelihoods and income, particularly for poorer populations. 4. Risk of loss of + ecosystems, biodiversity and ecosystem goods, functions and services. The overall + risks of future climate change impacts can be reduced by limiting the rate and + magnitude of climate change, including ocean acidification. Some risks are considerable + even at 1°C global mean temperature increase above pre-industrial levels. Many + global risks are high to very high for global temperature increases of 4°C or + more. These risks include severe and widespread impacts on unique and threatened + systems, the extinction of many species, large risks to food security and compromised + normal human activities, including growing food or working outdoors in some areas + for parts of the year, due to the combination of high temperature and humidity. + The precise levels of climate change sufficient to trigger abrupt and irreversible + change remain uncertain, but the risk associated with crossing such thresholds + in the earth system or in interlinked human and natural systems increases with + rising temperature. Adaptation can substantially reduce the risks of climate + change impacts, but greater rates and magnitude of climate change increase the + likelihood of exceeding adaptation limits . The potential for adaptation, as well + as constraints and limits to adaptation, varies among sectors, regions, communities + and ecosystems. The scope for adaptation changes over time and is closely linked + to socio-economic development pathways and circumstances. See Figure 2.4 and Table + 2.3, along with Topics 3 and 4.' + - Climate change beyond 2100, irreversibility and abrupt changes Many aspects of + climate change and its associated impacts will continue for centuries, even if + anthropogenic emissions of greenhouse gases are stopped. The risks of abrupt or + irreversible changes increase as the magnitude of the warming increases. Warming + will continue beyond 2100 under all RCP scenarios except RCP2.6. Surface temperatures + will remain approximately constant at elevated levels for many centuries after + a complete cessation of net anthropogenic CO2 emissions . A large fraction of + anthropogenic climate change resulting from CO2 emissions is irreversible on a + multi-century to millennial timescale, except in the case of a large net removal + of CO2 from the atmosphere over a sustained period. Stabilization of global average + surface temperature does not imply stabilization for all aspects of the climate + system. Shifting biomes, re-equilibrating soil carbon, ice sheets, ocean temperatures + and associated sea level rise all have their own intrinsic long timescales that + will result in ongoing changes for hundreds to thousands of years after global + surface temperature has been stabilized. Ocean acidification will continue for + centuries if CO2 emissions continue, it will strongly affect marine ecosystems + , and the impact will be exacerbated by rising temperature extremes. Global mean + sea level rise will continue for many centuries beyond 2100. The few available + analyses that go beyond 2100 indicate sea level rise to be less than 1 m above + the pre-industrial level by 2300 for GHG concentrations that peak and decline + and remain below 500 ppm CO2-eq, as in scenario RCP2.6. For a radiative forcing + that corresponds to a CO2-eq concentration in 2100 that is above 700 ppm but below + 1500 ppm, as in scenario RCP8.5, the projected rise is 1 m to more than 3 m by + 2300 . There is low confidence in the available models’ ability to project solid + ice discharge from the Antarctic ice sheet. Hence, these models likely underestimate + the Antarctica ice sheet contribution, resulting in an underestimation of projected + sea level rise beyond 2100. There is little evidence in global climate models + of a tipping point or critical threshold in the transition from a perennially + ice-covered to a seasonally ice-free Arctic Ocean, beyond which further sea-ice + loss is unstoppable and irreversible. There is low confidence in assessing the + evolution of the Atlantic Meridional Overturning Circulation beyond the 21st century + because of the limited number of analyses and equivocal results. However, a collapse + beyond the 21st century for large sustained warming cannot be excluded. Sustained + mass loss by ice sheets would cause larger sea level rise, and part of the mass + loss might be irreversible. There is high confidence that sustained global mean + warming greater than a threshold would lead to the near-complete loss of the Greenland + ice sheet over a millennium or more, causing a sea level rise of up to 7 m. Current + estimates indicate that the threshold is greater than about 1°C but less than + about 4°C of global warming with respect to pre-industrial temperatures. Abrupt + and irreversible ice loss from a potential instability of marine-based sectors + of the Antarctic ice sheet in response to climate forcing is possible, but current + evidence and understanding is insufficient to make a quantitative assessment. Within + the 21st century, magnitudes and rates of climate change associated with medium + to high emission scenarios pose a high risk of abrupt and irreversible regional-scale + change in the composition, structure and function of marine, terrestrial and freshwater + ecosystems, including wetlands, as well as warm water coral reefs . Examples that + could substantially amplify climate change are the boreal-tundra Arctic system + and the Amazon forest. A reduction in permafrost extent is virtually certain + with continued rise in global temperatures. Current permafrost areas are projected + to become a net emitter of carbon with a loss of 180 to 920 GtCO2 under RCP8.5 + over the 21st century . + 2.3c: + - Ecosystems and their services in the oceans, along coasts, on land and in freshwater + Risks of harmful impacts on ecosystems and human systems increase with the rates + and magnitudes of warming, ocean acidification, sea level rise and other dimensions + of climate change. Future risk is indicated to be high by the observation that + natural global climate change at rates lower than current anthropogenic climate + change caused significant ecosystem shifts and species extinctions during the + past millions of years on land and in the oceans. Many plant and animal species + will be unable to adapt locally or move fast enough during the 21st century to + track suitable climates under mid- and high range rates of climate change . Coral + reefs and polar ecosystems are highly vulnerable. A large fraction of terrestrial, + freshwater and marine species faces increased extinction risk due to climate change + during and beyond the 21st century, especially as climate change interacts with + other stressors. Extinction risk is increased relative to pre-industrial and present + periods, under all RCP scenarios, as a result of both the magnitude and rate of + climate change . Extinctions will be driven by several climate-associated drivers and + the interactions among these drivers and their interaction with simultaneous habitat + modification, over-exploitation of stocks, pollution, eutrophication and invasive + species. Global marine species redistribution and marine biodiversity reduction + in sensitive regions, under climate change, will challenge the sustained provision + of fisheries productivity and other ecosystem services, especially at low latitudes + . By the mid-21st century, under 2°C global warming relative to pre-industrial + temperatures, shifts in the geographical range of marine species will cause species + richness and fisheries catch potential to increase, on average, at mid and high + latitudes and to decrease at tropical latitudes and in semi-enclosed seas. The + progressive expansion of Oxygen Minimum Zones and anoxic ‘dead zones’ in the oceans + will further constrain fish habitats. Open-ocean net primary production is projected + to redistribute and to decrease globally, by 2100, under all RCP scenarios. Climate + change adds to the threats of over-fishing and other non-climatic stressors . Marine + ecosystems, especially coral reefs and polar ecosystems, are at risk from ocean + acidification. Ocean acidification has impacts on the physiology, behaviour and + population dynamics of organisms. The impacts on individual species and the number + of species affected in species groups increase from RCP4.5 to RCP8.5. Highly calcified + molluscs, echinoderms and reef-building corals are more sensitive than crustaceans + and fishes. Ocean acidification acts together with other global changes and with + local changes , leading to interactive, complex and amplified impacts for species + and ecosystems. Carbon stored in the terrestrial biosphere is susceptible to + loss to the atmosphere as a result of climate change, deforestation and ecosystem + degradation. The aspects of climate change with direct effects on stored terrestrial + carbon include high temperatures, drought and windstorms; indirect effects include + increased risk of fires, pest and disease outbreaks. Increased tree mortality + and associated forest dieback is projected to occur in many regions over the 21st + century, posing risks for carbon storage, biodiversity, wood production, water + quality, amenity and economic activity. There is a high risk of substantial carbon + and methane emissions as a result of permafrost thawing. Coastal systems and + low-lying areas will increasingly experience submergence, flooding and erosion + throughout the 21st century and beyond, due to sea level rise. The population + and assets projected to be exposed to coastal risks as well as human pressures + on coastal ecosystems will increase significantly in the coming decades due to + population growth, economic development and urbanization. Climatic and non-climatic + drivers affecting coral reefs will erode habitats, increase coastline exposure + to waves and storms and degrade environmental features important to fisheries + and tourism. Some low-lying developing countries and small island states are expected + to face very high impacts that could have associated damage and adaptation costs + of several percentage points of gross domestic product . + - Water, food and urban systems, human health, security and livelihoods The fractions + of the global population that will experience water scarcity and be affected by + major river floods are projected to increase with the level of warming in the + 21st century . Climate change over the 21st century is projected to reduce renewable + surface water and groundwater resources in most dry subtropical regions, intensifying + competition for water among sectors . In presently dry regions, the frequency + of droughts will likely increase by the end of the 21st century under RCP8.5. + In contrast, water resources are projected to increase at high latitudes. The + interaction of increased temperature; increased sediment, nutrient and pollutant + loadings from heavy rainfall; increased concentrations of pollutants during droughts; + and disruption of treatment facilities during floods will reduce raw water quality + and pose risks to drinking water quality. All aspects of food security are potentially + affected by climate change, including food production, access, use and price stability. + For wheat, rice and maize in tropical and temperate regions, climate change without + adaptation is projected to negatively impact production at local temperature increases + of 2°C or more above late 20th century levels, although individual locations may + benefit. Projected impacts vary across crops and regions and adaptation scenarios, + with about 10% of projections for the 2030–2049 period showing yield gains of + more than 10%, and about 10% of projections showing yield losses of more than + 25%, compared with the late 20th century. Global temperature increases of ~4°C + or more above late 20th century levels, combined with increasing food demand, + would pose large risks to food security, both globally and regionally. The relationship + between global and regional warming is explained in 2.2.1. Until mid-century, + projected climate change will impact human health mainly by exacerbating health + problems that already exist. Throughout the 21st century, climate change is expected + to lead to increases in ill-health in many regions and especially in developing + countries with low income, as compared to a baseline without climate change . + Health impacts include greater likelihood of injury and death due to more intense + heat waves and fires, increased risks from foodborne and waterborne diseases and + loss of work capacity and reduced labour productivity in vulnerable populations + . Risks of undernutrition in poor regions will increase . Risks from vector-borne + diseases are projected to generally increase with warming, due to the extension + of the infection area and season, despite reductions in some areas that become + too hot for disease vectors. Globally, the magnitude and severity of negative + impacts will increasingly outweigh positive impacts . By 2100 for RCP8.5, the + combination of high temperature and humidity in some areas for parts of the year + is expected to compromise common human activities, including growing food and + working outdoors. In urban areas, climate change is projected to increase risks + for people, assets, economies and ecosystems, including risks from heat stress, + storms and extreme precipitation, inland and coastal flooding, landslides, air + pollution, drought, water scarcity, sea level rise and storm surges. These risks + will be amplified for those lacking essential infrastructure and services or living + in exposed areas. Rural areas are expected to experience major impacts on water + availability and supply, food security, infrastructure and agricultural incomes, + including shifts in the production areas of food and non-food crops around the + world . These impacts will disproportionately affect the welfare of the poor in + rural areas, such as female-headed households and those with limited access to + land, modern agricultural inputs, infrastructure and education. Aggregate economic + losses accelerate with increasing temperature, but global economic impacts from + climate change are currently difficult to estimate. With recognized limitations, + the existing incomplete estimates of global annual economic losses for warming + of ~2.5°C above pre-industrial levels are 0.2 to 2.0% of income . Changes in population, + age structure, income, technology, relative prices, lifestyle, regulation and + governance are projected to have relatively larger impacts than climate change, + for most economic sectors. More severe and/or frequent weather hazards are projected + to increase disaster-related losses and loss variability, posing challenges for + affordable insurance, particularly in developing countries. International dimensions + such as trade and relations among states are also important for understanding + the risks of climate change at regional scales. From a poverty perspective, climate + change impacts are projected to slow down economic growth, make poverty reduction + more difficult, further erode food security and prolong existing poverty traps + and create new ones, the latter particularly in urban areas and emerging hotspots + of hunger . Climate change impacts are expected to exacerbate poverty in most + developing countries and create new poverty pockets in countries with increasing + inequality, in both developed and developing countries . Climate change is projected + to increase displacement of people . Displacement risk increases when populations + that lack the resources for planned migration experience higher exposure to extreme + weather events, such as floods and droughts. Expanding opportunities for mobility + can reduce vulnerability for such populations. Changes in migration patterns can + be responses to both extreme weather events and longer term climate variability + and change, and migration can also be an effective adaptation strategy. Climate + change can indirectly increase risks of violent conflict by amplifying well-documented + drivers of these conflicts, such as poverty and economic shocks. Multiple lines + of evidence relate climate variability to some forms of conflict. + 2.3e: + - Water, food and urban systems, human health, security and livelihoods The fractions + of the global population that will experience water scarcity and be affected by + major river floods are projected to increase with the level of warming in the + 21st century . Climate change over the 21st century is projected to reduce renewable + surface water and groundwater resources in most dry subtropical regions, intensifying + competition for water among sectors . In presently dry regions, the frequency + of droughts will likely increase by the end of the 21st century under RCP8.5. + In contrast, water resources are projected to increase at high latitudes. The + interaction of increased temperature; increased sediment, nutrient and pollutant + loadings from heavy rainfall; increased concentrations of pollutants during droughts; + and disruption of treatment facilities during floods will reduce raw water quality + and pose risks to drinking water quality. All aspects of food security are potentially + affected by climate change, including food production, access, use and price stability. + For wheat, rice and maize in tropical and temperate regions, climate change without + adaptation is projected to negatively impact production at local temperature increases + of 2°C or more above late 20th century levels, although individual locations may + benefit. Projected impacts vary across crops and regions and adaptation scenarios, + with about 10% of projections for the 2030–2049 period showing yield gains of + more than 10%, and about 10% of projections showing yield losses of more than + 25%, compared with the late 20th century. Global temperature increases of ~4°C + or more above late 20th century levels, combined with increasing food demand, + would pose large risks to food security, both globally and regionally. The relationship + between global and regional warming is explained in 2.2.1. Until mid-century, + projected climate change will impact human health mainly by exacerbating health + problems that already exist. Throughout the 21st century, climate change is expected + to lead to increases in ill-health in many regions and especially in developing + countries with low income, as compared to a baseline without climate change . + Health impacts include greater likelihood of injury and death due to more intense + heat waves and fires, increased risks from foodborne and waterborne diseases and + loss of work capacity and reduced labour productivity in vulnerable populations + . Risks of undernutrition in poor regions will increase . Risks from vector-borne + diseases are projected to generally increase with warming, due to the extension + of the infection area and season, despite reductions in some areas that become + too hot for disease vectors. Globally, the magnitude and severity of negative + impacts will increasingly outweigh positive impacts . By 2100 for RCP8.5, the + combination of high temperature and humidity in some areas for parts of the year + is expected to compromise common human activities, including growing food and + working outdoors. In urban areas, climate change is projected to increase risks + for people, assets, economies and ecosystems, including risks from heat stress, + storms and extreme precipitation, inland and coastal flooding, landslides, air + pollution, drought, water scarcity, sea level rise and storm surges. These risks + will be amplified for those lacking essential infrastructure and services or living + in exposed areas. Rural areas are expected to experience major impacts on water + availability and supply, food security, infrastructure and agricultural incomes, + including shifts in the production areas of food and non-food crops around the + world . These impacts will disproportionately affect the welfare of the poor in + rural areas, such as female-headed households and those with limited access to + land, modern agricultural inputs, infrastructure and education. Aggregate economic + losses accelerate with increasing temperature, but global economic impacts from + climate change are currently difficult to estimate. With recognized limitations, + the existing incomplete estimates of global annual economic losses for warming + of ~2.5°C above pre-industrial levels are 0.2 to 2.0% of income . Changes in population, + age structure, income, technology, relative prices, lifestyle, regulation and + governance are projected to have relatively larger impacts than climate change, + for most economic sectors. More severe and/or frequent weather hazards are projected + to increase disaster-related losses and loss variability, posing challenges for + affordable insurance, particularly in developing countries. International dimensions + such as trade and relations among states are also important for understanding + the risks of climate change at regional scales. From a poverty perspective, climate + change impacts are projected to slow down economic growth, make poverty reduction + more difficult, further erode food security and prolong existing poverty traps + and create new ones, the latter particularly in urban areas and emerging hotspots + of hunger . Climate change impacts are expected to exacerbate poverty in most + developing countries and create new poverty pockets in countries with increasing + inequality, in both developed and developing countries . Climate change is projected + to increase displacement of people . Displacement risk increases when populations + that lack the resources for planned migration experience higher exposure to extreme + weather events, such as floods and droughts. Expanding opportunities for mobility + can reduce vulnerability for such populations. Changes in migration patterns can + be responses to both extreme weather events and longer term climate variability + and change, and migration can also be an effective adaptation strategy. Climate + change can indirectly increase risks of violent conflict by amplifying well-documented + drivers of these conflicts, such as poverty and economic shocks. Multiple lines + of evidence relate climate variability to some forms of conflict. + 2.3f: + - Water, food and urban systems, human health, security and livelihoods The fractions + of the global population that will experience water scarcity and be affected by + major river floods are projected to increase with the level of warming in the + 21st century . Climate change over the 21st century is projected to reduce renewable + surface water and groundwater resources in most dry subtropical regions, intensifying + competition for water among sectors . In presently dry regions, the frequency + of droughts will likely increase by the end of the 21st century under RCP8.5. + In contrast, water resources are projected to increase at high latitudes. The + interaction of increased temperature; increased sediment, nutrient and pollutant + loadings from heavy rainfall; increased concentrations of pollutants during droughts; + and disruption of treatment facilities during floods will reduce raw water quality + and pose risks to drinking water quality. All aspects of food security are potentially + affected by climate change, including food production, access, use and price stability. + For wheat, rice and maize in tropical and temperate regions, climate change without + adaptation is projected to negatively impact production at local temperature increases + of 2°C or more above late 20th century levels, although individual locations may + benefit. Projected impacts vary across crops and regions and adaptation scenarios, + with about 10% of projections for the 2030–2049 period showing yield gains of + more than 10%, and about 10% of projections showing yield losses of more than + 25%, compared with the late 20th century. Global temperature increases of ~4°C + or more above late 20th century levels, combined with increasing food demand, + would pose large risks to food security, both globally and regionally. The relationship + between global and regional warming is explained in 2.2.1. Until mid-century, + projected climate change will impact human health mainly by exacerbating health + problems that already exist. Throughout the 21st century, climate change is expected + to lead to increases in ill-health in many regions and especially in developing + countries with low income, as compared to a baseline without climate change . + Health impacts include greater likelihood of injury and death due to more intense + heat waves and fires, increased risks from foodborne and waterborne diseases and + loss of work capacity and reduced labour productivity in vulnerable populations + . Risks of undernutrition in poor regions will increase . Risks from vector-borne + diseases are projected to generally increase with warming, due to the extension + of the infection area and season, despite reductions in some areas that become + too hot for disease vectors. Globally, the magnitude and severity of negative + impacts will increasingly outweigh positive impacts . By 2100 for RCP8.5, the + combination of high temperature and humidity in some areas for parts of the year + is expected to compromise common human activities, including growing food and + working outdoors. In urban areas, climate change is projected to increase risks + for people, assets, economies and ecosystems, including risks from heat stress, + storms and extreme precipitation, inland and coastal flooding, landslides, air + pollution, drought, water scarcity, sea level rise and storm surges. These risks + will be amplified for those lacking essential infrastructure and services or living + in exposed areas. Rural areas are expected to experience major impacts on water + availability and supply, food security, infrastructure and agricultural incomes, + including shifts in the production areas of food and non-food crops around the + world . These impacts will disproportionately affect the welfare of the poor in + rural areas, such as female-headed households and those with limited access to + land, modern agricultural inputs, infrastructure and education. Aggregate economic + losses accelerate with increasing temperature, but global economic impacts from + climate change are currently difficult to estimate. With recognized limitations, + the existing incomplete estimates of global annual economic losses for warming + of ~2.5°C above pre-industrial levels are 0.2 to 2.0% of income . Changes in population, + age structure, income, technology, relative prices, lifestyle, regulation and + governance are projected to have relatively larger impacts than climate change, + for most economic sectors. More severe and/or frequent weather hazards are projected + to increase disaster-related losses and loss variability, posing challenges for + affordable insurance, particularly in developing countries. International dimensions + such as trade and relations among states are also important for understanding + the risks of climate change at regional scales. From a poverty perspective, climate + change impacts are projected to slow down economic growth, make poverty reduction + more difficult, further erode food security and prolong existing poverty traps + and create new ones, the latter particularly in urban areas and emerging hotspots + of hunger . Climate change impacts are expected to exacerbate poverty in most + developing countries and create new poverty pockets in countries with increasing + inequality, in both developed and developing countries . Climate change is projected + to increase displacement of people . Displacement risk increases when populations + that lack the resources for planned migration experience higher exposure to extreme + weather events, such as floods and droughts. Expanding opportunities for mobility + can reduce vulnerability for such populations. Changes in migration patterns can + be responses to both extreme weather events and longer term climate variability + and change, and migration can also be an effective adaptation strategy. Climate + change can indirectly increase risks of violent conflict by amplifying well-documented + drivers of these conflicts, such as poverty and economic shocks. Multiple lines + of evidence relate climate variability to some forms of conflict. + 2.4a: + - Climate change beyond 2100, irreversibility and abrupt changes Many aspects of + climate change and its associated impacts will continue for centuries, even if + anthropogenic emissions of greenhouse gases are stopped. The risks of abrupt or + irreversible changes increase as the magnitude of the warming increases. Warming + will continue beyond 2100 under all RCP scenarios except RCP2.6. Surface temperatures + will remain approximately constant at elevated levels for many centuries after + a complete cessation of net anthropogenic CO2 emissions . A large fraction of + anthropogenic climate change resulting from CO2 emissions is irreversible on a + multi-century to millennial timescale, except in the case of a large net removal + of CO2 from the atmosphere over a sustained period. Stabilization of global average + surface temperature does not imply stabilization for all aspects of the climate + system. Shifting biomes, re-equilibrating soil carbon, ice sheets, ocean temperatures + and associated sea level rise all have their own intrinsic long timescales that + will result in ongoing changes for hundreds to thousands of years after global + surface temperature has been stabilized. Ocean acidification will continue for + centuries if CO2 emissions continue, it will strongly affect marine ecosystems + , and the impact will be exacerbated by rising temperature extremes. Global mean + sea level rise will continue for many centuries beyond 2100. The few available + analyses that go beyond 2100 indicate sea level rise to be less than 1 m above + the pre-industrial level by 2300 for GHG concentrations that peak and decline + and remain below 500 ppm CO2-eq, as in scenario RCP2.6. For a radiative forcing + that corresponds to a CO2-eq concentration in 2100 that is above 700 ppm but below + 1500 ppm, as in scenario RCP8.5, the projected rise is 1 m to more than 3 m by + 2300 . There is low confidence in the available models’ ability to project solid + ice discharge from the Antarctic ice sheet. Hence, these models likely underestimate + the Antarctica ice sheet contribution, resulting in an underestimation of projected + sea level rise beyond 2100. There is little evidence in global climate models + of a tipping point or critical threshold in the transition from a perennially + ice-covered to a seasonally ice-free Arctic Ocean, beyond which further sea-ice + loss is unstoppable and irreversible. There is low confidence in assessing the + evolution of the Atlantic Meridional Overturning Circulation beyond the 21st century + because of the limited number of analyses and equivocal results. However, a collapse + beyond the 21st century for large sustained warming cannot be excluded. Sustained + mass loss by ice sheets would cause larger sea level rise, and part of the mass + loss might be irreversible. There is high confidence that sustained global mean + warming greater than a threshold would lead to the near-complete loss of the Greenland + ice sheet over a millennium or more, causing a sea level rise of up to 7 m. Current + estimates indicate that the threshold is greater than about 1°C but less than + about 4°C of global warming with respect to pre-industrial temperatures. Abrupt + and irreversible ice loss from a potential instability of marine-based sectors + of the Antarctic ice sheet in response to climate forcing is possible, but current + evidence and understanding is insufficient to make a quantitative assessment. Within + the 21st century, magnitudes and rates of climate change associated with medium + to high emission scenarios pose a high risk of abrupt and irreversible regional-scale + change in the composition, structure and function of marine, terrestrial and freshwater + ecosystems, including wetlands, as well as warm water coral reefs . Examples that + could substantially amplify climate change are the boreal-tundra Arctic system + and the Amazon forest. A reduction in permafrost extent is virtually certain + with continued rise in global temperatures. Current permafrost areas are projected + to become a net emitter of carbon with a loss of 180 to 920 GtCO2 under RCP8.5 + over the 21st century . + 2.4b: + - Climate change beyond 2100, irreversibility and abrupt changes Many aspects of + climate change and its associated impacts will continue for centuries, even if + anthropogenic emissions of greenhouse gases are stopped. The risks of abrupt or + irreversible changes increase as the magnitude of the warming increases. Warming + will continue beyond 2100 under all RCP scenarios except RCP2.6. Surface temperatures + will remain approximately constant at elevated levels for many centuries after + a complete cessation of net anthropogenic CO2 emissions . A large fraction of + anthropogenic climate change resulting from CO2 emissions is irreversible on a + multi-century to millennial timescale, except in the case of a large net removal + of CO2 from the atmosphere over a sustained period. Stabilization of global average + surface temperature does not imply stabilization for all aspects of the climate + system. Shifting biomes, re-equilibrating soil carbon, ice sheets, ocean temperatures + and associated sea level rise all have their own intrinsic long timescales that + will result in ongoing changes for hundreds to thousands of years after global + surface temperature has been stabilized. Ocean acidification will continue for + centuries if CO2 emissions continue, it will strongly affect marine ecosystems + , and the impact will be exacerbated by rising temperature extremes. Global mean + sea level rise will continue for many centuries beyond 2100. The few available + analyses that go beyond 2100 indicate sea level rise to be less than 1 m above + the pre-industrial level by 2300 for GHG concentrations that peak and decline + and remain below 500 ppm CO2-eq, as in scenario RCP2.6. For a radiative forcing + that corresponds to a CO2-eq concentration in 2100 that is above 700 ppm but below + 1500 ppm, as in scenario RCP8.5, the projected rise is 1 m to more than 3 m by + 2300 . There is low confidence in the available models’ ability to project solid + ice discharge from the Antarctic ice sheet. Hence, these models likely underestimate + the Antarctica ice sheet contribution, resulting in an underestimation of projected + sea level rise beyond 2100. There is little evidence in global climate models + of a tipping point or critical threshold in the transition from a perennially + ice-covered to a seasonally ice-free Arctic Ocean, beyond which further sea-ice + loss is unstoppable and irreversible. There is low confidence in assessing the + evolution of the Atlantic Meridional Overturning Circulation beyond the 21st century + because of the limited number of analyses and equivocal results. However, a collapse + beyond the 21st century for large sustained warming cannot be excluded. Sustained + mass loss by ice sheets would cause larger sea level rise, and part of the mass + loss might be irreversible. There is high confidence that sustained global mean + warming greater than a threshold would lead to the near-complete loss of the Greenland + ice sheet over a millennium or more, causing a sea level rise of up to 7 m. Current + estimates indicate that the threshold is greater than about 1°C but less than + about 4°C of global warming with respect to pre-industrial temperatures. Abrupt + and irreversible ice loss from a potential instability of marine-based sectors + of the Antarctic ice sheet in response to climate forcing is possible, but current + evidence and understanding is insufficient to make a quantitative assessment. Within + the 21st century, magnitudes and rates of climate change associated with medium + to high emission scenarios pose a high risk of abrupt and irreversible regional-scale + change in the composition, structure and function of marine, terrestrial and freshwater + ecosystems, including wetlands, as well as warm water coral reefs . Examples that + could substantially amplify climate change are the boreal-tundra Arctic system + and the Amazon forest. A reduction in permafrost extent is virtually certain + with continued rise in global temperatures. Current permafrost areas are projected + to become a net emitter of carbon with a loss of 180 to 920 GtCO2 under RCP8.5 + over the 21st century . + 2.4c: + - Climate change beyond 2100, irreversibility and abrupt changes Many aspects of + climate change and its associated impacts will continue for centuries, even if + anthropogenic emissions of greenhouse gases are stopped. The risks of abrupt or + irreversible changes increase as the magnitude of the warming increases. Warming + will continue beyond 2100 under all RCP scenarios except RCP2.6. Surface temperatures + will remain approximately constant at elevated levels for many centuries after + a complete cessation of net anthropogenic CO2 emissions . A large fraction of + anthropogenic climate change resulting from CO2 emissions is irreversible on a + multi-century to millennial timescale, except in the case of a large net removal + of CO2 from the atmosphere over a sustained period. Stabilization of global average + surface temperature does not imply stabilization for all aspects of the climate + system. Shifting biomes, re-equilibrating soil carbon, ice sheets, ocean temperatures + and associated sea level rise all have their own intrinsic long timescales that + will result in ongoing changes for hundreds to thousands of years after global + surface temperature has been stabilized. Ocean acidification will continue for + centuries if CO2 emissions continue, it will strongly affect marine ecosystems + , and the impact will be exacerbated by rising temperature extremes. Global mean + sea level rise will continue for many centuries beyond 2100. The few available + analyses that go beyond 2100 indicate sea level rise to be less than 1 m above + the pre-industrial level by 2300 for GHG concentrations that peak and decline + and remain below 500 ppm CO2-eq, as in scenario RCP2.6. For a radiative forcing + that corresponds to a CO2-eq concentration in 2100 that is above 700 ppm but below + 1500 ppm, as in scenario RCP8.5, the projected rise is 1 m to more than 3 m by + 2300 . There is low confidence in the available models’ ability to project solid + ice discharge from the Antarctic ice sheet. Hence, these models likely underestimate + the Antarctica ice sheet contribution, resulting in an underestimation of projected + sea level rise beyond 2100. There is little evidence in global climate models + of a tipping point or critical threshold in the transition from a perennially + ice-covered to a seasonally ice-free Arctic Ocean, beyond which further sea-ice + loss is unstoppable and irreversible. There is low confidence in assessing the + evolution of the Atlantic Meridional Overturning Circulation beyond the 21st century + because of the limited number of analyses and equivocal results. However, a collapse + beyond the 21st century for large sustained warming cannot be excluded. Sustained + mass loss by ice sheets would cause larger sea level rise, and part of the mass + loss might be irreversible. There is high confidence that sustained global mean + warming greater than a threshold would lead to the near-complete loss of the Greenland + ice sheet over a millennium or more, causing a sea level rise of up to 7 m. Current + estimates indicate that the threshold is greater than about 1°C but less than + about 4°C of global warming with respect to pre-industrial temperatures. Abrupt + and irreversible ice loss from a potential instability of marine-based sectors + of the Antarctic ice sheet in response to climate forcing is possible, but current + evidence and understanding is insufficient to make a quantitative assessment. Within + the 21st century, magnitudes and rates of climate change associated with medium + to high emission scenarios pose a high risk of abrupt and irreversible regional-scale + change in the composition, structure and function of marine, terrestrial and freshwater + ecosystems, including wetlands, as well as warm water coral reefs . Examples that + could substantially amplify climate change are the boreal-tundra Arctic system + and the Amazon forest. A reduction in permafrost extent is virtually certain + with continued rise in global temperatures. Current permafrost areas are projected + to become a net emitter of carbon with a loss of 180 to 920 GtCO2 under RCP8.5 + over the 21st century . + 2.4d: + - Climate change beyond 2100, irreversibility and abrupt changes Many aspects of + climate change and its associated impacts will continue for centuries, even if + anthropogenic emissions of greenhouse gases are stopped. The risks of abrupt or + irreversible changes increase as the magnitude of the warming increases. Warming + will continue beyond 2100 under all RCP scenarios except RCP2.6. Surface temperatures + will remain approximately constant at elevated levels for many centuries after + a complete cessation of net anthropogenic CO2 emissions . A large fraction of + anthropogenic climate change resulting from CO2 emissions is irreversible on a + multi-century to millennial timescale, except in the case of a large net removal + of CO2 from the atmosphere over a sustained period. Stabilization of global average + surface temperature does not imply stabilization for all aspects of the climate + system. Shifting biomes, re-equilibrating soil carbon, ice sheets, ocean temperatures + and associated sea level rise all have their own intrinsic long timescales that + will result in ongoing changes for hundreds to thousands of years after global + surface temperature has been stabilized. Ocean acidification will continue for + centuries if CO2 emissions continue, it will strongly affect marine ecosystems + , and the impact will be exacerbated by rising temperature extremes. Global mean + sea level rise will continue for many centuries beyond 2100. The few available + analyses that go beyond 2100 indicate sea level rise to be less than 1 m above + the pre-industrial level by 2300 for GHG concentrations that peak and decline + and remain below 500 ppm CO2-eq, as in scenario RCP2.6. For a radiative forcing + that corresponds to a CO2-eq concentration in 2100 that is above 700 ppm but below + 1500 ppm, as in scenario RCP8.5, the projected rise is 1 m to more than 3 m by + 2300 . There is low confidence in the available models’ ability to project solid + ice discharge from the Antarctic ice sheet. Hence, these models likely underestimate + the Antarctica ice sheet contribution, resulting in an underestimation of projected + sea level rise beyond 2100. There is little evidence in global climate models + of a tipping point or critical threshold in the transition from a perennially + ice-covered to a seasonally ice-free Arctic Ocean, beyond which further sea-ice + loss is unstoppable and irreversible. There is low confidence in assessing the + evolution of the Atlantic Meridional Overturning Circulation beyond the 21st century + because of the limited number of analyses and equivocal results. However, a collapse + beyond the 21st century for large sustained warming cannot be excluded. Sustained + mass loss by ice sheets would cause larger sea level rise, and part of the mass + loss might be irreversible. There is high confidence that sustained global mean + warming greater than a threshold would lead to the near-complete loss of the Greenland + ice sheet over a millennium or more, causing a sea level rise of up to 7 m. Current + estimates indicate that the threshold is greater than about 1°C but less than + about 4°C of global warming with respect to pre-industrial temperatures. Abrupt + and irreversible ice loss from a potential instability of marine-based sectors + of the Antarctic ice sheet in response to climate forcing is possible, but current + evidence and understanding is insufficient to make a quantitative assessment. Within + the 21st century, magnitudes and rates of climate change associated with medium + to high emission scenarios pose a high risk of abrupt and irreversible regional-scale + change in the composition, structure and function of marine, terrestrial and freshwater + ecosystems, including wetlands, as well as warm water coral reefs . Examples that + could substantially amplify climate change are the boreal-tundra Arctic system + and the Amazon forest. A reduction in permafrost extent is virtually certain + with continued rise in global temperatures. Current permafrost areas are projected + to become a net emitter of carbon with a loss of 180 to 920 GtCO2 under RCP8.5 + over the 21st century . + 3.1a: + - 'Foundations of decision-making about climate change Effective decision-making + to limit climate change and its effects can be informed by a wide range of analytical + approaches for evaluating expected risks and benefits, recognizing the importance + of governance, ethical dimensions, equity, value judgments, economic assessments + and diverse perceptions and responses to risk and uncertainty. Sustainable development + and equity provide a basis for assessing climate policies. Limiting the effects + of climate change is necessary to achieve sustainable development and equity, + including poverty eradication. Countries’ past and future contributions to the + accumulation of GHGs in the atmosphere are different, and countries also face + varying challenges and circumstances and have different capacities to address + mitigation and adaptation. Mitigation and adaptation raise issues of equity, justice + and fairness and are necessary to achieve sustainable development and poverty + eradication. Many of those most vulnerable to climate change have contributed + and contribute little to GHG emissions. Delaying mitigation shifts burdens from + the present to the future, and insufficient adaptation responses to emerging impacts + are already eroding the basis for sustainable development. Both adaptation and + mitigation can have distributional effects locally, nationally and internationally, + depending on who pays and who benefits. The process of decision-making about climate + change, and the degree to which it respects the rights and views of all those + affected, is also a concern of justice. Effective mitigation will not be achieved + if individual agents advance their own interests independently. Climate change + has the characteristics of a collective action problem at the global scale, because + most GHGs accumulate over time and mix globally, and emissions by any agent affect + other agents. Cooperative responses, including international cooperation, are + therefore required to effectively mitigate GHG emissions and address other climate + change issues. The effectiveness of adaptation can be enhanced through complementary + actions across levels, including international cooperation. The evidence suggests + that outcomes seen as equitable can lead to more effective cooperation. Decision-making + about climate change involves valuation and mediation among diverse values and + may be aided by the analytic methods of several normative disciplines. Ethics + analyses the different values involved and the relations between them. Recent + political philosophy has investigated the question of responsibility for the effects + of emissions. Economics and decision analysis provide quantitative methods of + valuation which can be used for estimating the social cost of carbon, in cost–benefit + and costeffectiveness analyses, for optimization in integrated models and elsewhere. + Economic methods can reflect ethical principles, and take account of non-marketed + goods, equity, behavioural biases, ancillary benefits and costs and the differing + values of money to different people. They are, however, subject to well-documented + limitations. Analytical methods of valuation cannot identify a single best balance + between mitigation, adaptation and residual climate impacts. Important reasons + for this are that climate change involves extremely complex natural and social + processes, there is extensive disagreement about the values concerned, and climate + change impacts and mitigation approaches have important distributional effects. + Nevertheless, information on the consequences of emissions pathways to alternative + climate goals and risk levels can be a useful input into decision-making processes. + Evaluating responses to climate change involves assessment of the widest possible + range of impacts, including low-probability outcomes with large consequences. Effective + decision-making and risk management in the complex environment of climate change + may be iterative: strategies can often be adjusted as new information and understanding + develops during implementation. However, adaptation and mitigation choices in + the near term will affect the risks of climate change throughout the 21st century + and beyond, and prospects for climate-resilient pathways for sustainable development + depend on what is achieved through mitigation. Opportunities to take advantage + of positive synergies between adaptation and mitigation may decrease with time, + particularly if mitigation is delayed too long. Decision-making about climate + change is influenced by how individuals and organizations perceive risks and uncertainties + and take them into account. They sometimes use simplified decision rules, overestimate + or underestimate risks and are biased towards the status quo. They differ in their + degree of risk aversion and the relative importance placed on near-term versus + long-term ramifications of specific actions. Formalized analytical methods for + decision-making under uncertainty can account accurately for risk, and focus attention + on both short- and long-term consequences.' + 3.1b: + - 'Foundations of decision-making about climate change Effective decision-making + to limit climate change and its effects can be informed by a wide range of analytical + approaches for evaluating expected risks and benefits, recognizing the importance + of governance, ethical dimensions, equity, value judgments, economic assessments + and diverse perceptions and responses to risk and uncertainty. Sustainable development + and equity provide a basis for assessing climate policies. Limiting the effects + of climate change is necessary to achieve sustainable development and equity, + including poverty eradication. Countries’ past and future contributions to the + accumulation of GHGs in the atmosphere are different, and countries also face + varying challenges and circumstances and have different capacities to address + mitigation and adaptation. Mitigation and adaptation raise issues of equity, justice + and fairness and are necessary to achieve sustainable development and poverty + eradication. Many of those most vulnerable to climate change have contributed + and contribute little to GHG emissions. Delaying mitigation shifts burdens from + the present to the future, and insufficient adaptation responses to emerging impacts + are already eroding the basis for sustainable development. Both adaptation and + mitigation can have distributional effects locally, nationally and internationally, + depending on who pays and who benefits. The process of decision-making about climate + change, and the degree to which it respects the rights and views of all those + affected, is also a concern of justice. Effective mitigation will not be achieved + if individual agents advance their own interests independently. Climate change + has the characteristics of a collective action problem at the global scale, because + most GHGs accumulate over time and mix globally, and emissions by any agent affect + other agents. Cooperative responses, including international cooperation, are + therefore required to effectively mitigate GHG emissions and address other climate + change issues. The effectiveness of adaptation can be enhanced through complementary + actions across levels, including international cooperation. The evidence suggests + that outcomes seen as equitable can lead to more effective cooperation. Decision-making + about climate change involves valuation and mediation among diverse values and + may be aided by the analytic methods of several normative disciplines. Ethics + analyses the different values involved and the relations between them. Recent + political philosophy has investigated the question of responsibility for the effects + of emissions. Economics and decision analysis provide quantitative methods of + valuation which can be used for estimating the social cost of carbon, in cost–benefit + and costeffectiveness analyses, for optimization in integrated models and elsewhere. + Economic methods can reflect ethical principles, and take account of non-marketed + goods, equity, behavioural biases, ancillary benefits and costs and the differing + values of money to different people. They are, however, subject to well-documented + limitations. Analytical methods of valuation cannot identify a single best balance + between mitigation, adaptation and residual climate impacts. Important reasons + for this are that climate change involves extremely complex natural and social + processes, there is extensive disagreement about the values concerned, and climate + change impacts and mitigation approaches have important distributional effects. + Nevertheless, information on the consequences of emissions pathways to alternative + climate goals and risk levels can be a useful input into decision-making processes. + Evaluating responses to climate change involves assessment of the widest possible + range of impacts, including low-probability outcomes with large consequences. Effective + decision-making and risk management in the complex environment of climate change + may be iterative: strategies can often be adjusted as new information and understanding + develops during implementation. However, adaptation and mitigation choices in + the near term will affect the risks of climate change throughout the 21st century + and beyond, and prospects for climate-resilient pathways for sustainable development + depend on what is achieved through mitigation. Opportunities to take advantage + of positive synergies between adaptation and mitigation may decrease with time, + particularly if mitigation is delayed too long. Decision-making about climate + change is influenced by how individuals and organizations perceive risks and uncertainties + and take them into account. They sometimes use simplified decision rules, overestimate + or underestimate risks and are biased towards the status quo. They differ in their + degree of risk aversion and the relative importance placed on near-term versus + long-term ramifications of specific actions. Formalized analytical methods for + decision-making under uncertainty can account accurately for risk, and focus attention + on both short- and long-term consequences.' + - Interaction among mitigation, adaptation and sustainable development Climate + change is a threat to equitable and sustainable development. Adaptation, mitigation + and sustainable development are closely related, with potential for synergies + and trade-offs. Climate change poses an increasing threat to equitable and sustainable + development. Some climate-related impacts on development are already being observed. + Climate change is a threat multiplier. It exacerbates other threats to social + and natural systems, placing additional burdens particularly on the poor and constraining + possible development paths for all. Development along current global pathways + can contribute to climate risk and vulnerability, further eroding the basis for + sustainable development. Aligning climate policy with sustainable development + requires attention to both adaptation and mitigation. Interaction among adaptation, + mitigation and sustainable development occurs both within and across regions and + scales, often in the context of multiple stressors. Some options for responding + to climate change could impose risks of other environmental and social costs, + have adverse distributional effects and draw resources away from other development + priorities, including poverty eradication. Both adaptation and mitigation can + bring substantial co-benefits . Examples of actions with co-benefits include improved + air quality; enhanced energy security, reduced energy and water consumption in + urban areas through greening cities and recycling water; sustainable agriculture + and forestry; and protection of ecosystems for carbon storage and other ecosystem + services. Strategies and actions can be pursued now that will move towards climate-resilient + pathways for sustainable development, while at the same time helping to improve + livelihoods, social and economic well-being and effective environmental management. + Prospects for climate-resilient pathways are related fundamentally to what the + world accomplishes with climate change mitigation. Since mitigation reduces the + rate as well as the magnitude of warming, it also increases the time available + for adaptation to a particular level of climate change, potentially by several + decades. Delaying mitigation actions may reduce options for climate-resilient + pathways in the future. + 3.1c: + - 'Foundations of decision-making about climate change Effective decision-making + to limit climate change and its effects can be informed by a wide range of analytical + approaches for evaluating expected risks and benefits, recognizing the importance + of governance, ethical dimensions, equity, value judgments, economic assessments + and diverse perceptions and responses to risk and uncertainty. Sustainable development + and equity provide a basis for assessing climate policies. Limiting the effects + of climate change is necessary to achieve sustainable development and equity, + including poverty eradication. Countries’ past and future contributions to the + accumulation of GHGs in the atmosphere are different, and countries also face + varying challenges and circumstances and have different capacities to address + mitigation and adaptation. Mitigation and adaptation raise issues of equity, justice + and fairness and are necessary to achieve sustainable development and poverty + eradication. Many of those most vulnerable to climate change have contributed + and contribute little to GHG emissions. Delaying mitigation shifts burdens from + the present to the future, and insufficient adaptation responses to emerging impacts + are already eroding the basis for sustainable development. Both adaptation and + mitigation can have distributional effects locally, nationally and internationally, + depending on who pays and who benefits. The process of decision-making about climate + change, and the degree to which it respects the rights and views of all those + affected, is also a concern of justice. Effective mitigation will not be achieved + if individual agents advance their own interests independently. Climate change + has the characteristics of a collective action problem at the global scale, because + most GHGs accumulate over time and mix globally, and emissions by any agent affect + other agents. Cooperative responses, including international cooperation, are + therefore required to effectively mitigate GHG emissions and address other climate + change issues. The effectiveness of adaptation can be enhanced through complementary + actions across levels, including international cooperation. The evidence suggests + that outcomes seen as equitable can lead to more effective cooperation. Decision-making + about climate change involves valuation and mediation among diverse values and + may be aided by the analytic methods of several normative disciplines. Ethics + analyses the different values involved and the relations between them. Recent + political philosophy has investigated the question of responsibility for the effects + of emissions. Economics and decision analysis provide quantitative methods of + valuation which can be used for estimating the social cost of carbon, in cost–benefit + and costeffectiveness analyses, for optimization in integrated models and elsewhere. + Economic methods can reflect ethical principles, and take account of non-marketed + goods, equity, behavioural biases, ancillary benefits and costs and the differing + values of money to different people. They are, however, subject to well-documented + limitations. Analytical methods of valuation cannot identify a single best balance + between mitigation, adaptation and residual climate impacts. Important reasons + for this are that climate change involves extremely complex natural and social + processes, there is extensive disagreement about the values concerned, and climate + change impacts and mitigation approaches have important distributional effects. + Nevertheless, information on the consequences of emissions pathways to alternative + climate goals and risk levels can be a useful input into decision-making processes. + Evaluating responses to climate change involves assessment of the widest possible + range of impacts, including low-probability outcomes with large consequences. Effective + decision-making and risk management in the complex environment of climate change + may be iterative: strategies can often be adjusted as new information and understanding + develops during implementation. However, adaptation and mitigation choices in + the near term will affect the risks of climate change throughout the 21st century + and beyond, and prospects for climate-resilient pathways for sustainable development + depend on what is achieved through mitigation. Opportunities to take advantage + of positive synergies between adaptation and mitigation may decrease with time, + particularly if mitigation is delayed too long. Decision-making about climate + change is influenced by how individuals and organizations perceive risks and uncertainties + and take them into account. They sometimes use simplified decision rules, overestimate + or underestimate risks and are biased towards the status quo. They differ in their + degree of risk aversion and the relative importance placed on near-term versus + long-term ramifications of specific actions. Formalized analytical methods for + decision-making under uncertainty can account accurately for risk, and focus attention + on both short- and long-term consequences.' + 3.1d: + - 'Foundations of decision-making about climate change Effective decision-making + to limit climate change and its effects can be informed by a wide range of analytical + approaches for evaluating expected risks and benefits, recognizing the importance + of governance, ethical dimensions, equity, value judgments, economic assessments + and diverse perceptions and responses to risk and uncertainty. Sustainable development + and equity provide a basis for assessing climate policies. Limiting the effects + of climate change is necessary to achieve sustainable development and equity, + including poverty eradication. Countries’ past and future contributions to the + accumulation of GHGs in the atmosphere are different, and countries also face + varying challenges and circumstances and have different capacities to address + mitigation and adaptation. Mitigation and adaptation raise issues of equity, justice + and fairness and are necessary to achieve sustainable development and poverty + eradication. Many of those most vulnerable to climate change have contributed + and contribute little to GHG emissions. Delaying mitigation shifts burdens from + the present to the future, and insufficient adaptation responses to emerging impacts + are already eroding the basis for sustainable development. Both adaptation and + mitigation can have distributional effects locally, nationally and internationally, + depending on who pays and who benefits. The process of decision-making about climate + change, and the degree to which it respects the rights and views of all those + affected, is also a concern of justice. Effective mitigation will not be achieved + if individual agents advance their own interests independently. Climate change + has the characteristics of a collective action problem at the global scale, because + most GHGs accumulate over time and mix globally, and emissions by any agent affect + other agents. Cooperative responses, including international cooperation, are + therefore required to effectively mitigate GHG emissions and address other climate + change issues. The effectiveness of adaptation can be enhanced through complementary + actions across levels, including international cooperation. The evidence suggests + that outcomes seen as equitable can lead to more effective cooperation. Decision-making + about climate change involves valuation and mediation among diverse values and + may be aided by the analytic methods of several normative disciplines. Ethics + analyses the different values involved and the relations between them. Recent + political philosophy has investigated the question of responsibility for the effects + of emissions. Economics and decision analysis provide quantitative methods of + valuation which can be used for estimating the social cost of carbon, in cost–benefit + and costeffectiveness analyses, for optimization in integrated models and elsewhere. + Economic methods can reflect ethical principles, and take account of non-marketed + goods, equity, behavioural biases, ancillary benefits and costs and the differing + values of money to different people. They are, however, subject to well-documented + limitations. Analytical methods of valuation cannot identify a single best balance + between mitigation, adaptation and residual climate impacts. Important reasons + for this are that climate change involves extremely complex natural and social + processes, there is extensive disagreement about the values concerned, and climate + change impacts and mitigation approaches have important distributional effects. + Nevertheless, information on the consequences of emissions pathways to alternative + climate goals and risk levels can be a useful input into decision-making processes. + Evaluating responses to climate change involves assessment of the widest possible + range of impacts, including low-probability outcomes with large consequences. Effective + decision-making and risk management in the complex environment of climate change + may be iterative: strategies can often be adjusted as new information and understanding + develops during implementation. However, adaptation and mitigation choices in + the near term will affect the risks of climate change throughout the 21st century + and beyond, and prospects for climate-resilient pathways for sustainable development + depend on what is achieved through mitigation. Opportunities to take advantage + of positive synergies between adaptation and mitigation may decrease with time, + particularly if mitigation is delayed too long. Decision-making about climate + change is influenced by how individuals and organizations perceive risks and uncertainties + and take them into account. They sometimes use simplified decision rules, overestimate + or underestimate risks and are biased towards the status quo. They differ in their + degree of risk aversion and the relative importance placed on near-term versus + long-term ramifications of specific actions. Formalized analytical methods for + decision-making under uncertainty can account accurately for risk, and focus attention + on both short- and long-term consequences.' + 3.2b: + - Climate change risks reduced by adaptation and mitigation Without additional + mitigation efforts beyond those in place today, and even with adaptation, warming + by the end of the 21st century will lead to high to very high risk of severe, + widespread and irreversible impacts globally. Mitigation involves some level of + co-benefits and of risks due to adverse side effects, but these risks do not involve + the same possibility of severe, widespread and irreversible impacts as risks from + climate change, increasing the benefits from near-term mitigation efforts. The + risks of climate change, adaptation and mitigation differ in nature, timescale, + magnitude and persistence. Risks from adaptation include maladaptation and negative + ancillary impacts. Risks from mitigation include possible adverse side effects + of large-scale deployment of low-carbon technology options and economic costs. + Climate change risks may persist for millennia and can involve very high risk + of severe impacts and the presence of significant irreversibilities combined with + limited adaptive capacity. In contrast, the stringency of climate policies can + be adjusted much more quickly in response to observed consequences and costs and + create lower risks of irreversible consequences. Mitigation and adaptation are + complementary approaches for reducing risks of climate change impacts. They interact + with one another and reduce risks over different timescales . Benefits from adaptation + can already be realized in addressing current risks and can be realized in the + future for addressing emerging risks. Adaptation has the potential to reduce climate + change impacts over the next few decades, while mitigation has relatively little + influence on climate outcomes over this timescale. Near-term and longerterm mitigation + and adaptation, as well as development pathways, will determine the risks of climate + change beyond mid-century. The potential for adaptation differs across sectors + and will be limited by institutional and capacity constraints, increasing the + long-term benefits of mitigation. The level of mitigation will influence the rate + and magnitude of climate change, and greater rates and magnitude of climate change + increase the likelihood of exceeding adaptation limits. Without additional mitigation + efforts beyond those in place today, and even with adaptation, warming by the + end of the 21st century will lead to high to very high risk of severe, widespread + and irreversible impacts globally . Estimates of warming in 2100 without additional + climate mitigation efforts are from 3.7°C to 4.8°C compared with pre-industrial + levels; the range is 2.5°C to 7.8°C when using the 5th to 95th percentile range + of the median climate response. The risks associated with temperatures at or above + 4°C include severe and widespread impacts on unique and threatened systems, substantial + species extinction, large risks to global and regional food security, consequential + constraints on common human activities, increased likelihood of triggering tipping + points and limited potential for adaptation in some cases . Some risks of climate + change, such as risks to unique and threatened systems and risks associated with + extreme weather events, are moderate to high at temperatures 1°C to 2°C above + pre-industrial levels. Substantial cuts in GHG emissions over the next few decades + can substantially reduce risks of climate change by limiting warming in the second + half of the 21st century and beyond . Global mean surface warming is largely determined + by cumulative emissions, which are, in turn, linked to emissions over different + timescales. Limiting risks across Reasons For Concern would imply a limit for + cumulative emissions of CO2. Such a limit would require that global net emissions + of CO2 eventually decrease to zero. Reducing risks of climate change through mitigation + would involve substantial cuts in GHG emissions over the next few decades. But + some risks from residual damages are unavoidable, even with mitigation and adaptation. + A subset of relevant climate change risks has been estimated using aggregate economic + indicators. Such economic estimates have important limitations and are therefore + a useful but insufficient basis for decision-making on long-term mitigation targets. Mitigation + involves some level of co-benefits and risks, but these risks do not involve the + same possibility of severe, widespread and irreversible impacts as risks from + climate change . Scenarios that are likely to limit warming to below 2°C or even + 3°C compared with pre-industrial temperatures involve large-scale changes in energy + systems and potentially land use over the coming decades. Associated risks include + those linked to large-scale deployment of technology options for producing low-carbon + energy, the potential for high aggregate economic costs of mitigation and impacts + on vulnerable countries and industries. Other risks and co-benefits are associated + with human health, food security, energy security, poverty reduction, biodiversity + conservation, water availability, income distribution, efficiency of taxation + systems, labour supply and employment, urban sprawl, fossil fuel export revenues + and the economic growth of developing countries. Inertia in the economic and + climate systems and the possibility of irreversible impacts from climate change + increase the benefits of near-term mitigation efforts. The actions taken today + affect the options available in the future to reduce emissions, limit temperature + change and adapt to climate change. Near-term choices can create, amplify or limit + significant elements of lock-in that are important for decision-making. Lock-ins + and irreversibilities occur in the climate system due to large inertia in some + of its components such as heat transfer from the ocean surface to depth leading + to continued ocean warming for centuries regardless of emission scenario and the + irreversibility of a large fraction of anthropogenic climate change resulting + from CO2 emissions on a multi-century to millennial timescale unless CO2 were + to be removed from the atmosphere through large-scale human interventions over + a sustained period . Irreversibilities in socio-economic and biological systems + also result from infrastructure development and long-lived products and from climate + change impacts, such as species extinction. The larger potential for irreversibility + and pervasive impacts from climate change risks than from mitigation risks increases + the benefit of shortterm mitigation efforts. Delays in additional mitigation or + constraints on technological options limit the mitigation options and increase + the long-term mitigation costs as well as other risks that would be incurred in + the medium to long term to hold climate change impacts at a given level. + - Trade-offs, synergies and integrated responses There are many opportunities to + link mitigation, adaptation and the pursuit of other societal objectives through + integrated responses. Successful implementation relies on relevant tools, suitable + governance structures and enhanced capacity to respond. A growing evidence base + indicates close links between adaptation and mitigation, their co-benefits and + adverse side effects, and recognizes sustainable development as the overarching + context for climate policy . Developing tools to address these linkages is critical + to the success of climate policy in the context of sustainable development. This + section presents examples of integrated responses in specific policy arenas, as + well as some of the factors that promote or impede policies aimed at multiple + objectives. Increasing efforts to mitigate and adapt to climate change imply an + increasing complexity of interactions, encompassing connections among human health, + water, energy, land use and biodiversity. Mitigation can support the achievement + of other societal goals, such as those related to human health, food security, + environmental quality, energy access, livelihoods and sustainable development, + although there can also be negative effects. Adaptation measures also have the + potential to deliver mitigation co-benefits, and vice versa, and support other + societal goals, though trade-offs can also arise. Integration of adaptation and + mitigation into planning and decision-making can create synergies with sustainable + development. Synergies and trade-offs among mitigation and adaptation policies + and policies advancing other societal goals can be substantial, although sometimes + difficult to quantify especially in welfare terms. A multi-objective approach + to policy-making can help manage these synergies and trade-offs. Policies advancing + multiple goals may also attract greater support. Effective integrated responses + depend on suitable tools and governance structures, as well as adequate capacity + . Managing trade-offs and synergies is challenging and requires tools to help + understand interactions and support decision-making at local and regional scales. + Integrated responses also depend on governance that enables coordination across + scales and sectors, supported by appropriate institutions. Developing and implementing + suitable tools and governance structures often requires upgrading the human and + institutional capacity to design and deploy integrated responses. An integrated + approach to energy planning and implementation that explicitly assesses the potential + for co-benefits and the presence of adverse side effects can capture complementarities + across multiple climate, social and environmental objectives . There are strong + interactive effects across various energy policy objectives, such as energy security, + air quality, health and energy access and between a range of social and environmental + objectives and climate mitigation objectives . An integrated approach can be assisted + by tools such as cost-benefit analysis, cost-effectiveness analysis, multi-criteria + analysis and expected utility theory. It also requires appropriate coordinating + institutions. Explicit consideration of interactions among water, food, energy + and biological carbon sequestration plays an important role in supporting effective + decisions for climate resilient pathways . Both biofuel-based power generation + and large-scale afforestation designed to mitigate climate change can reduce catchment + run-off, which may conflict with alternative water uses for food production, human + consumption or the maintenance of ecosystem function and services. Conversely, + irrigation can increase the climate resilience of food and fibre production but + reduces water availability for other uses. An integrated response to urbanization + provides substantial opportunities for enhanced resilience, reduced emissions + and more sustainable development. Urban areas account for more than half of global + primary energy use and energy-related CO2 emissions and contain a high proportion + of the population and economic activities at risk from climate change. In rapidly + growing and urbanizing regions, mitigation strategies based on spatial planning + and efficient infrastructure supply can avoid the lock-in of high emission patterns. + Mixed-use zoning, transport-oriented development, increased density and co-located + jobs and homes can reduce direct and indirect energy use across sectors. Compact + development of urban spaces and intelligent densification can preserve land carbon + stocks and land for agriculture and bioenergy. Reduced energy and water consumption + in urban areas through greening cities and recycling water are examples of mitigation + actions with adaptation benefits. Building resilient infrastructure systems can + reduce vulnerability of urban settlements and cities to coastal flooding, sea + level rise and other climate-induced stresses. + 3.2d: + - 'Future risks and impacts caused by a changing climate Climate change will amplify + existing risks and create new risks for natural and human systems. Risks are unevenly + distributed and are generally greater for disadvantaged people and communities + in countries at all levels of development. Increasing magnitudes of warming increase + the likelihood of severe, pervasive and irreversible impacts for people, species + and ecosystems. Continued high emissions would lead to mostly negative impacts + for biodiversity, ecosystem services and economic development and amplify risks + for livelihoods and for food and human security. Risk of climate-related impacts + results from the interaction of climate-related hazards with the vulnerability + and exposure of human and natural systems, including their ability to adapt. Rising + rates and magnitudes of warming and other changes in the climate system, accompanied + by ocean acidification, increase the risk of severe, pervasive, and in some cases, + irreversible detrimental impacts. Future climate change will amplify existing + climate-related risks and create new risks. Key risks are potentially severe + impacts relevant to understanding dangerous anthropogenic interference with the + climate system. Risks are considered key due to high hazard or high vulnerability + of societies and systems exposed, or both. Their identification is based on large + magnitude or high probability of impacts; irreversibility or timing of impacts; + persistent vulnerability or exposure; or limited potential to reduce risks. Some + risks are particularly relevant for individual regions, while others are global. + For risk assessment it is important to evaluate the widest possible range of impacts, + including low-probability outcomes with large consequences. Risk levels often + increase with temperature and are sometimes more directly linked to other dimensions + of climate change, such as the rate of warming, as well as the magnitudes and + rates of ocean acidification and sea level rise . Key risks that span sectors + and regions include the following : 1. Risk of severe ill-health and disrupted + livelihoods resulting from storm surges, sea level rise and coastal flooding; + inland flooding in some urban regions; and periods of extreme heat. 2. Systemic + risks due to extreme weather events leading to breakdown of infrastructure networks + and critical services. 3. Risk of food and water insecurity and loss of rural + livelihoods and income, particularly for poorer populations. 4. Risk of loss of + ecosystems, biodiversity and ecosystem goods, functions and services. The overall + risks of future climate change impacts can be reduced by limiting the rate and + magnitude of climate change, including ocean acidification. Some risks are considerable + even at 1°C global mean temperature increase above pre-industrial levels. Many + global risks are high to very high for global temperature increases of 4°C or + more. These risks include severe and widespread impacts on unique and threatened + systems, the extinction of many species, large risks to food security and compromised + normal human activities, including growing food or working outdoors in some areas + for parts of the year, due to the combination of high temperature and humidity. + The precise levels of climate change sufficient to trigger abrupt and irreversible + change remain uncertain, but the risk associated with crossing such thresholds + in the earth system or in interlinked human and natural systems increases with + rising temperature. Adaptation can substantially reduce the risks of climate + change impacts, but greater rates and magnitude of climate change increase the + likelihood of exceeding adaptation limits . The potential for adaptation, as well + as constraints and limits to adaptation, varies among sectors, regions, communities + and ecosystems. The scope for adaptation changes over time and is closely linked + to socio-economic development pathways and circumstances. See Figure 2.4 and Table + 2.3, along with Topics 3 and 4.' + - Climate change risks reduced by adaptation and mitigation Without additional + mitigation efforts beyond those in place today, and even with adaptation, warming + by the end of the 21st century will lead to high to very high risk of severe, + widespread and irreversible impacts globally. Mitigation involves some level of + co-benefits and of risks due to adverse side effects, but these risks do not involve + the same possibility of severe, widespread and irreversible impacts as risks from + climate change, increasing the benefits from near-term mitigation efforts. The + risks of climate change, adaptation and mitigation differ in nature, timescale, + magnitude and persistence. Risks from adaptation include maladaptation and negative + ancillary impacts. Risks from mitigation include possible adverse side effects + of large-scale deployment of low-carbon technology options and economic costs. + Climate change risks may persist for millennia and can involve very high risk + of severe impacts and the presence of significant irreversibilities combined with + limited adaptive capacity. In contrast, the stringency of climate policies can + be adjusted much more quickly in response to observed consequences and costs and + create lower risks of irreversible consequences. Mitigation and adaptation are + complementary approaches for reducing risks of climate change impacts. They interact + with one another and reduce risks over different timescales . Benefits from adaptation + can already be realized in addressing current risks and can be realized in the + future for addressing emerging risks. Adaptation has the potential to reduce climate + change impacts over the next few decades, while mitigation has relatively little + influence on climate outcomes over this timescale. Near-term and longerterm mitigation + and adaptation, as well as development pathways, will determine the risks of climate + change beyond mid-century. The potential for adaptation differs across sectors + and will be limited by institutional and capacity constraints, increasing the + long-term benefits of mitigation. The level of mitigation will influence the rate + and magnitude of climate change, and greater rates and magnitude of climate change + increase the likelihood of exceeding adaptation limits. Without additional mitigation + efforts beyond those in place today, and even with adaptation, warming by the + end of the 21st century will lead to high to very high risk of severe, widespread + and irreversible impacts globally . Estimates of warming in 2100 without additional + climate mitigation efforts are from 3.7°C to 4.8°C compared with pre-industrial + levels; the range is 2.5°C to 7.8°C when using the 5th to 95th percentile range + of the median climate response. The risks associated with temperatures at or above + 4°C include severe and widespread impacts on unique and threatened systems, substantial + species extinction, large risks to global and regional food security, consequential + constraints on common human activities, increased likelihood of triggering tipping + points and limited potential for adaptation in some cases . Some risks of climate + change, such as risks to unique and threatened systems and risks associated with + extreme weather events, are moderate to high at temperatures 1°C to 2°C above + pre-industrial levels. Substantial cuts in GHG emissions over the next few decades + can substantially reduce risks of climate change by limiting warming in the second + half of the 21st century and beyond . Global mean surface warming is largely determined + by cumulative emissions, which are, in turn, linked to emissions over different + timescales. Limiting risks across Reasons For Concern would imply a limit for + cumulative emissions of CO2. Such a limit would require that global net emissions + of CO2 eventually decrease to zero. Reducing risks of climate change through mitigation + would involve substantial cuts in GHG emissions over the next few decades. But + some risks from residual damages are unavoidable, even with mitigation and adaptation. + A subset of relevant climate change risks has been estimated using aggregate economic + indicators. Such economic estimates have important limitations and are therefore + a useful but insufficient basis for decision-making on long-term mitigation targets. Mitigation + involves some level of co-benefits and risks, but these risks do not involve the + same possibility of severe, widespread and irreversible impacts as risks from + climate change . Scenarios that are likely to limit warming to below 2°C or even + 3°C compared with pre-industrial temperatures involve large-scale changes in energy + systems and potentially land use over the coming decades. Associated risks include + those linked to large-scale deployment of technology options for producing low-carbon + energy, the potential for high aggregate economic costs of mitigation and impacts + on vulnerable countries and industries. Other risks and co-benefits are associated + with human health, food security, energy security, poverty reduction, biodiversity + conservation, water availability, income distribution, efficiency of taxation + systems, labour supply and employment, urban sprawl, fossil fuel export revenues + and the economic growth of developing countries. Inertia in the economic and + climate systems and the possibility of irreversible impacts from climate change + increase the benefits of near-term mitigation efforts. The actions taken today + affect the options available in the future to reduce emissions, limit temperature + change and adapt to climate change. Near-term choices can create, amplify or limit + significant elements of lock-in that are important for decision-making. Lock-ins + and irreversibilities occur in the climate system due to large inertia in some + of its components such as heat transfer from the ocean surface to depth leading + to continued ocean warming for centuries regardless of emission scenario and the + irreversibility of a large fraction of anthropogenic climate change resulting + from CO2 emissions on a multi-century to millennial timescale unless CO2 were + to be removed from the atmosphere through large-scale human interventions over + a sustained period . Irreversibilities in socio-economic and biological systems + also result from infrastructure development and long-lived products and from climate + change impacts, such as species extinction. The larger potential for irreversibility + and pervasive impacts from climate change risks than from mitigation risks increases + the benefit of shortterm mitigation efforts. Delays in additional mitigation or + constraints on technological options limit the mitigation options and increase + the long-term mitigation costs as well as other risks that would be incurred in + the medium to long term to hold climate change impacts at a given level. + - Characteristics of mitigation pathways There are multiple mitigation pathways + that are likely to limit warming to below 2°C relative to pre-industrial levels. + These pathways would require substantial emissions reductions over the next few + decades and near zero emissions of CO2 and other long-lived greenhouse gases by + the end of the century. Implementing such reductions poses substantial technological, + economic, social and institutional challenges, which increase with delays in additional + mitigation and if key technologies are not available. Limiting warming to lower + or higher levels involves similar challenges but on different timescales. Without + additional efforts to reduce GHG emissions beyond those in place today, global + emission growth is expected to persist driven by growth in global population and + economic activities. Global GHG emissions under most scenarios without additional + mitigation are between about 75 GtCO2-eq/yr and almost 140 GtCO2-eq/yr in 21003520which + is approximately between the 2100 emission levels in the RCP6.0 and RCP8.5 pathways + 3621 . Baseline scenarios exceed 450 ppm CO2-eq by 2030 and reach CO2-eq concentration + levels between about 750 ppm CO2-eq and more than 1300 ppm CO2-eq by 2100. Global + mean surface temperature increases in 2100 range from about 3.7°C to 4.8°C above + the average for 1850–1900 for a median climate response. They range from 2.5°C + to 7.8°C when including climate uncertainty 3722 . The future scenarios do not + account for possible changes in natural forcings in the climate system. Many + different combinations of technological, behavioural and policy options can be + used to reduce emissions and limit temperature change. To evaluate possible pathways + to long-term climate goals, about 900 mitigation scenarios were collected for + this assessment, each of which describes different technological, socio-economic + and institutional changes. Emission reductions under these scenarios lead to concentrations + in 2100 from 430 ppm CO2-eq to above 720 ppm CO2-eq which is comparable to the + 2100 forcing levels between RCP2.6 and RCP6.0. Scenarios with concentration levels + of below 430 ppm CO2-eq by 2100 were also assessed. Scenarios leading to CO2-eq + concentrations in 2100 of about 450 ppm or lower are likely to maintain warming + below 2°C over the 21st century relative to pre-industrial levels. Mitigation + scenarios reaching concentration levels of about 500 ppm CO2-eq by 2100 are more + likely than not to limit warming to less than 2°C relative to pre-industrial levels, + unless concentration levels temporarily exceed roughly 530 ppm CO2-eq before 2100. + In this case, warming is about as likely as not to remain below 2°C relative to + pre-industrial levels. Scenarios that exceed about 650 ppm CO2-eq by 2100 are + unlikely to limit warming to below 2°C relative to pre-industrial levels. Mitigation + scenarios in which warming is more likely than not to be less than 1.5°C relative + to pre-industrial levels by 2100 are characterized by concentration levels by + 2100 of below 430 ppm CO2-eq. In these scenarios, temperature peaks during the + century and subsequently declines. Mitigation scenarios reaching about 450 ppm + CO2-eq in 2100 typically involve temporary overshootof atmospheric concentrations, + as do many scenarios reaching about 500 ppm CO2-eq to about 550 ppm CO2-eq by + 2100. Depending on the level of overshoot, overshoot scenarios typically rely + on the availability and widespread deployment of bioenergy with carbon dioxide + capture and storage and afforestation in the second half of the century. The availability + and scale of these and other Carbon Dioxide Removal technologies and methods are + uncertain, and CDR technologies and methods are, to varying degrees, associated + with challenges and risks 3924 . CDR is also prevalent in many scenarios without + overshoot to compensate for residual emissions from sectors where mitigation is + more expensive. Limiting warming with a likely chance to less than 2°C relative + to pre-industrial levels would require substantial cuts in anthropogenic GHG emissions + by mid-century through largescale changes in energy systems and possibly land + use. Limiting warming to higher levels would require similar changes but less + quickly. Limiting warming to lower levels would require these changes more quickly. + Scenarios that are likely to maintain warming at below 2°C are characterized by + a 40 to 70% reduction in GHG emissions by 2050, relative to 2010 levels, and emissions + levels near zero or below in 2100. Scenarios with higher emissions in 2050 are + characterized by a greater reliance on CDR technologies beyond mid-century, and + vice versa. Scenarios that are likely to maintain warming at below 2°C include + more rapid improvements in energy efficiency and a tripling to nearly a quadrupling + of the share of zero- and low-carbon energy supply from renewable energy, nuclear + energy and fossil energy with carbon dioxide capture and storage or BECCS by the + year 2050. The scenarios describe a wide range of changes in land use, reflecting + different assumptions about the scale of bioenergy production, afforestation and + reduced deforestation. Scenarios leading to concentrations of 500 ppm CO2-eq by + 2100 are characterized by a 25 to 55% reduction in GHG emissions by 2050, relative + to 2010 levels. Scenarios that are likely to limit warming to 3°C relative to + pre-industrial levels reduce emissions less rapidly than those limiting warming + to 2°C. Only a limited number of studies provide scenarios that are more likely + than not to limit warming to 1.5°C by 2100; these scenarios are characterized + by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission reduction between + 70 and 95% below 2010. For a comprehensive overview of the characteristics of + emissions scenarios, their CO2-equivalent concentrations and their likelihood + to keep warming to below a range of temperature levels, see Table 3.1. Reducing + emissions of non-CO2 climate forcing agents can be an important element of mitigation + strategies. Emissions of nonCO2 gases, nitrous oxide, and fluorinated gases) contributed + about 27% to the total emissions of Kyoto gases in 2010. For most non-CO2 gases, + near-term, low-cost options are available to reduce their emissions. However, + some sources of these non-CO2 gases are difficult to mitigate, such as N2O emissions + from fertilizer use and CH4 emissions from livestock. As a result, emissions of + most non-CO2 gases will not be reduced to zero, even under stringent mitigation + scenarios. The differences in radiative properties and lifetimes of CO2 and non-CO2 + climate forcing agents have important implications for mitigation strategies. All + current GHG emissions and other climate forcing agents affect the rate and magnitude + of climate change over the next few decades. Reducing the emissions of certain + short-lived climate forcing agents can reduce the rate of warming in the short + term but will have only a limited effect on long-term warming, which is driven + mainly by CO2 emissions. There are large uncertainties related to the climate + impacts of some of the short-lived climate forcing agents. Although the effects + of CH4 emissions are well understood, there are large uncertainties related to + the effects of black carbon. Co-emitted components with cooling effects may further + complicate and reduce the climate impacts of emission reductions. Reducing emissions + of sulfur dioxide would cause warming. Near-term reductions in short-lived climate + forcing agents can have a relatively fast impact on climate change and possible + co-benefits for air pollution. Delaying additional mitigation to 2030 will substantially + increase the challenges associated with limiting warming over the 21st century + to below 2°C relative to pre-industrial levels. GHG emissions in 2030 lie between + about 30 GtCO2-eq/yr and 50 GtCO2-eq/yr in cost-effective scenarios that are likely + to about as likely as not to limit warming to less than 2°C this century relative + to pre-industrial levels . Scenarios with GHG emission levels of above 55 GtCO2-eq/yr + require substantially higher rates of emissions reductions between 2030 and 2050 + ; much more rapid scale-up of zero and low-carbon energy over this period ; a + larger reliance on CDR technologies in the long term; and higher transitional + and long-term economic impacts. Estimated global emission levels by 2020 based + on the Cancún Pledges are not consistent with cost-effective long-term mitigation + trajectories that are at least about as likely as not to limit warming to below + 2°C relative to pre-industrial levels , but they do not preclude the option to + meet this goal . The Cancún Pledges are broadly consistent with cost-effective + scenarios that are likely to limit temperature change to below 3°C relative to + pre-industrial levels. Estimates of the aggregate economic costs of mitigation + vary widely depending on methodologies and assumptions but increase with the stringency + of mitigation. Scenarios in which all countries of the world begin mitigation + immediately, in which there is a single global carbon price, and in which all + key technologies are available have been used as a cost-effective benchmark for + estimating macroeconomic mitigation costs. Under these assumptions, mitigation + scenarios that are likely to limit warming to below 2°C through the 21st century + relative to pre-industrial levels entail losses in global consumption—not including + benefits of reduced climate change as well as co-benefits and adverse side effects + of mitigation —of 1 to 4% in 2030, 2 to 6% in 2050, and 3% to 11% in 2100, relative + to consumption in baseline scenarios that grows anywhere from 300% to more than + 900% over the century . These numbers correspond to an annualized reduction of + consumption growth by 0.04 to 0.14 percentage points over the century relative + to annualized consumption growth in the baseline that is between 1.6% and 3% per + year. In the absence or under limited availability of mitigation technologies + , mitigation costs can increase substantially depending on the technology considered + . Delaying additional mitigation reduces near-term costs but increases mitigation + costs in the medium- to long-term. Many models could not limit likely warming + to below 2°C over the 21st century relative to pre-industrial levels, if additional + mitigation is considerably delayed, or if availability of key technologies, such + as bioenergy, CCS and their combination are limited . Mitigation efforts and + associated cost are expected to vary across countries. The distribution of costs + can differ from the distribution of the actions themselves. In globally cost-effective + scenarios, the majority of mitigation efforts takes place in countries with the + highest future GHG emissions in baseline scenarios. Some studies exploring particular + effort-sharing frameworks, under the assumption of a global carbon market, have + estimated substantial global financial flows associated with mitigation in scenarios + that are likely to more unlikely than likely to limit warming during the 21st + century to less than 2°C relative to pre-industrial levels. + 3.2e: + - Climate system responses Climate system properties that determine the response + to external forcing have been estimated both from climate models and from analysis + of past and recent climate change. The equilibrium climate sensitivity 3325is + likely in the range 1.5°C to 4.5°C, extremely unlikely less than 1°C, and very + unlikely greater than 6°C. Cumulative emissions of CO2 largely determine global + mean surface warming by the late 21st century and beyond. Multiple lines of evidence + indicate a strong and consistent near-linear relationship across all scenarios + considered between net cumulative CO2 emissions and projected global temperature + change to the year 2100. Past emissions and observed warming support this relationship + within uncertainties. Any given level of warming is associated with a range of + cumulative CO2 emissions , and therefore, for example, higher emissions in earlier + decades imply lower emissions later. The global mean peak surface temperature + change per trillion tonnes of carbon emitted as CO2 is likely in the range of + 0.8°C to 2.5°C. This quantity, called the transient climate response to cumulative + carbon emissions, is supported by both modelling and observational evidence and + applies to cumulative emissions up to about 2000 GtC. Warming caused by CO2 emissions + is effectively irreversible over multi-century timescales unless measures are + taken to remove CO2 from the atmosphere. Ensuring CO2-induced warming remains + likely less than 2°C requires cumulative CO2 emissions from all anthropogenic + sources to remain below about 3650 GtCO2, over half of which were already emitted + by 2011. Multi-model results show that limiting total human-induced warming to + less than 2°C relative to the period 1861–1880 with a probability of >66% would + require total CO2 emissions from all anthropogenic sources since 1870 to be limited + to about 2900 GtCO2 when accounting for non-CO2 forcing as in the RCP2.6 scenario, + with a range of 2550 to 3150 GtCO2 arising from variations in non-CO2 climate + drivers across the scenarios considered by WGIII. About 1900 [1650 to 2150] GtCO2 + were emitted by 2011, leaving about 1000 GtCO2 to be consistent with this temperature + goal. Estimated total fossil carbon reserves exceed this remaining amount by a + factor of 4 to 7, with resources much larger still. + - Climate change risks reduced by adaptation and mitigation Without additional + mitigation efforts beyond those in place today, and even with adaptation, warming + by the end of the 21st century will lead to high to very high risk of severe, + widespread and irreversible impacts globally. Mitigation involves some level of + co-benefits and of risks due to adverse side effects, but these risks do not involve + the same possibility of severe, widespread and irreversible impacts as risks from + climate change, increasing the benefits from near-term mitigation efforts. The + risks of climate change, adaptation and mitigation differ in nature, timescale, + magnitude and persistence. Risks from adaptation include maladaptation and negative + ancillary impacts. Risks from mitigation include possible adverse side effects + of large-scale deployment of low-carbon technology options and economic costs. + Climate change risks may persist for millennia and can involve very high risk + of severe impacts and the presence of significant irreversibilities combined with + limited adaptive capacity. In contrast, the stringency of climate policies can + be adjusted much more quickly in response to observed consequences and costs and + create lower risks of irreversible consequences. Mitigation and adaptation are + complementary approaches for reducing risks of climate change impacts. They interact + with one another and reduce risks over different timescales . Benefits from adaptation + can already be realized in addressing current risks and can be realized in the + future for addressing emerging risks. Adaptation has the potential to reduce climate + change impacts over the next few decades, while mitigation has relatively little + influence on climate outcomes over this timescale. Near-term and longerterm mitigation + and adaptation, as well as development pathways, will determine the risks of climate + change beyond mid-century. The potential for adaptation differs across sectors + and will be limited by institutional and capacity constraints, increasing the + long-term benefits of mitigation. The level of mitigation will influence the rate + and magnitude of climate change, and greater rates and magnitude of climate change + increase the likelihood of exceeding adaptation limits. Without additional mitigation + efforts beyond those in place today, and even with adaptation, warming by the + end of the 21st century will lead to high to very high risk of severe, widespread + and irreversible impacts globally . Estimates of warming in 2100 without additional + climate mitigation efforts are from 3.7°C to 4.8°C compared with pre-industrial + levels; the range is 2.5°C to 7.8°C when using the 5th to 95th percentile range + of the median climate response. The risks associated with temperatures at or above + 4°C include severe and widespread impacts on unique and threatened systems, substantial + species extinction, large risks to global and regional food security, consequential + constraints on common human activities, increased likelihood of triggering tipping + points and limited potential for adaptation in some cases . Some risks of climate + change, such as risks to unique and threatened systems and risks associated with + extreme weather events, are moderate to high at temperatures 1°C to 2°C above + pre-industrial levels. Substantial cuts in GHG emissions over the next few decades + can substantially reduce risks of climate change by limiting warming in the second + half of the 21st century and beyond . Global mean surface warming is largely determined + by cumulative emissions, which are, in turn, linked to emissions over different + timescales. Limiting risks across Reasons For Concern would imply a limit for + cumulative emissions of CO2. Such a limit would require that global net emissions + of CO2 eventually decrease to zero. Reducing risks of climate change through mitigation + would involve substantial cuts in GHG emissions over the next few decades. But + some risks from residual damages are unavoidable, even with mitigation and adaptation. + A subset of relevant climate change risks has been estimated using aggregate economic + indicators. Such economic estimates have important limitations and are therefore + a useful but insufficient basis for decision-making on long-term mitigation targets. Mitigation + involves some level of co-benefits and risks, but these risks do not involve the + same possibility of severe, widespread and irreversible impacts as risks from + climate change . Scenarios that are likely to limit warming to below 2°C or even + 3°C compared with pre-industrial temperatures involve large-scale changes in energy + systems and potentially land use over the coming decades. Associated risks include + those linked to large-scale deployment of technology options for producing low-carbon + energy, the potential for high aggregate economic costs of mitigation and impacts + on vulnerable countries and industries. Other risks and co-benefits are associated + with human health, food security, energy security, poverty reduction, biodiversity + conservation, water availability, income distribution, efficiency of taxation + systems, labour supply and employment, urban sprawl, fossil fuel export revenues + and the economic growth of developing countries. Inertia in the economic and + climate systems and the possibility of irreversible impacts from climate change + increase the benefits of near-term mitigation efforts. The actions taken today + affect the options available in the future to reduce emissions, limit temperature + change and adapt to climate change. Near-term choices can create, amplify or limit + significant elements of lock-in that are important for decision-making. Lock-ins + and irreversibilities occur in the climate system due to large inertia in some + of its components such as heat transfer from the ocean surface to depth leading + to continued ocean warming for centuries regardless of emission scenario and the + irreversibility of a large fraction of anthropogenic climate change resulting + from CO2 emissions on a multi-century to millennial timescale unless CO2 were + to be removed from the atmosphere through large-scale human interventions over + a sustained period . Irreversibilities in socio-economic and biological systems + also result from infrastructure development and long-lived products and from climate + change impacts, such as species extinction. The larger potential for irreversibility + and pervasive impacts from climate change risks than from mitigation risks increases + the benefit of shortterm mitigation efforts. Delays in additional mitigation or + constraints on technological options limit the mitigation options and increase + the long-term mitigation costs as well as other risks that would be incurred in + the medium to long term to hold climate change impacts at a given level. + - Characteristics of mitigation pathways There are multiple mitigation pathways + that are likely to limit warming to below 2°C relative to pre-industrial levels. + These pathways would require substantial emissions reductions over the next few + decades and near zero emissions of CO2 and other long-lived greenhouse gases by + the end of the century. Implementing such reductions poses substantial technological, + economic, social and institutional challenges, which increase with delays in additional + mitigation and if key technologies are not available. Limiting warming to lower + or higher levels involves similar challenges but on different timescales. Without + additional efforts to reduce GHG emissions beyond those in place today, global + emission growth is expected to persist driven by growth in global population and + economic activities. Global GHG emissions under most scenarios without additional + mitigation are between about 75 GtCO2-eq/yr and almost 140 GtCO2-eq/yr in 21003520which + is approximately between the 2100 emission levels in the RCP6.0 and RCP8.5 pathways + 3621 . Baseline scenarios exceed 450 ppm CO2-eq by 2030 and reach CO2-eq concentration + levels between about 750 ppm CO2-eq and more than 1300 ppm CO2-eq by 2100. Global + mean surface temperature increases in 2100 range from about 3.7°C to 4.8°C above + the average for 1850–1900 for a median climate response. They range from 2.5°C + to 7.8°C when including climate uncertainty 3722 . The future scenarios do not + account for possible changes in natural forcings in the climate system. Many + different combinations of technological, behavioural and policy options can be + used to reduce emissions and limit temperature change. To evaluate possible pathways + to long-term climate goals, about 900 mitigation scenarios were collected for + this assessment, each of which describes different technological, socio-economic + and institutional changes. Emission reductions under these scenarios lead to concentrations + in 2100 from 430 ppm CO2-eq to above 720 ppm CO2-eq which is comparable to the + 2100 forcing levels between RCP2.6 and RCP6.0. Scenarios with concentration levels + of below 430 ppm CO2-eq by 2100 were also assessed. Scenarios leading to CO2-eq + concentrations in 2100 of about 450 ppm or lower are likely to maintain warming + below 2°C over the 21st century relative to pre-industrial levels. Mitigation + scenarios reaching concentration levels of about 500 ppm CO2-eq by 2100 are more + likely than not to limit warming to less than 2°C relative to pre-industrial levels, + unless concentration levels temporarily exceed roughly 530 ppm CO2-eq before 2100. + In this case, warming is about as likely as not to remain below 2°C relative to + pre-industrial levels. Scenarios that exceed about 650 ppm CO2-eq by 2100 are + unlikely to limit warming to below 2°C relative to pre-industrial levels. Mitigation + scenarios in which warming is more likely than not to be less than 1.5°C relative + to pre-industrial levels by 2100 are characterized by concentration levels by + 2100 of below 430 ppm CO2-eq. In these scenarios, temperature peaks during the + century and subsequently declines. Mitigation scenarios reaching about 450 ppm + CO2-eq in 2100 typically involve temporary overshootof atmospheric concentrations, + as do many scenarios reaching about 500 ppm CO2-eq to about 550 ppm CO2-eq by + 2100. Depending on the level of overshoot, overshoot scenarios typically rely + on the availability and widespread deployment of bioenergy with carbon dioxide + capture and storage and afforestation in the second half of the century. The availability + and scale of these and other Carbon Dioxide Removal technologies and methods are + uncertain, and CDR technologies and methods are, to varying degrees, associated + with challenges and risks 3924 . CDR is also prevalent in many scenarios without + overshoot to compensate for residual emissions from sectors where mitigation is + more expensive. Limiting warming with a likely chance to less than 2°C relative + to pre-industrial levels would require substantial cuts in anthropogenic GHG emissions + by mid-century through largescale changes in energy systems and possibly land + use. Limiting warming to higher levels would require similar changes but less + quickly. Limiting warming to lower levels would require these changes more quickly. + Scenarios that are likely to maintain warming at below 2°C are characterized by + a 40 to 70% reduction in GHG emissions by 2050, relative to 2010 levels, and emissions + levels near zero or below in 2100. Scenarios with higher emissions in 2050 are + characterized by a greater reliance on CDR technologies beyond mid-century, and + vice versa. Scenarios that are likely to maintain warming at below 2°C include + more rapid improvements in energy efficiency and a tripling to nearly a quadrupling + of the share of zero- and low-carbon energy supply from renewable energy, nuclear + energy and fossil energy with carbon dioxide capture and storage or BECCS by the + year 2050. The scenarios describe a wide range of changes in land use, reflecting + different assumptions about the scale of bioenergy production, afforestation and + reduced deforestation. Scenarios leading to concentrations of 500 ppm CO2-eq by + 2100 are characterized by a 25 to 55% reduction in GHG emissions by 2050, relative + to 2010 levels. Scenarios that are likely to limit warming to 3°C relative to + pre-industrial levels reduce emissions less rapidly than those limiting warming + to 2°C. Only a limited number of studies provide scenarios that are more likely + than not to limit warming to 1.5°C by 2100; these scenarios are characterized + by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission reduction between + 70 and 95% below 2010. For a comprehensive overview of the characteristics of + emissions scenarios, their CO2-equivalent concentrations and their likelihood + to keep warming to below a range of temperature levels, see Table 3.1. Reducing + emissions of non-CO2 climate forcing agents can be an important element of mitigation + strategies. Emissions of nonCO2 gases, nitrous oxide, and fluorinated gases) contributed + about 27% to the total emissions of Kyoto gases in 2010. For most non-CO2 gases, + near-term, low-cost options are available to reduce their emissions. However, + some sources of these non-CO2 gases are difficult to mitigate, such as N2O emissions + from fertilizer use and CH4 emissions from livestock. As a result, emissions of + most non-CO2 gases will not be reduced to zero, even under stringent mitigation + scenarios. The differences in radiative properties and lifetimes of CO2 and non-CO2 + climate forcing agents have important implications for mitigation strategies. All + current GHG emissions and other climate forcing agents affect the rate and magnitude + of climate change over the next few decades. Reducing the emissions of certain + short-lived climate forcing agents can reduce the rate of warming in the short + term but will have only a limited effect on long-term warming, which is driven + mainly by CO2 emissions. There are large uncertainties related to the climate + impacts of some of the short-lived climate forcing agents. Although the effects + of CH4 emissions are well understood, there are large uncertainties related to + the effects of black carbon. Co-emitted components with cooling effects may further + complicate and reduce the climate impacts of emission reductions. Reducing emissions + of sulfur dioxide would cause warming. Near-term reductions in short-lived climate + forcing agents can have a relatively fast impact on climate change and possible + co-benefits for air pollution. Delaying additional mitigation to 2030 will substantially + increase the challenges associated with limiting warming over the 21st century + to below 2°C relative to pre-industrial levels. GHG emissions in 2030 lie between + about 30 GtCO2-eq/yr and 50 GtCO2-eq/yr in cost-effective scenarios that are likely + to about as likely as not to limit warming to less than 2°C this century relative + to pre-industrial levels . Scenarios with GHG emission levels of above 55 GtCO2-eq/yr + require substantially higher rates of emissions reductions between 2030 and 2050 + ; much more rapid scale-up of zero and low-carbon energy over this period ; a + larger reliance on CDR technologies in the long term; and higher transitional + and long-term economic impacts. Estimated global emission levels by 2020 based + on the Cancún Pledges are not consistent with cost-effective long-term mitigation + trajectories that are at least about as likely as not to limit warming to below + 2°C relative to pre-industrial levels , but they do not preclude the option to + meet this goal . The Cancún Pledges are broadly consistent with cost-effective + scenarios that are likely to limit temperature change to below 3°C relative to + pre-industrial levels. Estimates of the aggregate economic costs of mitigation + vary widely depending on methodologies and assumptions but increase with the stringency + of mitigation. Scenarios in which all countries of the world begin mitigation + immediately, in which there is a single global carbon price, and in which all + key technologies are available have been used as a cost-effective benchmark for + estimating macroeconomic mitigation costs. Under these assumptions, mitigation + scenarios that are likely to limit warming to below 2°C through the 21st century + relative to pre-industrial levels entail losses in global consumption—not including + benefits of reduced climate change as well as co-benefits and adverse side effects + of mitigation —of 1 to 4% in 2030, 2 to 6% in 2050, and 3% to 11% in 2100, relative + to consumption in baseline scenarios that grows anywhere from 300% to more than + 900% over the century . These numbers correspond to an annualized reduction of + consumption growth by 0.04 to 0.14 percentage points over the century relative + to annualized consumption growth in the baseline that is between 1.6% and 3% per + year. In the absence or under limited availability of mitigation technologies + , mitigation costs can increase substantially depending on the technology considered + . Delaying additional mitigation reduces near-term costs but increases mitigation + costs in the medium- to long-term. Many models could not limit likely warming + to below 2°C over the 21st century relative to pre-industrial levels, if additional + mitigation is considerably delayed, or if availability of key technologies, such + as bioenergy, CCS and their combination are limited . Mitigation efforts and + associated cost are expected to vary across countries. The distribution of costs + can differ from the distribution of the actions themselves. In globally cost-effective + scenarios, the majority of mitigation efforts takes place in countries with the + highest future GHG emissions in baseline scenarios. Some studies exploring particular + effort-sharing frameworks, under the assumption of a global carbon market, have + estimated substantial global financial flows associated with mitigation in scenarios + that are likely to more unlikely than likely to limit warming during the 21st + century to less than 2°C relative to pre-industrial levels. + 3.2f: + - Climate change risks reduced by adaptation and mitigation Without additional + mitigation efforts beyond those in place today, and even with adaptation, warming + by the end of the 21st century will lead to high to very high risk of severe, + widespread and irreversible impacts globally. Mitigation involves some level of + co-benefits and of risks due to adverse side effects, but these risks do not involve + the same possibility of severe, widespread and irreversible impacts as risks from + climate change, increasing the benefits from near-term mitigation efforts. The + risks of climate change, adaptation and mitigation differ in nature, timescale, + magnitude and persistence. Risks from adaptation include maladaptation and negative + ancillary impacts. Risks from mitigation include possible adverse side effects + of large-scale deployment of low-carbon technology options and economic costs. + Climate change risks may persist for millennia and can involve very high risk + of severe impacts and the presence of significant irreversibilities combined with + limited adaptive capacity. In contrast, the stringency of climate policies can + be adjusted much more quickly in response to observed consequences and costs and + create lower risks of irreversible consequences. Mitigation and adaptation are + complementary approaches for reducing risks of climate change impacts. They interact + with one another and reduce risks over different timescales . Benefits from adaptation + can already be realized in addressing current risks and can be realized in the + future for addressing emerging risks. Adaptation has the potential to reduce climate + change impacts over the next few decades, while mitigation has relatively little + influence on climate outcomes over this timescale. Near-term and longerterm mitigation + and adaptation, as well as development pathways, will determine the risks of climate + change beyond mid-century. The potential for adaptation differs across sectors + and will be limited by institutional and capacity constraints, increasing the + long-term benefits of mitigation. The level of mitigation will influence the rate + and magnitude of climate change, and greater rates and magnitude of climate change + increase the likelihood of exceeding adaptation limits. Without additional mitigation + efforts beyond those in place today, and even with adaptation, warming by the + end of the 21st century will lead to high to very high risk of severe, widespread + and irreversible impacts globally . Estimates of warming in 2100 without additional + climate mitigation efforts are from 3.7°C to 4.8°C compared with pre-industrial + levels; the range is 2.5°C to 7.8°C when using the 5th to 95th percentile range + of the median climate response. The risks associated with temperatures at or above + 4°C include severe and widespread impacts on unique and threatened systems, substantial + species extinction, large risks to global and regional food security, consequential + constraints on common human activities, increased likelihood of triggering tipping + points and limited potential for adaptation in some cases . Some risks of climate + change, such as risks to unique and threatened systems and risks associated with + extreme weather events, are moderate to high at temperatures 1°C to 2°C above + pre-industrial levels. Substantial cuts in GHG emissions over the next few decades + can substantially reduce risks of climate change by limiting warming in the second + half of the 21st century and beyond . Global mean surface warming is largely determined + by cumulative emissions, which are, in turn, linked to emissions over different + timescales. Limiting risks across Reasons For Concern would imply a limit for + cumulative emissions of CO2. Such a limit would require that global net emissions + of CO2 eventually decrease to zero. Reducing risks of climate change through mitigation + would involve substantial cuts in GHG emissions over the next few decades. But + some risks from residual damages are unavoidable, even with mitigation and adaptation. + A subset of relevant climate change risks has been estimated using aggregate economic + indicators. Such economic estimates have important limitations and are therefore + a useful but insufficient basis for decision-making on long-term mitigation targets. Mitigation + involves some level of co-benefits and risks, but these risks do not involve the + same possibility of severe, widespread and irreversible impacts as risks from + climate change . Scenarios that are likely to limit warming to below 2°C or even + 3°C compared with pre-industrial temperatures involve large-scale changes in energy + systems and potentially land use over the coming decades. Associated risks include + those linked to large-scale deployment of technology options for producing low-carbon + energy, the potential for high aggregate economic costs of mitigation and impacts + on vulnerable countries and industries. Other risks and co-benefits are associated + with human health, food security, energy security, poverty reduction, biodiversity + conservation, water availability, income distribution, efficiency of taxation + systems, labour supply and employment, urban sprawl, fossil fuel export revenues + and the economic growth of developing countries. Inertia in the economic and + climate systems and the possibility of irreversible impacts from climate change + increase the benefits of near-term mitigation efforts. The actions taken today + affect the options available in the future to reduce emissions, limit temperature + change and adapt to climate change. Near-term choices can create, amplify or limit + significant elements of lock-in that are important for decision-making. Lock-ins + and irreversibilities occur in the climate system due to large inertia in some + of its components such as heat transfer from the ocean surface to depth leading + to continued ocean warming for centuries regardless of emission scenario and the + irreversibility of a large fraction of anthropogenic climate change resulting + from CO2 emissions on a multi-century to millennial timescale unless CO2 were + to be removed from the atmosphere through large-scale human interventions over + a sustained period . Irreversibilities in socio-economic and biological systems + also result from infrastructure development and long-lived products and from climate + change impacts, such as species extinction. The larger potential for irreversibility + and pervasive impacts from climate change risks than from mitigation risks increases + the benefit of shortterm mitigation efforts. Delays in additional mitigation or + constraints on technological options limit the mitigation options and increase + the long-term mitigation costs as well as other risks that would be incurred in + the medium to long term to hold climate change impacts at a given level. + - Characteristics of mitigation pathways There are multiple mitigation pathways + that are likely to limit warming to below 2°C relative to pre-industrial levels. + These pathways would require substantial emissions reductions over the next few + decades and near zero emissions of CO2 and other long-lived greenhouse gases by + the end of the century. Implementing such reductions poses substantial technological, + economic, social and institutional challenges, which increase with delays in additional + mitigation and if key technologies are not available. Limiting warming to lower + or higher levels involves similar challenges but on different timescales. Without + additional efforts to reduce GHG emissions beyond those in place today, global + emission growth is expected to persist driven by growth in global population and + economic activities. Global GHG emissions under most scenarios without additional + mitigation are between about 75 GtCO2-eq/yr and almost 140 GtCO2-eq/yr in 21003520which + is approximately between the 2100 emission levels in the RCP6.0 and RCP8.5 pathways + 3621 . Baseline scenarios exceed 450 ppm CO2-eq by 2030 and reach CO2-eq concentration + levels between about 750 ppm CO2-eq and more than 1300 ppm CO2-eq by 2100. Global + mean surface temperature increases in 2100 range from about 3.7°C to 4.8°C above + the average for 1850–1900 for a median climate response. They range from 2.5°C + to 7.8°C when including climate uncertainty 3722 . The future scenarios do not + account for possible changes in natural forcings in the climate system. Many + different combinations of technological, behavioural and policy options can be + used to reduce emissions and limit temperature change. To evaluate possible pathways + to long-term climate goals, about 900 mitigation scenarios were collected for + this assessment, each of which describes different technological, socio-economic + and institutional changes. Emission reductions under these scenarios lead to concentrations + in 2100 from 430 ppm CO2-eq to above 720 ppm CO2-eq which is comparable to the + 2100 forcing levels between RCP2.6 and RCP6.0. Scenarios with concentration levels + of below 430 ppm CO2-eq by 2100 were also assessed. Scenarios leading to CO2-eq + concentrations in 2100 of about 450 ppm or lower are likely to maintain warming + below 2°C over the 21st century relative to pre-industrial levels. Mitigation + scenarios reaching concentration levels of about 500 ppm CO2-eq by 2100 are more + likely than not to limit warming to less than 2°C relative to pre-industrial levels, + unless concentration levels temporarily exceed roughly 530 ppm CO2-eq before 2100. + In this case, warming is about as likely as not to remain below 2°C relative to + pre-industrial levels. Scenarios that exceed about 650 ppm CO2-eq by 2100 are + unlikely to limit warming to below 2°C relative to pre-industrial levels. Mitigation + scenarios in which warming is more likely than not to be less than 1.5°C relative + to pre-industrial levels by 2100 are characterized by concentration levels by + 2100 of below 430 ppm CO2-eq. In these scenarios, temperature peaks during the + century and subsequently declines. Mitigation scenarios reaching about 450 ppm + CO2-eq in 2100 typically involve temporary overshootof atmospheric concentrations, + as do many scenarios reaching about 500 ppm CO2-eq to about 550 ppm CO2-eq by + 2100. Depending on the level of overshoot, overshoot scenarios typically rely + on the availability and widespread deployment of bioenergy with carbon dioxide + capture and storage and afforestation in the second half of the century. The availability + and scale of these and other Carbon Dioxide Removal technologies and methods are + uncertain, and CDR technologies and methods are, to varying degrees, associated + with challenges and risks 3924 . CDR is also prevalent in many scenarios without + overshoot to compensate for residual emissions from sectors where mitigation is + more expensive. Limiting warming with a likely chance to less than 2°C relative + to pre-industrial levels would require substantial cuts in anthropogenic GHG emissions + by mid-century through largescale changes in energy systems and possibly land + use. Limiting warming to higher levels would require similar changes but less + quickly. Limiting warming to lower levels would require these changes more quickly. + Scenarios that are likely to maintain warming at below 2°C are characterized by + a 40 to 70% reduction in GHG emissions by 2050, relative to 2010 levels, and emissions + levels near zero or below in 2100. Scenarios with higher emissions in 2050 are + characterized by a greater reliance on CDR technologies beyond mid-century, and + vice versa. Scenarios that are likely to maintain warming at below 2°C include + more rapid improvements in energy efficiency and a tripling to nearly a quadrupling + of the share of zero- and low-carbon energy supply from renewable energy, nuclear + energy and fossil energy with carbon dioxide capture and storage or BECCS by the + year 2050. The scenarios describe a wide range of changes in land use, reflecting + different assumptions about the scale of bioenergy production, afforestation and + reduced deforestation. Scenarios leading to concentrations of 500 ppm CO2-eq by + 2100 are characterized by a 25 to 55% reduction in GHG emissions by 2050, relative + to 2010 levels. Scenarios that are likely to limit warming to 3°C relative to + pre-industrial levels reduce emissions less rapidly than those limiting warming + to 2°C. Only a limited number of studies provide scenarios that are more likely + than not to limit warming to 1.5°C by 2100; these scenarios are characterized + by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission reduction between + 70 and 95% below 2010. For a comprehensive overview of the characteristics of + emissions scenarios, their CO2-equivalent concentrations and their likelihood + to keep warming to below a range of temperature levels, see Table 3.1. Reducing + emissions of non-CO2 climate forcing agents can be an important element of mitigation + strategies. Emissions of nonCO2 gases, nitrous oxide, and fluorinated gases) contributed + about 27% to the total emissions of Kyoto gases in 2010. For most non-CO2 gases, + near-term, low-cost options are available to reduce their emissions. However, + some sources of these non-CO2 gases are difficult to mitigate, such as N2O emissions + from fertilizer use and CH4 emissions from livestock. As a result, emissions of + most non-CO2 gases will not be reduced to zero, even under stringent mitigation + scenarios. The differences in radiative properties and lifetimes of CO2 and non-CO2 + climate forcing agents have important implications for mitigation strategies. All + current GHG emissions and other climate forcing agents affect the rate and magnitude + of climate change over the next few decades. Reducing the emissions of certain + short-lived climate forcing agents can reduce the rate of warming in the short + term but will have only a limited effect on long-term warming, which is driven + mainly by CO2 emissions. There are large uncertainties related to the climate + impacts of some of the short-lived climate forcing agents. Although the effects + of CH4 emissions are well understood, there are large uncertainties related to + the effects of black carbon. Co-emitted components with cooling effects may further + complicate and reduce the climate impacts of emission reductions. Reducing emissions + of sulfur dioxide would cause warming. Near-term reductions in short-lived climate + forcing agents can have a relatively fast impact on climate change and possible + co-benefits for air pollution. Delaying additional mitigation to 2030 will substantially + increase the challenges associated with limiting warming over the 21st century + to below 2°C relative to pre-industrial levels. GHG emissions in 2030 lie between + about 30 GtCO2-eq/yr and 50 GtCO2-eq/yr in cost-effective scenarios that are likely + to about as likely as not to limit warming to less than 2°C this century relative + to pre-industrial levels . Scenarios with GHG emission levels of above 55 GtCO2-eq/yr + require substantially higher rates of emissions reductions between 2030 and 2050 + ; much more rapid scale-up of zero and low-carbon energy over this period ; a + larger reliance on CDR technologies in the long term; and higher transitional + and long-term economic impacts. Estimated global emission levels by 2020 based + on the Cancún Pledges are not consistent with cost-effective long-term mitigation + trajectories that are at least about as likely as not to limit warming to below + 2°C relative to pre-industrial levels , but they do not preclude the option to + meet this goal . The Cancún Pledges are broadly consistent with cost-effective + scenarios that are likely to limit temperature change to below 3°C relative to + pre-industrial levels. Estimates of the aggregate economic costs of mitigation + vary widely depending on methodologies and assumptions but increase with the stringency + of mitigation. Scenarios in which all countries of the world begin mitigation + immediately, in which there is a single global carbon price, and in which all + key technologies are available have been used as a cost-effective benchmark for + estimating macroeconomic mitigation costs. Under these assumptions, mitigation + scenarios that are likely to limit warming to below 2°C through the 21st century + relative to pre-industrial levels entail losses in global consumption—not including + benefits of reduced climate change as well as co-benefits and adverse side effects + of mitigation —of 1 to 4% in 2030, 2 to 6% in 2050, and 3% to 11% in 2100, relative + to consumption in baseline scenarios that grows anywhere from 300% to more than + 900% over the century . These numbers correspond to an annualized reduction of + consumption growth by 0.04 to 0.14 percentage points over the century relative + to annualized consumption growth in the baseline that is between 1.6% and 3% per + year. In the absence or under limited availability of mitigation technologies + , mitigation costs can increase substantially depending on the technology considered + . Delaying additional mitigation reduces near-term costs but increases mitigation + costs in the medium- to long-term. Many models could not limit likely warming + to below 2°C over the 21st century relative to pre-industrial levels, if additional + mitigation is considerably delayed, or if availability of key technologies, such + as bioenergy, CCS and their combination are limited . Mitigation efforts and + associated cost are expected to vary across countries. The distribution of costs + can differ from the distribution of the actions themselves. In globally cost-effective + scenarios, the majority of mitigation efforts takes place in countries with the + highest future GHG emissions in baseline scenarios. Some studies exploring particular + effort-sharing frameworks, under the assumption of a global carbon market, have + estimated substantial global financial flows associated with mitigation in scenarios + that are likely to more unlikely than likely to limit warming during the 21st + century to less than 2°C relative to pre-industrial levels. + 3.3a: + - 'Characteristics of adaptation pathways Adaptation can reduce the risks of climate + change impacts, but there are limits to its effectiveness, especially with greater + magnitudes and rates of climate change. Taking a longer-term perspective, in the + context of sustainable development, increases the likelihood that more immediate + adaptation actions will also enhance future options and preparedness. Adaptation + can contribute to the well-being of current and future populations, the security + of assets and the maintenance of ecosystem goods, functions and services now and + in the future. Adaptation is place- and context-specific, with no single approach + for reducing risks appropriate across all settings . Effective risk reduction + and adaptation strategies consider vulnerability and exposure and their linkages + with socio-economic processes, sustainable development, and climate change. Adaptation + research since the IPCC Fourth Assessment Report has evolved from a dominant consideration + of engineering and technological adaptation pathways to include more ecosystem-based, + institutional and social measures. A previous focus on cost–benefit analysis, + optimization and efficiency approaches has broadened with the development of multi-metric + evaluations that include risk and uncertainty dimensions integrated within wider + policy and ethical frameworks to assess tradeoffs and constraints. The range of + specific adaptation measures has also expanded, as have the links to sustainable + development. There are many studies on local and sectoral adaptation costs and + benefits, but few global analyses and very low confidence in their results. Adaptation + planning and implementation at all levels of governance are contingent on societal + values, objectives and risk perceptions. Recognition of diverse interests, circumstances, + social-cultural contexts and expectations can benefit decision-making processes. + Indigenous, local and traditional knowledge systems and practices, including indigenous + peoples’ holistic view of community and environment, are a major resource for + adapting to climate change, but these have not been used consistently in existing + adaptation efforts. Integrating such forms of knowledge into practices increases + the effectiveness of adaptation as do effective decision support, engagement and + policy processes. Adaptation planning and implementation can be enhanced through + complementary actions across levels, from individuals to governments. National + governments can coordinate adaptation efforts of local and sub-national governments, + for example by protecting vulnerable groups, by supporting economic diversification + and by providing information, policy and legal frameworks and financial support. + Local government and the private sector are increasingly recognized as critical + to progress in adaptation, given their roles in scaling up adaptation of communities, + households and civil society and in managing risk information and financing. A + first step towards adaptation to future climate change is reducing vulnerability + and exposure to present climate variability, but some near-term responses to climate + change may also limit future choices. Integration of adaptation into planning, + including policy design, and decision-making can promote synergies with development + and disaster risk reduction. However, poor planning or implementation, overemphasizing + short-term outcomes or failing to sufficiently anticipate consequences can result + in maladaptation, increasing the vulnerability or exposure of the target group + in the future or the vulnerability of other people, places or sectors. For example, + enhanced protection of exposed assets can lock in dependence on further protection + measures. Appropriate adaptation options can be better assessed by including co-benefits + and mitigation implications. Numerous interacting constraints can impede adaptation + planning and implementation. Common constraints on implementation arise from the + following: limited financial and human resources; limited integration or coordination + of governance; uncertainties about projected impacts; different perceptions of + risks; competing values; absence of key adaptation leaders and advocates; and + limited tools to monitor adaptation effectiveness. Other constraints include insufficient + research, monitoring and observation and the financial and other resources to + maintain them. Underestimating the complexity of adaptation as a social process + can create unrealistic expectations about achieving intended adaptation outcomes + . Greater rates and magnitude of climate change increase the likelihood of exceeding + adaptation limits. Limits to adaptation occur when adaptive actions to avoid intolerable + risks for an actor’s objectives or for the needs of a system are not possible + or are not currently available. Value-based judgments of what constitutes an intolerable + risk may differ. Limits to adaptation emerge from the interaction among climate + change and biophysical and/or socio-economic constraints. Opportunities to take + advantage of positive synergies between adaptation and mitigation may decrease + with time, particularly if limits to adaptation are exceeded. In some parts of + the world, insufficient responses to emerging impacts are already eroding the + basis for sustainable development. For most regions and sectors, empirical evidence + is not sufficient to quantify magnitudes of climate change that would constitute + a future adaptation limit. Furthermore, economic development, technology and cultural + norms and values can change over time to enhance or reduce the capacity of systems + to avoid limits. As a consequence, some limits are ‘soft’ in that they may be + alleviated over time. Other limits are ‘hard’ in that there are no reasonable + prospects for avoiding intolerable risks. Transformations in economic, social, + technological and political decisions and actions can enhance adaptation and promote + sustainable development. Restricting adaptation responses to incremental changes + to existing systems and structures without considering transformational change + may increase costs and losses and miss opportunities. For example, enhancing infrastructure + to protect other built assets can be expensive and ultimately not defray increasing + costs and risks, whereas options such as relocation or using ecosystem services + to adapt may provide a range of benefits now and in the future. Transformational + adaptation can include introduction of new technologies or practices, formation + of new financial structures or systems of governance, adaptation at greater scales + or magnitudes and shifts in the location of activities. Planning and implementation + of transformational adaptation could reflect strengthened, altered or aligned + paradigms and consequently may place new and increased demands on governance structures + to reconcile different goals and visions for the future and to address possible + equity and ethical implications: transformational adaptation pathways are enhanced + by iterative learning, deliberative processes, and innovation. At the national + level, transformation is considered most effective when it reflects a country’s + own visions and approaches to achieving sustainable development in accordance + with its national circumstances and priorities. Building adaptive capacity is + crucial for effective selection and implementation of adaptation options . Successful + adaptation requires not only identifying adaptation options and assessing their + costs and benefits, but also increasing the adaptive capacity of human and natural + systems . This can involve complex governance challenges and new institutions + and institutional arrangements. Significant co-benefits, synergies and trade-offs + exist between mitigation and adaptation and among different adaptation responses; + interactions occur both within and across regions . Increasing efforts to mitigate + and adapt to climate change imply an increasing complexity of interactions, particularly + at the intersections among water, energy, land use and biodiversity, but tools + to understand and manage these interactions remain limited. Examples of actions + with co-benefits include improved energy efficiency and cleaner energy sources, + leading to reduced emissions of health-damaging, climate-altering air pollutants; + reduced energy and water consumption in urban areas through greening cities and + recycling water; sustainable agriculture and forestry; and protection of ecosystems + for carbon storage and other ecosystem services.' + 3.3b: + - 'Characteristics of adaptation pathways Adaptation can reduce the risks of climate + change impacts, but there are limits to its effectiveness, especially with greater + magnitudes and rates of climate change. Taking a longer-term perspective, in the + context of sustainable development, increases the likelihood that more immediate + adaptation actions will also enhance future options and preparedness. Adaptation + can contribute to the well-being of current and future populations, the security + of assets and the maintenance of ecosystem goods, functions and services now and + in the future. Adaptation is place- and context-specific, with no single approach + for reducing risks appropriate across all settings . Effective risk reduction + and adaptation strategies consider vulnerability and exposure and their linkages + with socio-economic processes, sustainable development, and climate change. Adaptation + research since the IPCC Fourth Assessment Report has evolved from a dominant consideration + of engineering and technological adaptation pathways to include more ecosystem-based, + institutional and social measures. A previous focus on cost–benefit analysis, + optimization and efficiency approaches has broadened with the development of multi-metric + evaluations that include risk and uncertainty dimensions integrated within wider + policy and ethical frameworks to assess tradeoffs and constraints. The range of + specific adaptation measures has also expanded, as have the links to sustainable + development. There are many studies on local and sectoral adaptation costs and + benefits, but few global analyses and very low confidence in their results. Adaptation + planning and implementation at all levels of governance are contingent on societal + values, objectives and risk perceptions. Recognition of diverse interests, circumstances, + social-cultural contexts and expectations can benefit decision-making processes. + Indigenous, local and traditional knowledge systems and practices, including indigenous + peoples’ holistic view of community and environment, are a major resource for + adapting to climate change, but these have not been used consistently in existing + adaptation efforts. Integrating such forms of knowledge into practices increases + the effectiveness of adaptation as do effective decision support, engagement and + policy processes. Adaptation planning and implementation can be enhanced through + complementary actions across levels, from individuals to governments. National + governments can coordinate adaptation efforts of local and sub-national governments, + for example by protecting vulnerable groups, by supporting economic diversification + and by providing information, policy and legal frameworks and financial support. + Local government and the private sector are increasingly recognized as critical + to progress in adaptation, given their roles in scaling up adaptation of communities, + households and civil society and in managing risk information and financing. A + first step towards adaptation to future climate change is reducing vulnerability + and exposure to present climate variability, but some near-term responses to climate + change may also limit future choices. Integration of adaptation into planning, + including policy design, and decision-making can promote synergies with development + and disaster risk reduction. However, poor planning or implementation, overemphasizing + short-term outcomes or failing to sufficiently anticipate consequences can result + in maladaptation, increasing the vulnerability or exposure of the target group + in the future or the vulnerability of other people, places or sectors. For example, + enhanced protection of exposed assets can lock in dependence on further protection + measures. Appropriate adaptation options can be better assessed by including co-benefits + and mitigation implications. Numerous interacting constraints can impede adaptation + planning and implementation. Common constraints on implementation arise from the + following: limited financial and human resources; limited integration or coordination + of governance; uncertainties about projected impacts; different perceptions of + risks; competing values; absence of key adaptation leaders and advocates; and + limited tools to monitor adaptation effectiveness. Other constraints include insufficient + research, monitoring and observation and the financial and other resources to + maintain them. Underestimating the complexity of adaptation as a social process + can create unrealistic expectations about achieving intended adaptation outcomes + . Greater rates and magnitude of climate change increase the likelihood of exceeding + adaptation limits. Limits to adaptation occur when adaptive actions to avoid intolerable + risks for an actor’s objectives or for the needs of a system are not possible + or are not currently available. Value-based judgments of what constitutes an intolerable + risk may differ. Limits to adaptation emerge from the interaction among climate + change and biophysical and/or socio-economic constraints. Opportunities to take + advantage of positive synergies between adaptation and mitigation may decrease + with time, particularly if limits to adaptation are exceeded. In some parts of + the world, insufficient responses to emerging impacts are already eroding the + basis for sustainable development. For most regions and sectors, empirical evidence + is not sufficient to quantify magnitudes of climate change that would constitute + a future adaptation limit. Furthermore, economic development, technology and cultural + norms and values can change over time to enhance or reduce the capacity of systems + to avoid limits. As a consequence, some limits are ‘soft’ in that they may be + alleviated over time. Other limits are ‘hard’ in that there are no reasonable + prospects for avoiding intolerable risks. Transformations in economic, social, + technological and political decisions and actions can enhance adaptation and promote + sustainable development. Restricting adaptation responses to incremental changes + to existing systems and structures without considering transformational change + may increase costs and losses and miss opportunities. For example, enhancing infrastructure + to protect other built assets can be expensive and ultimately not defray increasing + costs and risks, whereas options such as relocation or using ecosystem services + to adapt may provide a range of benefits now and in the future. Transformational + adaptation can include introduction of new technologies or practices, formation + of new financial structures or systems of governance, adaptation at greater scales + or magnitudes and shifts in the location of activities. Planning and implementation + of transformational adaptation could reflect strengthened, altered or aligned + paradigms and consequently may place new and increased demands on governance structures + to reconcile different goals and visions for the future and to address possible + equity and ethical implications: transformational adaptation pathways are enhanced + by iterative learning, deliberative processes, and innovation. At the national + level, transformation is considered most effective when it reflects a country’s + own visions and approaches to achieving sustainable development in accordance + with its national circumstances and priorities. Building adaptive capacity is + crucial for effective selection and implementation of adaptation options . Successful + adaptation requires not only identifying adaptation options and assessing their + costs and benefits, but also increasing the adaptive capacity of human and natural + systems . This can involve complex governance challenges and new institutions + and institutional arrangements. Significant co-benefits, synergies and trade-offs + exist between mitigation and adaptation and among different adaptation responses; + interactions occur both within and across regions . Increasing efforts to mitigate + and adapt to climate change imply an increasing complexity of interactions, particularly + at the intersections among water, energy, land use and biodiversity, but tools + to understand and manage these interactions remain limited. Examples of actions + with co-benefits include improved energy efficiency and cleaner energy sources, + leading to reduced emissions of health-damaging, climate-altering air pollutants; + reduced energy and water consumption in urban areas through greening cities and + recycling water; sustainable agriculture and forestry; and protection of ecosystems + for carbon storage and other ecosystem services.' + 3.3c: + - 'Characteristics of adaptation pathways Adaptation can reduce the risks of climate + change impacts, but there are limits to its effectiveness, especially with greater + magnitudes and rates of climate change. Taking a longer-term perspective, in the + context of sustainable development, increases the likelihood that more immediate + adaptation actions will also enhance future options and preparedness. Adaptation + can contribute to the well-being of current and future populations, the security + of assets and the maintenance of ecosystem goods, functions and services now and + in the future. Adaptation is place- and context-specific, with no single approach + for reducing risks appropriate across all settings . Effective risk reduction + and adaptation strategies consider vulnerability and exposure and their linkages + with socio-economic processes, sustainable development, and climate change. Adaptation + research since the IPCC Fourth Assessment Report has evolved from a dominant consideration + of engineering and technological adaptation pathways to include more ecosystem-based, + institutional and social measures. A previous focus on cost–benefit analysis, + optimization and efficiency approaches has broadened with the development of multi-metric + evaluations that include risk and uncertainty dimensions integrated within wider + policy and ethical frameworks to assess tradeoffs and constraints. The range of + specific adaptation measures has also expanded, as have the links to sustainable + development. There are many studies on local and sectoral adaptation costs and + benefits, but few global analyses and very low confidence in their results. Adaptation + planning and implementation at all levels of governance are contingent on societal + values, objectives and risk perceptions. Recognition of diverse interests, circumstances, + social-cultural contexts and expectations can benefit decision-making processes. + Indigenous, local and traditional knowledge systems and practices, including indigenous + peoples’ holistic view of community and environment, are a major resource for + adapting to climate change, but these have not been used consistently in existing + adaptation efforts. Integrating such forms of knowledge into practices increases + the effectiveness of adaptation as do effective decision support, engagement and + policy processes. Adaptation planning and implementation can be enhanced through + complementary actions across levels, from individuals to governments. National + governments can coordinate adaptation efforts of local and sub-national governments, + for example by protecting vulnerable groups, by supporting economic diversification + and by providing information, policy and legal frameworks and financial support. + Local government and the private sector are increasingly recognized as critical + to progress in adaptation, given their roles in scaling up adaptation of communities, + households and civil society and in managing risk information and financing. A + first step towards adaptation to future climate change is reducing vulnerability + and exposure to present climate variability, but some near-term responses to climate + change may also limit future choices. Integration of adaptation into planning, + including policy design, and decision-making can promote synergies with development + and disaster risk reduction. However, poor planning or implementation, overemphasizing + short-term outcomes or failing to sufficiently anticipate consequences can result + in maladaptation, increasing the vulnerability or exposure of the target group + in the future or the vulnerability of other people, places or sectors. For example, + enhanced protection of exposed assets can lock in dependence on further protection + measures. Appropriate adaptation options can be better assessed by including co-benefits + and mitigation implications. Numerous interacting constraints can impede adaptation + planning and implementation. Common constraints on implementation arise from the + following: limited financial and human resources; limited integration or coordination + of governance; uncertainties about projected impacts; different perceptions of + risks; competing values; absence of key adaptation leaders and advocates; and + limited tools to monitor adaptation effectiveness. Other constraints include insufficient + research, monitoring and observation and the financial and other resources to + maintain them. Underestimating the complexity of adaptation as a social process + can create unrealistic expectations about achieving intended adaptation outcomes + . Greater rates and magnitude of climate change increase the likelihood of exceeding + adaptation limits. Limits to adaptation occur when adaptive actions to avoid intolerable + risks for an actor’s objectives or for the needs of a system are not possible + or are not currently available. Value-based judgments of what constitutes an intolerable + risk may differ. Limits to adaptation emerge from the interaction among climate + change and biophysical and/or socio-economic constraints. Opportunities to take + advantage of positive synergies between adaptation and mitigation may decrease + with time, particularly if limits to adaptation are exceeded. In some parts of + the world, insufficient responses to emerging impacts are already eroding the + basis for sustainable development. For most regions and sectors, empirical evidence + is not sufficient to quantify magnitudes of climate change that would constitute + a future adaptation limit. Furthermore, economic development, technology and cultural + norms and values can change over time to enhance or reduce the capacity of systems + to avoid limits. As a consequence, some limits are ‘soft’ in that they may be + alleviated over time. Other limits are ‘hard’ in that there are no reasonable + prospects for avoiding intolerable risks. Transformations in economic, social, + technological and political decisions and actions can enhance adaptation and promote + sustainable development. Restricting adaptation responses to incremental changes + to existing systems and structures without considering transformational change + may increase costs and losses and miss opportunities. For example, enhancing infrastructure + to protect other built assets can be expensive and ultimately not defray increasing + costs and risks, whereas options such as relocation or using ecosystem services + to adapt may provide a range of benefits now and in the future. Transformational + adaptation can include introduction of new technologies or practices, formation + of new financial structures or systems of governance, adaptation at greater scales + or magnitudes and shifts in the location of activities. Planning and implementation + of transformational adaptation could reflect strengthened, altered or aligned + paradigms and consequently may place new and increased demands on governance structures + to reconcile different goals and visions for the future and to address possible + equity and ethical implications: transformational adaptation pathways are enhanced + by iterative learning, deliberative processes, and innovation. At the national + level, transformation is considered most effective when it reflects a country’s + own visions and approaches to achieving sustainable development in accordance + with its national circumstances and priorities. Building adaptive capacity is + crucial for effective selection and implementation of adaptation options . Successful + adaptation requires not only identifying adaptation options and assessing their + costs and benefits, but also increasing the adaptive capacity of human and natural + systems . This can involve complex governance challenges and new institutions + and institutional arrangements. Significant co-benefits, synergies and trade-offs + exist between mitigation and adaptation and among different adaptation responses; + interactions occur both within and across regions . Increasing efforts to mitigate + and adapt to climate change imply an increasing complexity of interactions, particularly + at the intersections among water, energy, land use and biodiversity, but tools + to understand and manage these interactions remain limited. Examples of actions + with co-benefits include improved energy efficiency and cleaner energy sources, + leading to reduced emissions of health-damaging, climate-altering air pollutants; + reduced energy and water consumption in urban areas through greening cities and + recycling water; sustainable agriculture and forestry; and protection of ecosystems + for carbon storage and other ecosystem services.' + 3.3d: + - 'Characteristics of adaptation pathways Adaptation can reduce the risks of climate + change impacts, but there are limits to its effectiveness, especially with greater + magnitudes and rates of climate change. Taking a longer-term perspective, in the + context of sustainable development, increases the likelihood that more immediate + adaptation actions will also enhance future options and preparedness. Adaptation + can contribute to the well-being of current and future populations, the security + of assets and the maintenance of ecosystem goods, functions and services now and + in the future. Adaptation is place- and context-specific, with no single approach + for reducing risks appropriate across all settings . Effective risk reduction + and adaptation strategies consider vulnerability and exposure and their linkages + with socio-economic processes, sustainable development, and climate change. Adaptation + research since the IPCC Fourth Assessment Report has evolved from a dominant consideration + of engineering and technological adaptation pathways to include more ecosystem-based, + institutional and social measures. A previous focus on cost–benefit analysis, + optimization and efficiency approaches has broadened with the development of multi-metric + evaluations that include risk and uncertainty dimensions integrated within wider + policy and ethical frameworks to assess tradeoffs and constraints. The range of + specific adaptation measures has also expanded, as have the links to sustainable + development. There are many studies on local and sectoral adaptation costs and + benefits, but few global analyses and very low confidence in their results. Adaptation + planning and implementation at all levels of governance are contingent on societal + values, objectives and risk perceptions. Recognition of diverse interests, circumstances, + social-cultural contexts and expectations can benefit decision-making processes. + Indigenous, local and traditional knowledge systems and practices, including indigenous + peoples’ holistic view of community and environment, are a major resource for + adapting to climate change, but these have not been used consistently in existing + adaptation efforts. Integrating such forms of knowledge into practices increases + the effectiveness of adaptation as do effective decision support, engagement and + policy processes. Adaptation planning and implementation can be enhanced through + complementary actions across levels, from individuals to governments. National + governments can coordinate adaptation efforts of local and sub-national governments, + for example by protecting vulnerable groups, by supporting economic diversification + and by providing information, policy and legal frameworks and financial support. + Local government and the private sector are increasingly recognized as critical + to progress in adaptation, given their roles in scaling up adaptation of communities, + households and civil society and in managing risk information and financing. A + first step towards adaptation to future climate change is reducing vulnerability + and exposure to present climate variability, but some near-term responses to climate + change may also limit future choices. Integration of adaptation into planning, + including policy design, and decision-making can promote synergies with development + and disaster risk reduction. However, poor planning or implementation, overemphasizing + short-term outcomes or failing to sufficiently anticipate consequences can result + in maladaptation, increasing the vulnerability or exposure of the target group + in the future or the vulnerability of other people, places or sectors. For example, + enhanced protection of exposed assets can lock in dependence on further protection + measures. Appropriate adaptation options can be better assessed by including co-benefits + and mitigation implications. Numerous interacting constraints can impede adaptation + planning and implementation. Common constraints on implementation arise from the + following: limited financial and human resources; limited integration or coordination + of governance; uncertainties about projected impacts; different perceptions of + risks; competing values; absence of key adaptation leaders and advocates; and + limited tools to monitor adaptation effectiveness. Other constraints include insufficient + research, monitoring and observation and the financial and other resources to + maintain them. Underestimating the complexity of adaptation as a social process + can create unrealistic expectations about achieving intended adaptation outcomes + . Greater rates and magnitude of climate change increase the likelihood of exceeding + adaptation limits. Limits to adaptation occur when adaptive actions to avoid intolerable + risks for an actor’s objectives or for the needs of a system are not possible + or are not currently available. Value-based judgments of what constitutes an intolerable + risk may differ. Limits to adaptation emerge from the interaction among climate + change and biophysical and/or socio-economic constraints. Opportunities to take + advantage of positive synergies between adaptation and mitigation may decrease + with time, particularly if limits to adaptation are exceeded. In some parts of + the world, insufficient responses to emerging impacts are already eroding the + basis for sustainable development. For most regions and sectors, empirical evidence + is not sufficient to quantify magnitudes of climate change that would constitute + a future adaptation limit. Furthermore, economic development, technology and cultural + norms and values can change over time to enhance or reduce the capacity of systems + to avoid limits. As a consequence, some limits are ‘soft’ in that they may be + alleviated over time. Other limits are ‘hard’ in that there are no reasonable + prospects for avoiding intolerable risks. Transformations in economic, social, + technological and political decisions and actions can enhance adaptation and promote + sustainable development. Restricting adaptation responses to incremental changes + to existing systems and structures without considering transformational change + may increase costs and losses and miss opportunities. For example, enhancing infrastructure + to protect other built assets can be expensive and ultimately not defray increasing + costs and risks, whereas options such as relocation or using ecosystem services + to adapt may provide a range of benefits now and in the future. Transformational + adaptation can include introduction of new technologies or practices, formation + of new financial structures or systems of governance, adaptation at greater scales + or magnitudes and shifts in the location of activities. Planning and implementation + of transformational adaptation could reflect strengthened, altered or aligned + paradigms and consequently may place new and increased demands on governance structures + to reconcile different goals and visions for the future and to address possible + equity and ethical implications: transformational adaptation pathways are enhanced + by iterative learning, deliberative processes, and innovation. At the national + level, transformation is considered most effective when it reflects a country’s + own visions and approaches to achieving sustainable development in accordance + with its national circumstances and priorities. Building adaptive capacity is + crucial for effective selection and implementation of adaptation options . Successful + adaptation requires not only identifying adaptation options and assessing their + costs and benefits, but also increasing the adaptive capacity of human and natural + systems . This can involve complex governance challenges and new institutions + and institutional arrangements. Significant co-benefits, synergies and trade-offs + exist between mitigation and adaptation and among different adaptation responses; + interactions occur both within and across regions . Increasing efforts to mitigate + and adapt to climate change imply an increasing complexity of interactions, particularly + at the intersections among water, energy, land use and biodiversity, but tools + to understand and manage these interactions remain limited. Examples of actions + with co-benefits include improved energy efficiency and cleaner energy sources, + leading to reduced emissions of health-damaging, climate-altering air pollutants; + reduced energy and water consumption in urban areas through greening cities and + recycling water; sustainable agriculture and forestry; and protection of ecosystems + for carbon storage and other ecosystem services.' + 3.3f: + - 'Characteristics of adaptation pathways Adaptation can reduce the risks of climate + change impacts, but there are limits to its effectiveness, especially with greater + magnitudes and rates of climate change. Taking a longer-term perspective, in the + context of sustainable development, increases the likelihood that more immediate + adaptation actions will also enhance future options and preparedness. Adaptation + can contribute to the well-being of current and future populations, the security + of assets and the maintenance of ecosystem goods, functions and services now and + in the future. Adaptation is place- and context-specific, with no single approach + for reducing risks appropriate across all settings . Effective risk reduction + and adaptation strategies consider vulnerability and exposure and their linkages + with socio-economic processes, sustainable development, and climate change. Adaptation + research since the IPCC Fourth Assessment Report has evolved from a dominant consideration + of engineering and technological adaptation pathways to include more ecosystem-based, + institutional and social measures. A previous focus on cost–benefit analysis, + optimization and efficiency approaches has broadened with the development of multi-metric + evaluations that include risk and uncertainty dimensions integrated within wider + policy and ethical frameworks to assess tradeoffs and constraints. The range of + specific adaptation measures has also expanded, as have the links to sustainable + development. There are many studies on local and sectoral adaptation costs and + benefits, but few global analyses and very low confidence in their results. Adaptation + planning and implementation at all levels of governance are contingent on societal + values, objectives and risk perceptions. Recognition of diverse interests, circumstances, + social-cultural contexts and expectations can benefit decision-making processes. + Indigenous, local and traditional knowledge systems and practices, including indigenous + peoples’ holistic view of community and environment, are a major resource for + adapting to climate change, but these have not been used consistently in existing + adaptation efforts. Integrating such forms of knowledge into practices increases + the effectiveness of adaptation as do effective decision support, engagement and + policy processes. Adaptation planning and implementation can be enhanced through + complementary actions across levels, from individuals to governments. National + governments can coordinate adaptation efforts of local and sub-national governments, + for example by protecting vulnerable groups, by supporting economic diversification + and by providing information, policy and legal frameworks and financial support. + Local government and the private sector are increasingly recognized as critical + to progress in adaptation, given their roles in scaling up adaptation of communities, + households and civil society and in managing risk information and financing. A + first step towards adaptation to future climate change is reducing vulnerability + and exposure to present climate variability, but some near-term responses to climate + change may also limit future choices. Integration of adaptation into planning, + including policy design, and decision-making can promote synergies with development + and disaster risk reduction. However, poor planning or implementation, overemphasizing + short-term outcomes or failing to sufficiently anticipate consequences can result + in maladaptation, increasing the vulnerability or exposure of the target group + in the future or the vulnerability of other people, places or sectors. For example, + enhanced protection of exposed assets can lock in dependence on further protection + measures. Appropriate adaptation options can be better assessed by including co-benefits + and mitigation implications. Numerous interacting constraints can impede adaptation + planning and implementation. Common constraints on implementation arise from the + following: limited financial and human resources; limited integration or coordination + of governance; uncertainties about projected impacts; different perceptions of + risks; competing values; absence of key adaptation leaders and advocates; and + limited tools to monitor adaptation effectiveness. Other constraints include insufficient + research, monitoring and observation and the financial and other resources to + maintain them. Underestimating the complexity of adaptation as a social process + can create unrealistic expectations about achieving intended adaptation outcomes + . Greater rates and magnitude of climate change increase the likelihood of exceeding + adaptation limits. Limits to adaptation occur when adaptive actions to avoid intolerable + risks for an actor’s objectives or for the needs of a system are not possible + or are not currently available. Value-based judgments of what constitutes an intolerable + risk may differ. Limits to adaptation emerge from the interaction among climate + change and biophysical and/or socio-economic constraints. Opportunities to take + advantage of positive synergies between adaptation and mitigation may decrease + with time, particularly if limits to adaptation are exceeded. In some parts of + the world, insufficient responses to emerging impacts are already eroding the + basis for sustainable development. For most regions and sectors, empirical evidence + is not sufficient to quantify magnitudes of climate change that would constitute + a future adaptation limit. Furthermore, economic development, technology and cultural + norms and values can change over time to enhance or reduce the capacity of systems + to avoid limits. As a consequence, some limits are ‘soft’ in that they may be + alleviated over time. Other limits are ‘hard’ in that there are no reasonable + prospects for avoiding intolerable risks. Transformations in economic, social, + technological and political decisions and actions can enhance adaptation and promote + sustainable development. Restricting adaptation responses to incremental changes + to existing systems and structures without considering transformational change + may increase costs and losses and miss opportunities. For example, enhancing infrastructure + to protect other built assets can be expensive and ultimately not defray increasing + costs and risks, whereas options such as relocation or using ecosystem services + to adapt may provide a range of benefits now and in the future. Transformational + adaptation can include introduction of new technologies or practices, formation + of new financial structures or systems of governance, adaptation at greater scales + or magnitudes and shifts in the location of activities. Planning and implementation + of transformational adaptation could reflect strengthened, altered or aligned + paradigms and consequently may place new and increased demands on governance structures + to reconcile different goals and visions for the future and to address possible + equity and ethical implications: transformational adaptation pathways are enhanced + by iterative learning, deliberative processes, and innovation. At the national + level, transformation is considered most effective when it reflects a country’s + own visions and approaches to achieving sustainable development in accordance + with its national circumstances and priorities. Building adaptive capacity is + crucial for effective selection and implementation of adaptation options . Successful + adaptation requires not only identifying adaptation options and assessing their + costs and benefits, but also increasing the adaptive capacity of human and natural + systems . This can involve complex governance challenges and new institutions + and institutional arrangements. Significant co-benefits, synergies and trade-offs + exist between mitigation and adaptation and among different adaptation responses; + interactions occur both within and across regions . Increasing efforts to mitigate + and adapt to climate change imply an increasing complexity of interactions, particularly + at the intersections among water, energy, land use and biodiversity, but tools + to understand and manage these interactions remain limited. Examples of actions + with co-benefits include improved energy efficiency and cleaner energy sources, + leading to reduced emissions of health-damaging, climate-altering air pollutants; + reduced energy and water consumption in urban areas through greening cities and + recycling water; sustainable agriculture and forestry; and protection of ecosystems + for carbon storage and other ecosystem services.' + 3.3g: + - 'Characteristics of adaptation pathways Adaptation can reduce the risks of climate + change impacts, but there are limits to its effectiveness, especially with greater + magnitudes and rates of climate change. Taking a longer-term perspective, in the + context of sustainable development, increases the likelihood that more immediate + adaptation actions will also enhance future options and preparedness. Adaptation + can contribute to the well-being of current and future populations, the security + of assets and the maintenance of ecosystem goods, functions and services now and + in the future. Adaptation is place- and context-specific, with no single approach + for reducing risks appropriate across all settings . Effective risk reduction + and adaptation strategies consider vulnerability and exposure and their linkages + with socio-economic processes, sustainable development, and climate change. Adaptation + research since the IPCC Fourth Assessment Report has evolved from a dominant consideration + of engineering and technological adaptation pathways to include more ecosystem-based, + institutional and social measures. A previous focus on cost–benefit analysis, + optimization and efficiency approaches has broadened with the development of multi-metric + evaluations that include risk and uncertainty dimensions integrated within wider + policy and ethical frameworks to assess tradeoffs and constraints. The range of + specific adaptation measures has also expanded, as have the links to sustainable + development. There are many studies on local and sectoral adaptation costs and + benefits, but few global analyses and very low confidence in their results. Adaptation + planning and implementation at all levels of governance are contingent on societal + values, objectives and risk perceptions. Recognition of diverse interests, circumstances, + social-cultural contexts and expectations can benefit decision-making processes. + Indigenous, local and traditional knowledge systems and practices, including indigenous + peoples’ holistic view of community and environment, are a major resource for + adapting to climate change, but these have not been used consistently in existing + adaptation efforts. Integrating such forms of knowledge into practices increases + the effectiveness of adaptation as do effective decision support, engagement and + policy processes. Adaptation planning and implementation can be enhanced through + complementary actions across levels, from individuals to governments. National + governments can coordinate adaptation efforts of local and sub-national governments, + for example by protecting vulnerable groups, by supporting economic diversification + and by providing information, policy and legal frameworks and financial support. + Local government and the private sector are increasingly recognized as critical + to progress in adaptation, given their roles in scaling up adaptation of communities, + households and civil society and in managing risk information and financing. A + first step towards adaptation to future climate change is reducing vulnerability + and exposure to present climate variability, but some near-term responses to climate + change may also limit future choices. Integration of adaptation into planning, + including policy design, and decision-making can promote synergies with development + and disaster risk reduction. However, poor planning or implementation, overemphasizing + short-term outcomes or failing to sufficiently anticipate consequences can result + in maladaptation, increasing the vulnerability or exposure of the target group + in the future or the vulnerability of other people, places or sectors. For example, + enhanced protection of exposed assets can lock in dependence on further protection + measures. Appropriate adaptation options can be better assessed by including co-benefits + and mitigation implications. Numerous interacting constraints can impede adaptation + planning and implementation. Common constraints on implementation arise from the + following: limited financial and human resources; limited integration or coordination + of governance; uncertainties about projected impacts; different perceptions of + risks; competing values; absence of key adaptation leaders and advocates; and + limited tools to monitor adaptation effectiveness. Other constraints include insufficient + research, monitoring and observation and the financial and other resources to + maintain them. Underestimating the complexity of adaptation as a social process + can create unrealistic expectations about achieving intended adaptation outcomes + . Greater rates and magnitude of climate change increase the likelihood of exceeding + adaptation limits. Limits to adaptation occur when adaptive actions to avoid intolerable + risks for an actor’s objectives or for the needs of a system are not possible + or are not currently available. Value-based judgments of what constitutes an intolerable + risk may differ. Limits to adaptation emerge from the interaction among climate + change and biophysical and/or socio-economic constraints. Opportunities to take + advantage of positive synergies between adaptation and mitigation may decrease + with time, particularly if limits to adaptation are exceeded. In some parts of + the world, insufficient responses to emerging impacts are already eroding the + basis for sustainable development. For most regions and sectors, empirical evidence + is not sufficient to quantify magnitudes of climate change that would constitute + a future adaptation limit. Furthermore, economic development, technology and cultural + norms and values can change over time to enhance or reduce the capacity of systems + to avoid limits. As a consequence, some limits are ‘soft’ in that they may be + alleviated over time. Other limits are ‘hard’ in that there are no reasonable + prospects for avoiding intolerable risks. Transformations in economic, social, + technological and political decisions and actions can enhance adaptation and promote + sustainable development. Restricting adaptation responses to incremental changes + to existing systems and structures without considering transformational change + may increase costs and losses and miss opportunities. For example, enhancing infrastructure + to protect other built assets can be expensive and ultimately not defray increasing + costs and risks, whereas options such as relocation or using ecosystem services + to adapt may provide a range of benefits now and in the future. Transformational + adaptation can include introduction of new technologies or practices, formation + of new financial structures or systems of governance, adaptation at greater scales + or magnitudes and shifts in the location of activities. Planning and implementation + of transformational adaptation could reflect strengthened, altered or aligned + paradigms and consequently may place new and increased demands on governance structures + to reconcile different goals and visions for the future and to address possible + equity and ethical implications: transformational adaptation pathways are enhanced + by iterative learning, deliberative processes, and innovation. At the national + level, transformation is considered most effective when it reflects a country’s + own visions and approaches to achieving sustainable development in accordance + with its national circumstances and priorities. Building adaptive capacity is + crucial for effective selection and implementation of adaptation options . Successful + adaptation requires not only identifying adaptation options and assessing their + costs and benefits, but also increasing the adaptive capacity of human and natural + systems . This can involve complex governance challenges and new institutions + and institutional arrangements. Significant co-benefits, synergies and trade-offs + exist between mitigation and adaptation and among different adaptation responses; + interactions occur both within and across regions . Increasing efforts to mitigate + and adapt to climate change imply an increasing complexity of interactions, particularly + at the intersections among water, energy, land use and biodiversity, but tools + to understand and manage these interactions remain limited. Examples of actions + with co-benefits include improved energy efficiency and cleaner energy sources, + leading to reduced emissions of health-damaging, climate-altering air pollutants; + reduced energy and water consumption in urban areas through greening cities and + recycling water; sustainable agriculture and forestry; and protection of ecosystems + for carbon storage and other ecosystem services.' + 3.4a: + - Characteristics of mitigation pathways There are multiple mitigation pathways + that are likely to limit warming to below 2°C relative to pre-industrial levels. + These pathways would require substantial emissions reductions over the next few + decades and near zero emissions of CO2 and other long-lived greenhouse gases by + the end of the century. Implementing such reductions poses substantial technological, + economic, social and institutional challenges, which increase with delays in additional + mitigation and if key technologies are not available. Limiting warming to lower + or higher levels involves similar challenges but on different timescales. Without + additional efforts to reduce GHG emissions beyond those in place today, global + emission growth is expected to persist driven by growth in global population and + economic activities. Global GHG emissions under most scenarios without additional + mitigation are between about 75 GtCO2-eq/yr and almost 140 GtCO2-eq/yr in 21003520which + is approximately between the 2100 emission levels in the RCP6.0 and RCP8.5 pathways + 3621 . Baseline scenarios exceed 450 ppm CO2-eq by 2030 and reach CO2-eq concentration + levels between about 750 ppm CO2-eq and more than 1300 ppm CO2-eq by 2100. Global + mean surface temperature increases in 2100 range from about 3.7°C to 4.8°C above + the average for 1850–1900 for a median climate response. They range from 2.5°C + to 7.8°C when including climate uncertainty 3722 . The future scenarios do not + account for possible changes in natural forcings in the climate system. Many + different combinations of technological, behavioural and policy options can be + used to reduce emissions and limit temperature change. To evaluate possible pathways + to long-term climate goals, about 900 mitigation scenarios were collected for + this assessment, each of which describes different technological, socio-economic + and institutional changes. Emission reductions under these scenarios lead to concentrations + in 2100 from 430 ppm CO2-eq to above 720 ppm CO2-eq which is comparable to the + 2100 forcing levels between RCP2.6 and RCP6.0. Scenarios with concentration levels + of below 430 ppm CO2-eq by 2100 were also assessed. Scenarios leading to CO2-eq + concentrations in 2100 of about 450 ppm or lower are likely to maintain warming + below 2°C over the 21st century relative to pre-industrial levels. Mitigation + scenarios reaching concentration levels of about 500 ppm CO2-eq by 2100 are more + likely than not to limit warming to less than 2°C relative to pre-industrial levels, + unless concentration levels temporarily exceed roughly 530 ppm CO2-eq before 2100. + In this case, warming is about as likely as not to remain below 2°C relative to + pre-industrial levels. Scenarios that exceed about 650 ppm CO2-eq by 2100 are + unlikely to limit warming to below 2°C relative to pre-industrial levels. Mitigation + scenarios in which warming is more likely than not to be less than 1.5°C relative + to pre-industrial levels by 2100 are characterized by concentration levels by + 2100 of below 430 ppm CO2-eq. In these scenarios, temperature peaks during the + century and subsequently declines. Mitigation scenarios reaching about 450 ppm + CO2-eq in 2100 typically involve temporary overshootof atmospheric concentrations, + as do many scenarios reaching about 500 ppm CO2-eq to about 550 ppm CO2-eq by + 2100. Depending on the level of overshoot, overshoot scenarios typically rely + on the availability and widespread deployment of bioenergy with carbon dioxide + capture and storage and afforestation in the second half of the century. The availability + and scale of these and other Carbon Dioxide Removal technologies and methods are + uncertain, and CDR technologies and methods are, to varying degrees, associated + with challenges and risks 3924 . CDR is also prevalent in many scenarios without + overshoot to compensate for residual emissions from sectors where mitigation is + more expensive. Limiting warming with a likely chance to less than 2°C relative + to pre-industrial levels would require substantial cuts in anthropogenic GHG emissions + by mid-century through largescale changes in energy systems and possibly land + use. Limiting warming to higher levels would require similar changes but less + quickly. Limiting warming to lower levels would require these changes more quickly. + Scenarios that are likely to maintain warming at below 2°C are characterized by + a 40 to 70% reduction in GHG emissions by 2050, relative to 2010 levels, and emissions + levels near zero or below in 2100. Scenarios with higher emissions in 2050 are + characterized by a greater reliance on CDR technologies beyond mid-century, and + vice versa. Scenarios that are likely to maintain warming at below 2°C include + more rapid improvements in energy efficiency and a tripling to nearly a quadrupling + of the share of zero- and low-carbon energy supply from renewable energy, nuclear + energy and fossil energy with carbon dioxide capture and storage or BECCS by the + year 2050. The scenarios describe a wide range of changes in land use, reflecting + different assumptions about the scale of bioenergy production, afforestation and + reduced deforestation. Scenarios leading to concentrations of 500 ppm CO2-eq by + 2100 are characterized by a 25 to 55% reduction in GHG emissions by 2050, relative + to 2010 levels. Scenarios that are likely to limit warming to 3°C relative to + pre-industrial levels reduce emissions less rapidly than those limiting warming + to 2°C. Only a limited number of studies provide scenarios that are more likely + than not to limit warming to 1.5°C by 2100; these scenarios are characterized + by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission reduction between + 70 and 95% below 2010. For a comprehensive overview of the characteristics of + emissions scenarios, their CO2-equivalent concentrations and their likelihood + to keep warming to below a range of temperature levels, see Table 3.1. Reducing + emissions of non-CO2 climate forcing agents can be an important element of mitigation + strategies. Emissions of nonCO2 gases, nitrous oxide, and fluorinated gases) contributed + about 27% to the total emissions of Kyoto gases in 2010. For most non-CO2 gases, + near-term, low-cost options are available to reduce their emissions. However, + some sources of these non-CO2 gases are difficult to mitigate, such as N2O emissions + from fertilizer use and CH4 emissions from livestock. As a result, emissions of + most non-CO2 gases will not be reduced to zero, even under stringent mitigation + scenarios. The differences in radiative properties and lifetimes of CO2 and non-CO2 + climate forcing agents have important implications for mitigation strategies. All + current GHG emissions and other climate forcing agents affect the rate and magnitude + of climate change over the next few decades. Reducing the emissions of certain + short-lived climate forcing agents can reduce the rate of warming in the short + term but will have only a limited effect on long-term warming, which is driven + mainly by CO2 emissions. There are large uncertainties related to the climate + impacts of some of the short-lived climate forcing agents. Although the effects + of CH4 emissions are well understood, there are large uncertainties related to + the effects of black carbon. Co-emitted components with cooling effects may further + complicate and reduce the climate impacts of emission reductions. Reducing emissions + of sulfur dioxide would cause warming. Near-term reductions in short-lived climate + forcing agents can have a relatively fast impact on climate change and possible + co-benefits for air pollution. Delaying additional mitigation to 2030 will substantially + increase the challenges associated with limiting warming over the 21st century + to below 2°C relative to pre-industrial levels. GHG emissions in 2030 lie between + about 30 GtCO2-eq/yr and 50 GtCO2-eq/yr in cost-effective scenarios that are likely + to about as likely as not to limit warming to less than 2°C this century relative + to pre-industrial levels . Scenarios with GHG emission levels of above 55 GtCO2-eq/yr + require substantially higher rates of emissions reductions between 2030 and 2050 + ; much more rapid scale-up of zero and low-carbon energy over this period ; a + larger reliance on CDR technologies in the long term; and higher transitional + and long-term economic impacts. Estimated global emission levels by 2020 based + on the Cancún Pledges are not consistent with cost-effective long-term mitigation + trajectories that are at least about as likely as not to limit warming to below + 2°C relative to pre-industrial levels , but they do not preclude the option to + meet this goal . The Cancún Pledges are broadly consistent with cost-effective + scenarios that are likely to limit temperature change to below 3°C relative to + pre-industrial levels. Estimates of the aggregate economic costs of mitigation + vary widely depending on methodologies and assumptions but increase with the stringency + of mitigation. Scenarios in which all countries of the world begin mitigation + immediately, in which there is a single global carbon price, and in which all + key technologies are available have been used as a cost-effective benchmark for + estimating macroeconomic mitigation costs. Under these assumptions, mitigation + scenarios that are likely to limit warming to below 2°C through the 21st century + relative to pre-industrial levels entail losses in global consumption—not including + benefits of reduced climate change as well as co-benefits and adverse side effects + of mitigation —of 1 to 4% in 2030, 2 to 6% in 2050, and 3% to 11% in 2100, relative + to consumption in baseline scenarios that grows anywhere from 300% to more than + 900% over the century . These numbers correspond to an annualized reduction of + consumption growth by 0.04 to 0.14 percentage points over the century relative + to annualized consumption growth in the baseline that is between 1.6% and 3% per + year. In the absence or under limited availability of mitigation technologies + , mitigation costs can increase substantially depending on the technology considered + . Delaying additional mitigation reduces near-term costs but increases mitigation + costs in the medium- to long-term. Many models could not limit likely warming + to below 2°C over the 21st century relative to pre-industrial levels, if additional + mitigation is considerably delayed, or if availability of key technologies, such + as bioenergy, CCS and their combination are limited . Mitigation efforts and + associated cost are expected to vary across countries. The distribution of costs + can differ from the distribution of the actions themselves. In globally cost-effective + scenarios, the majority of mitigation efforts takes place in countries with the + highest future GHG emissions in baseline scenarios. Some studies exploring particular + effort-sharing frameworks, under the assumption of a global carbon market, have + estimated substantial global financial flows associated with mitigation in scenarios + that are likely to more unlikely than likely to limit warming during the 21st + century to less than 2°C relative to pre-industrial levels. + 3.4b: + - Characteristics of mitigation pathways There are multiple mitigation pathways + that are likely to limit warming to below 2°C relative to pre-industrial levels. + These pathways would require substantial emissions reductions over the next few + decades and near zero emissions of CO2 and other long-lived greenhouse gases by + the end of the century. Implementing such reductions poses substantial technological, + economic, social and institutional challenges, which increase with delays in additional + mitigation and if key technologies are not available. Limiting warming to lower + or higher levels involves similar challenges but on different timescales. Without + additional efforts to reduce GHG emissions beyond those in place today, global + emission growth is expected to persist driven by growth in global population and + economic activities. Global GHG emissions under most scenarios without additional + mitigation are between about 75 GtCO2-eq/yr and almost 140 GtCO2-eq/yr in 21003520which + is approximately between the 2100 emission levels in the RCP6.0 and RCP8.5 pathways + 3621 . Baseline scenarios exceed 450 ppm CO2-eq by 2030 and reach CO2-eq concentration + levels between about 750 ppm CO2-eq and more than 1300 ppm CO2-eq by 2100. Global + mean surface temperature increases in 2100 range from about 3.7°C to 4.8°C above + the average for 1850–1900 for a median climate response. They range from 2.5°C + to 7.8°C when including climate uncertainty 3722 . The future scenarios do not + account for possible changes in natural forcings in the climate system. Many + different combinations of technological, behavioural and policy options can be + used to reduce emissions and limit temperature change. To evaluate possible pathways + to long-term climate goals, about 900 mitigation scenarios were collected for + this assessment, each of which describes different technological, socio-economic + and institutional changes. Emission reductions under these scenarios lead to concentrations + in 2100 from 430 ppm CO2-eq to above 720 ppm CO2-eq which is comparable to the + 2100 forcing levels between RCP2.6 and RCP6.0. Scenarios with concentration levels + of below 430 ppm CO2-eq by 2100 were also assessed. Scenarios leading to CO2-eq + concentrations in 2100 of about 450 ppm or lower are likely to maintain warming + below 2°C over the 21st century relative to pre-industrial levels. Mitigation + scenarios reaching concentration levels of about 500 ppm CO2-eq by 2100 are more + likely than not to limit warming to less than 2°C relative to pre-industrial levels, + unless concentration levels temporarily exceed roughly 530 ppm CO2-eq before 2100. + In this case, warming is about as likely as not to remain below 2°C relative to + pre-industrial levels. Scenarios that exceed about 650 ppm CO2-eq by 2100 are + unlikely to limit warming to below 2°C relative to pre-industrial levels. Mitigation + scenarios in which warming is more likely than not to be less than 1.5°C relative + to pre-industrial levels by 2100 are characterized by concentration levels by + 2100 of below 430 ppm CO2-eq. In these scenarios, temperature peaks during the + century and subsequently declines. Mitigation scenarios reaching about 450 ppm + CO2-eq in 2100 typically involve temporary overshootof atmospheric concentrations, + as do many scenarios reaching about 500 ppm CO2-eq to about 550 ppm CO2-eq by + 2100. Depending on the level of overshoot, overshoot scenarios typically rely + on the availability and widespread deployment of bioenergy with carbon dioxide + capture and storage and afforestation in the second half of the century. The availability + and scale of these and other Carbon Dioxide Removal technologies and methods are + uncertain, and CDR technologies and methods are, to varying degrees, associated + with challenges and risks 3924 . CDR is also prevalent in many scenarios without + overshoot to compensate for residual emissions from sectors where mitigation is + more expensive. Limiting warming with a likely chance to less than 2°C relative + to pre-industrial levels would require substantial cuts in anthropogenic GHG emissions + by mid-century through largescale changes in energy systems and possibly land + use. Limiting warming to higher levels would require similar changes but less + quickly. Limiting warming to lower levels would require these changes more quickly. + Scenarios that are likely to maintain warming at below 2°C are characterized by + a 40 to 70% reduction in GHG emissions by 2050, relative to 2010 levels, and emissions + levels near zero or below in 2100. Scenarios with higher emissions in 2050 are + characterized by a greater reliance on CDR technologies beyond mid-century, and + vice versa. Scenarios that are likely to maintain warming at below 2°C include + more rapid improvements in energy efficiency and a tripling to nearly a quadrupling + of the share of zero- and low-carbon energy supply from renewable energy, nuclear + energy and fossil energy with carbon dioxide capture and storage or BECCS by the + year 2050. The scenarios describe a wide range of changes in land use, reflecting + different assumptions about the scale of bioenergy production, afforestation and + reduced deforestation. Scenarios leading to concentrations of 500 ppm CO2-eq by + 2100 are characterized by a 25 to 55% reduction in GHG emissions by 2050, relative + to 2010 levels. Scenarios that are likely to limit warming to 3°C relative to + pre-industrial levels reduce emissions less rapidly than those limiting warming + to 2°C. Only a limited number of studies provide scenarios that are more likely + than not to limit warming to 1.5°C by 2100; these scenarios are characterized + by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission reduction between + 70 and 95% below 2010. For a comprehensive overview of the characteristics of + emissions scenarios, their CO2-equivalent concentrations and their likelihood + to keep warming to below a range of temperature levels, see Table 3.1. Reducing + emissions of non-CO2 climate forcing agents can be an important element of mitigation + strategies. Emissions of nonCO2 gases, nitrous oxide, and fluorinated gases) contributed + about 27% to the total emissions of Kyoto gases in 2010. For most non-CO2 gases, + near-term, low-cost options are available to reduce their emissions. However, + some sources of these non-CO2 gases are difficult to mitigate, such as N2O emissions + from fertilizer use and CH4 emissions from livestock. As a result, emissions of + most non-CO2 gases will not be reduced to zero, even under stringent mitigation + scenarios. The differences in radiative properties and lifetimes of CO2 and non-CO2 + climate forcing agents have important implications for mitigation strategies. All + current GHG emissions and other climate forcing agents affect the rate and magnitude + of climate change over the next few decades. Reducing the emissions of certain + short-lived climate forcing agents can reduce the rate of warming in the short + term but will have only a limited effect on long-term warming, which is driven + mainly by CO2 emissions. There are large uncertainties related to the climate + impacts of some of the short-lived climate forcing agents. Although the effects + of CH4 emissions are well understood, there are large uncertainties related to + the effects of black carbon. Co-emitted components with cooling effects may further + complicate and reduce the climate impacts of emission reductions. Reducing emissions + of sulfur dioxide would cause warming. Near-term reductions in short-lived climate + forcing agents can have a relatively fast impact on climate change and possible + co-benefits for air pollution. Delaying additional mitigation to 2030 will substantially + increase the challenges associated with limiting warming over the 21st century + to below 2°C relative to pre-industrial levels. GHG emissions in 2030 lie between + about 30 GtCO2-eq/yr and 50 GtCO2-eq/yr in cost-effective scenarios that are likely + to about as likely as not to limit warming to less than 2°C this century relative + to pre-industrial levels . Scenarios with GHG emission levels of above 55 GtCO2-eq/yr + require substantially higher rates of emissions reductions between 2030 and 2050 + ; much more rapid scale-up of zero and low-carbon energy over this period ; a + larger reliance on CDR technologies in the long term; and higher transitional + and long-term economic impacts. Estimated global emission levels by 2020 based + on the Cancún Pledges are not consistent with cost-effective long-term mitigation + trajectories that are at least about as likely as not to limit warming to below + 2°C relative to pre-industrial levels , but they do not preclude the option to + meet this goal . The Cancún Pledges are broadly consistent with cost-effective + scenarios that are likely to limit temperature change to below 3°C relative to + pre-industrial levels. Estimates of the aggregate economic costs of mitigation + vary widely depending on methodologies and assumptions but increase with the stringency + of mitigation. Scenarios in which all countries of the world begin mitigation + immediately, in which there is a single global carbon price, and in which all + key technologies are available have been used as a cost-effective benchmark for + estimating macroeconomic mitigation costs. Under these assumptions, mitigation + scenarios that are likely to limit warming to below 2°C through the 21st century + relative to pre-industrial levels entail losses in global consumption—not including + benefits of reduced climate change as well as co-benefits and adverse side effects + of mitigation —of 1 to 4% in 2030, 2 to 6% in 2050, and 3% to 11% in 2100, relative + to consumption in baseline scenarios that grows anywhere from 300% to more than + 900% over the century . These numbers correspond to an annualized reduction of + consumption growth by 0.04 to 0.14 percentage points over the century relative + to annualized consumption growth in the baseline that is between 1.6% and 3% per + year. In the absence or under limited availability of mitigation technologies + , mitigation costs can increase substantially depending on the technology considered + . Delaying additional mitigation reduces near-term costs but increases mitigation + costs in the medium- to long-term. Many models could not limit likely warming + to below 2°C over the 21st century relative to pre-industrial levels, if additional + mitigation is considerably delayed, or if availability of key technologies, such + as bioenergy, CCS and their combination are limited . Mitigation efforts and + associated cost are expected to vary across countries. The distribution of costs + can differ from the distribution of the actions themselves. In globally cost-effective + scenarios, the majority of mitigation efforts takes place in countries with the + highest future GHG emissions in baseline scenarios. Some studies exploring particular + effort-sharing frameworks, under the assumption of a global carbon market, have + estimated substantial global financial flows associated with mitigation in scenarios + that are likely to more unlikely than likely to limit warming during the 21st + century to less than 2°C relative to pre-industrial levels. + 3.4c: + - Characteristics of mitigation pathways There are multiple mitigation pathways + that are likely to limit warming to below 2°C relative to pre-industrial levels. + These pathways would require substantial emissions reductions over the next few + decades and near zero emissions of CO2 and other long-lived greenhouse gases by + the end of the century. Implementing such reductions poses substantial technological, + economic, social and institutional challenges, which increase with delays in additional + mitigation and if key technologies are not available. Limiting warming to lower + or higher levels involves similar challenges but on different timescales. Without + additional efforts to reduce GHG emissions beyond those in place today, global + emission growth is expected to persist driven by growth in global population and + economic activities. Global GHG emissions under most scenarios without additional + mitigation are between about 75 GtCO2-eq/yr and almost 140 GtCO2-eq/yr in 21003520which + is approximately between the 2100 emission levels in the RCP6.0 and RCP8.5 pathways + 3621 . Baseline scenarios exceed 450 ppm CO2-eq by 2030 and reach CO2-eq concentration + levels between about 750 ppm CO2-eq and more than 1300 ppm CO2-eq by 2100. Global + mean surface temperature increases in 2100 range from about 3.7°C to 4.8°C above + the average for 1850–1900 for a median climate response. They range from 2.5°C + to 7.8°C when including climate uncertainty 3722 . The future scenarios do not + account for possible changes in natural forcings in the climate system. Many + different combinations of technological, behavioural and policy options can be + used to reduce emissions and limit temperature change. To evaluate possible pathways + to long-term climate goals, about 900 mitigation scenarios were collected for + this assessment, each of which describes different technological, socio-economic + and institutional changes. Emission reductions under these scenarios lead to concentrations + in 2100 from 430 ppm CO2-eq to above 720 ppm CO2-eq which is comparable to the + 2100 forcing levels between RCP2.6 and RCP6.0. Scenarios with concentration levels + of below 430 ppm CO2-eq by 2100 were also assessed. Scenarios leading to CO2-eq + concentrations in 2100 of about 450 ppm or lower are likely to maintain warming + below 2°C over the 21st century relative to pre-industrial levels. Mitigation + scenarios reaching concentration levels of about 500 ppm CO2-eq by 2100 are more + likely than not to limit warming to less than 2°C relative to pre-industrial levels, + unless concentration levels temporarily exceed roughly 530 ppm CO2-eq before 2100. + In this case, warming is about as likely as not to remain below 2°C relative to + pre-industrial levels. Scenarios that exceed about 650 ppm CO2-eq by 2100 are + unlikely to limit warming to below 2°C relative to pre-industrial levels. Mitigation + scenarios in which warming is more likely than not to be less than 1.5°C relative + to pre-industrial levels by 2100 are characterized by concentration levels by + 2100 of below 430 ppm CO2-eq. In these scenarios, temperature peaks during the + century and subsequently declines. Mitigation scenarios reaching about 450 ppm + CO2-eq in 2100 typically involve temporary overshootof atmospheric concentrations, + as do many scenarios reaching about 500 ppm CO2-eq to about 550 ppm CO2-eq by + 2100. Depending on the level of overshoot, overshoot scenarios typically rely + on the availability and widespread deployment of bioenergy with carbon dioxide + capture and storage and afforestation in the second half of the century. The availability + and scale of these and other Carbon Dioxide Removal technologies and methods are + uncertain, and CDR technologies and methods are, to varying degrees, associated + with challenges and risks 3924 . CDR is also prevalent in many scenarios without + overshoot to compensate for residual emissions from sectors where mitigation is + more expensive. Limiting warming with a likely chance to less than 2°C relative + to pre-industrial levels would require substantial cuts in anthropogenic GHG emissions + by mid-century through largescale changes in energy systems and possibly land + use. Limiting warming to higher levels would require similar changes but less + quickly. Limiting warming to lower levels would require these changes more quickly. + Scenarios that are likely to maintain warming at below 2°C are characterized by + a 40 to 70% reduction in GHG emissions by 2050, relative to 2010 levels, and emissions + levels near zero or below in 2100. Scenarios with higher emissions in 2050 are + characterized by a greater reliance on CDR technologies beyond mid-century, and + vice versa. Scenarios that are likely to maintain warming at below 2°C include + more rapid improvements in energy efficiency and a tripling to nearly a quadrupling + of the share of zero- and low-carbon energy supply from renewable energy, nuclear + energy and fossil energy with carbon dioxide capture and storage or BECCS by the + year 2050. The scenarios describe a wide range of changes in land use, reflecting + different assumptions about the scale of bioenergy production, afforestation and + reduced deforestation. Scenarios leading to concentrations of 500 ppm CO2-eq by + 2100 are characterized by a 25 to 55% reduction in GHG emissions by 2050, relative + to 2010 levels. Scenarios that are likely to limit warming to 3°C relative to + pre-industrial levels reduce emissions less rapidly than those limiting warming + to 2°C. Only a limited number of studies provide scenarios that are more likely + than not to limit warming to 1.5°C by 2100; these scenarios are characterized + by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission reduction between + 70 and 95% below 2010. For a comprehensive overview of the characteristics of + emissions scenarios, their CO2-equivalent concentrations and their likelihood + to keep warming to below a range of temperature levels, see Table 3.1. Reducing + emissions of non-CO2 climate forcing agents can be an important element of mitigation + strategies. Emissions of nonCO2 gases, nitrous oxide, and fluorinated gases) contributed + about 27% to the total emissions of Kyoto gases in 2010. For most non-CO2 gases, + near-term, low-cost options are available to reduce their emissions. However, + some sources of these non-CO2 gases are difficult to mitigate, such as N2O emissions + from fertilizer use and CH4 emissions from livestock. As a result, emissions of + most non-CO2 gases will not be reduced to zero, even under stringent mitigation + scenarios. The differences in radiative properties and lifetimes of CO2 and non-CO2 + climate forcing agents have important implications for mitigation strategies. All + current GHG emissions and other climate forcing agents affect the rate and magnitude + of climate change over the next few decades. Reducing the emissions of certain + short-lived climate forcing agents can reduce the rate of warming in the short + term but will have only a limited effect on long-term warming, which is driven + mainly by CO2 emissions. There are large uncertainties related to the climate + impacts of some of the short-lived climate forcing agents. Although the effects + of CH4 emissions are well understood, there are large uncertainties related to + the effects of black carbon. Co-emitted components with cooling effects may further + complicate and reduce the climate impacts of emission reductions. Reducing emissions + of sulfur dioxide would cause warming. Near-term reductions in short-lived climate + forcing agents can have a relatively fast impact on climate change and possible + co-benefits for air pollution. Delaying additional mitigation to 2030 will substantially + increase the challenges associated with limiting warming over the 21st century + to below 2°C relative to pre-industrial levels. GHG emissions in 2030 lie between + about 30 GtCO2-eq/yr and 50 GtCO2-eq/yr in cost-effective scenarios that are likely + to about as likely as not to limit warming to less than 2°C this century relative + to pre-industrial levels . Scenarios with GHG emission levels of above 55 GtCO2-eq/yr + require substantially higher rates of emissions reductions between 2030 and 2050 + ; much more rapid scale-up of zero and low-carbon energy over this period ; a + larger reliance on CDR technologies in the long term; and higher transitional + and long-term economic impacts. Estimated global emission levels by 2020 based + on the Cancún Pledges are not consistent with cost-effective long-term mitigation + trajectories that are at least about as likely as not to limit warming to below + 2°C relative to pre-industrial levels , but they do not preclude the option to + meet this goal . The Cancún Pledges are broadly consistent with cost-effective + scenarios that are likely to limit temperature change to below 3°C relative to + pre-industrial levels. Estimates of the aggregate economic costs of mitigation + vary widely depending on methodologies and assumptions but increase with the stringency + of mitigation. Scenarios in which all countries of the world begin mitigation + immediately, in which there is a single global carbon price, and in which all + key technologies are available have been used as a cost-effective benchmark for + estimating macroeconomic mitigation costs. Under these assumptions, mitigation + scenarios that are likely to limit warming to below 2°C through the 21st century + relative to pre-industrial levels entail losses in global consumption—not including + benefits of reduced climate change as well as co-benefits and adverse side effects + of mitigation —of 1 to 4% in 2030, 2 to 6% in 2050, and 3% to 11% in 2100, relative + to consumption in baseline scenarios that grows anywhere from 300% to more than + 900% over the century . These numbers correspond to an annualized reduction of + consumption growth by 0.04 to 0.14 percentage points over the century relative + to annualized consumption growth in the baseline that is between 1.6% and 3% per + year. In the absence or under limited availability of mitigation technologies + , mitigation costs can increase substantially depending on the technology considered + . Delaying additional mitigation reduces near-term costs but increases mitigation + costs in the medium- to long-term. Many models could not limit likely warming + to below 2°C over the 21st century relative to pre-industrial levels, if additional + mitigation is considerably delayed, or if availability of key technologies, such + as bioenergy, CCS and their combination are limited . Mitigation efforts and + associated cost are expected to vary across countries. The distribution of costs + can differ from the distribution of the actions themselves. In globally cost-effective + scenarios, the majority of mitigation efforts takes place in countries with the + highest future GHG emissions in baseline scenarios. Some studies exploring particular + effort-sharing frameworks, under the assumption of a global carbon market, have + estimated substantial global financial flows associated with mitigation in scenarios + that are likely to more unlikely than likely to limit warming during the 21st + century to less than 2°C relative to pre-industrial levels. + 3.4d: + - Characteristics of mitigation pathways There are multiple mitigation pathways + that are likely to limit warming to below 2°C relative to pre-industrial levels. + These pathways would require substantial emissions reductions over the next few + decades and near zero emissions of CO2 and other long-lived greenhouse gases by + the end of the century. Implementing such reductions poses substantial technological, + economic, social and institutional challenges, which increase with delays in additional + mitigation and if key technologies are not available. Limiting warming to lower + or higher levels involves similar challenges but on different timescales. Without + additional efforts to reduce GHG emissions beyond those in place today, global + emission growth is expected to persist driven by growth in global population and + economic activities. Global GHG emissions under most scenarios without additional + mitigation are between about 75 GtCO2-eq/yr and almost 140 GtCO2-eq/yr in 21003520which + is approximately between the 2100 emission levels in the RCP6.0 and RCP8.5 pathways + 3621 . Baseline scenarios exceed 450 ppm CO2-eq by 2030 and reach CO2-eq concentration + levels between about 750 ppm CO2-eq and more than 1300 ppm CO2-eq by 2100. Global + mean surface temperature increases in 2100 range from about 3.7°C to 4.8°C above + the average for 1850–1900 for a median climate response. They range from 2.5°C + to 7.8°C when including climate uncertainty 3722 . The future scenarios do not + account for possible changes in natural forcings in the climate system. Many + different combinations of technological, behavioural and policy options can be + used to reduce emissions and limit temperature change. To evaluate possible pathways + to long-term climate goals, about 900 mitigation scenarios were collected for + this assessment, each of which describes different technological, socio-economic + and institutional changes. Emission reductions under these scenarios lead to concentrations + in 2100 from 430 ppm CO2-eq to above 720 ppm CO2-eq which is comparable to the + 2100 forcing levels between RCP2.6 and RCP6.0. Scenarios with concentration levels + of below 430 ppm CO2-eq by 2100 were also assessed. Scenarios leading to CO2-eq + concentrations in 2100 of about 450 ppm or lower are likely to maintain warming + below 2°C over the 21st century relative to pre-industrial levels. Mitigation + scenarios reaching concentration levels of about 500 ppm CO2-eq by 2100 are more + likely than not to limit warming to less than 2°C relative to pre-industrial levels, + unless concentration levels temporarily exceed roughly 530 ppm CO2-eq before 2100. + In this case, warming is about as likely as not to remain below 2°C relative to + pre-industrial levels. Scenarios that exceed about 650 ppm CO2-eq by 2100 are + unlikely to limit warming to below 2°C relative to pre-industrial levels. Mitigation + scenarios in which warming is more likely than not to be less than 1.5°C relative + to pre-industrial levels by 2100 are characterized by concentration levels by + 2100 of below 430 ppm CO2-eq. In these scenarios, temperature peaks during the + century and subsequently declines. Mitigation scenarios reaching about 450 ppm + CO2-eq in 2100 typically involve temporary overshootof atmospheric concentrations, + as do many scenarios reaching about 500 ppm CO2-eq to about 550 ppm CO2-eq by + 2100. Depending on the level of overshoot, overshoot scenarios typically rely + on the availability and widespread deployment of bioenergy with carbon dioxide + capture and storage and afforestation in the second half of the century. The availability + and scale of these and other Carbon Dioxide Removal technologies and methods are + uncertain, and CDR technologies and methods are, to varying degrees, associated + with challenges and risks 3924 . CDR is also prevalent in many scenarios without + overshoot to compensate for residual emissions from sectors where mitigation is + more expensive. Limiting warming with a likely chance to less than 2°C relative + to pre-industrial levels would require substantial cuts in anthropogenic GHG emissions + by mid-century through largescale changes in energy systems and possibly land + use. Limiting warming to higher levels would require similar changes but less + quickly. Limiting warming to lower levels would require these changes more quickly. + Scenarios that are likely to maintain warming at below 2°C are characterized by + a 40 to 70% reduction in GHG emissions by 2050, relative to 2010 levels, and emissions + levels near zero or below in 2100. Scenarios with higher emissions in 2050 are + characterized by a greater reliance on CDR technologies beyond mid-century, and + vice versa. Scenarios that are likely to maintain warming at below 2°C include + more rapid improvements in energy efficiency and a tripling to nearly a quadrupling + of the share of zero- and low-carbon energy supply from renewable energy, nuclear + energy and fossil energy with carbon dioxide capture and storage or BECCS by the + year 2050. The scenarios describe a wide range of changes in land use, reflecting + different assumptions about the scale of bioenergy production, afforestation and + reduced deforestation. Scenarios leading to concentrations of 500 ppm CO2-eq by + 2100 are characterized by a 25 to 55% reduction in GHG emissions by 2050, relative + to 2010 levels. Scenarios that are likely to limit warming to 3°C relative to + pre-industrial levels reduce emissions less rapidly than those limiting warming + to 2°C. Only a limited number of studies provide scenarios that are more likely + than not to limit warming to 1.5°C by 2100; these scenarios are characterized + by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission reduction between + 70 and 95% below 2010. For a comprehensive overview of the characteristics of + emissions scenarios, their CO2-equivalent concentrations and their likelihood + to keep warming to below a range of temperature levels, see Table 3.1. Reducing + emissions of non-CO2 climate forcing agents can be an important element of mitigation + strategies. Emissions of nonCO2 gases, nitrous oxide, and fluorinated gases) contributed + about 27% to the total emissions of Kyoto gases in 2010. For most non-CO2 gases, + near-term, low-cost options are available to reduce their emissions. However, + some sources of these non-CO2 gases are difficult to mitigate, such as N2O emissions + from fertilizer use and CH4 emissions from livestock. As a result, emissions of + most non-CO2 gases will not be reduced to zero, even under stringent mitigation + scenarios. The differences in radiative properties and lifetimes of CO2 and non-CO2 + climate forcing agents have important implications for mitigation strategies. All + current GHG emissions and other climate forcing agents affect the rate and magnitude + of climate change over the next few decades. Reducing the emissions of certain + short-lived climate forcing agents can reduce the rate of warming in the short + term but will have only a limited effect on long-term warming, which is driven + mainly by CO2 emissions. There are large uncertainties related to the climate + impacts of some of the short-lived climate forcing agents. Although the effects + of CH4 emissions are well understood, there are large uncertainties related to + the effects of black carbon. Co-emitted components with cooling effects may further + complicate and reduce the climate impacts of emission reductions. Reducing emissions + of sulfur dioxide would cause warming. Near-term reductions in short-lived climate + forcing agents can have a relatively fast impact on climate change and possible + co-benefits for air pollution. Delaying additional mitigation to 2030 will substantially + increase the challenges associated with limiting warming over the 21st century + to below 2°C relative to pre-industrial levels. GHG emissions in 2030 lie between + about 30 GtCO2-eq/yr and 50 GtCO2-eq/yr in cost-effective scenarios that are likely + to about as likely as not to limit warming to less than 2°C this century relative + to pre-industrial levels . Scenarios with GHG emission levels of above 55 GtCO2-eq/yr + require substantially higher rates of emissions reductions between 2030 and 2050 + ; much more rapid scale-up of zero and low-carbon energy over this period ; a + larger reliance on CDR technologies in the long term; and higher transitional + and long-term economic impacts. Estimated global emission levels by 2020 based + on the Cancún Pledges are not consistent with cost-effective long-term mitigation + trajectories that are at least about as likely as not to limit warming to below + 2°C relative to pre-industrial levels , but they do not preclude the option to + meet this goal . The Cancún Pledges are broadly consistent with cost-effective + scenarios that are likely to limit temperature change to below 3°C relative to + pre-industrial levels. Estimates of the aggregate economic costs of mitigation + vary widely depending on methodologies and assumptions but increase with the stringency + of mitigation. Scenarios in which all countries of the world begin mitigation + immediately, in which there is a single global carbon price, and in which all + key technologies are available have been used as a cost-effective benchmark for + estimating macroeconomic mitigation costs. Under these assumptions, mitigation + scenarios that are likely to limit warming to below 2°C through the 21st century + relative to pre-industrial levels entail losses in global consumption—not including + benefits of reduced climate change as well as co-benefits and adverse side effects + of mitigation —of 1 to 4% in 2030, 2 to 6% in 2050, and 3% to 11% in 2100, relative + to consumption in baseline scenarios that grows anywhere from 300% to more than + 900% over the century . These numbers correspond to an annualized reduction of + consumption growth by 0.04 to 0.14 percentage points over the century relative + to annualized consumption growth in the baseline that is between 1.6% and 3% per + year. In the absence or under limited availability of mitigation technologies + , mitigation costs can increase substantially depending on the technology considered + . Delaying additional mitigation reduces near-term costs but increases mitigation + costs in the medium- to long-term. Many models could not limit likely warming + to below 2°C over the 21st century relative to pre-industrial levels, if additional + mitigation is considerably delayed, or if availability of key technologies, such + as bioenergy, CCS and their combination are limited . Mitigation efforts and + associated cost are expected to vary across countries. The distribution of costs + can differ from the distribution of the actions themselves. In globally cost-effective + scenarios, the majority of mitigation efforts takes place in countries with the + highest future GHG emissions in baseline scenarios. Some studies exploring particular + effort-sharing frameworks, under the assumption of a global carbon market, have + estimated substantial global financial flows associated with mitigation in scenarios + that are likely to more unlikely than likely to limit warming during the 21st + century to less than 2°C relative to pre-industrial levels. + 3.4e: + - Characteristics of mitigation pathways There are multiple mitigation pathways + that are likely to limit warming to below 2°C relative to pre-industrial levels. + These pathways would require substantial emissions reductions over the next few + decades and near zero emissions of CO2 and other long-lived greenhouse gases by + the end of the century. Implementing such reductions poses substantial technological, + economic, social and institutional challenges, which increase with delays in additional + mitigation and if key technologies are not available. Limiting warming to lower + or higher levels involves similar challenges but on different timescales. Without + additional efforts to reduce GHG emissions beyond those in place today, global + emission growth is expected to persist driven by growth in global population and + economic activities. Global GHG emissions under most scenarios without additional + mitigation are between about 75 GtCO2-eq/yr and almost 140 GtCO2-eq/yr in 21003520which + is approximately between the 2100 emission levels in the RCP6.0 and RCP8.5 pathways + 3621 . Baseline scenarios exceed 450 ppm CO2-eq by 2030 and reach CO2-eq concentration + levels between about 750 ppm CO2-eq and more than 1300 ppm CO2-eq by 2100. Global + mean surface temperature increases in 2100 range from about 3.7°C to 4.8°C above + the average for 1850–1900 for a median climate response. They range from 2.5°C + to 7.8°C when including climate uncertainty 3722 . The future scenarios do not + account for possible changes in natural forcings in the climate system. Many + different combinations of technological, behavioural and policy options can be + used to reduce emissions and limit temperature change. To evaluate possible pathways + to long-term climate goals, about 900 mitigation scenarios were collected for + this assessment, each of which describes different technological, socio-economic + and institutional changes. Emission reductions under these scenarios lead to concentrations + in 2100 from 430 ppm CO2-eq to above 720 ppm CO2-eq which is comparable to the + 2100 forcing levels between RCP2.6 and RCP6.0. Scenarios with concentration levels + of below 430 ppm CO2-eq by 2100 were also assessed. Scenarios leading to CO2-eq + concentrations in 2100 of about 450 ppm or lower are likely to maintain warming + below 2°C over the 21st century relative to pre-industrial levels. Mitigation + scenarios reaching concentration levels of about 500 ppm CO2-eq by 2100 are more + likely than not to limit warming to less than 2°C relative to pre-industrial levels, + unless concentration levels temporarily exceed roughly 530 ppm CO2-eq before 2100. + In this case, warming is about as likely as not to remain below 2°C relative to + pre-industrial levels. Scenarios that exceed about 650 ppm CO2-eq by 2100 are + unlikely to limit warming to below 2°C relative to pre-industrial levels. Mitigation + scenarios in which warming is more likely than not to be less than 1.5°C relative + to pre-industrial levels by 2100 are characterized by concentration levels by + 2100 of below 430 ppm CO2-eq. In these scenarios, temperature peaks during the + century and subsequently declines. Mitigation scenarios reaching about 450 ppm + CO2-eq in 2100 typically involve temporary overshootof atmospheric concentrations, + as do many scenarios reaching about 500 ppm CO2-eq to about 550 ppm CO2-eq by + 2100. Depending on the level of overshoot, overshoot scenarios typically rely + on the availability and widespread deployment of bioenergy with carbon dioxide + capture and storage and afforestation in the second half of the century. The availability + and scale of these and other Carbon Dioxide Removal technologies and methods are + uncertain, and CDR technologies and methods are, to varying degrees, associated + with challenges and risks 3924 . CDR is also prevalent in many scenarios without + overshoot to compensate for residual emissions from sectors where mitigation is + more expensive. Limiting warming with a likely chance to less than 2°C relative + to pre-industrial levels would require substantial cuts in anthropogenic GHG emissions + by mid-century through largescale changes in energy systems and possibly land + use. Limiting warming to higher levels would require similar changes but less + quickly. Limiting warming to lower levels would require these changes more quickly. + Scenarios that are likely to maintain warming at below 2°C are characterized by + a 40 to 70% reduction in GHG emissions by 2050, relative to 2010 levels, and emissions + levels near zero or below in 2100. Scenarios with higher emissions in 2050 are + characterized by a greater reliance on CDR technologies beyond mid-century, and + vice versa. Scenarios that are likely to maintain warming at below 2°C include + more rapid improvements in energy efficiency and a tripling to nearly a quadrupling + of the share of zero- and low-carbon energy supply from renewable energy, nuclear + energy and fossil energy with carbon dioxide capture and storage or BECCS by the + year 2050. The scenarios describe a wide range of changes in land use, reflecting + different assumptions about the scale of bioenergy production, afforestation and + reduced deforestation. Scenarios leading to concentrations of 500 ppm CO2-eq by + 2100 are characterized by a 25 to 55% reduction in GHG emissions by 2050, relative + to 2010 levels. Scenarios that are likely to limit warming to 3°C relative to + pre-industrial levels reduce emissions less rapidly than those limiting warming + to 2°C. Only a limited number of studies provide scenarios that are more likely + than not to limit warming to 1.5°C by 2100; these scenarios are characterized + by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission reduction between + 70 and 95% below 2010. For a comprehensive overview of the characteristics of + emissions scenarios, their CO2-equivalent concentrations and their likelihood + to keep warming to below a range of temperature levels, see Table 3.1. Reducing + emissions of non-CO2 climate forcing agents can be an important element of mitigation + strategies. Emissions of nonCO2 gases, nitrous oxide, and fluorinated gases) contributed + about 27% to the total emissions of Kyoto gases in 2010. For most non-CO2 gases, + near-term, low-cost options are available to reduce their emissions. However, + some sources of these non-CO2 gases are difficult to mitigate, such as N2O emissions + from fertilizer use and CH4 emissions from livestock. As a result, emissions of + most non-CO2 gases will not be reduced to zero, even under stringent mitigation + scenarios. The differences in radiative properties and lifetimes of CO2 and non-CO2 + climate forcing agents have important implications for mitigation strategies. All + current GHG emissions and other climate forcing agents affect the rate and magnitude + of climate change over the next few decades. Reducing the emissions of certain + short-lived climate forcing agents can reduce the rate of warming in the short + term but will have only a limited effect on long-term warming, which is driven + mainly by CO2 emissions. There are large uncertainties related to the climate + impacts of some of the short-lived climate forcing agents. Although the effects + of CH4 emissions are well understood, there are large uncertainties related to + the effects of black carbon. Co-emitted components with cooling effects may further + complicate and reduce the climate impacts of emission reductions. Reducing emissions + of sulfur dioxide would cause warming. Near-term reductions in short-lived climate + forcing agents can have a relatively fast impact on climate change and possible + co-benefits for air pollution. Delaying additional mitigation to 2030 will substantially + increase the challenges associated with limiting warming over the 21st century + to below 2°C relative to pre-industrial levels. GHG emissions in 2030 lie between + about 30 GtCO2-eq/yr and 50 GtCO2-eq/yr in cost-effective scenarios that are likely + to about as likely as not to limit warming to less than 2°C this century relative + to pre-industrial levels . Scenarios with GHG emission levels of above 55 GtCO2-eq/yr + require substantially higher rates of emissions reductions between 2030 and 2050 + ; much more rapid scale-up of zero and low-carbon energy over this period ; a + larger reliance on CDR technologies in the long term; and higher transitional + and long-term economic impacts. Estimated global emission levels by 2020 based + on the Cancún Pledges are not consistent with cost-effective long-term mitigation + trajectories that are at least about as likely as not to limit warming to below + 2°C relative to pre-industrial levels , but they do not preclude the option to + meet this goal . The Cancún Pledges are broadly consistent with cost-effective + scenarios that are likely to limit temperature change to below 3°C relative to + pre-industrial levels. Estimates of the aggregate economic costs of mitigation + vary widely depending on methodologies and assumptions but increase with the stringency + of mitigation. Scenarios in which all countries of the world begin mitigation + immediately, in which there is a single global carbon price, and in which all + key technologies are available have been used as a cost-effective benchmark for + estimating macroeconomic mitigation costs. Under these assumptions, mitigation + scenarios that are likely to limit warming to below 2°C through the 21st century + relative to pre-industrial levels entail losses in global consumption—not including + benefits of reduced climate change as well as co-benefits and adverse side effects + of mitigation —of 1 to 4% in 2030, 2 to 6% in 2050, and 3% to 11% in 2100, relative + to consumption in baseline scenarios that grows anywhere from 300% to more than + 900% over the century . These numbers correspond to an annualized reduction of + consumption growth by 0.04 to 0.14 percentage points over the century relative + to annualized consumption growth in the baseline that is between 1.6% and 3% per + year. In the absence or under limited availability of mitigation technologies + , mitigation costs can increase substantially depending on the technology considered + . Delaying additional mitigation reduces near-term costs but increases mitigation + costs in the medium- to long-term. Many models could not limit likely warming + to below 2°C over the 21st century relative to pre-industrial levels, if additional + mitigation is considerably delayed, or if availability of key technologies, such + as bioenergy, CCS and their combination are limited . Mitigation efforts and + associated cost are expected to vary across countries. The distribution of costs + can differ from the distribution of the actions themselves. In globally cost-effective + scenarios, the majority of mitigation efforts takes place in countries with the + highest future GHG emissions in baseline scenarios. Some studies exploring particular + effort-sharing frameworks, under the assumption of a global carbon market, have + estimated substantial global financial flows associated with mitigation in scenarios + that are likely to more unlikely than likely to limit warming during the 21st + century to less than 2°C relative to pre-industrial levels. + 3.4f: + - Characteristics of mitigation pathways There are multiple mitigation pathways + that are likely to limit warming to below 2°C relative to pre-industrial levels. + These pathways would require substantial emissions reductions over the next few + decades and near zero emissions of CO2 and other long-lived greenhouse gases by + the end of the century. Implementing such reductions poses substantial technological, + economic, social and institutional challenges, which increase with delays in additional + mitigation and if key technologies are not available. Limiting warming to lower + or higher levels involves similar challenges but on different timescales. Without + additional efforts to reduce GHG emissions beyond those in place today, global + emission growth is expected to persist driven by growth in global population and + economic activities. Global GHG emissions under most scenarios without additional + mitigation are between about 75 GtCO2-eq/yr and almost 140 GtCO2-eq/yr in 21003520which + is approximately between the 2100 emission levels in the RCP6.0 and RCP8.5 pathways + 3621 . Baseline scenarios exceed 450 ppm CO2-eq by 2030 and reach CO2-eq concentration + levels between about 750 ppm CO2-eq and more than 1300 ppm CO2-eq by 2100. Global + mean surface temperature increases in 2100 range from about 3.7°C to 4.8°C above + the average for 1850–1900 for a median climate response. They range from 2.5°C + to 7.8°C when including climate uncertainty 3722 . The future scenarios do not + account for possible changes in natural forcings in the climate system. Many + different combinations of technological, behavioural and policy options can be + used to reduce emissions and limit temperature change. To evaluate possible pathways + to long-term climate goals, about 900 mitigation scenarios were collected for + this assessment, each of which describes different technological, socio-economic + and institutional changes. Emission reductions under these scenarios lead to concentrations + in 2100 from 430 ppm CO2-eq to above 720 ppm CO2-eq which is comparable to the + 2100 forcing levels between RCP2.6 and RCP6.0. Scenarios with concentration levels + of below 430 ppm CO2-eq by 2100 were also assessed. Scenarios leading to CO2-eq + concentrations in 2100 of about 450 ppm or lower are likely to maintain warming + below 2°C over the 21st century relative to pre-industrial levels. Mitigation + scenarios reaching concentration levels of about 500 ppm CO2-eq by 2100 are more + likely than not to limit warming to less than 2°C relative to pre-industrial levels, + unless concentration levels temporarily exceed roughly 530 ppm CO2-eq before 2100. + In this case, warming is about as likely as not to remain below 2°C relative to + pre-industrial levels. Scenarios that exceed about 650 ppm CO2-eq by 2100 are + unlikely to limit warming to below 2°C relative to pre-industrial levels. Mitigation + scenarios in which warming is more likely than not to be less than 1.5°C relative + to pre-industrial levels by 2100 are characterized by concentration levels by + 2100 of below 430 ppm CO2-eq. In these scenarios, temperature peaks during the + century and subsequently declines. Mitigation scenarios reaching about 450 ppm + CO2-eq in 2100 typically involve temporary overshootof atmospheric concentrations, + as do many scenarios reaching about 500 ppm CO2-eq to about 550 ppm CO2-eq by + 2100. Depending on the level of overshoot, overshoot scenarios typically rely + on the availability and widespread deployment of bioenergy with carbon dioxide + capture and storage and afforestation in the second half of the century. The availability + and scale of these and other Carbon Dioxide Removal technologies and methods are + uncertain, and CDR technologies and methods are, to varying degrees, associated + with challenges and risks 3924 . CDR is also prevalent in many scenarios without + overshoot to compensate for residual emissions from sectors where mitigation is + more expensive. Limiting warming with a likely chance to less than 2°C relative + to pre-industrial levels would require substantial cuts in anthropogenic GHG emissions + by mid-century through largescale changes in energy systems and possibly land + use. Limiting warming to higher levels would require similar changes but less + quickly. Limiting warming to lower levels would require these changes more quickly. + Scenarios that are likely to maintain warming at below 2°C are characterized by + a 40 to 70% reduction in GHG emissions by 2050, relative to 2010 levels, and emissions + levels near zero or below in 2100. Scenarios with higher emissions in 2050 are + characterized by a greater reliance on CDR technologies beyond mid-century, and + vice versa. Scenarios that are likely to maintain warming at below 2°C include + more rapid improvements in energy efficiency and a tripling to nearly a quadrupling + of the share of zero- and low-carbon energy supply from renewable energy, nuclear + energy and fossil energy with carbon dioxide capture and storage or BECCS by the + year 2050. The scenarios describe a wide range of changes in land use, reflecting + different assumptions about the scale of bioenergy production, afforestation and + reduced deforestation. Scenarios leading to concentrations of 500 ppm CO2-eq by + 2100 are characterized by a 25 to 55% reduction in GHG emissions by 2050, relative + to 2010 levels. Scenarios that are likely to limit warming to 3°C relative to + pre-industrial levels reduce emissions less rapidly than those limiting warming + to 2°C. Only a limited number of studies provide scenarios that are more likely + than not to limit warming to 1.5°C by 2100; these scenarios are characterized + by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission reduction between + 70 and 95% below 2010. For a comprehensive overview of the characteristics of + emissions scenarios, their CO2-equivalent concentrations and their likelihood + to keep warming to below a range of temperature levels, see Table 3.1. Reducing + emissions of non-CO2 climate forcing agents can be an important element of mitigation + strategies. Emissions of nonCO2 gases, nitrous oxide, and fluorinated gases) contributed + about 27% to the total emissions of Kyoto gases in 2010. For most non-CO2 gases, + near-term, low-cost options are available to reduce their emissions. However, + some sources of these non-CO2 gases are difficult to mitigate, such as N2O emissions + from fertilizer use and CH4 emissions from livestock. As a result, emissions of + most non-CO2 gases will not be reduced to zero, even under stringent mitigation + scenarios. The differences in radiative properties and lifetimes of CO2 and non-CO2 + climate forcing agents have important implications for mitigation strategies. All + current GHG emissions and other climate forcing agents affect the rate and magnitude + of climate change over the next few decades. Reducing the emissions of certain + short-lived climate forcing agents can reduce the rate of warming in the short + term but will have only a limited effect on long-term warming, which is driven + mainly by CO2 emissions. There are large uncertainties related to the climate + impacts of some of the short-lived climate forcing agents. Although the effects + of CH4 emissions are well understood, there are large uncertainties related to + the effects of black carbon. Co-emitted components with cooling effects may further + complicate and reduce the climate impacts of emission reductions. Reducing emissions + of sulfur dioxide would cause warming. Near-term reductions in short-lived climate + forcing agents can have a relatively fast impact on climate change and possible + co-benefits for air pollution. Delaying additional mitigation to 2030 will substantially + increase the challenges associated with limiting warming over the 21st century + to below 2°C relative to pre-industrial levels. GHG emissions in 2030 lie between + about 30 GtCO2-eq/yr and 50 GtCO2-eq/yr in cost-effective scenarios that are likely + to about as likely as not to limit warming to less than 2°C this century relative + to pre-industrial levels . Scenarios with GHG emission levels of above 55 GtCO2-eq/yr + require substantially higher rates of emissions reductions between 2030 and 2050 + ; much more rapid scale-up of zero and low-carbon energy over this period ; a + larger reliance on CDR technologies in the long term; and higher transitional + and long-term economic impacts. Estimated global emission levels by 2020 based + on the Cancún Pledges are not consistent with cost-effective long-term mitigation + trajectories that are at least about as likely as not to limit warming to below + 2°C relative to pre-industrial levels , but they do not preclude the option to + meet this goal . The Cancún Pledges are broadly consistent with cost-effective + scenarios that are likely to limit temperature change to below 3°C relative to + pre-industrial levels. Estimates of the aggregate economic costs of mitigation + vary widely depending on methodologies and assumptions but increase with the stringency + of mitigation. Scenarios in which all countries of the world begin mitigation + immediately, in which there is a single global carbon price, and in which all + key technologies are available have been used as a cost-effective benchmark for + estimating macroeconomic mitigation costs. Under these assumptions, mitigation + scenarios that are likely to limit warming to below 2°C through the 21st century + relative to pre-industrial levels entail losses in global consumption—not including + benefits of reduced climate change as well as co-benefits and adverse side effects + of mitigation —of 1 to 4% in 2030, 2 to 6% in 2050, and 3% to 11% in 2100, relative + to consumption in baseline scenarios that grows anywhere from 300% to more than + 900% over the century . These numbers correspond to an annualized reduction of + consumption growth by 0.04 to 0.14 percentage points over the century relative + to annualized consumption growth in the baseline that is between 1.6% and 3% per + year. In the absence or under limited availability of mitigation technologies + , mitigation costs can increase substantially depending on the technology considered + . Delaying additional mitigation reduces near-term costs but increases mitigation + costs in the medium- to long-term. Many models could not limit likely warming + to below 2°C over the 21st century relative to pre-industrial levels, if additional + mitigation is considerably delayed, or if availability of key technologies, such + as bioenergy, CCS and their combination are limited . Mitigation efforts and + associated cost are expected to vary across countries. The distribution of costs + can differ from the distribution of the actions themselves. In globally cost-effective + scenarios, the majority of mitigation efforts takes place in countries with the + highest future GHG emissions in baseline scenarios. Some studies exploring particular + effort-sharing frameworks, under the assumption of a global carbon market, have + estimated substantial global financial flows associated with mitigation in scenarios + that are likely to more unlikely than likely to limit warming during the 21st + century to less than 2°C relative to pre-industrial levels. + 3.4g: + - Characteristics of mitigation pathways There are multiple mitigation pathways + that are likely to limit warming to below 2°C relative to pre-industrial levels. + These pathways would require substantial emissions reductions over the next few + decades and near zero emissions of CO2 and other long-lived greenhouse gases by + the end of the century. Implementing such reductions poses substantial technological, + economic, social and institutional challenges, which increase with delays in additional + mitigation and if key technologies are not available. Limiting warming to lower + or higher levels involves similar challenges but on different timescales. Without + additional efforts to reduce GHG emissions beyond those in place today, global + emission growth is expected to persist driven by growth in global population and + economic activities. Global GHG emissions under most scenarios without additional + mitigation are between about 75 GtCO2-eq/yr and almost 140 GtCO2-eq/yr in 21003520which + is approximately between the 2100 emission levels in the RCP6.0 and RCP8.5 pathways + 3621 . Baseline scenarios exceed 450 ppm CO2-eq by 2030 and reach CO2-eq concentration + levels between about 750 ppm CO2-eq and more than 1300 ppm CO2-eq by 2100. Global + mean surface temperature increases in 2100 range from about 3.7°C to 4.8°C above + the average for 1850–1900 for a median climate response. They range from 2.5°C + to 7.8°C when including climate uncertainty 3722 . The future scenarios do not + account for possible changes in natural forcings in the climate system. Many + different combinations of technological, behavioural and policy options can be + used to reduce emissions and limit temperature change. To evaluate possible pathways + to long-term climate goals, about 900 mitigation scenarios were collected for + this assessment, each of which describes different technological, socio-economic + and institutional changes. Emission reductions under these scenarios lead to concentrations + in 2100 from 430 ppm CO2-eq to above 720 ppm CO2-eq which is comparable to the + 2100 forcing levels between RCP2.6 and RCP6.0. Scenarios with concentration levels + of below 430 ppm CO2-eq by 2100 were also assessed. Scenarios leading to CO2-eq + concentrations in 2100 of about 450 ppm or lower are likely to maintain warming + below 2°C over the 21st century relative to pre-industrial levels. Mitigation + scenarios reaching concentration levels of about 500 ppm CO2-eq by 2100 are more + likely than not to limit warming to less than 2°C relative to pre-industrial levels, + unless concentration levels temporarily exceed roughly 530 ppm CO2-eq before 2100. + In this case, warming is about as likely as not to remain below 2°C relative to + pre-industrial levels. Scenarios that exceed about 650 ppm CO2-eq by 2100 are + unlikely to limit warming to below 2°C relative to pre-industrial levels. Mitigation + scenarios in which warming is more likely than not to be less than 1.5°C relative + to pre-industrial levels by 2100 are characterized by concentration levels by + 2100 of below 430 ppm CO2-eq. In these scenarios, temperature peaks during the + century and subsequently declines. Mitigation scenarios reaching about 450 ppm + CO2-eq in 2100 typically involve temporary overshootof atmospheric concentrations, + as do many scenarios reaching about 500 ppm CO2-eq to about 550 ppm CO2-eq by + 2100. Depending on the level of overshoot, overshoot scenarios typically rely + on the availability and widespread deployment of bioenergy with carbon dioxide + capture and storage and afforestation in the second half of the century. The availability + and scale of these and other Carbon Dioxide Removal technologies and methods are + uncertain, and CDR technologies and methods are, to varying degrees, associated + with challenges and risks 3924 . CDR is also prevalent in many scenarios without + overshoot to compensate for residual emissions from sectors where mitigation is + more expensive. Limiting warming with a likely chance to less than 2°C relative + to pre-industrial levels would require substantial cuts in anthropogenic GHG emissions + by mid-century through largescale changes in energy systems and possibly land + use. Limiting warming to higher levels would require similar changes but less + quickly. Limiting warming to lower levels would require these changes more quickly. + Scenarios that are likely to maintain warming at below 2°C are characterized by + a 40 to 70% reduction in GHG emissions by 2050, relative to 2010 levels, and emissions + levels near zero or below in 2100. Scenarios with higher emissions in 2050 are + characterized by a greater reliance on CDR technologies beyond mid-century, and + vice versa. Scenarios that are likely to maintain warming at below 2°C include + more rapid improvements in energy efficiency and a tripling to nearly a quadrupling + of the share of zero- and low-carbon energy supply from renewable energy, nuclear + energy and fossil energy with carbon dioxide capture and storage or BECCS by the + year 2050. The scenarios describe a wide range of changes in land use, reflecting + different assumptions about the scale of bioenergy production, afforestation and + reduced deforestation. Scenarios leading to concentrations of 500 ppm CO2-eq by + 2100 are characterized by a 25 to 55% reduction in GHG emissions by 2050, relative + to 2010 levels. Scenarios that are likely to limit warming to 3°C relative to + pre-industrial levels reduce emissions less rapidly than those limiting warming + to 2°C. Only a limited number of studies provide scenarios that are more likely + than not to limit warming to 1.5°C by 2100; these scenarios are characterized + by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission reduction between + 70 and 95% below 2010. For a comprehensive overview of the characteristics of + emissions scenarios, their CO2-equivalent concentrations and their likelihood + to keep warming to below a range of temperature levels, see Table 3.1. Reducing + emissions of non-CO2 climate forcing agents can be an important element of mitigation + strategies. Emissions of nonCO2 gases, nitrous oxide, and fluorinated gases) contributed + about 27% to the total emissions of Kyoto gases in 2010. For most non-CO2 gases, + near-term, low-cost options are available to reduce their emissions. However, + some sources of these non-CO2 gases are difficult to mitigate, such as N2O emissions + from fertilizer use and CH4 emissions from livestock. As a result, emissions of + most non-CO2 gases will not be reduced to zero, even under stringent mitigation + scenarios. The differences in radiative properties and lifetimes of CO2 and non-CO2 + climate forcing agents have important implications for mitigation strategies. All + current GHG emissions and other climate forcing agents affect the rate and magnitude + of climate change over the next few decades. Reducing the emissions of certain + short-lived climate forcing agents can reduce the rate of warming in the short + term but will have only a limited effect on long-term warming, which is driven + mainly by CO2 emissions. There are large uncertainties related to the climate + impacts of some of the short-lived climate forcing agents. Although the effects + of CH4 emissions are well understood, there are large uncertainties related to + the effects of black carbon. Co-emitted components with cooling effects may further + complicate and reduce the climate impacts of emission reductions. Reducing emissions + of sulfur dioxide would cause warming. Near-term reductions in short-lived climate + forcing agents can have a relatively fast impact on climate change and possible + co-benefits for air pollution. Delaying additional mitigation to 2030 will substantially + increase the challenges associated with limiting warming over the 21st century + to below 2°C relative to pre-industrial levels. GHG emissions in 2030 lie between + about 30 GtCO2-eq/yr and 50 GtCO2-eq/yr in cost-effective scenarios that are likely + to about as likely as not to limit warming to less than 2°C this century relative + to pre-industrial levels . Scenarios with GHG emission levels of above 55 GtCO2-eq/yr + require substantially higher rates of emissions reductions between 2030 and 2050 + ; much more rapid scale-up of zero and low-carbon energy over this period ; a + larger reliance on CDR technologies in the long term; and higher transitional + and long-term economic impacts. Estimated global emission levels by 2020 based + on the Cancún Pledges are not consistent with cost-effective long-term mitigation + trajectories that are at least about as likely as not to limit warming to below + 2°C relative to pre-industrial levels , but they do not preclude the option to + meet this goal . The Cancún Pledges are broadly consistent with cost-effective + scenarios that are likely to limit temperature change to below 3°C relative to + pre-industrial levels. Estimates of the aggregate economic costs of mitigation + vary widely depending on methodologies and assumptions but increase with the stringency + of mitigation. Scenarios in which all countries of the world begin mitigation + immediately, in which there is a single global carbon price, and in which all + key technologies are available have been used as a cost-effective benchmark for + estimating macroeconomic mitigation costs. Under these assumptions, mitigation + scenarios that are likely to limit warming to below 2°C through the 21st century + relative to pre-industrial levels entail losses in global consumption—not including + benefits of reduced climate change as well as co-benefits and adverse side effects + of mitigation —of 1 to 4% in 2030, 2 to 6% in 2050, and 3% to 11% in 2100, relative + to consumption in baseline scenarios that grows anywhere from 300% to more than + 900% over the century . These numbers correspond to an annualized reduction of + consumption growth by 0.04 to 0.14 percentage points over the century relative + to annualized consumption growth in the baseline that is between 1.6% and 3% per + year. In the absence or under limited availability of mitigation technologies + , mitigation costs can increase substantially depending on the technology considered + . Delaying additional mitigation reduces near-term costs but increases mitigation + costs in the medium- to long-term. Many models could not limit likely warming + to below 2°C over the 21st century relative to pre-industrial levels, if additional + mitigation is considerably delayed, or if availability of key technologies, such + as bioenergy, CCS and their combination are limited . Mitigation efforts and + associated cost are expected to vary across countries. The distribution of costs + can differ from the distribution of the actions themselves. In globally cost-effective + scenarios, the majority of mitigation efforts takes place in countries with the + highest future GHG emissions in baseline scenarios. Some studies exploring particular + effort-sharing frameworks, under the assumption of a global carbon market, have + estimated substantial global financial flows associated with mitigation in scenarios + that are likely to more unlikely than likely to limit warming during the 21st + century to less than 2°C relative to pre-industrial levels. + 3.4h: + - Characteristics of mitigation pathways There are multiple mitigation pathways + that are likely to limit warming to below 2°C relative to pre-industrial levels. + These pathways would require substantial emissions reductions over the next few + decades and near zero emissions of CO2 and other long-lived greenhouse gases by + the end of the century. Implementing such reductions poses substantial technological, + economic, social and institutional challenges, which increase with delays in additional + mitigation and if key technologies are not available. Limiting warming to lower + or higher levels involves similar challenges but on different timescales. Without + additional efforts to reduce GHG emissions beyond those in place today, global + emission growth is expected to persist driven by growth in global population and + economic activities. Global GHG emissions under most scenarios without additional + mitigation are between about 75 GtCO2-eq/yr and almost 140 GtCO2-eq/yr in 21003520which + is approximately between the 2100 emission levels in the RCP6.0 and RCP8.5 pathways + 3621 . Baseline scenarios exceed 450 ppm CO2-eq by 2030 and reach CO2-eq concentration + levels between about 750 ppm CO2-eq and more than 1300 ppm CO2-eq by 2100. Global + mean surface temperature increases in 2100 range from about 3.7°C to 4.8°C above + the average for 1850–1900 for a median climate response. They range from 2.5°C + to 7.8°C when including climate uncertainty 3722 . The future scenarios do not + account for possible changes in natural forcings in the climate system. Many + different combinations of technological, behavioural and policy options can be + used to reduce emissions and limit temperature change. To evaluate possible pathways + to long-term climate goals, about 900 mitigation scenarios were collected for + this assessment, each of which describes different technological, socio-economic + and institutional changes. Emission reductions under these scenarios lead to concentrations + in 2100 from 430 ppm CO2-eq to above 720 ppm CO2-eq which is comparable to the + 2100 forcing levels between RCP2.6 and RCP6.0. Scenarios with concentration levels + of below 430 ppm CO2-eq by 2100 were also assessed. Scenarios leading to CO2-eq + concentrations in 2100 of about 450 ppm or lower are likely to maintain warming + below 2°C over the 21st century relative to pre-industrial levels. Mitigation + scenarios reaching concentration levels of about 500 ppm CO2-eq by 2100 are more + likely than not to limit warming to less than 2°C relative to pre-industrial levels, + unless concentration levels temporarily exceed roughly 530 ppm CO2-eq before 2100. + In this case, warming is about as likely as not to remain below 2°C relative to + pre-industrial levels. Scenarios that exceed about 650 ppm CO2-eq by 2100 are + unlikely to limit warming to below 2°C relative to pre-industrial levels. Mitigation + scenarios in which warming is more likely than not to be less than 1.5°C relative + to pre-industrial levels by 2100 are characterized by concentration levels by + 2100 of below 430 ppm CO2-eq. In these scenarios, temperature peaks during the + century and subsequently declines. Mitigation scenarios reaching about 450 ppm + CO2-eq in 2100 typically involve temporary overshootof atmospheric concentrations, + as do many scenarios reaching about 500 ppm CO2-eq to about 550 ppm CO2-eq by + 2100. Depending on the level of overshoot, overshoot scenarios typically rely + on the availability and widespread deployment of bioenergy with carbon dioxide + capture and storage and afforestation in the second half of the century. The availability + and scale of these and other Carbon Dioxide Removal technologies and methods are + uncertain, and CDR technologies and methods are, to varying degrees, associated + with challenges and risks 3924 . CDR is also prevalent in many scenarios without + overshoot to compensate for residual emissions from sectors where mitigation is + more expensive. Limiting warming with a likely chance to less than 2°C relative + to pre-industrial levels would require substantial cuts in anthropogenic GHG emissions + by mid-century through largescale changes in energy systems and possibly land + use. Limiting warming to higher levels would require similar changes but less + quickly. Limiting warming to lower levels would require these changes more quickly. + Scenarios that are likely to maintain warming at below 2°C are characterized by + a 40 to 70% reduction in GHG emissions by 2050, relative to 2010 levels, and emissions + levels near zero or below in 2100. Scenarios with higher emissions in 2050 are + characterized by a greater reliance on CDR technologies beyond mid-century, and + vice versa. Scenarios that are likely to maintain warming at below 2°C include + more rapid improvements in energy efficiency and a tripling to nearly a quadrupling + of the share of zero- and low-carbon energy supply from renewable energy, nuclear + energy and fossil energy with carbon dioxide capture and storage or BECCS by the + year 2050. The scenarios describe a wide range of changes in land use, reflecting + different assumptions about the scale of bioenergy production, afforestation and + reduced deforestation. Scenarios leading to concentrations of 500 ppm CO2-eq by + 2100 are characterized by a 25 to 55% reduction in GHG emissions by 2050, relative + to 2010 levels. Scenarios that are likely to limit warming to 3°C relative to + pre-industrial levels reduce emissions less rapidly than those limiting warming + to 2°C. Only a limited number of studies provide scenarios that are more likely + than not to limit warming to 1.5°C by 2100; these scenarios are characterized + by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission reduction between + 70 and 95% below 2010. For a comprehensive overview of the characteristics of + emissions scenarios, their CO2-equivalent concentrations and their likelihood + to keep warming to below a range of temperature levels, see Table 3.1. Reducing + emissions of non-CO2 climate forcing agents can be an important element of mitigation + strategies. Emissions of nonCO2 gases, nitrous oxide, and fluorinated gases) contributed + about 27% to the total emissions of Kyoto gases in 2010. For most non-CO2 gases, + near-term, low-cost options are available to reduce their emissions. However, + some sources of these non-CO2 gases are difficult to mitigate, such as N2O emissions + from fertilizer use and CH4 emissions from livestock. As a result, emissions of + most non-CO2 gases will not be reduced to zero, even under stringent mitigation + scenarios. The differences in radiative properties and lifetimes of CO2 and non-CO2 + climate forcing agents have important implications for mitigation strategies. All + current GHG emissions and other climate forcing agents affect the rate and magnitude + of climate change over the next few decades. Reducing the emissions of certain + short-lived climate forcing agents can reduce the rate of warming in the short + term but will have only a limited effect on long-term warming, which is driven + mainly by CO2 emissions. There are large uncertainties related to the climate + impacts of some of the short-lived climate forcing agents. Although the effects + of CH4 emissions are well understood, there are large uncertainties related to + the effects of black carbon. Co-emitted components with cooling effects may further + complicate and reduce the climate impacts of emission reductions. Reducing emissions + of sulfur dioxide would cause warming. Near-term reductions in short-lived climate + forcing agents can have a relatively fast impact on climate change and possible + co-benefits for air pollution. Delaying additional mitigation to 2030 will substantially + increase the challenges associated with limiting warming over the 21st century + to below 2°C relative to pre-industrial levels. GHG emissions in 2030 lie between + about 30 GtCO2-eq/yr and 50 GtCO2-eq/yr in cost-effective scenarios that are likely + to about as likely as not to limit warming to less than 2°C this century relative + to pre-industrial levels . Scenarios with GHG emission levels of above 55 GtCO2-eq/yr + require substantially higher rates of emissions reductions between 2030 and 2050 + ; much more rapid scale-up of zero and low-carbon energy over this period ; a + larger reliance on CDR technologies in the long term; and higher transitional + and long-term economic impacts. Estimated global emission levels by 2020 based + on the Cancún Pledges are not consistent with cost-effective long-term mitigation + trajectories that are at least about as likely as not to limit warming to below + 2°C relative to pre-industrial levels , but they do not preclude the option to + meet this goal . The Cancún Pledges are broadly consistent with cost-effective + scenarios that are likely to limit temperature change to below 3°C relative to + pre-industrial levels. Estimates of the aggregate economic costs of mitigation + vary widely depending on methodologies and assumptions but increase with the stringency + of mitigation. Scenarios in which all countries of the world begin mitigation + immediately, in which there is a single global carbon price, and in which all + key technologies are available have been used as a cost-effective benchmark for + estimating macroeconomic mitigation costs. Under these assumptions, mitigation + scenarios that are likely to limit warming to below 2°C through the 21st century + relative to pre-industrial levels entail losses in global consumption—not including + benefits of reduced climate change as well as co-benefits and adverse side effects + of mitigation —of 1 to 4% in 2030, 2 to 6% in 2050, and 3% to 11% in 2100, relative + to consumption in baseline scenarios that grows anywhere from 300% to more than + 900% over the century . These numbers correspond to an annualized reduction of + consumption growth by 0.04 to 0.14 percentage points over the century relative + to annualized consumption growth in the baseline that is between 1.6% and 3% per + year. In the absence or under limited availability of mitigation technologies + , mitigation costs can increase substantially depending on the technology considered + . Delaying additional mitigation reduces near-term costs but increases mitigation + costs in the medium- to long-term. Many models could not limit likely warming + to below 2°C over the 21st century relative to pre-industrial levels, if additional + mitigation is considerably delayed, or if availability of key technologies, such + as bioenergy, CCS and their combination are limited . Mitigation efforts and + associated cost are expected to vary across countries. The distribution of costs + can differ from the distribution of the actions themselves. In globally cost-effective + scenarios, the majority of mitigation efforts takes place in countries with the + highest future GHG emissions in baseline scenarios. Some studies exploring particular + effort-sharing frameworks, under the assumption of a global carbon market, have + estimated substantial global financial flows associated with mitigation in scenarios + that are likely to more unlikely than likely to limit warming during the 21st + century to less than 2°C relative to pre-industrial levels. + 3.4i: + - 'Mitigation There has been a considerable increase in national and subnational + mitigation plans and strategies since AR4. In 2012, 67% of global GHG emissions + were subject to national legislation or strategies versus 45% in 2007. However, + there has not yet been a substantial deviation in global emissions from the past + trend. These plans and strategies are in their early stages of development and + implementation in many countries, making it difficult to assess their aggregate + impact on future global emissions. Since AR4, there has been an increased focus + on policies designed to integrate multiple objectives, increase co-benefits and + reduce adverse side effects. Governments often explicitly reference co-benefits + in climate and sectoral plans and strategies. Sector-specific policies have been + more widely used than economy-wide policies . Although most economic theory suggests + that economy-wide policies for mitigation would be more cost-effective than sector-specific + policies, administrative and political barriers may make economy-wide policies + harder to design and implement than sector-specific policies. The latter may be + better suited to address barriers or market failures specific to certain sectors + and may be bundled in packages of complementary policies In principle, mechanisms + that set a carbon price, including cap and trade systems and carbon taxes, can + achieve mitigation in a cost-effective way, but have been implemented with diverse + effects due in part to national circumstances as well as policy design. The short-run + environmental effects of cap and trade systems have been limited as a result of + loose caps or caps that have not proved to be constraining. In some countries, + tax-based policies specifically aimed at reducing GHG emissions—alongside technology + and other policies—have helped to weaken the link between GHG emissions and gross + domestic product . In addition, in a large group of countries, fuel taxes have + had effects that are akin to sectoral carbon taxes . Revenues from carbon taxes + or auctioned emission allowances are used in some countries to reduce other taxes + and/or to provide transfers to low-income groups. This illustrates the general + principle that mitigation policies that raise government revenue generally have + lower social costs than approaches which do not. Economic instruments in the + form of subsidies may be applied across sectors, and include a variety of policy + designs, such as tax rebates or exemptions, grants, loans and credit lines. An + increasing number and variety of RE policies including subsidies—motivated by + many factors—have driven escalated growth of RE technologies in recent years. + Government policies play a crucial role in accelerating the deployment of RE technologies. + Energy access and social and economic development have been the primary drivers + in most developing countries whereas secure energy supply and environmental concerns + have been most important in developed countries. The focus of policies is broadening + from a concentration primarily on RE electricity to include RE heating and cooling + and transportation. The reduction of subsidies for GHG-related activities in + various sectors can achieve emission reductions, depending on the social and economic + context. While subsidies can affect emissions in many sectors, most of the recent + literature has focused on subsidies for fossil fuels. Since AR4 a small but growing + literature based on economy-wide models has projected that complete removal of + subsidies to fossil fuels in all countries could result in reductions in global + aggregate emissions by mid-century . Studies vary in methodology, the type and + definition of subsidies and the time frame for phase out considered. In particular, + the studies assess the impacts of complete removal of all fossil fuel subsides + without seeking to assess which subsidies are wasteful and inefficient, keeping + in mind national circumstances. Regulatory approaches and information measures + are widely used and are often environmentally effective . Examples of regulatory + approaches include energy efficiency standards; examples of information programmes + include labelling programmes that can help consumers make better-informed decisions. Mitigation + policy could devalue fossil fuel assets and reduce revenues for fossil fuel exporters, + but differences between regions and fuels exist. Most mitigation scenarios are + associated with reduced revenues from coal and oil trade for major exporters. + The effect on natural gas export revenues is more uncertain. The availability + of CCS would reduce the adverse effect of mitigation on the value of fossil fuel + assets. Interactions between or among mitigation policies may be synergistic + or may have no additive effect on reducing emissions . For instance, a carbon + tax can have an additive environmental effect to policies such as subsidies for + the supply of RE. By contrast, if a cap and trade system has a sufficiently stringent + cap to affect emission-related decisions, then other policies have no further + impact on reducing emissions . In either case, additional policies may be needed + to address market failures relating to innovation and technology diffusion. Sub-national + climate policies are increasingly prevalent, both in countries with national policies + and in those without. These policies include state and provincial climate plans + combining market, regulatory and information instruments, and sub-national cap-and-trade + systems. In addition, transnational cooperation has arisen among sub-national + actors, notably among institutional investors, NGOs seeking to govern carbon offset + markets, and networks of cities seeking to collaborate in generating low-carbon + urban development. Co-benefits and adverse side effects of mitigation could affect + achievement of other objectives such as those related to human health, food security, + biodiversity, local environmental quality, energy access, livelihoods and equitable + sustainable development: • Mitigation scenarios reaching about 450 or 500 ppm + CO2-equivalent by 2100 show reduced costs for achieving air quality and energy + security objectives, with significant co-benefits for human health, ecosystem + impacts and sufficiency of resources and resilience of the energy system. • Some + mitigation policies raise the prices for some energy services and could hamper + the ability of societies to expand access to modern energy services to underserved + populations . These potential adverse side effects can be avoided with the adoption + of complementary policies such as income tax rebates or other benefit transfer + mechanisms. The costs of achieving nearly universal access to electricity and + clean fuels for cooking and heating are projected to be between USD 72 to 95 billion + per year until 2030 with minimal effects on GHG emissions and multiple benefits + in health and air pollutant reduction. Whether or not side effects materialize, + and to what extent side effects materialize, will be case- and site-specific, + and depend on local circumstances and the scale, scope and pace of implementation. + Many co-benefits and adverse side effects have not been well-quantified.' + 3.4l: + - 'Mitigation There has been a considerable increase in national and subnational + mitigation plans and strategies since AR4. In 2012, 67% of global GHG emissions + were subject to national legislation or strategies versus 45% in 2007. However, + there has not yet been a substantial deviation in global emissions from the past + trend. These plans and strategies are in their early stages of development and + implementation in many countries, making it difficult to assess their aggregate + impact on future global emissions. Since AR4, there has been an increased focus + on policies designed to integrate multiple objectives, increase co-benefits and + reduce adverse side effects. Governments often explicitly reference co-benefits + in climate and sectoral plans and strategies. Sector-specific policies have been + more widely used than economy-wide policies . Although most economic theory suggests + that economy-wide policies for mitigation would be more cost-effective than sector-specific + policies, administrative and political barriers may make economy-wide policies + harder to design and implement than sector-specific policies. The latter may be + better suited to address barriers or market failures specific to certain sectors + and may be bundled in packages of complementary policies In principle, mechanisms + that set a carbon price, including cap and trade systems and carbon taxes, can + achieve mitigation in a cost-effective way, but have been implemented with diverse + effects due in part to national circumstances as well as policy design. The short-run + environmental effects of cap and trade systems have been limited as a result of + loose caps or caps that have not proved to be constraining. In some countries, + tax-based policies specifically aimed at reducing GHG emissions—alongside technology + and other policies—have helped to weaken the link between GHG emissions and gross + domestic product . In addition, in a large group of countries, fuel taxes have + had effects that are akin to sectoral carbon taxes . Revenues from carbon taxes + or auctioned emission allowances are used in some countries to reduce other taxes + and/or to provide transfers to low-income groups. This illustrates the general + principle that mitigation policies that raise government revenue generally have + lower social costs than approaches which do not. Economic instruments in the + form of subsidies may be applied across sectors, and include a variety of policy + designs, such as tax rebates or exemptions, grants, loans and credit lines. An + increasing number and variety of RE policies including subsidies—motivated by + many factors—have driven escalated growth of RE technologies in recent years. + Government policies play a crucial role in accelerating the deployment of RE technologies. + Energy access and social and economic development have been the primary drivers + in most developing countries whereas secure energy supply and environmental concerns + have been most important in developed countries. The focus of policies is broadening + from a concentration primarily on RE electricity to include RE heating and cooling + and transportation. The reduction of subsidies for GHG-related activities in + various sectors can achieve emission reductions, depending on the social and economic + context. While subsidies can affect emissions in many sectors, most of the recent + literature has focused on subsidies for fossil fuels. Since AR4 a small but growing + literature based on economy-wide models has projected that complete removal of + subsidies to fossil fuels in all countries could result in reductions in global + aggregate emissions by mid-century . Studies vary in methodology, the type and + definition of subsidies and the time frame for phase out considered. In particular, + the studies assess the impacts of complete removal of all fossil fuel subsides + without seeking to assess which subsidies are wasteful and inefficient, keeping + in mind national circumstances. Regulatory approaches and information measures + are widely used and are often environmentally effective . Examples of regulatory + approaches include energy efficiency standards; examples of information programmes + include labelling programmes that can help consumers make better-informed decisions. Mitigation + policy could devalue fossil fuel assets and reduce revenues for fossil fuel exporters, + but differences between regions and fuels exist. Most mitigation scenarios are + associated with reduced revenues from coal and oil trade for major exporters. + The effect on natural gas export revenues is more uncertain. The availability + of CCS would reduce the adverse effect of mitigation on the value of fossil fuel + assets. Interactions between or among mitigation policies may be synergistic + or may have no additive effect on reducing emissions . For instance, a carbon + tax can have an additive environmental effect to policies such as subsidies for + the supply of RE. By contrast, if a cap and trade system has a sufficiently stringent + cap to affect emission-related decisions, then other policies have no further + impact on reducing emissions . In either case, additional policies may be needed + to address market failures relating to innovation and technology diffusion. Sub-national + climate policies are increasingly prevalent, both in countries with national policies + and in those without. These policies include state and provincial climate plans + combining market, regulatory and information instruments, and sub-national cap-and-trade + systems. In addition, transnational cooperation has arisen among sub-national + actors, notably among institutional investors, NGOs seeking to govern carbon offset + markets, and networks of cities seeking to collaborate in generating low-carbon + urban development. Co-benefits and adverse side effects of mitigation could affect + achievement of other objectives such as those related to human health, food security, + biodiversity, local environmental quality, energy access, livelihoods and equitable + sustainable development: • Mitigation scenarios reaching about 450 or 500 ppm + CO2-equivalent by 2100 show reduced costs for achieving air quality and energy + security objectives, with significant co-benefits for human health, ecosystem + impacts and sufficiency of resources and resilience of the energy system. • Some + mitigation policies raise the prices for some energy services and could hamper + the ability of societies to expand access to modern energy services to underserved + populations . These potential adverse side effects can be avoided with the adoption + of complementary policies such as income tax rebates or other benefit transfer + mechanisms. The costs of achieving nearly universal access to electricity and + clean fuels for cooking and heating are projected to be between USD 72 to 95 billion + per year until 2030 with minimal effects on GHG emissions and multiple benefits + in health and air pollutant reduction. Whether or not side effects materialize, + and to what extent side effects materialize, will be case- and site-specific, + and depend on local circumstances and the scale, scope and pace of implementation. + Many co-benefits and adverse side effects have not been well-quantified.' + 4.1a: + - Common enabling factors and constraints for adaptation and mitigation responses + Adaptation and mitigation responses are underpinned by common enabling factors. + These include effective institutions and governance, innovation and investments + in environmentally sound technologies and infrastructure, sustainable livelihoods + and behavioural and lifestyle choices. Innovation and investments in environmentally + sound infrastructure and technologies can reduce greenhouse gas emissions and + enhance resilience to climate change . Innovation and change can expand the availability + and/ or effectiveness of adaptation and mitigation options. For example, investments + in low-carbon and carbon-neutral energy technologies can reduce the energy intensity + of economic development, the carbon intensity of energy, GHG emissions, and the + long-term costs of mitigation. Similarly, new technologies and infrastructure + can increase the resilience of human systems while reducing adverse impacts on + natural systems. Investments in technology and infrastructure rely on an enabling + policy environment, access to finance and technology and broader economic development + that builds capacity . Adaptation and mitigation are constrained by the inertia + of global and regional trends in economic development, GHG emissions, resource + consumption, infrastructure and settlement patterns, institutional behaviour and + technology . Such inertia may limit the capacity to reduce GHG emissions, remain + below particular climate thresholds or avoid adverse impacts. Some constraints + may be overcome through new technologies, financial resources, increased institutional + effectiveness and governance or changes in social and cultural attitudes and behaviours. Vulnerability + to climate change, GHG emissions, and the capacity for adaptation and mitigation + are strongly influenced by livelihoods, lifestyles, behaviour and culture . Shifts + toward more energy-intensive lifestyles can contribute to higher energy and resource + consumption, driving greater energy production and GHG emissions and increasing + mitigation costs. In contrast, emissions can be substantially lowered through + changes in consumption patterns. The social acceptability and/or effectiveness + of climate policies are influenced by the extent to which they incentivize or + depend on regionally appropriate changes in lifestyles or behaviours. Similarly, + livelihoods that depend on climate-sensitive sectors or resources may be particularly + vulnerable to climate change and climate change policies. Economic development + and urbanization of landscapes exposed to climate hazards may increase the exposure + of human settlements and reduce the resilience of natural systems. For many regions + and sectors, enhanced capacities to mitigate and adapt are part of the foundation + essential for managing climate change risks. Such capacities are place- and context-specific + and therefore there is no single approach for reducing risk that is appropriate + across all settings. For example, developing nations with low income levels have + the lowest financial, technological and institutional capacities to pursue low-carbon, + climate-resilient development pathways. Although developed nations generally have + greater relative capacity to manage the risks of climate change, such capacity + does not necessarily translate into the implementation of adaptation and mitigation + options. Improving institutions as well as enhancing coordination and cooperation + in governance can help overcome regional constraints associated with mitigation, + adaptation and disaster risk reduction. Despite the presence of a wide array of + multilateral, national and sub-national institutions focused on adaptation and + mitigation, global GHG emissions continue to increase and identified adaptation + needs have not been adequately addressed. The implementation of effective adaptation + and mitigation options may necessitate new institutions and institutional arrangements + that span multiple scales . + 4.1b: + - Common enabling factors and constraints for adaptation and mitigation responses + Adaptation and mitigation responses are underpinned by common enabling factors. + These include effective institutions and governance, innovation and investments + in environmentally sound technologies and infrastructure, sustainable livelihoods + and behavioural and lifestyle choices. Innovation and investments in environmentally + sound infrastructure and technologies can reduce greenhouse gas emissions and + enhance resilience to climate change . Innovation and change can expand the availability + and/ or effectiveness of adaptation and mitigation options. For example, investments + in low-carbon and carbon-neutral energy technologies can reduce the energy intensity + of economic development, the carbon intensity of energy, GHG emissions, and the + long-term costs of mitigation. Similarly, new technologies and infrastructure + can increase the resilience of human systems while reducing adverse impacts on + natural systems. Investments in technology and infrastructure rely on an enabling + policy environment, access to finance and technology and broader economic development + that builds capacity . Adaptation and mitigation are constrained by the inertia + of global and regional trends in economic development, GHG emissions, resource + consumption, infrastructure and settlement patterns, institutional behaviour and + technology . Such inertia may limit the capacity to reduce GHG emissions, remain + below particular climate thresholds or avoid adverse impacts. Some constraints + may be overcome through new technologies, financial resources, increased institutional + effectiveness and governance or changes in social and cultural attitudes and behaviours. Vulnerability + to climate change, GHG emissions, and the capacity for adaptation and mitigation + are strongly influenced by livelihoods, lifestyles, behaviour and culture . Shifts + toward more energy-intensive lifestyles can contribute to higher energy and resource + consumption, driving greater energy production and GHG emissions and increasing + mitigation costs. In contrast, emissions can be substantially lowered through + changes in consumption patterns. The social acceptability and/or effectiveness + of climate policies are influenced by the extent to which they incentivize or + depend on regionally appropriate changes in lifestyles or behaviours. Similarly, + livelihoods that depend on climate-sensitive sectors or resources may be particularly + vulnerable to climate change and climate change policies. Economic development + and urbanization of landscapes exposed to climate hazards may increase the exposure + of human settlements and reduce the resilience of natural systems. For many regions + and sectors, enhanced capacities to mitigate and adapt are part of the foundation + essential for managing climate change risks. Such capacities are place- and context-specific + and therefore there is no single approach for reducing risk that is appropriate + across all settings. For example, developing nations with low income levels have + the lowest financial, technological and institutional capacities to pursue low-carbon, + climate-resilient development pathways. Although developed nations generally have + greater relative capacity to manage the risks of climate change, such capacity + does not necessarily translate into the implementation of adaptation and mitigation + options. Improving institutions as well as enhancing coordination and cooperation + in governance can help overcome regional constraints associated with mitigation, + adaptation and disaster risk reduction. Despite the presence of a wide array of + multilateral, national and sub-national institutions focused on adaptation and + mitigation, global GHG emissions continue to increase and identified adaptation + needs have not been adequately addressed. The implementation of effective adaptation + and mitigation options may necessitate new institutions and institutional arrangements + that span multiple scales . + 4.1c: + - Common enabling factors and constraints for adaptation and mitigation responses + Adaptation and mitigation responses are underpinned by common enabling factors. + These include effective institutions and governance, innovation and investments + in environmentally sound technologies and infrastructure, sustainable livelihoods + and behavioural and lifestyle choices. Innovation and investments in environmentally + sound infrastructure and technologies can reduce greenhouse gas emissions and + enhance resilience to climate change . Innovation and change can expand the availability + and/ or effectiveness of adaptation and mitigation options. For example, investments + in low-carbon and carbon-neutral energy technologies can reduce the energy intensity + of economic development, the carbon intensity of energy, GHG emissions, and the + long-term costs of mitigation. Similarly, new technologies and infrastructure + can increase the resilience of human systems while reducing adverse impacts on + natural systems. Investments in technology and infrastructure rely on an enabling + policy environment, access to finance and technology and broader economic development + that builds capacity . Adaptation and mitigation are constrained by the inertia + of global and regional trends in economic development, GHG emissions, resource + consumption, infrastructure and settlement patterns, institutional behaviour and + technology . Such inertia may limit the capacity to reduce GHG emissions, remain + below particular climate thresholds or avoid adverse impacts. Some constraints + may be overcome through new technologies, financial resources, increased institutional + effectiveness and governance or changes in social and cultural attitudes and behaviours. Vulnerability + to climate change, GHG emissions, and the capacity for adaptation and mitigation + are strongly influenced by livelihoods, lifestyles, behaviour and culture . Shifts + toward more energy-intensive lifestyles can contribute to higher energy and resource + consumption, driving greater energy production and GHG emissions and increasing + mitigation costs. In contrast, emissions can be substantially lowered through + changes in consumption patterns. The social acceptability and/or effectiveness + of climate policies are influenced by the extent to which they incentivize or + depend on regionally appropriate changes in lifestyles or behaviours. Similarly, + livelihoods that depend on climate-sensitive sectors or resources may be particularly + vulnerable to climate change and climate change policies. Economic development + and urbanization of landscapes exposed to climate hazards may increase the exposure + of human settlements and reduce the resilience of natural systems. For many regions + and sectors, enhanced capacities to mitigate and adapt are part of the foundation + essential for managing climate change risks. Such capacities are place- and context-specific + and therefore there is no single approach for reducing risk that is appropriate + across all settings. For example, developing nations with low income levels have + the lowest financial, technological and institutional capacities to pursue low-carbon, + climate-resilient development pathways. Although developed nations generally have + greater relative capacity to manage the risks of climate change, such capacity + does not necessarily translate into the implementation of adaptation and mitigation + options. Improving institutions as well as enhancing coordination and cooperation + in governance can help overcome regional constraints associated with mitigation, + adaptation and disaster risk reduction. Despite the presence of a wide array of + multilateral, national and sub-national institutions focused on adaptation and + mitigation, global GHG emissions continue to increase and identified adaptation + needs have not been adequately addressed. The implementation of effective adaptation + and mitigation options may necessitate new institutions and institutional arrangements + that span multiple scales . + 4.2a: + - 'Response options for adaptation Adaptation options exist in all sectors, but + their context for implementation and potential to reduce climate-related risks + differs across sectors and regions. Some adaptation responses involve significant + co-benefits, synergies and trade-offs. Increasing climate change will increase + challenges for many adaptation options. People, governments and the private sector + are starting to adapt to a changing climate. Since the IPCC Fourth Assessment + Report , understanding of response options has increased, with improved knowledge + of their benefits, costs and links to sustainable development. Adaptation can + take a variety of approaches depending on its context in vulnerability reduction, + disaster risk management or proactive adaptation planning. These include : • Social, + ecological asset and infrastructure development • Technological process optimization + • Integrated natural resources management • Institutional, educational and behavioural + change or reinforcement • Financial services, including risk transfer • Information + systems to support early warning and proactive planning There is increasing recognition + of the value of social , institutional, and ecosystem-based measures and of the + extent of constraints to adaptation. Effective strategies and actions consider + the potential for co-benefits and opportunities within wider strategic goals and + development plans. Opportunities to enable adaptation planning and implementation + exist in all sectors and regions, with diverse potential and approaches depending + on context. The need for adaptation along with associated challenges is expected + to increase with climate change . Examples of key adaptation approaches for particular + sectors, including constraints and limits, are summarized below. Freshwater resources + Adaptive water management techniques, including scenario planning, learning-based + approaches and flexible and low-regret solutions, can help adjust to uncertain + hydrological changes due to climate change and their impacts . Strategies include + adopting integrated water management, augmenting supply, reducing the mismatch + between water supply and demand, reducing non-climate stressors, strengthening + institutional capacities and adopting more water-efficient technologies and water-saving + strategies. Terrestrial and freshwater ecosystems Management actions can reduce + but not eliminate risks of impacts to terrestrial and freshwater ecosystems due + to climate change. Actions include maintenance of genetic diversity, assisted + species migration and dispersal, manipulation of disturbance regimes and reduction + of other stressors. Management options that reduce non-climatic stressors, such + as habitat modification, overexploitation, pollution and invasive species, increase + the inherent capacity of ecosystems and their species to adapt to a changing climate. + Other options include improving early warning systems and associated response + systems. Enhanced connectivity of vulnerable ecosystems may also assist autonomous + adaptation. Translocation of species is controversial and is expected to become + less feasible where whole ecosystems are at risk. Coastal systems and low-lying + areas Increasingly, coastal adaptation options include those based on integrated + coastal zone management, local community participation, ecosystems-based approaches + and disaster risk reduction, mainstreamed into relevant strategies and management + plans. The analysis and implementation of coastal adaptation has progressed more + significantly in developed countries than in developing countries. The relative + costs of coastal adaptation are expected to vary strongly among and within regions + and countries. Marine systems and oceans Marine forecasting and early warning + systems as well as reducing non-climatic stressors have the potential to reduce + risks for some fisheries and aquaculture industries, but options for unique ecosystems + such as coral reefs are limited. Fisheries and some aquaculture industries with + high-technology and/or large investments have high capacities for adaptation due + to greater development of environmental monitoring, modelling and resource assessments. + Adaptation options include large-scale translocation of industrial fishing activities + and flexible management that can react to variability and change. For smaller-scale + fisheries and nations with limited adaptive capacities, building social resilience, + alternative livelihoods and occupational flexibility are important strategies. + Adaptation options for coral reef systems are generally limited to reducing other + stressors, mainly by enhancing water quality and limiting pressures from tourism + and fishing, but their efficacy will be severely reduced as thermal stress and + ocean acidification increase. Food production system/Rural areas Adaptation options + for agriculture include technological responses, enhancing smallholder access + to credit and other critical production resources, strengthening institutions + at local to regional levels and improving market access through trade reform. + Responses to decreased food production and quality include: developing new crop + varieties adapted to changes in CO2, temperature, and drought; enhancing the capacity + for climate risk management; and offsetting economic impacts of land use change. + Improving financial support and investing in the production of small-scale farms + can also provide benefits. Expanding agricultural markets and improving the predictability + and reliability of the world trading system could result in reduced market volatility + and help manage food supply shortages caused by climate change. Urban areas/Key + economic sectors and services Urban adaptation benefits from effective multi-level + governance, alignment of policies and incentives, strengthened local government + and community adaptation capacity, synergies with the private sector and appropriate + financing and institutional development. Enhancing the capacity of low-income + groups and vulnerable communities and their partnerships with local governments + can also be an effective urban climate adaptation strategy. Examples of adaptation + mechanisms include large-scale public-private risk reduction initiatives and economic + diversification and government insurance for the non-diversifiable portion of + risk. In some locations, especially at the upper end of projected climate changes, + responses could also require transformational changes such as managed retreat. Human + health, security and livelihoods Adaptation options that focus on strengthening + existing delivery systems and institutions, as well as insurance and social protection + strategies, can improve health, security and livelihoods in the near term. The + most effective vulnerability reduction measures for health in the near term are + programmes that implement and improve basic public health measures such as provision + of clean water and sanitation, secure essential health care including vaccination + and child health services, increase capacity for disaster preparedness and response + and alleviate poverty. Options to address heat related mortality include health + warning systems linked to response strategies, urban planning and improvements + to the built environment to reduce heat stress. Robust institutions can manage + many transboundary impacts of climate change to reduce risk of conflicts over + shared natural resources. Insurance programmes, social protection measures and + disaster risk management may enhance long-term livelihood resilience among the + poor and marginalized people, if policies address multi-dimensional poverty. Significant + co-benefits, synergies and trade-offs exist between adaptation and mitigation + and among different adaptation responses; interactions occur both within and across + regions and sectors. For example, investments in crop varieties adapted to climate + change can increase the capacity to cope with drought, and public health measures + to address vector-borne diseases can enhance the capacity of health systems to + address other challenges. Similarly, locating infrastructure away from low-lying + coastal areas helps settlements and ecosystems adapt to sea level rise while also + protecting against tsunamis. However, some adaptation options may have adverse + side effects that imply real or perceived trade-offs with other adaptation objectives, + mitigation objectives or broader development goals. For example, while protection + of ecosystems can assist adaptation to climate change and enhance carbon storage, + increased use of air conditioning to maintain thermal comfort in buildings or + the use of desalination to enhance water resource security can increase energy + demand, and therefore, GHG emissions.' + 4.2b: + - 'Human responses to climate change: adaptation and mitigation Adaptation and + mitigation experience is accumulating across regions and scales, even while global + anthropogenic greenhouse gas emissions have continued to increase. Throughout + history, people and societies have adjusted to and coped with climate, climate + variability and extremes, with varying degrees of success. In today’s changing + climate, accumulating experience with adaptation and mitigation efforts can provide + opportunities for learning and refinement. Adaptation is becoming embedded in + some planning processes, with more limited implementation of responses . Engineered + and technological options are commonly implemented adaptive responses, often integrated + within existing programmes, such as disaster risk management and water management. + There is increasing recognition of the value of social, institutional and ecosystem-based + measures and of the extent of constraints to adaptation. Governments at various + levels have begun to develop adaptation plans and policies and integrate climate + change considerations into broader development plans. Examples of adaptation are + now available from all regions of the world . Global increases in anthropogenic + emissions and climate impacts have occurred, even while mitigation activities + have taken place in many parts of the world. Though various mitigation initiatives + between the sub-national and global scales have been developed or implemented, + a full assessment of their impact may be premature.' + - 'Response options for adaptation Adaptation options exist in all sectors, but + their context for implementation and potential to reduce climate-related risks + differs across sectors and regions. Some adaptation responses involve significant + co-benefits, synergies and trade-offs. Increasing climate change will increase + challenges for many adaptation options. People, governments and the private sector + are starting to adapt to a changing climate. Since the IPCC Fourth Assessment + Report , understanding of response options has increased, with improved knowledge + of their benefits, costs and links to sustainable development. Adaptation can + take a variety of approaches depending on its context in vulnerability reduction, + disaster risk management or proactive adaptation planning. These include : • Social, + ecological asset and infrastructure development • Technological process optimization + • Integrated natural resources management • Institutional, educational and behavioural + change or reinforcement • Financial services, including risk transfer • Information + systems to support early warning and proactive planning There is increasing recognition + of the value of social , institutional, and ecosystem-based measures and of the + extent of constraints to adaptation. Effective strategies and actions consider + the potential for co-benefits and opportunities within wider strategic goals and + development plans. Opportunities to enable adaptation planning and implementation + exist in all sectors and regions, with diverse potential and approaches depending + on context. The need for adaptation along with associated challenges is expected + to increase with climate change . Examples of key adaptation approaches for particular + sectors, including constraints and limits, are summarized below. Freshwater resources + Adaptive water management techniques, including scenario planning, learning-based + approaches and flexible and low-regret solutions, can help adjust to uncertain + hydrological changes due to climate change and their impacts . Strategies include + adopting integrated water management, augmenting supply, reducing the mismatch + between water supply and demand, reducing non-climate stressors, strengthening + institutional capacities and adopting more water-efficient technologies and water-saving + strategies. Terrestrial and freshwater ecosystems Management actions can reduce + but not eliminate risks of impacts to terrestrial and freshwater ecosystems due + to climate change. Actions include maintenance of genetic diversity, assisted + species migration and dispersal, manipulation of disturbance regimes and reduction + of other stressors. Management options that reduce non-climatic stressors, such + as habitat modification, overexploitation, pollution and invasive species, increase + the inherent capacity of ecosystems and their species to adapt to a changing climate. + Other options include improving early warning systems and associated response + systems. Enhanced connectivity of vulnerable ecosystems may also assist autonomous + adaptation. Translocation of species is controversial and is expected to become + less feasible where whole ecosystems are at risk. Coastal systems and low-lying + areas Increasingly, coastal adaptation options include those based on integrated + coastal zone management, local community participation, ecosystems-based approaches + and disaster risk reduction, mainstreamed into relevant strategies and management + plans. The analysis and implementation of coastal adaptation has progressed more + significantly in developed countries than in developing countries. The relative + costs of coastal adaptation are expected to vary strongly among and within regions + and countries. Marine systems and oceans Marine forecasting and early warning + systems as well as reducing non-climatic stressors have the potential to reduce + risks for some fisheries and aquaculture industries, but options for unique ecosystems + such as coral reefs are limited. Fisheries and some aquaculture industries with + high-technology and/or large investments have high capacities for adaptation due + to greater development of environmental monitoring, modelling and resource assessments. + Adaptation options include large-scale translocation of industrial fishing activities + and flexible management that can react to variability and change. For smaller-scale + fisheries and nations with limited adaptive capacities, building social resilience, + alternative livelihoods and occupational flexibility are important strategies. + Adaptation options for coral reef systems are generally limited to reducing other + stressors, mainly by enhancing water quality and limiting pressures from tourism + and fishing, but their efficacy will be severely reduced as thermal stress and + ocean acidification increase. Food production system/Rural areas Adaptation options + for agriculture include technological responses, enhancing smallholder access + to credit and other critical production resources, strengthening institutions + at local to regional levels and improving market access through trade reform. + Responses to decreased food production and quality include: developing new crop + varieties adapted to changes in CO2, temperature, and drought; enhancing the capacity + for climate risk management; and offsetting economic impacts of land use change. + Improving financial support and investing in the production of small-scale farms + can also provide benefits. Expanding agricultural markets and improving the predictability + and reliability of the world trading system could result in reduced market volatility + and help manage food supply shortages caused by climate change. Urban areas/Key + economic sectors and services Urban adaptation benefits from effective multi-level + governance, alignment of policies and incentives, strengthened local government + and community adaptation capacity, synergies with the private sector and appropriate + financing and institutional development. Enhancing the capacity of low-income + groups and vulnerable communities and their partnerships with local governments + can also be an effective urban climate adaptation strategy. Examples of adaptation + mechanisms include large-scale public-private risk reduction initiatives and economic + diversification and government insurance for the non-diversifiable portion of + risk. In some locations, especially at the upper end of projected climate changes, + responses could also require transformational changes such as managed retreat. Human + health, security and livelihoods Adaptation options that focus on strengthening + existing delivery systems and institutions, as well as insurance and social protection + strategies, can improve health, security and livelihoods in the near term. The + most effective vulnerability reduction measures for health in the near term are + programmes that implement and improve basic public health measures such as provision + of clean water and sanitation, secure essential health care including vaccination + and child health services, increase capacity for disaster preparedness and response + and alleviate poverty. Options to address heat related mortality include health + warning systems linked to response strategies, urban planning and improvements + to the built environment to reduce heat stress. Robust institutions can manage + many transboundary impacts of climate change to reduce risk of conflicts over + shared natural resources. Insurance programmes, social protection measures and + disaster risk management may enhance long-term livelihood resilience among the + poor and marginalized people, if policies address multi-dimensional poverty. Significant + co-benefits, synergies and trade-offs exist between adaptation and mitigation + and among different adaptation responses; interactions occur both within and across + regions and sectors. For example, investments in crop varieties adapted to climate + change can increase the capacity to cope with drought, and public health measures + to address vector-borne diseases can enhance the capacity of health systems to + address other challenges. Similarly, locating infrastructure away from low-lying + coastal areas helps settlements and ecosystems adapt to sea level rise while also + protecting against tsunamis. However, some adaptation options may have adverse + side effects that imply real or perceived trade-offs with other adaptation objectives, + mitigation objectives or broader development goals. For example, while protection + of ecosystems can assist adaptation to climate change and enhance carbon storage, + increased use of air conditioning to maintain thermal comfort in buildings or + the use of desalination to enhance water resource security can increase energy + demand, and therefore, GHG emissions.' + - 'Adaptation Adaptation experience is accumulating across regions in the public + and private sector and within communities . Adaptation options adopted to date + emphasize incremental adjustments and co-benefits and are starting to emphasize + flexibility and learning. Most assessments of adaptation have been restricted + to impacts, vulnerability and adaptation planning, with very few assessing the + processes of implementation or the effects of adaptation actions . National governments + play key roles in adaptation planning and implementation. There has been substantial + progress since the AR4 in the development of national adaptation strategies and + plans. This includes National Adaptation Programmes of Action by least developed + countries, the National Adaptation Plan process, and strategic frameworks for + national adaptation in Organisation for Economic Co-operation and Development + countries. National governments can coordinate adaptation efforts of local and + sub-national governments, for example by protecting vulnerable groups, by supporting + economic diversification, and by providing information, policy and legal frameworks + and financial support. While local government and the private sector have different + functions, which vary regionally, they are increasingly recognized as critical + to progress in adaptation, given their roles in scaling up adaptation of communities, + households and civil society and in managing risk information and financing . + There is a significant increase in the number of planned adaptation responses + at the local level in rural and urban communities of developed and developing + countries since the AR4. However, local councils and planners are often confronted + by the complexity of adaptation without adequate access to guiding information + or data on local vulnerabilities and potential impacts. Steps for mainstreaming + adaptation into local decision-making have been identified but challenges remain + in their implementation. Hence, scholars stress the important role of linkages + with national and sub-national levels of government as well as partnerships among + public, civic and private sectors in implementing local adaptation responses. Institutional + dimensions of adaptation governance, including the integration of adaptation into + planning and decision-making, play a key role in promoting the transition from + planning to implementation of adaptation . The most commonly emphasized institutional + barriers or enablers for adaptation planning and implementation are: 1) multilevel + institutional co-ordination between different political and administrative levels + in society; 2) key actors, advocates and champions initiating, mainstreaming and + sustaining momentum for climate adaptation; 3) horizontal interplay between sectors, + actors and policies operating at similar administrative levels; 4) political dimensions + in planning and implementation; and 5) coordination between formal governmental, + administrative agencies and private sectors and stakeholders to increase efficiency, + representation and support for climate adaptation measures. Existing and emerging + economic instruments can foster adaptation by providing incentives for anticipating + and reducing impacts. Instruments include public-private finance partnerships, + loans, payments for environmental services, improved resource pricing, charges + and subsidies, norms and regulations and risk sharing and transfer mechanisms. + Risk financing mechanisms in the public and private sector, such as insurance + and risk pools, can contribute to increasing resilience, but without attention + to major design challenges, they can also provide disincentives, cause market + failure and decrease equity. Governments often play key roles as regulators, providers + or insurers of last resort.' + 4.2c: + - 'Response options for adaptation Adaptation options exist in all sectors, but + their context for implementation and potential to reduce climate-related risks + differs across sectors and regions. Some adaptation responses involve significant + co-benefits, synergies and trade-offs. Increasing climate change will increase + challenges for many adaptation options. People, governments and the private sector + are starting to adapt to a changing climate. Since the IPCC Fourth Assessment + Report , understanding of response options has increased, with improved knowledge + of their benefits, costs and links to sustainable development. Adaptation can + take a variety of approaches depending on its context in vulnerability reduction, + disaster risk management or proactive adaptation planning. These include : • Social, + ecological asset and infrastructure development • Technological process optimization + • Integrated natural resources management • Institutional, educational and behavioural + change or reinforcement • Financial services, including risk transfer • Information + systems to support early warning and proactive planning There is increasing recognition + of the value of social , institutional, and ecosystem-based measures and of the + extent of constraints to adaptation. Effective strategies and actions consider + the potential for co-benefits and opportunities within wider strategic goals and + development plans. Opportunities to enable adaptation planning and implementation + exist in all sectors and regions, with diverse potential and approaches depending + on context. The need for adaptation along with associated challenges is expected + to increase with climate change . Examples of key adaptation approaches for particular + sectors, including constraints and limits, are summarized below. Freshwater resources + Adaptive water management techniques, including scenario planning, learning-based + approaches and flexible and low-regret solutions, can help adjust to uncertain + hydrological changes due to climate change and their impacts . Strategies include + adopting integrated water management, augmenting supply, reducing the mismatch + between water supply and demand, reducing non-climate stressors, strengthening + institutional capacities and adopting more water-efficient technologies and water-saving + strategies. Terrestrial and freshwater ecosystems Management actions can reduce + but not eliminate risks of impacts to terrestrial and freshwater ecosystems due + to climate change. Actions include maintenance of genetic diversity, assisted + species migration and dispersal, manipulation of disturbance regimes and reduction + of other stressors. Management options that reduce non-climatic stressors, such + as habitat modification, overexploitation, pollution and invasive species, increase + the inherent capacity of ecosystems and their species to adapt to a changing climate. + Other options include improving early warning systems and associated response + systems. Enhanced connectivity of vulnerable ecosystems may also assist autonomous + adaptation. Translocation of species is controversial and is expected to become + less feasible where whole ecosystems are at risk. Coastal systems and low-lying + areas Increasingly, coastal adaptation options include those based on integrated + coastal zone management, local community participation, ecosystems-based approaches + and disaster risk reduction, mainstreamed into relevant strategies and management + plans. The analysis and implementation of coastal adaptation has progressed more + significantly in developed countries than in developing countries. The relative + costs of coastal adaptation are expected to vary strongly among and within regions + and countries. Marine systems and oceans Marine forecasting and early warning + systems as well as reducing non-climatic stressors have the potential to reduce + risks for some fisheries and aquaculture industries, but options for unique ecosystems + such as coral reefs are limited. Fisheries and some aquaculture industries with + high-technology and/or large investments have high capacities for adaptation due + to greater development of environmental monitoring, modelling and resource assessments. + Adaptation options include large-scale translocation of industrial fishing activities + and flexible management that can react to variability and change. For smaller-scale + fisheries and nations with limited adaptive capacities, building social resilience, + alternative livelihoods and occupational flexibility are important strategies. + Adaptation options for coral reef systems are generally limited to reducing other + stressors, mainly by enhancing water quality and limiting pressures from tourism + and fishing, but their efficacy will be severely reduced as thermal stress and + ocean acidification increase. Food production system/Rural areas Adaptation options + for agriculture include technological responses, enhancing smallholder access + to credit and other critical production resources, strengthening institutions + at local to regional levels and improving market access through trade reform. + Responses to decreased food production and quality include: developing new crop + varieties adapted to changes in CO2, temperature, and drought; enhancing the capacity + for climate risk management; and offsetting economic impacts of land use change. + Improving financial support and investing in the production of small-scale farms + can also provide benefits. Expanding agricultural markets and improving the predictability + and reliability of the world trading system could result in reduced market volatility + and help manage food supply shortages caused by climate change. Urban areas/Key + economic sectors and services Urban adaptation benefits from effective multi-level + governance, alignment of policies and incentives, strengthened local government + and community adaptation capacity, synergies with the private sector and appropriate + financing and institutional development. Enhancing the capacity of low-income + groups and vulnerable communities and their partnerships with local governments + can also be an effective urban climate adaptation strategy. Examples of adaptation + mechanisms include large-scale public-private risk reduction initiatives and economic + diversification and government insurance for the non-diversifiable portion of + risk. In some locations, especially at the upper end of projected climate changes, + responses could also require transformational changes such as managed retreat. Human + health, security and livelihoods Adaptation options that focus on strengthening + existing delivery systems and institutions, as well as insurance and social protection + strategies, can improve health, security and livelihoods in the near term. The + most effective vulnerability reduction measures for health in the near term are + programmes that implement and improve basic public health measures such as provision + of clean water and sanitation, secure essential health care including vaccination + and child health services, increase capacity for disaster preparedness and response + and alleviate poverty. Options to address heat related mortality include health + warning systems linked to response strategies, urban planning and improvements + to the built environment to reduce heat stress. Robust institutions can manage + many transboundary impacts of climate change to reduce risk of conflicts over + shared natural resources. Insurance programmes, social protection measures and + disaster risk management may enhance long-term livelihood resilience among the + poor and marginalized people, if policies address multi-dimensional poverty. Significant + co-benefits, synergies and trade-offs exist between adaptation and mitigation + and among different adaptation responses; interactions occur both within and across + regions and sectors. For example, investments in crop varieties adapted to climate + change can increase the capacity to cope with drought, and public health measures + to address vector-borne diseases can enhance the capacity of health systems to + address other challenges. Similarly, locating infrastructure away from low-lying + coastal areas helps settlements and ecosystems adapt to sea level rise while also + protecting against tsunamis. However, some adaptation options may have adverse + side effects that imply real or perceived trade-offs with other adaptation objectives, + mitigation objectives or broader development goals. For example, while protection + of ecosystems can assist adaptation to climate change and enhance carbon storage, + increased use of air conditioning to maintain thermal comfort in buildings or + the use of desalination to enhance water resource security can increase energy + demand, and therefore, GHG emissions.' + 4.3a: + - Response options for mitigation Mitigation options are available in every major + sector. Mitigation can be more cost-effective if using an integrated approach + that combines measures to reduce energy use and the greenhouse gas intensity of + end-use sectors, decarbonize energy supply, reduce net emissions and enhance carbon + sinks in land-based sectors. A broad range of sectoral mitigation options is available + that can reduce GHG emission intensity, improve energy intensity through enhancements + of technology, behaviour, production and resource efficiency and enable structural + changes or changes in activity. In addition, direct options in agriculture, forestry + and other land use involve reducing CO2 emissions by reducing deforestation, forest + degradation and forest fires; storing carbon in terrestrial systems; and providing + bioenergy feedstocks. Options to reduce non-CO2 emissions exist across all sectors + but most notably in agriculture, energy supply and industry. An overview of sectoral + mitigation options and potentials is provided in Table 4.4. Well-designed systemic + and cross-sectoral mitigation strategies are more cost-effective in cutting emissions + than a focus on individual technologies and sectors with efforts in one sector + affecting the need for mitigation in others . In baseline scenarios without new + mitigation policies, GHG emissions are projected to grow in all sectors, except + for net CO2 emissions in the AFOLU sector. Mitigation scenarios reaching around + 450 ppm CO2-eq concentration by 21004328 show largescale global changes in the + energy supply sector . While rapid decarbonization of energy supply generally + entails more flexibility for end-use and AFOLU sectors, stronger demand reductions + lessen the mitigation challenge for the supply side of the energy system. There + are thus strong interdependencies across sectors and the resulting distribution + of the mitigation effort is strongly influenced by the availability and performance + of future technologies, particularly BECCS and large scale afforestation . The + next two decades present a window of opportunity for mitigation in urban areas, + as a large portion of the world’s urban areas will be developed during this period. Decarbonizing + electricity generation is a key component of cost-effective mitigation strategies + in achieving low stabilization levels . In most integrated modelling scenarios, + decarbonization happens more rapidly in electricity generation than in the industry, + buildings and transport sectors. In scenarios reaching 450 ppm CO2-eq concentrations + by 2100, global CO2 emissions from the energy supply sector are projected to decline + over the next decade and are characterized by reductions of 90% or more below + 2010 levels between 2040 and 2070. Efficiency enhancements and behavioural changes, + in order to reduce energy demand compared to baseline scenarios without compromising + development, are a key mitigation strategy in scenarios reaching atmospheric CO2-eq + concentrations of about 450 to about 500 ppm by 2100 . Near-term reductions in + energy demand are an important element of cost-effective mitigation strategies, + provide more flexibility for reducing carbon intensity in the energy supply sector, + hedge against related supply-side risks, avoid lock-in to carbon-intensive infrastructures + and are associated with important co-benefits . Emissions can be substantially + lowered through changes in consumption patterns and dietary change and reduction + in food wastes. A number of options including monetary and non-monetary incentives + as well as information measures may facilitate behavioural changes. Decarbonization + of the energy supply sector requires upscaling of low- and zero-carbon electricity + generation technologies. In the majority of low-concentration stabilization scenarios + , the share of low-carbon electricity supply, nuclear and CCS, including BECCS) + increases from the current share of approximately 30% to more than 80% by 2050 + and 90% by 2100, and fossil fuel power generation without CCS is phased out almost + entirely by 2100. Among these low-carbon technologies, a growing number of RE + technologies have achieved a level of maturity to enable deployment at significant + scale since AR4 and nuclear energy is a mature low-GHG emission source of baseload + power, but its share of global electricity generation has been declining. GHG + emissions from energy supply can be reduced significantly by replacing current + world average coal-fired power plants with modern, highly efficient natural gas + combined-cycle power plants or combined heat and power plants, provided that natural + gas is available and the fugitive emissions associated with extraction and supply + are low or mitigated. Behaviour, lifestyle and culture have a considerable influence + on energy use and associated emissions, with high mitigation potential in some + sectors, in particular when complementing technological and structural change + . In the transport sector, technical and behavioural mitigation measures for all + modes, plus new infrastructure and urban redevelopment investments, could reduce + final energy demand significantly below baseline levels. While opportunities for + switching to low-carbon fuels exist, the rate of decarbonization in the transport + sector might be constrained by challenges associated with energy storage and the + relatively low energy density of low-carbon transport fuels. In the building sector, + recent advances in technologies, know-how and policies provide opportunities to + stabilize or reduce global energy use to about current levels by mid-century. + In addition, recent improvements in performance and costs make very low energy + construction and retrofits of buildings economically attractive, sometimes even + at net negative costs. In the industry sector, improvements in GHG emission efficiency + and in the efficiency of material use, recycling and reuse of materials and products, + and overall reductions in product demand and service demand could, in addition + to energy efficiency, help reduce GHG emissions below the baseline level. Prevalent + approaches for promoting energy efficiency in industry include information programmes + followed by economic instruments, regulatory approaches and voluntary actions. + Important options for mitigation in waste management are waste reduction, followed + by re-use, recycling and energy recovery. The most cost-effective mitigation + options in forestry are afforestation, sustainable forest management and reducing + deforestation, with large differences in their relative importance across regions. + In agriculture, the most cost-effective mitigation options are cropland management, + grazing land management and restoration of organic soils . About a third of mitigation + potential in forestry can be achieved at a cost <20 USD/tCO2-eq emission. Demand-side + measures, such as changes in diet and reductions of losses in the food supply + chain, have a significant, but uncertain, potential to reduce GHG emissions from + food production . Bioenergy can play a critical role for mitigation, but there + are issues to consider, such as the sustainability of practices and the efficiency + of bioenergy systems . Evidence suggests that bioenergy options with low lifecycle + emissions, some already available, can reduce GHG emissions; outcomes are site-specific + and rely on efficient integrated ‘biomassto-bioenergy systems’, and sustainable + land use management and governance. Barriers to large-scale deployment of bioenergy + include concerns about GHG emissions from land, food security, water resources, + biodiversity conservation and livelihoods. Mitigation measures intersect with + other societal goals, creating the possibility of co-benefits or adverse side-effects. + These intersections, if well-managed, can strengthen the basis for undertaking + climate mitigation actions . Mitigation can positively or negatively influence + the achievement of other societal goals, such as those related to human health, + food security, biodiversity, local environmental quality, energy access, livelihoods + and equitable sustainable development . On the other hand, policies towards other + societal goals can influence the achievement of mitigation and adaptation objectives. + These influences can be substantial, although sometimes difficult to quantify, + especially in welfare terms. This multi-objective perspective is important in + part because it helps to identify areas where support for policies that advance + multiple goals will be robust. Potential co-benefits and adverse side effects + of the main sectoral mitigation measures are summarized in Table 4.5. Overall, + the potential for co-benefits for energy end-use measures outweigh the potential + for adverse side effects, whereas the evidence suggests this may not be the case + for all energy supply and AFOLU measures. + 4.3b: + - Response options for mitigation Mitigation options are available in every major + sector. Mitigation can be more cost-effective if using an integrated approach + that combines measures to reduce energy use and the greenhouse gas intensity of + end-use sectors, decarbonize energy supply, reduce net emissions and enhance carbon + sinks in land-based sectors. A broad range of sectoral mitigation options is available + that can reduce GHG emission intensity, improve energy intensity through enhancements + of technology, behaviour, production and resource efficiency and enable structural + changes or changes in activity. In addition, direct options in agriculture, forestry + and other land use involve reducing CO2 emissions by reducing deforestation, forest + degradation and forest fires; storing carbon in terrestrial systems; and providing + bioenergy feedstocks. Options to reduce non-CO2 emissions exist across all sectors + but most notably in agriculture, energy supply and industry. An overview of sectoral + mitigation options and potentials is provided in Table 4.4. Well-designed systemic + and cross-sectoral mitigation strategies are more cost-effective in cutting emissions + than a focus on individual technologies and sectors with efforts in one sector + affecting the need for mitigation in others . In baseline scenarios without new + mitigation policies, GHG emissions are projected to grow in all sectors, except + for net CO2 emissions in the AFOLU sector. Mitigation scenarios reaching around + 450 ppm CO2-eq concentration by 21004328 show largescale global changes in the + energy supply sector . While rapid decarbonization of energy supply generally + entails more flexibility for end-use and AFOLU sectors, stronger demand reductions + lessen the mitigation challenge for the supply side of the energy system. There + are thus strong interdependencies across sectors and the resulting distribution + of the mitigation effort is strongly influenced by the availability and performance + of future technologies, particularly BECCS and large scale afforestation . The + next two decades present a window of opportunity for mitigation in urban areas, + as a large portion of the world’s urban areas will be developed during this period. Decarbonizing + electricity generation is a key component of cost-effective mitigation strategies + in achieving low stabilization levels . In most integrated modelling scenarios, + decarbonization happens more rapidly in electricity generation than in the industry, + buildings and transport sectors. In scenarios reaching 450 ppm CO2-eq concentrations + by 2100, global CO2 emissions from the energy supply sector are projected to decline + over the next decade and are characterized by reductions of 90% or more below + 2010 levels between 2040 and 2070. Efficiency enhancements and behavioural changes, + in order to reduce energy demand compared to baseline scenarios without compromising + development, are a key mitigation strategy in scenarios reaching atmospheric CO2-eq + concentrations of about 450 to about 500 ppm by 2100 . Near-term reductions in + energy demand are an important element of cost-effective mitigation strategies, + provide more flexibility for reducing carbon intensity in the energy supply sector, + hedge against related supply-side risks, avoid lock-in to carbon-intensive infrastructures + and are associated with important co-benefits . Emissions can be substantially + lowered through changes in consumption patterns and dietary change and reduction + in food wastes. A number of options including monetary and non-monetary incentives + as well as information measures may facilitate behavioural changes. Decarbonization + of the energy supply sector requires upscaling of low- and zero-carbon electricity + generation technologies. In the majority of low-concentration stabilization scenarios + , the share of low-carbon electricity supply, nuclear and CCS, including BECCS) + increases from the current share of approximately 30% to more than 80% by 2050 + and 90% by 2100, and fossil fuel power generation without CCS is phased out almost + entirely by 2100. Among these low-carbon technologies, a growing number of RE + technologies have achieved a level of maturity to enable deployment at significant + scale since AR4 and nuclear energy is a mature low-GHG emission source of baseload + power, but its share of global electricity generation has been declining. GHG + emissions from energy supply can be reduced significantly by replacing current + world average coal-fired power plants with modern, highly efficient natural gas + combined-cycle power plants or combined heat and power plants, provided that natural + gas is available and the fugitive emissions associated with extraction and supply + are low or mitigated. Behaviour, lifestyle and culture have a considerable influence + on energy use and associated emissions, with high mitigation potential in some + sectors, in particular when complementing technological and structural change + . In the transport sector, technical and behavioural mitigation measures for all + modes, plus new infrastructure and urban redevelopment investments, could reduce + final energy demand significantly below baseline levels. While opportunities for + switching to low-carbon fuels exist, the rate of decarbonization in the transport + sector might be constrained by challenges associated with energy storage and the + relatively low energy density of low-carbon transport fuels. In the building sector, + recent advances in technologies, know-how and policies provide opportunities to + stabilize or reduce global energy use to about current levels by mid-century. + In addition, recent improvements in performance and costs make very low energy + construction and retrofits of buildings economically attractive, sometimes even + at net negative costs. In the industry sector, improvements in GHG emission efficiency + and in the efficiency of material use, recycling and reuse of materials and products, + and overall reductions in product demand and service demand could, in addition + to energy efficiency, help reduce GHG emissions below the baseline level. Prevalent + approaches for promoting energy efficiency in industry include information programmes + followed by economic instruments, regulatory approaches and voluntary actions. + Important options for mitigation in waste management are waste reduction, followed + by re-use, recycling and energy recovery. The most cost-effective mitigation + options in forestry are afforestation, sustainable forest management and reducing + deforestation, with large differences in their relative importance across regions. + In agriculture, the most cost-effective mitigation options are cropland management, + grazing land management and restoration of organic soils . About a third of mitigation + potential in forestry can be achieved at a cost <20 USD/tCO2-eq emission. Demand-side + measures, such as changes in diet and reductions of losses in the food supply + chain, have a significant, but uncertain, potential to reduce GHG emissions from + food production . Bioenergy can play a critical role for mitigation, but there + are issues to consider, such as the sustainability of practices and the efficiency + of bioenergy systems . Evidence suggests that bioenergy options with low lifecycle + emissions, some already available, can reduce GHG emissions; outcomes are site-specific + and rely on efficient integrated ‘biomassto-bioenergy systems’, and sustainable + land use management and governance. Barriers to large-scale deployment of bioenergy + include concerns about GHG emissions from land, food security, water resources, + biodiversity conservation and livelihoods. Mitigation measures intersect with + other societal goals, creating the possibility of co-benefits or adverse side-effects. + These intersections, if well-managed, can strengthen the basis for undertaking + climate mitigation actions . Mitigation can positively or negatively influence + the achievement of other societal goals, such as those related to human health, + food security, biodiversity, local environmental quality, energy access, livelihoods + and equitable sustainable development . On the other hand, policies towards other + societal goals can influence the achievement of mitigation and adaptation objectives. + These influences can be substantial, although sometimes difficult to quantify, + especially in welfare terms. This multi-objective perspective is important in + part because it helps to identify areas where support for policies that advance + multiple goals will be robust. Potential co-benefits and adverse side effects + of the main sectoral mitigation measures are summarized in Table 4.5. Overall, + the potential for co-benefits for energy end-use measures outweigh the potential + for adverse side effects, whereas the evidence suggests this may not be the case + for all energy supply and AFOLU measures. + 4.3d: + - Common enabling factors and constraints for adaptation and mitigation responses + Adaptation and mitigation responses are underpinned by common enabling factors. + These include effective institutions and governance, innovation and investments + in environmentally sound technologies and infrastructure, sustainable livelihoods + and behavioural and lifestyle choices. Innovation and investments in environmentally + sound infrastructure and technologies can reduce greenhouse gas emissions and + enhance resilience to climate change . Innovation and change can expand the availability + and/ or effectiveness of adaptation and mitigation options. For example, investments + in low-carbon and carbon-neutral energy technologies can reduce the energy intensity + of economic development, the carbon intensity of energy, GHG emissions, and the + long-term costs of mitigation. Similarly, new technologies and infrastructure + can increase the resilience of human systems while reducing adverse impacts on + natural systems. Investments in technology and infrastructure rely on an enabling + policy environment, access to finance and technology and broader economic development + that builds capacity . Adaptation and mitigation are constrained by the inertia + of global and regional trends in economic development, GHG emissions, resource + consumption, infrastructure and settlement patterns, institutional behaviour and + technology . Such inertia may limit the capacity to reduce GHG emissions, remain + below particular climate thresholds or avoid adverse impacts. Some constraints + may be overcome through new technologies, financial resources, increased institutional + effectiveness and governance or changes in social and cultural attitudes and behaviours. Vulnerability + to climate change, GHG emissions, and the capacity for adaptation and mitigation + are strongly influenced by livelihoods, lifestyles, behaviour and culture . Shifts + toward more energy-intensive lifestyles can contribute to higher energy and resource + consumption, driving greater energy production and GHG emissions and increasing + mitigation costs. In contrast, emissions can be substantially lowered through + changes in consumption patterns. The social acceptability and/or effectiveness + of climate policies are influenced by the extent to which they incentivize or + depend on regionally appropriate changes in lifestyles or behaviours. Similarly, + livelihoods that depend on climate-sensitive sectors or resources may be particularly + vulnerable to climate change and climate change policies. Economic development + and urbanization of landscapes exposed to climate hazards may increase the exposure + of human settlements and reduce the resilience of natural systems. For many regions + and sectors, enhanced capacities to mitigate and adapt are part of the foundation + essential for managing climate change risks. Such capacities are place- and context-specific + and therefore there is no single approach for reducing risk that is appropriate + across all settings. For example, developing nations with low income levels have + the lowest financial, technological and institutional capacities to pursue low-carbon, + climate-resilient development pathways. Although developed nations generally have + greater relative capacity to manage the risks of climate change, such capacity + does not necessarily translate into the implementation of adaptation and mitigation + options. Improving institutions as well as enhancing coordination and cooperation + in governance can help overcome regional constraints associated with mitigation, + adaptation and disaster risk reduction. Despite the presence of a wide array of + multilateral, national and sub-national institutions focused on adaptation and + mitigation, global GHG emissions continue to increase and identified adaptation + needs have not been adequately addressed. The implementation of effective adaptation + and mitigation options may necessitate new institutions and institutional arrangements + that span multiple scales . + - Response options for mitigation Mitigation options are available in every major + sector. Mitigation can be more cost-effective if using an integrated approach + that combines measures to reduce energy use and the greenhouse gas intensity of + end-use sectors, decarbonize energy supply, reduce net emissions and enhance carbon + sinks in land-based sectors. A broad range of sectoral mitigation options is available + that can reduce GHG emission intensity, improve energy intensity through enhancements + of technology, behaviour, production and resource efficiency and enable structural + changes or changes in activity. In addition, direct options in agriculture, forestry + and other land use involve reducing CO2 emissions by reducing deforestation, forest + degradation and forest fires; storing carbon in terrestrial systems; and providing + bioenergy feedstocks. Options to reduce non-CO2 emissions exist across all sectors + but most notably in agriculture, energy supply and industry. An overview of sectoral + mitigation options and potentials is provided in Table 4.4. Well-designed systemic + and cross-sectoral mitigation strategies are more cost-effective in cutting emissions + than a focus on individual technologies and sectors with efforts in one sector + affecting the need for mitigation in others . In baseline scenarios without new + mitigation policies, GHG emissions are projected to grow in all sectors, except + for net CO2 emissions in the AFOLU sector. Mitigation scenarios reaching around + 450 ppm CO2-eq concentration by 21004328 show largescale global changes in the + energy supply sector . While rapid decarbonization of energy supply generally + entails more flexibility for end-use and AFOLU sectors, stronger demand reductions + lessen the mitigation challenge for the supply side of the energy system. There + are thus strong interdependencies across sectors and the resulting distribution + of the mitigation effort is strongly influenced by the availability and performance + of future technologies, particularly BECCS and large scale afforestation . The + next two decades present a window of opportunity for mitigation in urban areas, + as a large portion of the world’s urban areas will be developed during this period. Decarbonizing + electricity generation is a key component of cost-effective mitigation strategies + in achieving low stabilization levels . In most integrated modelling scenarios, + decarbonization happens more rapidly in electricity generation than in the industry, + buildings and transport sectors. In scenarios reaching 450 ppm CO2-eq concentrations + by 2100, global CO2 emissions from the energy supply sector are projected to decline + over the next decade and are characterized by reductions of 90% or more below + 2010 levels between 2040 and 2070. Efficiency enhancements and behavioural changes, + in order to reduce energy demand compared to baseline scenarios without compromising + development, are a key mitigation strategy in scenarios reaching atmospheric CO2-eq + concentrations of about 450 to about 500 ppm by 2100 . Near-term reductions in + energy demand are an important element of cost-effective mitigation strategies, + provide more flexibility for reducing carbon intensity in the energy supply sector, + hedge against related supply-side risks, avoid lock-in to carbon-intensive infrastructures + and are associated with important co-benefits . Emissions can be substantially + lowered through changes in consumption patterns and dietary change and reduction + in food wastes. A number of options including monetary and non-monetary incentives + as well as information measures may facilitate behavioural changes. Decarbonization + of the energy supply sector requires upscaling of low- and zero-carbon electricity + generation technologies. In the majority of low-concentration stabilization scenarios + , the share of low-carbon electricity supply, nuclear and CCS, including BECCS) + increases from the current share of approximately 30% to more than 80% by 2050 + and 90% by 2100, and fossil fuel power generation without CCS is phased out almost + entirely by 2100. Among these low-carbon technologies, a growing number of RE + technologies have achieved a level of maturity to enable deployment at significant + scale since AR4 and nuclear energy is a mature low-GHG emission source of baseload + power, but its share of global electricity generation has been declining. GHG + emissions from energy supply can be reduced significantly by replacing current + world average coal-fired power plants with modern, highly efficient natural gas + combined-cycle power plants or combined heat and power plants, provided that natural + gas is available and the fugitive emissions associated with extraction and supply + are low or mitigated. Behaviour, lifestyle and culture have a considerable influence + on energy use and associated emissions, with high mitigation potential in some + sectors, in particular when complementing technological and structural change + . In the transport sector, technical and behavioural mitigation measures for all + modes, plus new infrastructure and urban redevelopment investments, could reduce + final energy demand significantly below baseline levels. While opportunities for + switching to low-carbon fuels exist, the rate of decarbonization in the transport + sector might be constrained by challenges associated with energy storage and the + relatively low energy density of low-carbon transport fuels. In the building sector, + recent advances in technologies, know-how and policies provide opportunities to + stabilize or reduce global energy use to about current levels by mid-century. + In addition, recent improvements in performance and costs make very low energy + construction and retrofits of buildings economically attractive, sometimes even + at net negative costs. In the industry sector, improvements in GHG emission efficiency + and in the efficiency of material use, recycling and reuse of materials and products, + and overall reductions in product demand and service demand could, in addition + to energy efficiency, help reduce GHG emissions below the baseline level. Prevalent + approaches for promoting energy efficiency in industry include information programmes + followed by economic instruments, regulatory approaches and voluntary actions. + Important options for mitigation in waste management are waste reduction, followed + by re-use, recycling and energy recovery. The most cost-effective mitigation + options in forestry are afforestation, sustainable forest management and reducing + deforestation, with large differences in their relative importance across regions. + In agriculture, the most cost-effective mitigation options are cropland management, + grazing land management and restoration of organic soils . About a third of mitigation + potential in forestry can be achieved at a cost <20 USD/tCO2-eq emission. Demand-side + measures, such as changes in diet and reductions of losses in the food supply + chain, have a significant, but uncertain, potential to reduce GHG emissions from + food production . Bioenergy can play a critical role for mitigation, but there + are issues to consider, such as the sustainability of practices and the efficiency + of bioenergy systems . Evidence suggests that bioenergy options with low lifecycle + emissions, some already available, can reduce GHG emissions; outcomes are site-specific + and rely on efficient integrated ‘biomassto-bioenergy systems’, and sustainable + land use management and governance. Barriers to large-scale deployment of bioenergy + include concerns about GHG emissions from land, food security, water resources, + biodiversity conservation and livelihoods. Mitigation measures intersect with + other societal goals, creating the possibility of co-benefits or adverse side-effects. + These intersections, if well-managed, can strengthen the basis for undertaking + climate mitigation actions . Mitigation can positively or negatively influence + the achievement of other societal goals, such as those related to human health, + food security, biodiversity, local environmental quality, energy access, livelihoods + and equitable sustainable development . On the other hand, policies towards other + societal goals can influence the achievement of mitigation and adaptation objectives. + These influences can be substantial, although sometimes difficult to quantify, + especially in welfare terms. This multi-objective perspective is important in + part because it helps to identify areas where support for policies that advance + multiple goals will be robust. Potential co-benefits and adverse side effects + of the main sectoral mitigation measures are summarized in Table 4.5. Overall, + the potential for co-benefits for energy end-use measures outweigh the potential + for adverse side effects, whereas the evidence suggests this may not be the case + for all energy supply and AFOLU measures. + 4.4b: + - 'International and regional cooperation on adaptation and mitigation Because + climate change has the characteristics of a collective action problem at the global + scale, effective mitigation will not be achieved if individual agents advance + their own interests independently, even though mitigation can also have local + co-benefits. Cooperative responses, including international cooperation, are therefore + required to effectively mitigate GHG emissions and address other climate change + issues. While adaptation focuses primarily on local to national scale outcomes, + its effectiveness can be enhanced through coordination across governance scales, + including international cooperation. In fact, international cooperation has helped + to facilitate the creation of adaptation strategies, plans, and actions at national, + sub-national, and local levels. A variety of climate policy instruments have been + employed, and even more could be employed, at international and regional levels + to address mitigation and to support and promote adaptation at national and sub-national + scales. Evidence suggests that outcomes seen as equitable can lead to more effective + cooperation. The United Nations Framework Convention on Climate Change is the + main multilateral forum focused on addressing climate change, with nearly universal + participation. UNFCCC activities since 2007, which include the 2010 Cancún Agreements + and the 2011 Durban Platform for Enhanced Action, have sought to enhance actions + under the Convention, and have led to an increasing number of institutions and + other arrangements for international climate change cooperation. Other institutions + organized at different levels of governance have resulted in diversifying international + climate change cooperation. Existing and proposed international climate change + cooperation arrangements vary in their focus and degree of centralization and + coordination. They span: multilateral agreements, harmonized national policies + and decentralized but coordinated national policies, as well as regional and regionally-coordinated + policies . While a number of new institutions are focused on adaptation funding + and coordination, adaptation has historically received less attention than mitigation + in international climate policy . Inclusion of adaptation is increasingly important + to reduce the risk from climate change impacts and may engage a greater number + of countries. The Kyoto Protocol offers lessons towards achieving the ultimate + objective of the UNFCCC, particularly with respect to participation, implementation, + flexibility mechanisms, and environmental effectiveness. The Protocol was the + first binding step toward implementing the principles and goals provided by the + UNFCCC. According to national GHG inventories through 2012 submitted to the UNFCCC + by October 2013, Annex B Parties with quantified emission limitations in aggregate + may have bettered their collective emission reduction target in the first commitment + period, but some emissions reductions that would have occurred even in its absence + were also counted. The Protocol’s Clean Development Mechanism created a market + for emissions offsets from developing countries, the purpose being two-fold: to + help Annex I countries fulfill their commitments and to assist non-Annex I countries + achieve sustainable development. The CDM generated Certified Emission Reductions + equivalent to emissions of over 1.4 GtCO2-eqby October 2013, led to significant + project investments, and generated investment flows for a variety of functions, + including the UNFCCC Adaptation Fund. However, its environmental effectiveness + has been questioned by some, particularly in regard to its early years, due to + concerns about the additionality of projects , the validity of baselines, and + the possibility of emissions leakage . Such concerns about additionality are common + to any emission-reduction-credit program, and are not specific to the CDM. Due + to market forces, the majority of single CDM projects have been concentrated in + a limited number of countries, while Programmes of Activities, though less frequent, + have been more evenly distributed. In addition, the Kyoto Protocol created two + other ‘flexibility mechanisms’: Joint Implementation and International Emissions + Trading. Several conceptual models for effort-sharing have been identified in + research. However, realized distributional impacts from actual international cooperative + agreements depend not only on the approach taken but also on criteria applied + to operationalize equity and the manner in which developing countries’ emissions + reduction plans are financed. Policy linkages among regional, national and sub-national + climate policies offer potential climate change mitigation benefits. Linkages + have been established between carbon markets and in principle could also be established + between and among a heterogeneous set of policy instruments including non-market-based + policies, such as performance standards. Potential advantages include lower mitigation + costs, decreased emission leakage and increased market liquidity. Regional initiatives + between national and global scales are being developed and implemented, but their + impact on global mitigation has been limited to date. Some climate policies could + be more environmentally and economically effective if implemented across broad + regions, such as by embodying mitigation objectives in trade agreements or jointly + constructing infrastructures that facilitate reduction in carbon emissions. International + cooperation for supporting adaptation planning and implementation has assisted + in the creation of adaptation strategies, plans and actions at national, sub-national + and local levels. For example, a range of multilateral and regionally targeted + funding mechanisms have been established for adaptation; UN agencies, international + development organizations and non-governmental organisations have provided information, + methodologies and guidelines; and global and regional initiatives supported and + promoted the creation of national adaptation strategies in both developing and + developed countries. Closer integration of disaster risk reduction and climate + change adaptation at the international level, and the mainstreaming of both into + international development assistance, may foster greater efficiency in the use + of resources and capacity. However, stronger efforts at the international level + do not necessarily lead to substantive and rapid results at the local level.' + 4.4g: + - 'Adaptation Adaptation experience is accumulating across regions in the public + and private sector and within communities . Adaptation options adopted to date + emphasize incremental adjustments and co-benefits and are starting to emphasize + flexibility and learning. Most assessments of adaptation have been restricted + to impacts, vulnerability and adaptation planning, with very few assessing the + processes of implementation or the effects of adaptation actions . National governments + play key roles in adaptation planning and implementation. There has been substantial + progress since the AR4 in the development of national adaptation strategies and + plans. This includes National Adaptation Programmes of Action by least developed + countries, the National Adaptation Plan process, and strategic frameworks for + national adaptation in Organisation for Economic Co-operation and Development + countries. National governments can coordinate adaptation efforts of local and + sub-national governments, for example by protecting vulnerable groups, by supporting + economic diversification, and by providing information, policy and legal frameworks + and financial support. While local government and the private sector have different + functions, which vary regionally, they are increasingly recognized as critical + to progress in adaptation, given their roles in scaling up adaptation of communities, + households and civil society and in managing risk information and financing . + There is a significant increase in the number of planned adaptation responses + at the local level in rural and urban communities of developed and developing + countries since the AR4. However, local councils and planners are often confronted + by the complexity of adaptation without adequate access to guiding information + or data on local vulnerabilities and potential impacts. Steps for mainstreaming + adaptation into local decision-making have been identified but challenges remain + in their implementation. Hence, scholars stress the important role of linkages + with national and sub-national levels of government as well as partnerships among + public, civic and private sectors in implementing local adaptation responses. Institutional + dimensions of adaptation governance, including the integration of adaptation into + planning and decision-making, play a key role in promoting the transition from + planning to implementation of adaptation . The most commonly emphasized institutional + barriers or enablers for adaptation planning and implementation are: 1) multilevel + institutional co-ordination between different political and administrative levels + in society; 2) key actors, advocates and champions initiating, mainstreaming and + sustaining momentum for climate adaptation; 3) horizontal interplay between sectors, + actors and policies operating at similar administrative levels; 4) political dimensions + in planning and implementation; and 5) coordination between formal governmental, + administrative agencies and private sectors and stakeholders to increase efficiency, + representation and support for climate adaptation measures. Existing and emerging + economic instruments can foster adaptation by providing incentives for anticipating + and reducing impacts. Instruments include public-private finance partnerships, + loans, payments for environmental services, improved resource pricing, charges + and subsidies, norms and regulations and risk sharing and transfer mechanisms. + Risk financing mechanisms in the public and private sector, such as insurance + and risk pools, can contribute to increasing resilience, but without attention + to major design challenges, they can also provide disincentives, cause market + failure and decrease equity. Governments often play key roles as regulators, providers + or insurers of last resort.' + - 'Mitigation There has been a considerable increase in national and subnational + mitigation plans and strategies since AR4. In 2012, 67% of global GHG emissions + were subject to national legislation or strategies versus 45% in 2007. However, + there has not yet been a substantial deviation in global emissions from the past + trend. These plans and strategies are in their early stages of development and + implementation in many countries, making it difficult to assess their aggregate + impact on future global emissions. Since AR4, there has been an increased focus + on policies designed to integrate multiple objectives, increase co-benefits and + reduce adverse side effects. Governments often explicitly reference co-benefits + in climate and sectoral plans and strategies. Sector-specific policies have been + more widely used than economy-wide policies . Although most economic theory suggests + that economy-wide policies for mitigation would be more cost-effective than sector-specific + policies, administrative and political barriers may make economy-wide policies + harder to design and implement than sector-specific policies. The latter may be + better suited to address barriers or market failures specific to certain sectors + and may be bundled in packages of complementary policies In principle, mechanisms + that set a carbon price, including cap and trade systems and carbon taxes, can + achieve mitigation in a cost-effective way, but have been implemented with diverse + effects due in part to national circumstances as well as policy design. The short-run + environmental effects of cap and trade systems have been limited as a result of + loose caps or caps that have not proved to be constraining. In some countries, + tax-based policies specifically aimed at reducing GHG emissions—alongside technology + and other policies—have helped to weaken the link between GHG emissions and gross + domestic product . In addition, in a large group of countries, fuel taxes have + had effects that are akin to sectoral carbon taxes . Revenues from carbon taxes + or auctioned emission allowances are used in some countries to reduce other taxes + and/or to provide transfers to low-income groups. This illustrates the general + principle that mitigation policies that raise government revenue generally have + lower social costs than approaches which do not. Economic instruments in the + form of subsidies may be applied across sectors, and include a variety of policy + designs, such as tax rebates or exemptions, grants, loans and credit lines. An + increasing number and variety of RE policies including subsidies—motivated by + many factors—have driven escalated growth of RE technologies in recent years. + Government policies play a crucial role in accelerating the deployment of RE technologies. + Energy access and social and economic development have been the primary drivers + in most developing countries whereas secure energy supply and environmental concerns + have been most important in developed countries. The focus of policies is broadening + from a concentration primarily on RE electricity to include RE heating and cooling + and transportation. The reduction of subsidies for GHG-related activities in + various sectors can achieve emission reductions, depending on the social and economic + context. While subsidies can affect emissions in many sectors, most of the recent + literature has focused on subsidies for fossil fuels. Since AR4 a small but growing + literature based on economy-wide models has projected that complete removal of + subsidies to fossil fuels in all countries could result in reductions in global + aggregate emissions by mid-century . Studies vary in methodology, the type and + definition of subsidies and the time frame for phase out considered. In particular, + the studies assess the impacts of complete removal of all fossil fuel subsides + without seeking to assess which subsidies are wasteful and inefficient, keeping + in mind national circumstances. Regulatory approaches and information measures + are widely used and are often environmentally effective . Examples of regulatory + approaches include energy efficiency standards; examples of information programmes + include labelling programmes that can help consumers make better-informed decisions. Mitigation + policy could devalue fossil fuel assets and reduce revenues for fossil fuel exporters, + but differences between regions and fuels exist. Most mitigation scenarios are + associated with reduced revenues from coal and oil trade for major exporters. + The effect on natural gas export revenues is more uncertain. The availability + of CCS would reduce the adverse effect of mitigation on the value of fossil fuel + assets. Interactions between or among mitigation policies may be synergistic + or may have no additive effect on reducing emissions . For instance, a carbon + tax can have an additive environmental effect to policies such as subsidies for + the supply of RE. By contrast, if a cap and trade system has a sufficiently stringent + cap to affect emission-related decisions, then other policies have no further + impact on reducing emissions . In either case, additional policies may be needed + to address market failures relating to innovation and technology diffusion. Sub-national + climate policies are increasingly prevalent, both in countries with national policies + and in those without. These policies include state and provincial climate plans + combining market, regulatory and information instruments, and sub-national cap-and-trade + systems. In addition, transnational cooperation has arisen among sub-national + actors, notably among institutional investors, NGOs seeking to govern carbon offset + markets, and networks of cities seeking to collaborate in generating low-carbon + urban development. Co-benefits and adverse side effects of mitigation could affect + achievement of other objectives such as those related to human health, food security, + biodiversity, local environmental quality, energy access, livelihoods and equitable + sustainable development: • Mitigation scenarios reaching about 450 or 500 ppm + CO2-equivalent by 2100 show reduced costs for achieving air quality and energy + security objectives, with significant co-benefits for human health, ecosystem + impacts and sufficiency of resources and resilience of the energy system. • Some + mitigation policies raise the prices for some energy services and could hamper + the ability of societies to expand access to modern energy services to underserved + populations . These potential adverse side effects can be avoided with the adoption + of complementary policies such as income tax rebates or other benefit transfer + mechanisms. The costs of achieving nearly universal access to electricity and + clean fuels for cooking and heating are projected to be between USD 72 to 95 billion + per year until 2030 with minimal effects on GHG emissions and multiple benefits + in health and air pollutant reduction. Whether or not side effects materialize, + and to what extent side effects materialize, will be case- and site-specific, + and depend on local circumstances and the scale, scope and pace of implementation. + Many co-benefits and adverse side effects have not been well-quantified.' + 4.4l: + - 'Mitigation There has been a considerable increase in national and subnational + mitigation plans and strategies since AR4. In 2012, 67% of global GHG emissions + were subject to national legislation or strategies versus 45% in 2007. However, + there has not yet been a substantial deviation in global emissions from the past + trend. These plans and strategies are in their early stages of development and + implementation in many countries, making it difficult to assess their aggregate + impact on future global emissions. Since AR4, there has been an increased focus + on policies designed to integrate multiple objectives, increase co-benefits and + reduce adverse side effects. Governments often explicitly reference co-benefits + in climate and sectoral plans and strategies. Sector-specific policies have been + more widely used than economy-wide policies . Although most economic theory suggests + that economy-wide policies for mitigation would be more cost-effective than sector-specific + policies, administrative and political barriers may make economy-wide policies + harder to design and implement than sector-specific policies. The latter may be + better suited to address barriers or market failures specific to certain sectors + and may be bundled in packages of complementary policies In principle, mechanisms + that set a carbon price, including cap and trade systems and carbon taxes, can + achieve mitigation in a cost-effective way, but have been implemented with diverse + effects due in part to national circumstances as well as policy design. The short-run + environmental effects of cap and trade systems have been limited as a result of + loose caps or caps that have not proved to be constraining. In some countries, + tax-based policies specifically aimed at reducing GHG emissions—alongside technology + and other policies—have helped to weaken the link between GHG emissions and gross + domestic product . In addition, in a large group of countries, fuel taxes have + had effects that are akin to sectoral carbon taxes . Revenues from carbon taxes + or auctioned emission allowances are used in some countries to reduce other taxes + and/or to provide transfers to low-income groups. This illustrates the general + principle that mitigation policies that raise government revenue generally have + lower social costs than approaches which do not. Economic instruments in the + form of subsidies may be applied across sectors, and include a variety of policy + designs, such as tax rebates or exemptions, grants, loans and credit lines. An + increasing number and variety of RE policies including subsidies—motivated by + many factors—have driven escalated growth of RE technologies in recent years. + Government policies play a crucial role in accelerating the deployment of RE technologies. + Energy access and social and economic development have been the primary drivers + in most developing countries whereas secure energy supply and environmental concerns + have been most important in developed countries. The focus of policies is broadening + from a concentration primarily on RE electricity to include RE heating and cooling + and transportation. The reduction of subsidies for GHG-related activities in + various sectors can achieve emission reductions, depending on the social and economic + context. While subsidies can affect emissions in many sectors, most of the recent + literature has focused on subsidies for fossil fuels. Since AR4 a small but growing + literature based on economy-wide models has projected that complete removal of + subsidies to fossil fuels in all countries could result in reductions in global + aggregate emissions by mid-century . Studies vary in methodology, the type and + definition of subsidies and the time frame for phase out considered. In particular, + the studies assess the impacts of complete removal of all fossil fuel subsides + without seeking to assess which subsidies are wasteful and inefficient, keeping + in mind national circumstances. Regulatory approaches and information measures + are widely used and are often environmentally effective . Examples of regulatory + approaches include energy efficiency standards; examples of information programmes + include labelling programmes that can help consumers make better-informed decisions. Mitigation + policy could devalue fossil fuel assets and reduce revenues for fossil fuel exporters, + but differences between regions and fuels exist. Most mitigation scenarios are + associated with reduced revenues from coal and oil trade for major exporters. + The effect on natural gas export revenues is more uncertain. The availability + of CCS would reduce the adverse effect of mitigation on the value of fossil fuel + assets. Interactions between or among mitigation policies may be synergistic + or may have no additive effect on reducing emissions . For instance, a carbon + tax can have an additive environmental effect to policies such as subsidies for + the supply of RE. By contrast, if a cap and trade system has a sufficiently stringent + cap to affect emission-related decisions, then other policies have no further + impact on reducing emissions . In either case, additional policies may be needed + to address market failures relating to innovation and technology diffusion. Sub-national + climate policies are increasingly prevalent, both in countries with national policies + and in those without. These policies include state and provincial climate plans + combining market, regulatory and information instruments, and sub-national cap-and-trade + systems. In addition, transnational cooperation has arisen among sub-national + actors, notably among institutional investors, NGOs seeking to govern carbon offset + markets, and networks of cities seeking to collaborate in generating low-carbon + urban development. Co-benefits and adverse side effects of mitigation could affect + achievement of other objectives such as those related to human health, food security, + biodiversity, local environmental quality, energy access, livelihoods and equitable + sustainable development: • Mitigation scenarios reaching about 450 or 500 ppm + CO2-equivalent by 2100 show reduced costs for achieving air quality and energy + security objectives, with significant co-benefits for human health, ecosystem + impacts and sufficiency of resources and resilience of the energy system. • Some + mitigation policies raise the prices for some energy services and could hamper + the ability of societies to expand access to modern energy services to underserved + populations . These potential adverse side effects can be avoided with the adoption + of complementary policies such as income tax rebates or other benefit transfer + mechanisms. The costs of achieving nearly universal access to electricity and + clean fuels for cooking and heating are projected to be between USD 72 to 95 billion + per year until 2030 with minimal effects on GHG emissions and multiple benefits + in health and air pollutant reduction. Whether or not side effects materialize, + and to what extent side effects materialize, will be case- and site-specific, + and depend on local circumstances and the scale, scope and pace of implementation. + Many co-benefits and adverse side effects have not been well-quantified.' + 4.4m: + - 'Mitigation There has been a considerable increase in national and subnational + mitigation plans and strategies since AR4. In 2012, 67% of global GHG emissions + were subject to national legislation or strategies versus 45% in 2007. However, + there has not yet been a substantial deviation in global emissions from the past + trend. These plans and strategies are in their early stages of development and + implementation in many countries, making it difficult to assess their aggregate + impact on future global emissions. Since AR4, there has been an increased focus + on policies designed to integrate multiple objectives, increase co-benefits and + reduce adverse side effects. Governments often explicitly reference co-benefits + in climate and sectoral plans and strategies. Sector-specific policies have been + more widely used than economy-wide policies . Although most economic theory suggests + that economy-wide policies for mitigation would be more cost-effective than sector-specific + policies, administrative and political barriers may make economy-wide policies + harder to design and implement than sector-specific policies. The latter may be + better suited to address barriers or market failures specific to certain sectors + and may be bundled in packages of complementary policies In principle, mechanisms + that set a carbon price, including cap and trade systems and carbon taxes, can + achieve mitigation in a cost-effective way, but have been implemented with diverse + effects due in part to national circumstances as well as policy design. The short-run + environmental effects of cap and trade systems have been limited as a result of + loose caps or caps that have not proved to be constraining. In some countries, + tax-based policies specifically aimed at reducing GHG emissions—alongside technology + and other policies—have helped to weaken the link between GHG emissions and gross + domestic product . In addition, in a large group of countries, fuel taxes have + had effects that are akin to sectoral carbon taxes . Revenues from carbon taxes + or auctioned emission allowances are used in some countries to reduce other taxes + and/or to provide transfers to low-income groups. This illustrates the general + principle that mitigation policies that raise government revenue generally have + lower social costs than approaches which do not. Economic instruments in the + form of subsidies may be applied across sectors, and include a variety of policy + designs, such as tax rebates or exemptions, grants, loans and credit lines. An + increasing number and variety of RE policies including subsidies—motivated by + many factors—have driven escalated growth of RE technologies in recent years. + Government policies play a crucial role in accelerating the deployment of RE technologies. + Energy access and social and economic development have been the primary drivers + in most developing countries whereas secure energy supply and environmental concerns + have been most important in developed countries. The focus of policies is broadening + from a concentration primarily on RE electricity to include RE heating and cooling + and transportation. The reduction of subsidies for GHG-related activities in + various sectors can achieve emission reductions, depending on the social and economic + context. While subsidies can affect emissions in many sectors, most of the recent + literature has focused on subsidies for fossil fuels. Since AR4 a small but growing + literature based on economy-wide models has projected that complete removal of + subsidies to fossil fuels in all countries could result in reductions in global + aggregate emissions by mid-century . Studies vary in methodology, the type and + definition of subsidies and the time frame for phase out considered. In particular, + the studies assess the impacts of complete removal of all fossil fuel subsides + without seeking to assess which subsidies are wasteful and inefficient, keeping + in mind national circumstances. Regulatory approaches and information measures + are widely used and are often environmentally effective . Examples of regulatory + approaches include energy efficiency standards; examples of information programmes + include labelling programmes that can help consumers make better-informed decisions. Mitigation + policy could devalue fossil fuel assets and reduce revenues for fossil fuel exporters, + but differences between regions and fuels exist. Most mitigation scenarios are + associated with reduced revenues from coal and oil trade for major exporters. + The effect on natural gas export revenues is more uncertain. The availability + of CCS would reduce the adverse effect of mitigation on the value of fossil fuel + assets. Interactions between or among mitigation policies may be synergistic + or may have no additive effect on reducing emissions . For instance, a carbon + tax can have an additive environmental effect to policies such as subsidies for + the supply of RE. By contrast, if a cap and trade system has a sufficiently stringent + cap to affect emission-related decisions, then other policies have no further + impact on reducing emissions . In either case, additional policies may be needed + to address market failures relating to innovation and technology diffusion. Sub-national + climate policies are increasingly prevalent, both in countries with national policies + and in those without. These policies include state and provincial climate plans + combining market, regulatory and information instruments, and sub-national cap-and-trade + systems. In addition, transnational cooperation has arisen among sub-national + actors, notably among institutional investors, NGOs seeking to govern carbon offset + markets, and networks of cities seeking to collaborate in generating low-carbon + urban development. Co-benefits and adverse side effects of mitigation could affect + achievement of other objectives such as those related to human health, food security, + biodiversity, local environmental quality, energy access, livelihoods and equitable + sustainable development: • Mitigation scenarios reaching about 450 or 500 ppm + CO2-equivalent by 2100 show reduced costs for achieving air quality and energy + security objectives, with significant co-benefits for human health, ecosystem + impacts and sufficiency of resources and resilience of the energy system. • Some + mitigation policies raise the prices for some energy services and could hamper + the ability of societies to expand access to modern energy services to underserved + populations . These potential adverse side effects can be avoided with the adoption + of complementary policies such as income tax rebates or other benefit transfer + mechanisms. The costs of achieving nearly universal access to electricity and + clean fuels for cooking and heating are projected to be between USD 72 to 95 billion + per year until 2030 with minimal effects on GHG emissions and multiple benefits + in health and air pollutant reduction. Whether or not side effects materialize, + and to what extent side effects materialize, will be case- and site-specific, + and depend on local circumstances and the scale, scope and pace of implementation. + Many co-benefits and adverse side effects have not been well-quantified.' + 4.4n: + - 'Mitigation There has been a considerable increase in national and subnational + mitigation plans and strategies since AR4. In 2012, 67% of global GHG emissions + were subject to national legislation or strategies versus 45% in 2007. However, + there has not yet been a substantial deviation in global emissions from the past + trend. These plans and strategies are in their early stages of development and + implementation in many countries, making it difficult to assess their aggregate + impact on future global emissions. Since AR4, there has been an increased focus + on policies designed to integrate multiple objectives, increase co-benefits and + reduce adverse side effects. Governments often explicitly reference co-benefits + in climate and sectoral plans and strategies. Sector-specific policies have been + more widely used than economy-wide policies . Although most economic theory suggests + that economy-wide policies for mitigation would be more cost-effective than sector-specific + policies, administrative and political barriers may make economy-wide policies + harder to design and implement than sector-specific policies. The latter may be + better suited to address barriers or market failures specific to certain sectors + and may be bundled in packages of complementary policies In principle, mechanisms + that set a carbon price, including cap and trade systems and carbon taxes, can + achieve mitigation in a cost-effective way, but have been implemented with diverse + effects due in part to national circumstances as well as policy design. The short-run + environmental effects of cap and trade systems have been limited as a result of + loose caps or caps that have not proved to be constraining. In some countries, + tax-based policies specifically aimed at reducing GHG emissions—alongside technology + and other policies—have helped to weaken the link between GHG emissions and gross + domestic product . In addition, in a large group of countries, fuel taxes have + had effects that are akin to sectoral carbon taxes . Revenues from carbon taxes + or auctioned emission allowances are used in some countries to reduce other taxes + and/or to provide transfers to low-income groups. This illustrates the general + principle that mitigation policies that raise government revenue generally have + lower social costs than approaches which do not. Economic instruments in the + form of subsidies may be applied across sectors, and include a variety of policy + designs, such as tax rebates or exemptions, grants, loans and credit lines. An + increasing number and variety of RE policies including subsidies—motivated by + many factors—have driven escalated growth of RE technologies in recent years. + Government policies play a crucial role in accelerating the deployment of RE technologies. + Energy access and social and economic development have been the primary drivers + in most developing countries whereas secure energy supply and environmental concerns + have been most important in developed countries. The focus of policies is broadening + from a concentration primarily on RE electricity to include RE heating and cooling + and transportation. The reduction of subsidies for GHG-related activities in + various sectors can achieve emission reductions, depending on the social and economic + context. While subsidies can affect emissions in many sectors, most of the recent + literature has focused on subsidies for fossil fuels. Since AR4 a small but growing + literature based on economy-wide models has projected that complete removal of + subsidies to fossil fuels in all countries could result in reductions in global + aggregate emissions by mid-century . Studies vary in methodology, the type and + definition of subsidies and the time frame for phase out considered. In particular, + the studies assess the impacts of complete removal of all fossil fuel subsides + without seeking to assess which subsidies are wasteful and inefficient, keeping + in mind national circumstances. Regulatory approaches and information measures + are widely used and are often environmentally effective . Examples of regulatory + approaches include energy efficiency standards; examples of information programmes + include labelling programmes that can help consumers make better-informed decisions. Mitigation + policy could devalue fossil fuel assets and reduce revenues for fossil fuel exporters, + but differences between regions and fuels exist. Most mitigation scenarios are + associated with reduced revenues from coal and oil trade for major exporters. + The effect on natural gas export revenues is more uncertain. The availability + of CCS would reduce the adverse effect of mitigation on the value of fossil fuel + assets. Interactions between or among mitigation policies may be synergistic + or may have no additive effect on reducing emissions . For instance, a carbon + tax can have an additive environmental effect to policies such as subsidies for + the supply of RE. By contrast, if a cap and trade system has a sufficiently stringent + cap to affect emission-related decisions, then other policies have no further + impact on reducing emissions . In either case, additional policies may be needed + to address market failures relating to innovation and technology diffusion. Sub-national + climate policies are increasingly prevalent, both in countries with national policies + and in those without. These policies include state and provincial climate plans + combining market, regulatory and information instruments, and sub-national cap-and-trade + systems. In addition, transnational cooperation has arisen among sub-national + actors, notably among institutional investors, NGOs seeking to govern carbon offset + markets, and networks of cities seeking to collaborate in generating low-carbon + urban development. Co-benefits and adverse side effects of mitigation could affect + achievement of other objectives such as those related to human health, food security, + biodiversity, local environmental quality, energy access, livelihoods and equitable + sustainable development: • Mitigation scenarios reaching about 450 or 500 ppm + CO2-equivalent by 2100 show reduced costs for achieving air quality and energy + security objectives, with significant co-benefits for human health, ecosystem + impacts and sufficiency of resources and resilience of the energy system. • Some + mitigation policies raise the prices for some energy services and could hamper + the ability of societies to expand access to modern energy services to underserved + populations . These potential adverse side effects can be avoided with the adoption + of complementary policies such as income tax rebates or other benefit transfer + mechanisms. The costs of achieving nearly universal access to electricity and + clean fuels for cooking and heating are projected to be between USD 72 to 95 billion + per year until 2030 with minimal effects on GHG emissions and multiple benefits + in health and air pollutant reduction. Whether or not side effects materialize, + and to what extent side effects materialize, will be case- and site-specific, + and depend on local circumstances and the scale, scope and pace of implementation. + Many co-benefits and adverse side effects have not been well-quantified.' + 4.4p: + - Response options for mitigation Mitigation options are available in every major + sector. Mitigation can be more cost-effective if using an integrated approach + that combines measures to reduce energy use and the greenhouse gas intensity of + end-use sectors, decarbonize energy supply, reduce net emissions and enhance carbon + sinks in land-based sectors. A broad range of sectoral mitigation options is available + that can reduce GHG emission intensity, improve energy intensity through enhancements + of technology, behaviour, production and resource efficiency and enable structural + changes or changes in activity. In addition, direct options in agriculture, forestry + and other land use involve reducing CO2 emissions by reducing deforestation, forest + degradation and forest fires; storing carbon in terrestrial systems; and providing + bioenergy feedstocks. Options to reduce non-CO2 emissions exist across all sectors + but most notably in agriculture, energy supply and industry. An overview of sectoral + mitigation options and potentials is provided in Table 4.4. Well-designed systemic + and cross-sectoral mitigation strategies are more cost-effective in cutting emissions + than a focus on individual technologies and sectors with efforts in one sector + affecting the need for mitigation in others . In baseline scenarios without new + mitigation policies, GHG emissions are projected to grow in all sectors, except + for net CO2 emissions in the AFOLU sector. Mitigation scenarios reaching around + 450 ppm CO2-eq concentration by 21004328 show largescale global changes in the + energy supply sector . While rapid decarbonization of energy supply generally + entails more flexibility for end-use and AFOLU sectors, stronger demand reductions + lessen the mitigation challenge for the supply side of the energy system. There + are thus strong interdependencies across sectors and the resulting distribution + of the mitigation effort is strongly influenced by the availability and performance + of future technologies, particularly BECCS and large scale afforestation . The + next two decades present a window of opportunity for mitigation in urban areas, + as a large portion of the world’s urban areas will be developed during this period. Decarbonizing + electricity generation is a key component of cost-effective mitigation strategies + in achieving low stabilization levels . In most integrated modelling scenarios, + decarbonization happens more rapidly in electricity generation than in the industry, + buildings and transport sectors. In scenarios reaching 450 ppm CO2-eq concentrations + by 2100, global CO2 emissions from the energy supply sector are projected to decline + over the next decade and are characterized by reductions of 90% or more below + 2010 levels between 2040 and 2070. Efficiency enhancements and behavioural changes, + in order to reduce energy demand compared to baseline scenarios without compromising + development, are a key mitigation strategy in scenarios reaching atmospheric CO2-eq + concentrations of about 450 to about 500 ppm by 2100 . Near-term reductions in + energy demand are an important element of cost-effective mitigation strategies, + provide more flexibility for reducing carbon intensity in the energy supply sector, + hedge against related supply-side risks, avoid lock-in to carbon-intensive infrastructures + and are associated with important co-benefits . Emissions can be substantially + lowered through changes in consumption patterns and dietary change and reduction + in food wastes. A number of options including monetary and non-monetary incentives + as well as information measures may facilitate behavioural changes. Decarbonization + of the energy supply sector requires upscaling of low- and zero-carbon electricity + generation technologies. In the majority of low-concentration stabilization scenarios + , the share of low-carbon electricity supply, nuclear and CCS, including BECCS) + increases from the current share of approximately 30% to more than 80% by 2050 + and 90% by 2100, and fossil fuel power generation without CCS is phased out almost + entirely by 2100. Among these low-carbon technologies, a growing number of RE + technologies have achieved a level of maturity to enable deployment at significant + scale since AR4 and nuclear energy is a mature low-GHG emission source of baseload + power, but its share of global electricity generation has been declining. GHG + emissions from energy supply can be reduced significantly by replacing current + world average coal-fired power plants with modern, highly efficient natural gas + combined-cycle power plants or combined heat and power plants, provided that natural + gas is available and the fugitive emissions associated with extraction and supply + are low or mitigated. Behaviour, lifestyle and culture have a considerable influence + on energy use and associated emissions, with high mitigation potential in some + sectors, in particular when complementing technological and structural change + . In the transport sector, technical and behavioural mitigation measures for all + modes, plus new infrastructure and urban redevelopment investments, could reduce + final energy demand significantly below baseline levels. While opportunities for + switching to low-carbon fuels exist, the rate of decarbonization in the transport + sector might be constrained by challenges associated with energy storage and the + relatively low energy density of low-carbon transport fuels. In the building sector, + recent advances in technologies, know-how and policies provide opportunities to + stabilize or reduce global energy use to about current levels by mid-century. + In addition, recent improvements in performance and costs make very low energy + construction and retrofits of buildings economically attractive, sometimes even + at net negative costs. In the industry sector, improvements in GHG emission efficiency + and in the efficiency of material use, recycling and reuse of materials and products, + and overall reductions in product demand and service demand could, in addition + to energy efficiency, help reduce GHG emissions below the baseline level. Prevalent + approaches for promoting energy efficiency in industry include information programmes + followed by economic instruments, regulatory approaches and voluntary actions. + Important options for mitigation in waste management are waste reduction, followed + by re-use, recycling and energy recovery. The most cost-effective mitigation + options in forestry are afforestation, sustainable forest management and reducing + deforestation, with large differences in their relative importance across regions. + In agriculture, the most cost-effective mitigation options are cropland management, + grazing land management and restoration of organic soils . About a third of mitigation + potential in forestry can be achieved at a cost <20 USD/tCO2-eq emission. Demand-side + measures, such as changes in diet and reductions of losses in the food supply + chain, have a significant, but uncertain, potential to reduce GHG emissions from + food production . Bioenergy can play a critical role for mitigation, but there + are issues to consider, such as the sustainability of practices and the efficiency + of bioenergy systems . Evidence suggests that bioenergy options with low lifecycle + emissions, some already available, can reduce GHG emissions; outcomes are site-specific + and rely on efficient integrated ‘biomassto-bioenergy systems’, and sustainable + land use management and governance. Barriers to large-scale deployment of bioenergy + include concerns about GHG emissions from land, food security, water resources, + biodiversity conservation and livelihoods. Mitigation measures intersect with + other societal goals, creating the possibility of co-benefits or adverse side-effects. + These intersections, if well-managed, can strengthen the basis for undertaking + climate mitigation actions . Mitigation can positively or negatively influence + the achievement of other societal goals, such as those related to human health, + food security, biodiversity, local environmental quality, energy access, livelihoods + and equitable sustainable development . On the other hand, policies towards other + societal goals can influence the achievement of mitigation and adaptation objectives. + These influences can be substantial, although sometimes difficult to quantify, + especially in welfare terms. This multi-objective perspective is important in + part because it helps to identify areas where support for policies that advance + multiple goals will be robust. Potential co-benefits and adverse side effects + of the main sectoral mitigation measures are summarized in Table 4.5. Overall, + the potential for co-benefits for energy end-use measures outweigh the potential + for adverse side effects, whereas the evidence suggests this may not be the case + for all energy supply and AFOLU measures. + - 'Mitigation There has been a considerable increase in national and subnational + mitigation plans and strategies since AR4. In 2012, 67% of global GHG emissions + were subject to national legislation or strategies versus 45% in 2007. However, + there has not yet been a substantial deviation in global emissions from the past + trend. These plans and strategies are in their early stages of development and + implementation in many countries, making it difficult to assess their aggregate + impact on future global emissions. Since AR4, there has been an increased focus + on policies designed to integrate multiple objectives, increase co-benefits and + reduce adverse side effects. Governments often explicitly reference co-benefits + in climate and sectoral plans and strategies. Sector-specific policies have been + more widely used than economy-wide policies . Although most economic theory suggests + that economy-wide policies for mitigation would be more cost-effective than sector-specific + policies, administrative and political barriers may make economy-wide policies + harder to design and implement than sector-specific policies. The latter may be + better suited to address barriers or market failures specific to certain sectors + and may be bundled in packages of complementary policies In principle, mechanisms + that set a carbon price, including cap and trade systems and carbon taxes, can + achieve mitigation in a cost-effective way, but have been implemented with diverse + effects due in part to national circumstances as well as policy design. The short-run + environmental effects of cap and trade systems have been limited as a result of + loose caps or caps that have not proved to be constraining. In some countries, + tax-based policies specifically aimed at reducing GHG emissions—alongside technology + and other policies—have helped to weaken the link between GHG emissions and gross + domestic product . In addition, in a large group of countries, fuel taxes have + had effects that are akin to sectoral carbon taxes . Revenues from carbon taxes + or auctioned emission allowances are used in some countries to reduce other taxes + and/or to provide transfers to low-income groups. This illustrates the general + principle that mitigation policies that raise government revenue generally have + lower social costs than approaches which do not. Economic instruments in the + form of subsidies may be applied across sectors, and include a variety of policy + designs, such as tax rebates or exemptions, grants, loans and credit lines. An + increasing number and variety of RE policies including subsidies—motivated by + many factors—have driven escalated growth of RE technologies in recent years. + Government policies play a crucial role in accelerating the deployment of RE technologies. + Energy access and social and economic development have been the primary drivers + in most developing countries whereas secure energy supply and environmental concerns + have been most important in developed countries. The focus of policies is broadening + from a concentration primarily on RE electricity to include RE heating and cooling + and transportation. The reduction of subsidies for GHG-related activities in + various sectors can achieve emission reductions, depending on the social and economic + context. While subsidies can affect emissions in many sectors, most of the recent + literature has focused on subsidies for fossil fuels. Since AR4 a small but growing + literature based on economy-wide models has projected that complete removal of + subsidies to fossil fuels in all countries could result in reductions in global + aggregate emissions by mid-century . Studies vary in methodology, the type and + definition of subsidies and the time frame for phase out considered. In particular, + the studies assess the impacts of complete removal of all fossil fuel subsides + without seeking to assess which subsidies are wasteful and inefficient, keeping + in mind national circumstances. Regulatory approaches and information measures + are widely used and are often environmentally effective . Examples of regulatory + approaches include energy efficiency standards; examples of information programmes + include labelling programmes that can help consumers make better-informed decisions. Mitigation + policy could devalue fossil fuel assets and reduce revenues for fossil fuel exporters, + but differences between regions and fuels exist. Most mitigation scenarios are + associated with reduced revenues from coal and oil trade for major exporters. + The effect on natural gas export revenues is more uncertain. The availability + of CCS would reduce the adverse effect of mitigation on the value of fossil fuel + assets. Interactions between or among mitigation policies may be synergistic + or may have no additive effect on reducing emissions . For instance, a carbon + tax can have an additive environmental effect to policies such as subsidies for + the supply of RE. By contrast, if a cap and trade system has a sufficiently stringent + cap to affect emission-related decisions, then other policies have no further + impact on reducing emissions . In either case, additional policies may be needed + to address market failures relating to innovation and technology diffusion. Sub-national + climate policies are increasingly prevalent, both in countries with national policies + and in those without. These policies include state and provincial climate plans + combining market, regulatory and information instruments, and sub-national cap-and-trade + systems. In addition, transnational cooperation has arisen among sub-national + actors, notably among institutional investors, NGOs seeking to govern carbon offset + markets, and networks of cities seeking to collaborate in generating low-carbon + urban development. Co-benefits and adverse side effects of mitigation could affect + achievement of other objectives such as those related to human health, food security, + biodiversity, local environmental quality, energy access, livelihoods and equitable + sustainable development: • Mitigation scenarios reaching about 450 or 500 ppm + CO2-equivalent by 2100 show reduced costs for achieving air quality and energy + security objectives, with significant co-benefits for human health, ecosystem + impacts and sufficiency of resources and resilience of the energy system. • Some + mitigation policies raise the prices for some energy services and could hamper + the ability of societies to expand access to modern energy services to underserved + populations . These potential adverse side effects can be avoided with the adoption + of complementary policies such as income tax rebates or other benefit transfer + mechanisms. The costs of achieving nearly universal access to electricity and + clean fuels for cooking and heating are projected to be between USD 72 to 95 billion + per year until 2030 with minimal effects on GHG emissions and multiple benefits + in health and air pollutant reduction. Whether or not side effects materialize, + and to what extent side effects materialize, will be case- and site-specific, + and depend on local circumstances and the scale, scope and pace of implementation. + Many co-benefits and adverse side effects have not been well-quantified.' + 4.4q: + - Technology development and transfer Technology policy complements other mitigation + policies across all scales from international to sub-national, but worldwide investment + in research in support of GHG mitigation is small relative to overall public research + spending. Technology policy includes technology-push and demand-pull . Such policies + address a pervasive market failure because, in the absence of government policy + such as patent protection, the invention of new technologies and practices from + R&D efforts has aspects of a public good and thus tends to be under-provided by + market forces alone. Technology support policies have promoted substantial innovation + and diffusion of new technologies, but the cost-effectiveness of such policies + is often difficult to assess. Technology policy can increase incentives for participation + and compliance with international cooperative efforts, particularly in the long + run. Many adaptation efforts also critically rely on diffusion and transfer of + technologies and management practices, but their effective use depends on a suitable + institutional, regulatory, social and cultural context. Adaptation technologies + are often familiar and already applied elsewhere. However, the success of technology + transfer may involve not only the provision of finance and information, but also + strengthening of policy and regulatory environments and capacities to absorb, + employ and improve technologies appropriate to local circumstances. + 4.4r: + - Investment and finance Substantial reductions in emissions would require large + changes in investment patterns. Mitigation scenarios in which policies stabilize + atmospheric concentrations in the range from 430 to 530 ppm CO2-eq by 21004530 + lead to substantial shifts in annual investment flows during the period 2010–2029 + compared to baseline scenarios. Over the next two decades , annual investments + in conventional fossil fuel technologies associated with the electricity supply + sector are projected to decline in the scenarios by about USD 30 billion while + annual investment in low carbon electricity supply is projected to rise in the + scenarios by about USD 147 billion . In addition, annual incremental energy efficiency + investments in transport, industry and buildings is projected to rise in the scenarios + by about USD 336 billion. Global total annual investment in the energy system + is presently about USD 1, billion. This number includes only energy supply of + electricity and heat and respective upstream and downstream activities. Energy + efficiency investment or underlying sector investment is not included. There + is no widely agreed definition of what constitutes climate finance, but estimates + of the financial flows associated with climate change mitigation and adaptation + are available. See Figure 4.5 for an overview of climate finance flows. Published + assessments of all current annual financial flows whose expected effect is to + reduce net GHG emissions and/or to enhance resilience to climate change and climate + variability show USD 343 to 385 billion per year globally. Out of this, total + public climate finance that flowed to developing countries is estimated to be + between USD 35 and 49 billion per year in 2011 and 2012. Estimates of international + private climate finance flowing to developing countries range from USD 10 to 72 + billion per year including foreign direct investment as equity and loans in the + range of USD 10 to 37 billion per year over the period of 2008–2011. In many + countries, the private sector plays central roles in the processes that lead to + emissions as well as to mitigation and adaptation. Within appropriate enabling + environments, the private sector, along with the public sector, can play an important + role in financing mitigation and adaptation . The share of total mitigation finance + from the private sector, acknowledging data limitations, is estimated to be on + average between two-thirds and three-fourths on the global level . In many countries, + public finance interventions by governments and international development banks + encourage climate investments by the private sector and provide finance where + private sector investment is limited. The quality of a country’s enabling environment + includes the effectiveness of its institutions, regulations and guidelines regarding + the private sector, security of property rights, credibility of policies and other + factors that have a substantial impact on whether private firms invest in new + technologies and infrastructures. Dedicated policy instruments and financial arrangements, + for example, credit insurance, feed-in tariffs, concessional finance or rebates + provide an incentive for mitigation investment by improving the return adjusted + for the risk for private actors. Public-private risk reduction initiatives and + economic diversification are examples of adaptation action enabling and relying + on private sector participation. Financial resources for adaptation have become + available more slowly than for mitigation in both developed and developing countries. + Limited evidence indicates that there is a gap between global adaptation needs + and the funds available for adaptation. Potential synergies between international + finance for disaster risk management and adaptation to climate change have not + yet been fully realized. There is a need for better assessment of global adaptation + costs, funding and investment. Studies estimating the global cost of adaptation + are characterized by shortcomings in data, methods and coverage . + 4.5a: + - Interaction among mitigation, adaptation and sustainable development Climate + change is a threat to equitable and sustainable development. Adaptation, mitigation + and sustainable development are closely related, with potential for synergies + and trade-offs. Climate change poses an increasing threat to equitable and sustainable + development. Some climate-related impacts on development are already being observed. + Climate change is a threat multiplier. It exacerbates other threats to social + and natural systems, placing additional burdens particularly on the poor and constraining + possible development paths for all. Development along current global pathways + can contribute to climate risk and vulnerability, further eroding the basis for + sustainable development. Aligning climate policy with sustainable development + requires attention to both adaptation and mitigation. Interaction among adaptation, + mitigation and sustainable development occurs both within and across regions and + scales, often in the context of multiple stressors. Some options for responding + to climate change could impose risks of other environmental and social costs, + have adverse distributional effects and draw resources away from other development + priorities, including poverty eradication. Both adaptation and mitigation can + bring substantial co-benefits . Examples of actions with co-benefits include improved + air quality; enhanced energy security, reduced energy and water consumption in + urban areas through greening cities and recycling water; sustainable agriculture + and forestry; and protection of ecosystems for carbon storage and other ecosystem + services. Strategies and actions can be pursued now that will move towards climate-resilient + pathways for sustainable development, while at the same time helping to improve + livelihoods, social and economic well-being and effective environmental management. + Prospects for climate-resilient pathways are related fundamentally to what the + world accomplishes with climate change mitigation. Since mitigation reduces the + rate as well as the magnitude of warming, it also increases the time available + for adaptation to a particular level of climate change, potentially by several + decades. Delaying mitigation actions may reduce options for climate-resilient + pathways in the future. + - Trade-offs, synergies and integrated responses There are many opportunities to + link mitigation, adaptation and the pursuit of other societal objectives through + integrated responses. Successful implementation relies on relevant tools, suitable + governance structures and enhanced capacity to respond. A growing evidence base + indicates close links between adaptation and mitigation, their co-benefits and + adverse side effects, and recognizes sustainable development as the overarching + context for climate policy . Developing tools to address these linkages is critical + to the success of climate policy in the context of sustainable development. This + section presents examples of integrated responses in specific policy arenas, as + well as some of the factors that promote or impede policies aimed at multiple + objectives. Increasing efforts to mitigate and adapt to climate change imply an + increasing complexity of interactions, encompassing connections among human health, + water, energy, land use and biodiversity. Mitigation can support the achievement + of other societal goals, such as those related to human health, food security, + environmental quality, energy access, livelihoods and sustainable development, + although there can also be negative effects. Adaptation measures also have the + potential to deliver mitigation co-benefits, and vice versa, and support other + societal goals, though trade-offs can also arise. Integration of adaptation and + mitigation into planning and decision-making can create synergies with sustainable + development. Synergies and trade-offs among mitigation and adaptation policies + and policies advancing other societal goals can be substantial, although sometimes + difficult to quantify especially in welfare terms. A multi-objective approach + to policy-making can help manage these synergies and trade-offs. Policies advancing + multiple goals may also attract greater support. Effective integrated responses + depend on suitable tools and governance structures, as well as adequate capacity + . Managing trade-offs and synergies is challenging and requires tools to help + understand interactions and support decision-making at local and regional scales. + Integrated responses also depend on governance that enables coordination across + scales and sectors, supported by appropriate institutions. Developing and implementing + suitable tools and governance structures often requires upgrading the human and + institutional capacity to design and deploy integrated responses. An integrated + approach to energy planning and implementation that explicitly assesses the potential + for co-benefits and the presence of adverse side effects can capture complementarities + across multiple climate, social and environmental objectives . There are strong + interactive effects across various energy policy objectives, such as energy security, + air quality, health and energy access and between a range of social and environmental + objectives and climate mitigation objectives . An integrated approach can be assisted + by tools such as cost-benefit analysis, cost-effectiveness analysis, multi-criteria + analysis and expected utility theory. It also requires appropriate coordinating + institutions. Explicit consideration of interactions among water, food, energy + and biological carbon sequestration plays an important role in supporting effective + decisions for climate resilient pathways . Both biofuel-based power generation + and large-scale afforestation designed to mitigate climate change can reduce catchment + run-off, which may conflict with alternative water uses for food production, human + consumption or the maintenance of ecosystem function and services. Conversely, + irrigation can increase the climate resilience of food and fibre production but + reduces water availability for other uses. An integrated response to urbanization + provides substantial opportunities for enhanced resilience, reduced emissions + and more sustainable development. Urban areas account for more than half of global + primary energy use and energy-related CO2 emissions and contain a high proportion + of the population and economic activities at risk from climate change. In rapidly + growing and urbanizing regions, mitigation strategies based on spatial planning + and efficient infrastructure supply can avoid the lock-in of high emission patterns. + Mixed-use zoning, transport-oriented development, increased density and co-located + jobs and homes can reduce direct and indirect energy use across sectors. Compact + development of urban spaces and intelligent densification can preserve land carbon + stocks and land for agriculture and bioenergy. Reduced energy and water consumption + in urban areas through greening cities and recycling water are examples of mitigation + actions with adaptation benefits. Building resilient infrastructure systems can + reduce vulnerability of urban settlements and cities to coastal flooding, sea + level rise and other climate-induced stresses. + 4.5b: + - 'Foundations of decision-making about climate change Effective decision-making + to limit climate change and its effects can be informed by a wide range of analytical + approaches for evaluating expected risks and benefits, recognizing the importance + of governance, ethical dimensions, equity, value judgments, economic assessments + and diverse perceptions and responses to risk and uncertainty. Sustainable development + and equity provide a basis for assessing climate policies. Limiting the effects + of climate change is necessary to achieve sustainable development and equity, + including poverty eradication. Countries’ past and future contributions to the + accumulation of GHGs in the atmosphere are different, and countries also face + varying challenges and circumstances and have different capacities to address + mitigation and adaptation. Mitigation and adaptation raise issues of equity, justice + and fairness and are necessary to achieve sustainable development and poverty + eradication. Many of those most vulnerable to climate change have contributed + and contribute little to GHG emissions. Delaying mitigation shifts burdens from + the present to the future, and insufficient adaptation responses to emerging impacts + are already eroding the basis for sustainable development. Both adaptation and + mitigation can have distributional effects locally, nationally and internationally, + depending on who pays and who benefits. The process of decision-making about climate + change, and the degree to which it respects the rights and views of all those + affected, is also a concern of justice. Effective mitigation will not be achieved + if individual agents advance their own interests independently. Climate change + has the characteristics of a collective action problem at the global scale, because + most GHGs accumulate over time and mix globally, and emissions by any agent affect + other agents. Cooperative responses, including international cooperation, are + therefore required to effectively mitigate GHG emissions and address other climate + change issues. The effectiveness of adaptation can be enhanced through complementary + actions across levels, including international cooperation. The evidence suggests + that outcomes seen as equitable can lead to more effective cooperation. Decision-making + about climate change involves valuation and mediation among diverse values and + may be aided by the analytic methods of several normative disciplines. Ethics + analyses the different values involved and the relations between them. Recent + political philosophy has investigated the question of responsibility for the effects + of emissions. Economics and decision analysis provide quantitative methods of + valuation which can be used for estimating the social cost of carbon, in cost–benefit + and costeffectiveness analyses, for optimization in integrated models and elsewhere. + Economic methods can reflect ethical principles, and take account of non-marketed + goods, equity, behavioural biases, ancillary benefits and costs and the differing + values of money to different people. They are, however, subject to well-documented + limitations. Analytical methods of valuation cannot identify a single best balance + between mitigation, adaptation and residual climate impacts. Important reasons + for this are that climate change involves extremely complex natural and social + processes, there is extensive disagreement about the values concerned, and climate + change impacts and mitigation approaches have important distributional effects. + Nevertheless, information on the consequences of emissions pathways to alternative + climate goals and risk levels can be a useful input into decision-making processes. + Evaluating responses to climate change involves assessment of the widest possible + range of impacts, including low-probability outcomes with large consequences. Effective + decision-making and risk management in the complex environment of climate change + may be iterative: strategies can often be adjusted as new information and understanding + develops during implementation. However, adaptation and mitigation choices in + the near term will affect the risks of climate change throughout the 21st century + and beyond, and prospects for climate-resilient pathways for sustainable development + depend on what is achieved through mitigation. Opportunities to take advantage + of positive synergies between adaptation and mitigation may decrease with time, + particularly if mitigation is delayed too long. Decision-making about climate + change is influenced by how individuals and organizations perceive risks and uncertainties + and take them into account. They sometimes use simplified decision rules, overestimate + or underestimate risks and are biased towards the status quo. They differ in their + degree of risk aversion and the relative importance placed on near-term versus + long-term ramifications of specific actions. Formalized analytical methods for + decision-making under uncertainty can account accurately for risk, and focus attention + on both short- and long-term consequences.' + - Interaction among mitigation, adaptation and sustainable development Climate + change is a threat to equitable and sustainable development. Adaptation, mitigation + and sustainable development are closely related, with potential for synergies + and trade-offs. Climate change poses an increasing threat to equitable and sustainable + development. Some climate-related impacts on development are already being observed. + Climate change is a threat multiplier. It exacerbates other threats to social + and natural systems, placing additional burdens particularly on the poor and constraining + possible development paths for all. Development along current global pathways + can contribute to climate risk and vulnerability, further eroding the basis for + sustainable development. Aligning climate policy with sustainable development + requires attention to both adaptation and mitigation. Interaction among adaptation, + mitigation and sustainable development occurs both within and across regions and + scales, often in the context of multiple stressors. Some options for responding + to climate change could impose risks of other environmental and social costs, + have adverse distributional effects and draw resources away from other development + priorities, including poverty eradication. Both adaptation and mitigation can + bring substantial co-benefits . Examples of actions with co-benefits include improved + air quality; enhanced energy security, reduced energy and water consumption in + urban areas through greening cities and recycling water; sustainable agriculture + and forestry; and protection of ecosystems for carbon storage and other ecosystem + services. Strategies and actions can be pursued now that will move towards climate-resilient + pathways for sustainable development, while at the same time helping to improve + livelihoods, social and economic well-being and effective environmental management. + Prospects for climate-resilient pathways are related fundamentally to what the + world accomplishes with climate change mitigation. Since mitigation reduces the + rate as well as the magnitude of warming, it also increases the time available + for adaptation to a particular level of climate change, potentially by several + decades. Delaying mitigation actions may reduce options for climate-resilient + pathways in the future. + - Trade-offs, synergies and integrated responses There are many opportunities to + link mitigation, adaptation and the pursuit of other societal objectives through + integrated responses. Successful implementation relies on relevant tools, suitable + governance structures and enhanced capacity to respond. A growing evidence base + indicates close links between adaptation and mitigation, their co-benefits and + adverse side effects, and recognizes sustainable development as the overarching + context for climate policy . Developing tools to address these linkages is critical + to the success of climate policy in the context of sustainable development. This + section presents examples of integrated responses in specific policy arenas, as + well as some of the factors that promote or impede policies aimed at multiple + objectives. Increasing efforts to mitigate and adapt to climate change imply an + increasing complexity of interactions, encompassing connections among human health, + water, energy, land use and biodiversity. Mitigation can support the achievement + of other societal goals, such as those related to human health, food security, + environmental quality, energy access, livelihoods and sustainable development, + although there can also be negative effects. Adaptation measures also have the + potential to deliver mitigation co-benefits, and vice versa, and support other + societal goals, though trade-offs can also arise. Integration of adaptation and + mitigation into planning and decision-making can create synergies with sustainable + development. Synergies and trade-offs among mitigation and adaptation policies + and policies advancing other societal goals can be substantial, although sometimes + difficult to quantify especially in welfare terms. A multi-objective approach + to policy-making can help manage these synergies and trade-offs. Policies advancing + multiple goals may also attract greater support. Effective integrated responses + depend on suitable tools and governance structures, as well as adequate capacity + . Managing trade-offs and synergies is challenging and requires tools to help + understand interactions and support decision-making at local and regional scales. + Integrated responses also depend on governance that enables coordination across + scales and sectors, supported by appropriate institutions. Developing and implementing + suitable tools and governance structures often requires upgrading the human and + institutional capacity to design and deploy integrated responses. An integrated + approach to energy planning and implementation that explicitly assesses the potential + for co-benefits and the presence of adverse side effects can capture complementarities + across multiple climate, social and environmental objectives . There are strong + interactive effects across various energy policy objectives, such as energy security, + air quality, health and energy access and between a range of social and environmental + objectives and climate mitigation objectives . An integrated approach can be assisted + by tools such as cost-benefit analysis, cost-effectiveness analysis, multi-criteria + analysis and expected utility theory. It also requires appropriate coordinating + institutions. Explicit consideration of interactions among water, food, energy + and biological carbon sequestration plays an important role in supporting effective + decisions for climate resilient pathways . Both biofuel-based power generation + and large-scale afforestation designed to mitigate climate change can reduce catchment + run-off, which may conflict with alternative water uses for food production, human + consumption or the maintenance of ecosystem function and services. Conversely, + irrigation can increase the climate resilience of food and fibre production but + reduces water availability for other uses. An integrated response to urbanization + provides substantial opportunities for enhanced resilience, reduced emissions + and more sustainable development. Urban areas account for more than half of global + primary energy use and energy-related CO2 emissions and contain a high proportion + of the population and economic activities at risk from climate change. In rapidly + growing and urbanizing regions, mitigation strategies based on spatial planning + and efficient infrastructure supply can avoid the lock-in of high emission patterns. + Mixed-use zoning, transport-oriented development, increased density and co-located + jobs and homes can reduce direct and indirect energy use across sectors. Compact + development of urban spaces and intelligent densification can preserve land carbon + stocks and land for agriculture and bioenergy. Reduced energy and water consumption + in urban areas through greening cities and recycling water are examples of mitigation + actions with adaptation benefits. Building resilient infrastructure systems can + reduce vulnerability of urban settlements and cities to coastal flooding, sea + level rise and other climate-induced stresses. +paragraph_topics: + 1.1a: Observed changes in the climate system + 1.1b: Observed changes in the climate system + 1.1c: Observed changes in the climate system + 1.1d: Observed changes in the climate system + 1.1e: Observed changes in the climate system + 1.1g: Observed changes in the climate system + 1.2a: Causes of climate change + 1.2c: Causes of climate change + 1.3a: Impacts of climate change + 1.4a: Extreme events + 2.1b: Key drivers of future climate + 2.1c: Key drivers of future climate + 2.1d: Key drivers of future climate + 2.2e: Projected changes in the climate system + 2.2f: Projected changes in the climate system + 2.2g: Projected changes in the climate system + 2.2h: Projected changes in the climate system + 2.2m: Projected changes in the climate system + 2.3a: Future risks and impacts caused by a changing climate + 2.3b: Future risks and impacts caused by a changing climate + 2.3c: Future risks and impacts caused by a changing climate + 2.3e: Future risks and impacts caused by a changing climate + 2.3f: Future risks and impacts caused by a changing climate + 2.4a: Climate change beyond 2010, irreversibility and abrupt changes + 2.4b: Climate change beyond 2010, irreversibility and abrupt changes + 2.4c: Climate change beyond 2010, irreversibility and abrupt changes + 2.4d: Climate change beyond 2010, irreversibility and abrupt changes + 3.1a: Foundations of decion-making about climate change + 3.1b: Foundations of decion-making about climate change + 3.1c: Foundations of decion-making about climate change + 3.1d: Foundations of decion-making about climate change + 3.2b: Climate change risks reduced by mitigation and adaptation + 3.2d: Climate change risks reduced by mitigation and adaptation + 3.2e: Climate change risks reduced by mitigation and adaptation + 3.2f: Climate change risks reduced by mitigation and adaptation + 3.3a: Characteristics of adaptation pathways + 3.3b: Characteristics of adaptation pathways + 3.3c: Characteristics of adaptation pathways + 3.3d: Characteristics of adaptation pathways + 3.3f: Characteristics of adaptation pathways + 3.3g: Characteristics of adaptation pathways + 3.4a: Characteristics of mitigation pathways + 3.4b: Characteristics of mitigation pathways + 3.4c: Characteristics of mitigation pathways + 3.4d: Characteristics of mitigation pathways + 3.4e: Characteristics of mitigation pathways + 3.4f: Characteristics of mitigation pathways + 3.4g: Characteristics of mitigation pathways + 3.4h: Characteristics of mitigation pathways + 3.4i: Characteristics of mitigation pathways + 3.4l: Characteristics of mitigation pathways + 4.1a: Common enabling factors and constraints for adaptation and mitigation responses + 4.1b: Common enabling factors and constraints for adaptation and mitigation responses + 4.1c: Common enabling factors and constraints for adaptation and mitigation responses + 4.2a: Response options for adaptation + 4.2b: Response options for adaptation + 4.2c: Response options for adaptation + 4.3a: Response options for mitigations + 4.3b: Response options for mitigations + 4.3d: Response options for mitigations + 4.4b: Policy approaches for adaptation and mitigation, technology and finance + 4.4g: Policy approaches for adaptation and mitigation, technology and finance + 4.4l: Policy approaches for adaptation and mitigation, technology and finance + 4.4m: Policy approaches for adaptation and mitigation, technology and finance + 4.4n: Policy approaches for adaptation and mitigation, technology and finance + 4.4p: Policy approaches for adaptation and mitigation, technology and finance + 4.4q: Policy approaches for adaptation and mitigation, technology and finance + 4.4r: Policy approaches for adaptation and mitigation, technology and finance + 4.5a: Trade-offs, synergies and interactions with sustainable development + 4.5b: Trade-offs, synergies and interactions with sustainable development +pointers: + 1.1a: + - 1.1.1 + 1.1b: + - 1.1.2 + 1.1c: + - 1.1.1 + - 1.1.2 + 1.1d: + - 1.1.2 + 1.1e: + - 1.1.3 + 1.1g: + - 1.1.4 + 1.2a: + - 1.2.1 + - 1.2.2 + 1.2c: + - '1.3' + 1.3a: + - 1.3.2 + 1.4a: + - '1.4' + 2.1b: + - '2.1' + - '4.3' + 2.1c: + - 2.2.5 + 2.1d: + - 2.2.5 + 2.2e: + - 2.2.2 + 2.2f: + - 2.2.3 + 2.2g: + - 2.2.4 + 2.2h: + - 2.2.3 + 2.2m: + - 2.2.3 + 2.3a: + - '1.5' + - '2.3' + - '2.4' + - '3.3' + 2.3b: + - '2.3' + - '2.4' + 2.3c: + - 2.3.1 + - 2.3.2 + 2.3e: + - 2.3.2 + 2.3f: + - 2.3.2 + 2.4a: + - '2.4' + 2.4b: + - '2.4' + 2.4c: + - '2.4' + 2.4d: + - '2.4' + 3.1a: + - '3.1' + 3.1b: + - '3.1' + - '3.5' + 3.1c: + - '3.1' + 3.1d: + - '3.1' + 3.2b: + - '3.2' + - '4.5' + 3.2d: + - '2.3' + - '3.2' + - '3.4' + 3.2e: + - 2.2.5 + - '3.2' + - '3.4' + 3.2f: + - '3.2' + - '3.4' + 3.3a: + - '3.3' + 3.3b: + - '3.3' + 3.3c: + - '3.3' + 3.3d: + - '3.3' + 3.3f: + - '3.3' + 3.3g: + - '3.3' + 3.4a: + - '3.4' + 3.4b: + - '3.4' + 3.4c: + - '3.4' + 3.4d: + - '3.4' + 3.4e: + - '3.4' + 3.4f: + - '3.4' + 3.4g: + - '3.4' + 3.4h: + - '3.4' + 3.4i: + - 4.4.2.2 + 3.4l: + - 4.4.2.2 + 4.1a: + - '4.1' + 4.1b: + - '4.1' + 4.1c: + - '4.1' + 4.2a: + - '4.2' + 4.2b: + - '1.6' + - '4.2' + - 4.4.2.1 + 4.2c: + - '4.2' + 4.3a: + - '4.3' + 4.3b: + - '4.3' + 4.3d: + - '4.1' + - '4.3' + 4.4b: + - 4.4.1 + 4.4g: + - 4.4.2.1 + - 4.4.2.2 + 4.4l: + - 4.4.2.2 + 4.4m: + - 4.4.2.2 + 4.4n: + - 4.4.2.2 + 4.4p: + - '4.3' + - 4.4.2.2 + 4.4q: + - 4.4.3 + 4.4r: + - 4.4.4 + 4.5a: + - '3.5' + - '4.5' + 4.5b: + - '3.1' + - '3.5' + - '4.5' +section_topics: + 1.1a: Observed Changes amd their Causes + 1.1b: Observed Changes amd their Causes + 1.1c: Observed Changes amd their Causes + 1.1d: Observed Changes amd their Causes + 1.1e: Observed Changes amd their Causes + 1.1g: Observed Changes amd their Causes + 1.2a: Observed Changes amd their Causes + 1.2c: Observed Changes amd their Causes + 1.3a: Observed Changes amd their Causes + 1.4a: Observed Changes amd their Causes + 2.1b: Future Climate Changes, Risks and Impacts + 2.1c: Future Climate Changes, Risks and Impacts + 2.1d: Future Climate Changes, Risks and Impacts + 2.2e: Future Climate Changes, Risks and Impacts + 2.2f: Future Climate Changes, Risks and Impacts + 2.2g: Future Climate Changes, Risks and Impacts + 2.2h: Future Climate Changes, Risks and Impacts + 2.2m: Future Climate Changes, Risks and Impacts + 2.3a: Future Climate Changes, Risks and Impacts + 2.3b: Future Climate Changes, Risks and Impacts + 2.3c: Future Climate Changes, Risks and Impacts + 2.3e: Future Climate Changes, Risks and Impacts + 2.3f: Future Climate Changes, Risks and Impacts + 2.4a: Future Climate Changes, Risks and Impacts + 2.4b: Future Climate Changes, Risks and Impacts + 2.4c: Future Climate Changes, Risks and Impacts + 2.4d: Future Climate Changes, Risks and Impacts + 3.1a: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.1b: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.1c: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.1d: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.2b: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.2d: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.2e: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.2f: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.3a: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.3b: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.3c: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.3d: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.3f: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.3g: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.4a: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.4b: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.4c: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.4d: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.4e: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.4f: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.4g: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.4h: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.4i: Future Pathways for Adaptation, Mitigation and Sustainable Development + 3.4l: Future Pathways for Adaptation, Mitigation and Sustainable Development + 4.1a: Adaptation and Mitigation + 4.1b: Adaptation and Mitigation + 4.1c: Adaptation and Mitigation + 4.2a: Adaptation and Mitigation + 4.2b: Adaptation and Mitigation + 4.2c: Adaptation and Mitigation + 4.3a: Adaptation and Mitigation + 4.3b: Adaptation and Mitigation + 4.3d: Adaptation and Mitigation + 4.4b: Adaptation and Mitigation + 4.4g: Adaptation and Mitigation + 4.4l: Adaptation and Mitigation + 4.4m: Adaptation and Mitigation + 4.4n: Adaptation and Mitigation + 4.4p: Adaptation and Mitigation + 4.4q: Adaptation and Mitigation + 4.4r: Adaptation and Mitigation + 4.5a: Adaptation and Mitigation + 4.5b: Adaptation and Mitigation +summaries: + 1.1a: Each of the last three decades has been successively warmer at the Earth’s + surface than any preceding decade since 1850. The period from 1983 to 2012 was + likely the warmest 30-year period of the last 1400 years in the Northern Hemisphere, + where such assessment is possible. The globally averaged combined land and ocean + surface temperature data as calculated by a linear trend show a warming of 0.85 + [0.65 to 1.06] °C 2 over the period 1880 to 2012, when multiple independently + produced datasets exist. In addition to robust multi-decadal warming, the globally + averaged surface temperature exhibits substantial decadal and interannual variability. + Due to this natural variability, trends based on short records are very sensitive + to the beginning and end dates and do not in general reflect long-term climate + trends. As one example, the rate of warming over the past 15 years, which begins + with a strong El Niño, is smaller than the rate calculated since 1951. + 1.1b: Ocean warming dominates the increase in energy stored in the climate system, + accounting for more than 90% of the energy accumulated between 1971 and 2010, + with only about 1% stored in the atmosphere. On a global scale, the ocean warming + is largest near the surface, and the upper 75 m warmed by 0.11 [0.09 to 0.13] + °C per decade over the period 1971 to 2010. It is virtually certain that the upper + ocean warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971. + 1.1c: Averaged over the mid-latitude land areas of the Northern Hemisphere, precipitation + has increased since 1901 . For other latitudes, area-averaged long-term positive + or negative trends have low confidence. Observations of changes in ocean surface + salinity also provide indirect evidence for changes in the global water cycle + over the ocean. It is very likely that regions of high salinity, where evaporation + dominates, have become more saline, while regions of low salinity, where precipitation + dominates, have become fresher since the 1950s. + 1.1d: Since the beginning of the industrial era, oceanic uptake of CO2 has resulted + in acidification of the ocean; the pH of ocean surface water has decreased by + 0.1, corresponding to a 26% increase in acidity, measured as hydrogen ion concentration. + 1.1e: Over the period 1992 to 2011, the Greenland and Antarctic ice sheets have + been losing mass , likely at a larger rate over 2002 to 2011. Glaciers have continued + to shrink almost worldwide. Northern Hemisphere spring snow cover has continued + to decrease in extent. There is high confidence that permafrost temperatures have + increased in most regions since the early 1980s in response to increased surface + temperature and changing snow cover. The annual mean Arctic sea-ice extent decreased + over the period 1979 to 2012, with a rate that was very likely in the range 3.5 + to 4.1% per decade. Arctic sea-ice extent has decreased in every season and in + every successive decade since 1979, with the most rapid decrease in decadal mean + extent in summer. It is very likely that the annual mean Antarctic sea-ice extent + increased in the range of 1.2 to 1.8% per decade between 1979 and 2012. However, + there is high confidence that there are strong regional differences in Antarctica, + with extent increasing in some regions and decreasing in others. + 1.1g: Over the period 1901 to 2010, global mean sea level rose by 0.19 [0.17 to + 0.21] m . The rate of sea level rise since the mid-19th century has been larger + than the mean rate during the previous two millennia. + 1.2a: Anthropogenic greenhouse gas emissions since the pre-industrial era have + driven large increases in the atmospheric concentrations of carbon dioxide, methane + and nitrous oxide. Between 1750 and 2011, cumulative anthropogenic CO2 emissions + to the atmosphere were 2040 ± 310 GtCO2. About 40% of these emissions have remained + in the atmosphere; the rest was removed from the atmosphere and stored on land and + in the ocean. The ocean has absorbed about 30% of the emitted anthropogenic CO2, + causing ocean acidification. About half of the anthropogenic CO2 emissions between + 1750 and 2011 have occurred in the last 40 years . Total anthropogenic GHG emissions + have continued to increase over 1970 to 2010 with larger absolute increases between 2000 + and 2010, despite a growing number of climate change mitigation policies. Anthropogenic + GHG emissions in 2010 have reached 49 ± 4.5 GtCO2-eq/yr 3. Emissions of CO2 from + fossil fuel combustion and industrial processes contributed about 78% of the total + GHG emissions increase from 1970 to 2010, with a similar percentage contribution + for the increase during the period 2000 to 2010. Globally, economic and population + growth continued to be the most important drivers of increases in CO2 emissions + from fossil fuel combustion. The contribution of population growth between 2000 + and 2010 remained roughly identical to the previous three decades, while the contribution + of economic growth has risen sharply. Increased use of coal has reversed the long-standing + trend of gradual decarbonization of the world’s energy supply. + 1.2c: The evidence for human influence on the climate system has grown since the + IPCC Fourth Assessment Report . It is extremely likely that more than half of + the observed increase in global average surface temperature from 1951 to 2010 + was caused by the anthropogenic increase in GHG concentrations and other anthropogenic + forcings together. The best estimate of the human-induced contribution to warming + is similar to the observed warming over this period. Anthropogenic forcings have + likely made a substantial contribution to surface temperature increases since + the mid-20th century over every continental region except Antarctica. Anthropogenic + influences have likely affected the global water cycle since 1960 and contributed + to the retreat of glaciers since the 1960s and to the increased surface melting + of the Greenland ice sheet since 1993. Anthropogenic influences have very likely + contributed to Arctic sea-ice loss since 1979 and have very likely made a substantial + contribution to increases in global upper ocean heat content and to global mean + sea level rise observed since the 1970s. + 1.3a: Evidence of observed climate change impacts is strongest and most comprehensive + for natural systems. In many regions, changing precipitation or melting snow + and ice are altering hydrological systems, affecting water resources in terms + of quantity and quality. Many terrestrial, freshwater and marine species have + shifted their geographic ranges, seasonal activities, migration patterns, abundances + and species interactions in response to ongoing climate change . Some impacts + on human systems have also been attributed to climate change, with a major or + minor contribution of climate change distinguishable from other influences. Assessment + of many studies covering a wide range of regions and crops shows that negative + impacts of climate change on crop yields have been more common than positive impacts. + Some impacts of ocean acidification on marine organisms have been attributed to + human influence. + 1.4a: It is very likely that the number of cold days and nights has decreased and + the number of warm days and nights has increased on the global scale. It is likely + that the frequency of heat waves has increased in large parts of Europe, Asia + and Australia. It is very likely that human influence has contributed to the observed + global scale changes in the frequency and intensity of daily temperature extremes + since the mid-20th century. It is likely that human influence has more than doubled + the probability of occurrence of heat waves in some locations. There is medium + confidence that the observed warming has increased heat-related human mortality + and decreased cold-related human mortality in some regions. There are likely + more land regions where the number of heavy precipitation events has increased + than where it has decreased. Recent detection of increasing trends in extreme + precipitation and discharge in some catchments implies greater risks of flooding + at regional scale. It is likely that extreme sea levels have increased since + 1970, being mainly a result of rising mean sea level. Impacts from recent climate-related + extremes, such as heat waves, droughts, floods, cyclones and wildfires, reveal + significant vulnerability and exposure of some ecosystems and many human systems + to current climate variability . + 2.1b: Anthropogenic GHG emissions are mainly driven by population size, economic + activity, lifestyle, energy use, land use patterns, technology and climate policy. + The Representative Concentration Pathways, which are used for making projections + based on these factors, describe four different 21st century pathways of GHG emissions + and atmospheric concentrations, air pollutant emissions and land use. The RCPs + include a stringent mitigation scenario, two intermediate scenarios and one scenario + with very high GHG emissions. Scenarios without additional efforts to constrain + emissions lead to pathways ranging between RCP6.0 and RCP8.5. RCP2.6 is representative + of a scenario that aims to keep global warming likely below 2°C above pre-industrial + temperatures. The RCPs are consistent with the wide range of scenarios in the + literature as assessed by WGIII5. + 2.1c: Multiple lines of evidence indicate a strong, consistent, almost linear relationship + between cumulative CO2 emissions and projected global temperature change to the + year 2100 in both the RCPs and the wider set of mitigation scenarios analysed + in WGIII. Any given level of warming is associated with a range of cumulative + CO2 emissions, and therefore, e.g., higher emissions in earlier decades imply + lower emissions later. + 2.1d: Multi-model results show that limiting total human-induced warming to less + than 2°C relative to the period 1861–1880 with a probability of >66%7 would require + cumulative CO2 emissions from all anthropogenic sources since 1870 to remain below + about 2900 GtCO2. About 1900 GtCO28 had already been emitted by 2011. For additional + context see Table 2.2. + 2.2e: Changes in precipitation will not be uniform. The high latitudes and the equatorial + Pacific are likely to experience an increase in annual mean precipitation under + the RCP8.5 scenario. In many mid-latitude and subtropical dry regions, mean precipitation + will likely decrease, while in many mid-latitude wet regions, mean precipitation + will likely increase under the RCP8.5 scenario. Extreme precipitation events over + most of the mid-latitude land masses and over wet tropical regions will very likely + become more intense and more frequent. + 2.2f: The global ocean will continue to warm during the 21st century, with the strongest + warming projected for the surface in tropical and Northern Hemisphere subtropical + regions. + 2.2g: Earth System Models project a global increase in ocean acidification for all + RCP scenarios by the end of the 21st century, with a slow recovery after mid-century + under RCP2.6. The decrease in surface ocean pH is in the range of 0.06 to 0.07 for + RCP2.6, 0.14 to 0.15 for RCP4.5, 0.20 to 0.21 for RCP6.0 and 0.30 to 0.32 for + RCP8.5. + 2.2h: Year-round reductions in Arctic sea ice are projected for all RCP scenarios. + A nearly ice-free11 Arctic Ocean in the summer sea- ice minimum in September + before mid-century is likely for RCP8.512. It is virtually certain that near-surface + permafrost extent at high northern latitudes will be reduced as global mean surface temperature + increases, with the area of permafrost near the surface projected to decrease + by 37% to 81% for the multi-model average. The global glacier volume, excluding + glaciers on the periphery of Antarctica , is projected to decrease by 15 to 55% + for RCP2.6 and by 35 to 85% for RCP8.5. + 2.2m: Summary for Policymakers13SPM There has been significant improvement in understanding + and projection of sea level change since the AR4. Global mean sea level rise will + continue during the 21st century, very likely at a faster rate than observed from + 1971 to 2010. For the period 2081–2100 relative to 1986–2005, the rise will likely + be in the ranges of 0.26 to 0.55 m for RCP2.6, and of 0.45 to 0.82 m for RCP8.5 + 10. Sea level rise will not be uniform across regions. By the end of the 21st + century, it is very likely that sea level will rise in more than about 95% of + the ocean area. About 70% of the coastlines worldwide are projected to experience + a sea level change within ±20% of the global mean. + 2.3a: Risk of climate-related impacts results from the interaction of climate-related + hazards with the vulnerability and exposure of human and natural systems, including + their ability to adapt. Rising rates and magnitudes of warming and other changes + in the climate system, accompanied by ocean acidification, increase the risk of + severe, pervasive and in some cases irreversible detrimental impacts. Some risks + are particularly relevant for individual regions, while others are global. The + overall risks of future climate change impacts can be reduced by limiting the + rate and magnitude of climate change, including ocean acidification. The precise + levels of climate change sufficient to trigger abrupt and irreversible change + remain uncertain, but the risk associated with crossing such thresholds increases + with rising temperature. For risk assessment, it is important to evaluate the + widest possible range of impacts, including low-probability outcomes with large + consequences. + 2.3b: A large fraction of species faces increased extinction risk due to climate + change during and beyond the 21st century, espe- cially as climate change interacts + with other stressors. Most plant species cannot naturally shift their geographical + ranges sufficiently fast to keep up with current and high projected rates of climate + change in most landscapes; most small mammals and freshwater molluscs will not + be able to keep up at the rates projected under RCP4.5 and above in flat landscapes + in this century. Future risk is indicated to be high by the observation that natural + global climate change at rates lower than current anthropogenic climate change + caused significant ecosystem shifts and species extinctions during the past millions + of years. Marine organisms will face progressively lower oxygen levels and high + rates and magnitudes of ocean acidification, with associated risks exacerbated + by rising ocean temperature extremes . Coral reefs and polar ecosystems are highly + vulnerable. Coastal systems and low-lying areas are at risk from sea level rise, + which will continue for centuries even if the global mean temperature is stabilized. + 2.3c: Climate change is projected to undermine food security . Due to projected + climate change by the mid-21st century and beyond, global marine species redistribution + and marine biodiversity reduction in sensitive regions will challenge the sustained + provision of fisheries productivity and other ecosystem services. For wheat, rice + and maize in tropical and temperate regions, climate change without adaptation + is projected to negatively impact production for local temperature increases of + 2°C or more above late 20th century levels, although individual locations may + benefit. Global temperature increases of ~4°C or more above late 20th century + levels, combined with increasing food demand, would pose large risks to food security + globally. Climate change is projected to reduce renewable surface water and groundwater + resources in most dry subtropical regions, intensifying competition for water + among sectors. Rural areas are expected to experience major impacts on water availability + and supply, food security, infrastructure and agricultural incomes, including + shifts in the production areas of food and non-food crops around the world. + 2.3e: Aggregate economic losses accelerate with increasing temperature , but global + economic impacts from climate change are currently difficult to estimate. From + a poverty perspective, climate change impacts are projected to slow down economic + growth, make poverty reduction more difficult, further erode food security and + prolong existing and create new poverty traps, the latter particularly in urban + areas and emerging hotspots of hunger . International dimensions such as trade + and relations among states are also important for understanding the risks of climate + change at regional scales. + 2.3f: Climate change is projected to increase displacement of people . Populations + that lack the resources for planned migration experience higher exposure to extreme + weather events, particularly in developing countries with low income. Climate + change can indirectly increase risks of violent conflicts by amplifying well-documented + drivers of these conflicts such as poverty and economic shocks. + 2.4a: Warming will continue beyond 2100 under all RCP scenarios except RCP2.6. Surface + temperatures will remain approximately constant at elevated levels for many centuries + after a complete cessation of net anthropogenic CO2 emissions. A large fraction + of anthropogenic climate change resulting from CO2 emissions is irreversible on + a multi-century to millennial timescale, except in the case of a large net removal + of CO2 from the atmosphere over a sustained period. + 2.4b: Stabilization of global average surface temperature does not imply stabilization + for all aspects of the climate system. Shifting biomes, soil carbon, ice sheets, + ocean temperatures and associated sea level rise all have their own intrinsic + long timescales which will result in changes lasting hundreds to thousands of + years after global surface temperature is stabilized. There is high confidence + that ocean acidification will increase for centuries if CO2 emissions continue, + and will strongly affect marine ecosystems. + 2.4c: It is virtually certain that global mean sea level rise will continue for + many centuries beyond 2100, with the amount of rise dependent on future emissions. + The threshold for the loss of the Greenland ice sheet over a millennium or more, + and an associated sea level rise of up to 7 m, is greater than about 1°C but less + than about 4°C of global warming with respect to pre-industrial temperatures. + Abrupt and irreversible ice loss from the Antarctic ice sheet is possible, but + current evidence and understanding is insufficient to make a quantitative assessment. + 2.4d: Magnitudes and rates of climate change associated with medium- to high-emission + scenarios pose an increased risk of abrupt and irreversible regional-scale change + in the composition, structure and function of marine, terrestrial and freshwater + ecosystems, including wetlands. A reduction in permafrost extent is virtually + certain with continued rise in global temperatures. + 3.1a: Effective decision-making to limit climate change and its effects can be informed + by a wide range of analytical approaches for evaluating expected risks and benefits, + recognizing the importance of governance, ethical dimensions, equity, value judgments, + economic assessments and diverse perceptions and responses to risk and uncertainty. + 3.1b: Sustainable development and equity provide a basis for assessing climate policies. + Limiting the effects of climate change is necessary to achieve sustainable development + and equity, including poverty eradication. Countries’ past and future contributions + to the accumulation of GHGs in the atmosphere are different, and countries also + face varying challenges and circumstances and have different capacities to address + mitigation and adaptation. Mitigation and adaptation raise issues of equity, justice + and fairness. Many of those most vulnerable to climate change have contributed + and contribute little to GHG emissions. Delaying mitigation shifts burdens from + the present to the future, and insufficient adaptation responses to emerging impacts + are already eroding the basis for sustainable development. Comprehensive strategies + in response to climate change that are consistent with sustainable development + take into account the co-benefits, adverse side effects and risks that may arise + from both adaptation and mitigation options. + 3.1c: The design of climate policy is influenced by how individuals and organizations + perceive risks and uncertainties and take them into account. Methods of valuation + from economic, social and ethical analysis are available to assist decision-making. + These methods can take account of a wide range of possible impacts, including + low-probability outcomes with large consequences. But they cannot identify a single + best balance between mitigation, adaptation and residual climate impacts. + 3.1d: Climate change has the characteristics of a collective action problem at the + global scale, because most GHGs accumulate over time and mix globally, and emissions + by any agent affect other agents. Effective mitigation will not be achieved if + individual agents advance their own interests independently. Cooperative responses, + including international cooperation, are therefore required to effectively mitigate + GHG emissions and address other climate change issues. The effectiveness of adaptation + can be enhanced through complementary actions across levels, including international + cooperation. The evidence suggests that outcomes seen as equitable can lead to + more effective cooperation. + 3.2b: Mitigation and adaptation are complementary approaches for reducing risks + of climate change impacts over different time- scales. Mitigation, in the near + term and through the century, can substantially reduce climate change impacts + in the latter decades of the 21st century and beyond. Benefits from adaptation + can already be realized in addressing current risks, and can be realized in the + future for addressing emerging risks. + 3.2d: Without additional mitigation efforts beyond those in place today, and even + with adaptation, warming by the end of the 21st century will lead to high to + very high risk of severe, widespread and irreversible impacts globally . In most + scenarios without additional mitigation efforts, warming is more likely than not + to exceed 4°C above pre-industrial levels by 2100. The risks associated with temperatures + at or above 4°C include substantial species extinction, global and regional food + insecurity, consequential constraints on common human activities and limited potential + for adaptation in some cases. Some risks of climate change, such as risks to unique + and threatened systems and risks associated with extreme weather events, are moderate + to high at temperatures 1°C to 2°C above pre-industrial levels. + 3.2e: Substantial cuts in GHG emissions over the next few decades can substantially + reduce risks of climate change by limiting warming in the second half of the + 21st century and beyond. Cumulative emissions of CO2 largely determine global + mean surface warming by the late 21st century and beyond. Limiting risks across + RFCs would imply a limit for cumulative emissions of CO2. Such a limit would require + that global net emissions of CO2 eventually decrease to zero and would constrain + annual emissions over the next few decades. But some risks from climate damages + are unavoidable, even with mitigation and adaptation. + 3.2f: Mitigation involves some level of co-benefits and risks, but these risks do + not involve the same possibility of severe, wide- spread and irreversible impacts + as risks from climate change. Inertia in the economic and climate system and the + possibility of irreversible impacts from climate change increase the benefits + from near-term mitigation efforts. Delays in additional mitigation or constraints + on technological options increase the longer-term mitigation costs to hold climate + change risks at a given level. + 3.3a: Adaptation can contribute to the well-being of populations, the security of + assets and the maintenance of ecosystem goods, functions and services now and + in the future. Adaptation is place- and context-specific. A first step towards + adaptation to future climate change is reducing vulnerability and exposure to + present climate variability. Integration of adaptation into planning, including + policy design, and decision-making can promote synergies with development and + disaster risk reduction. Building adaptive capacity is crucial for effective selection + and implementation of adaptation options. + 3.3b: Adaptation planning and implementation can be enhanced through complementary + actions across levels, from individuals to governments. National governments + can coordinate adaptation efforts of local and sub-national governments, for example + by protecting vulnerable groups, by supporting economic diversification and by + providing information, policy and legal frameworks and financial support. Local + government and the private sector are increasingly recognized as critical to progress + in adaptation, given their roles in scaling up adaptation of communities, households + and civil society and in managing risk information and financing. + 3.3c: Adaptation planning and implementation at all levels of governance are contingent + on societal values, objectives and risk perceptions. Recognition of diverse interests, + circumstances, social-cultural contexts and expectations can benefit decision-making + processes. Indigenous, local and traditional knowledge systems and practices, + including indigenous peoples’ holistic view of community and environment, are + a major resource for adapting to climate change, but these have not been used + consistently in existing adaptation efforts. Integrating such forms of knowledge + with existing practices increases the effectiveness of adaptation. + 3.3d: 'Constraints can interact to impede adaptation planning and implementation + . Common constraints on implementation arise from the following: limited financial + and human resources; limited integration or coordination of governance; uncertainties + about projected impacts; different perceptions of risks; competing values; absence + of key adaptation leaders and advocates; and limited tools to monitor adaptation + effectiveness. Another constraint includes insufficient research, monitoring, + and observation and the finance to maintain them. Greater rates and magnitude + of climate change increase the likelihood of exceeding adaptation limits . Limits + to adaptation emerge from the interaction among climate change and biophysical + and/or socio-economic constraints. Further, poor planning or implementation, overemphasizing + short-term outcomes or failing to sufficiently anticipate consequences can result + in maladaptation, increasing the vulnerability or exposure of the target group + in the future or the vulnerability of other people, places or sectors. Underestimating + the complexity of adaptation as a social process can create unrealistic expectations + about achieving intended adaptation outcomes.' + 3.3f: Significant co-benefits, synergies and trade-offs exist between mitigation + and adaptation and among different adap- tation responses; interactions occur + both within and across regions. Increasing efforts to mitigate and adapt to climate + change imply an increasing complexity of interactions, particularly at the intersections + among water, energy, land use and biodiversity, but tools to understand and manage + these interactions remain limited. Examples of actions with co-benefits include + improved energy efficiency and cleaner energy sources, leading to reduced emissions + of health-damaging, climate-altering air pollutants; reduced energy and water + consumption in urban areas through greening cities and recycling water; sustainable + agriculture and forestry; and protection of ecosystems for carbon storage and + other ecosystem services. + 3.3g: Transformations in economic, social, technological and political decisions + and actions can enhance adaptation and promote sustainable development. At the + national level, transformation is considered most effective when it reflects a + country’s own visions and approaches to achieving sustainable development in accordance + with its national circumstances and priorities. Restricting adaptation responses + to incremental changes to existing systems and structures, without considering + transformational change, may increase costs and losses and miss opportunities. + Planning and implementation of transformational adaptation could reflect strengthened, + altered or aligned paradigms and may place new and increased demands on governance + structures to reconcile different goals and visions for the future and to address + possible equity and ethical implications. Adaptation pathways are enhanced by + iterative learning, deliberative processes and innovation. + 3.4a: There are multiple mitigation pathways that are likely to limit warming to + below 2°C relative to pre-industrial levels. These pathways would require substantial + emissions reductions over the next few decades and near zero emissions of CO2 + and other long-lived greenhouse gases by the end of the century. Implementing + such reductions poses substantial technological, economic, social and institutional + challenges, which increase with delays in additional mitigation and if key technologies + are not available. Limiting warming to lower or higher levels involves similar + challenges but on different timescales. + 3.4b: Without additional efforts to reduce GHG emissions beyond those in place today, + global emissions growth is expected to persist, driven by growth in global population + and economic activities. Global mean surface temperature increases in 2100 in + baseline scenarios—those without additional mitigation—range from 3.7°C to 4.8°C + above the average for 1850–1900 for a median climate response. They range from + 2.5°C to 7.8°C when including climate uncertainty . + 3.4c: Emissions scenarios leading to CO2-equivalent concentrations in 2100 of about + 450 ppm or lower are likely to maintain warming below 2°C over the 21st century + relative to pre-industrial levels. These scenarios are characterized by 40 to + 70% global anthropogenic GHG emissions reductions by 2050 compared to 201016, + and emissions levels near zero or below in 2100. Mitigation scenarios reaching + concentration levels of about 500 ppm CO2-eq by 2100 are more likely than not + to limit temperature change to less than 2°C, unless they temporarily overshoot + concentration levels of roughly 530 ppm CO2-eq before 2100, in which case they + are about as likely as not to achieve that goal. In these 500 ppm CO2-eq scenarios, + global 2050 emissions levels are 25 to 55% lower than in 2010. Scenarios with + higher emissions in 2050 are characterized by a greater reliance on Carbon Dioxide + Removal technologies beyond mid-century. Trajectories that are likely to limit + warming to 3°C relative to pre-industrial levels reduce emissions less rapidly + than those limiting warming to 2°C. A limited number of studies provide scenarios + that are more likely than not to limit warming to 1.5°C by 2100; these scenarios + are characterized by concentrations below 430 ppm CO2-eq by 2100 and 2050 emission + reduction between 70% and 95% below 2010. For a comprehensive overview of the + characteristics of emissions scenarios, their CO2-equivalent concentrations and + their likelihood to keep warming to below a range of temperature levels, see Figure + SPM.11 and Table SPM.1. + 3.4d: Mitigation scenarios reaching about 450 ppm CO2-eq in 2100 typically involve + temporary overshoot of atmospheric concentrations, as do many scenarios reaching + about 500 ppm CO2-eq to about 550 ppm CO2-eq in 2100. Depending on the level of + overshoot, overshoot scenarios typically rely on the availability and widespread + deployment of bioenergy with carbon dioxide capture and storage and afforestation + in the second half of the century. The availability and scale of these and other + CDR technologies and methods are uncertain and CDR technologies are, to varying + degrees, associated with challenges and risks. CDR is also prevalent in many scenarios + without overshoot to compensate for residual emissions from sectors where mitigation + is more expensive. + 3.4e: Reducing emissions of non-CO2 agents can be an important element of mitigation + strategies. All current GHG emissions and other forcing agents affect the rate + and magnitude of climate change over the next few decades, although long-term + warming is mainly driven by CO2 emissions. Emissions of non-CO2 forcers are often + expressed as ‘CO2-equivalent emissions’, but the choice of metric to calculate + these emissions, and the implications for the emphasis and timing of abatement + of the various climate forcers, depends on application and policy context and + contains value judgments. + 3.4f: Delaying additional mitigation to 2030 will substantially increase the challenges + associated with limiting warming over the 21st century to below 2°C relative + to pre-industrial levels. It will require substantially higher rates of emissions + reductions from 2030 to 2050; a much more rapid scale-up of low-carbon energy + over this period; a larger reliance on CDR in the long term; and higher transitional + and long-term economic impacts. Estimated global emissions levels in 2020 based + on the Cancún Pledges are not consistent with cost-effective mitigation trajectories + that are at least about as likely as not to limit warming to below 2°C relative + to pre-industrial levels, but they do not preclude the option to meet this goal + . + 3.4g: Estimates of the aggregate economic costs of mitigation vary widely depending + on methodologies and assumptions, but increase with the stringency of mitigation. + Scenarios in which all countries of the world begin mitigation immediately, in + which there is a single global carbon price, and in which all key technologies + are available have been used as a cost-effective benchmark for estimating macro-economic + mitigation costs. Under these assumptions mitigation scenarios that are likely + to limit warming to below 2°C through the 21st century relative to pre-industrial + levels entail losses in global consumption—not including benefits of reduced climate + change as well as co-benefits and adverse side effects of mitigation—of 1 to 4% + in 2030, 2 to 6% in 2050 and 3 to 11% in 2100 relative to consumption in baseline + scenarios that grows anywhere from 300% to more than 900% over the century. These + numbers correspond to an annualized reduction of consumption growth by 0.04 to + 0.14 percentage points over the century relative to annualized consumption growth + in the baseline that is between 1.6 and 3% per year . + 3.4h: In the absence or under limited availability of mitigation technologies , + mitigation costs can increase substantially depending on the technology considered. + Delaying additional mitigation increases mitigation costs in the medium to long + term. Many models could not limit likely warming to below 2°C over the 21st century + relative to pre-industrial levels if additional mitigation is considerably delayed. + Many models could not limit likely warming to below 2°C if bioenergy, CCS and + their combination are limited . + 3.4i: Mitigation scenarios reaching about 450 or 500 ppm CO2-eq by 2100 show reduced + costs for achieving air quality and energy security objectives, with significant + co-benefits for human health, ecosystem impacts and sufficiency of resources and + resilience of the energy system. + 3.4l: Mitigation policy could devalue fossil fuel assets and reduce revenues for + fossil fuel exporters, but differences between regions and fuels exist. Most + mitigation scenarios are associated with reduced revenues from coal and oil trade + for major exporters. The availability of CCS would reduce the adverse effects + of mitigation on the value of fossil fuel assets. + 4.1a: Adaptation and mitigation responses are underpinned by common enabling factors. + These include effective institutions and governance, innovation and investments + in environmentally sound technologies and infrastructure, sustainable livelihoods + and behavioural and lifestyle choices. For many regions and sectors, enhanced + capacities to mitigate and adapt are part of the foundation essential for managing climate + change risks. Improving institutions as well as coordination and cooperation in + governance can help overcome regional constraints associated with mitigation, + adaptation and disaster risk reduction. + 4.1b: Inertia in many aspects of the socio-economic system constrains adaptation + and mitigation options . Innovation and investments in environmentally sound infrastructure + and technologies can reduce GHG emissions and enhance resilience to climate change. + 4.1c: Vulnerability to climate change, GHG emissions and the capacity for adaptation + and mitigation are strongly influenced by livelihoods, lifestyles, behaviour + and culture. Also, the social acceptability and/or effectiveness of climate policies + are influenced by the extent to which they incentivize or depend on regionally + appropriate changes in lifestyles or behaviours. + 4.2a: Adaptation options exist in all sectors, but their context for implementation + and potential to reduce climate-related risks differs across sectors and regions. + Some adaptation responses involve significant co-benefits, synergies and trade-offs. + Increasing climate change will increase challenges for many adaptation options. + 4.2b: Adaptation experience is accumulating across regions in the public and private + sectors and within communities. There is increasing recognition of the value + of social, institutional, and ecosystem-based measures and of the extent of constraints + to adaptation. Adaptation is becoming embedded in some planning processes, with + more limited implementation of responses. + 4.2c: The need for adaptation along with associated challenges is expected to increase + with climate change . Adaptation options exist in all sectors and regions, with + diverse potential and approaches depending on their context in vulnerability reduction, + disaster risk management or proactive adaptation planning. Effective strategies + and actions consider the potential for co-benefits and opportunities within wider + strategic goals and development plans. + 4.3a: Mitigation options are available in every major sector. Mitigation can be + more cost-effective if using an integrated approach that combines measures to + reduce energy use and the greenhouse gas intensity of end-use sectors, decarbonize + energy supply, reduce net emissions and enhance carbon sinks in land-based sectors. Well-designed + systemic and cross-sectoral mitigation strategies are more cost-effective in cutting + emissions than a focus on individual technologies and sectors, with efforts in + one sector affecting the need for mitigation in others . Mitigation measures intersect + with other societal goals, creating the possibility of co-benefits or adverse + side effects. These intersections, if well-managed, can strengthen the basis for + undertaking climate action. Near-term reductions in energy demand are an important + element of cost-effective mitigation strategies, provide more flexibility for + reducing carbon intensity in the energy supply sector, hedge against related supply-side + risks, avoid lock-in to carbon-intensive infrastructures, and are associated with + important co-benefits. The most cost-effective mitigation options in forestry + are afforestation, sustainable forest management and reducing deforestation, with + large differences in their relative importance across regions; and in agriculture, + cropland management, grazing land management and restoration of organic soils. + 4.3b: Emissions ranges for baseline scenarios and mitigation scenarios that limit + CO2-equivalent concentrations to low levels are shown for different sectors and + gases in Figure SPM.14. Key measures to achieve such mitigation goals include + decarbonizing electricity generation as well as efficiency enhancements and behavioural + changes, in order to reduce energy demand compared to baseline scenarios without + compromising development . In scenarios reaching 450 ppm CO2-eq concentrations + by 2100, global CO2 emissions from the energy supply sector are projected to decline + over the next decade and are characterized by reductions of 90% or more below + 2010 levels between 2040 and 2070. In the majority of low-concentration stabilization + scenarios , the share of low-carbon electricity supply , nuclear and carbon dioxide + capture and storage including bioenergy with carbon dioxide capture and storage + ) increases from the current share of approximately 30% to more than 80% by 2050, + and fossil fuel power generation without CCS is phased out almost entirely by + 2100. + 4.3d: Behaviour, lifestyle and culture have a considerable influence on energy use + and associated emissions, with high mitigation potential in some sectors, in + particular when complementing technological and structural change . Emissions + can be substantially lowered through changes in consumption patterns, adoption + of energy savings measures, dietary change and reduction in food wastes. + 4.4b: 'International cooperation is critical for effective mitigation, even though + mitigation can also have local co-benefits. Adapta- tion focuses primarily on + local to national scale outcomes, but its effectiveness can be enhanced through + coordination across governance scales, including international cooperation: • + The United Nations Framework Convention on Climate Change is the main multilateral + forum focused on addressing climate change, with nearly universal participation. + Other institutions organized at different levels of governance have resulted in + diversifying international climate change cooperation. • The Kyoto Protocol offers + lessons towards achieving the ultimate objective of the UNFCCC, particularly with + respect to participation, implementation, flexibility mechanisms and environmental + effectiveness . • Policy linkages among regional, national and sub-national climate + policies offer potential climate change mitigation ben- efits. Potential advantages + include lower mitigation costs, decreased emission leakage and increased market + liquidity. International cooperation for supporting adaptation planning and implementation + has received less attention histori- cally than mitigation but is increasing + and has assisted in the creation of adaptation strategies, plans and actions at + the national, sub-national and local level.' + 4.4g: 'There has been a considerable increase in national and sub-national plans + and strategies on both adaptation and mitigation since the AR4, with an increased + focus on policies designed to integrate multiple objectives, increase co-benefits + and reduce adverse side effects: • National governments play key roles in adaptation + planning and implementation through coordinating actions and providing frameworks + and support. While local government and the private sector have different functions, + which vary regionally, they are increasingly recognized as critical to progress + in adaptation, given their roles in scaling up adaptation of communities, households + and civil society and in managing risk information and financing. • Institutional + dimensions of adaptation governance, including the integration of adaptation into + planning and decision- making, play a key role in promoting the transition from + planning to implementation of adaptation. Examples of institutional approaches + to adaptation involving multiple actors include economic options , laws and regulations + and national and government policies and programmes.' + 4.4l: • In principle, mechanisms that set a carbon price, including cap and trade + systems and carbon taxes, can achieve mitiga- tion in a cost-effective way but + have been implemented with diverse effects due in part to national circumstances + as well as policy design. The short-run effects of cap and trade systems have + been limited as a result of loose caps or caps that have not proved to be constraining. + In some countries, tax-based policies specifically aimed at reducing GHG emissions—alongside + technology and other policies—have helped to weaken the link between GHG emissions + and GDP. In addition, in a large group of countries, fuel taxes have had effects + that are akin to sectoral carbon taxes. + 4.4m: • Regulatory approaches and information measures are widely used and are often + environmentally effective . Examples of regulatory approaches include energy efficiency + standards; examples of information programmes include labelling programmes that + can help consumers make better-informed decisions. + 4.4n: • Sector-specific mitigation policies have been more widely used than economy-wide + policies . Sector-specific policies may be better suited to address sector-specific + barriers or market failures and may be bundled in packages of complementary policies. + Although theoretically more cost-effective, administrative and political barriers + may make economy-wide policies harder to implement. Interactions between or among + mitigation policies may be synergistic or may have no additive effect on reducing + emissions. • Economic instruments in the form of subsidies may be applied across + sectors, and include a variety of policy designs, such as tax rebates or exemptions, + grants, loans and credit lines. An increasing number and variety of renewable + energy policies including subsidies—motivated by many factors—have driven escalated + growth of RE technologies in recent years. At the same time, reducing subsidies + for GHG-related activities in various sectors can achieve emission reductions, + depending on the social and economic context. + 4.4p: Co-benefits and adverse side effects of mitigation could affect achievement + of other objectives such as those related to human health, food security, biodiversity, + local environmental quality, energy access, livelihoods and equitable sustainable + development. The potential for co-benefits for energy end-use measures outweighs + the potential for adverse side effects whereas the evidence suggests this may + not be the case for all energy supply and agriculture, forestry and other land + use measures. Some mitigation policies raise the prices for some energy services + and could hamper the ability of societies to expand access to modern energy services + to underserved populations. These potential adverse side effects on energy access + can be avoided with the adoption of complementary policies such as income tax + rebates or other benefit transfer mechanisms. Whether or not side effects materialize, + and to what extent side effects materialize, will be case- and site-specific, + and depend on local circumstances and the scale, scope and pace of implementation. + Many co-benefits and adverse side effects have not been well-quantified. + 4.4q: Technology policy complements other mitigation policies across all scales, + from international to sub-national; many adaptation efforts also critically + rely on diffusion and transfer of technologies and management practices. Policies + exist to address market failures in R&D, but the effective use of technologies + can also depend on capacities to adopt technologies appropriate to local circumstances. + 4.4r: Substantial reductions in emissions would require large changes in investment + patterns . For mitigation scenarios that stabilize concentrations in the range + of 430 to 530 ppm CO2-eq by 210019, annual investments in low carbon electricity + supply and energy efficiency in key sectors are projected in the scenarios to + rise by several hundred billion dollars per year before 2030. Within appropriate + enabling environments, the private sector, along with the public sector, can play + important roles in financing mitigation and adaptation . Financial resources for + adaptation have become available more slowly than for mitigation in both developed + and developing countries. Limited evidence indicates that there is a gap between + global adaptation needs and the funds available for adaptation. There is a need + for better assessment of global adaptation costs, funding and investment. Potential + synergies between international finance for disaster risk management and adaptation + have not yet been fully realized . + 4.5a: Climate change is a threat to sustainable development. Nonetheless, there + are many opportu- nities to link mitigation, adaptation and the pursuit of other + societal objectives through integrated responses. Successful implementation relies + on relevant tools, suitable governance structures and enhanced capacity to respond. + 4.5b: Climate change exacerbates other threats to social and natural systems, placing + additional burdens particularly on the poor . Aligning climate policy with sustainable + development requires attention to both adaptation and mitigation . Delaying global + mitigation actions may reduce options for climate-resilient pathways and adaptation + in the future. Opportunities to take advantage of positive synergies between adaptation + and mitigation may decrease with time, particularly if limits to adaptation are + exceeded. Increasing efforts to mitigate and adapt to climate change imply an + increasing complexity of interactions, encompassing connections among human health, + water, energy, land use and biodiversity . +summary_topics: + 1.1a: Climate Change Trend + 1.1b: Ocean Warming + 1.1c: Precipitations and Ocean Salinity + 1.1d: Acidification + 1.1e: Ice Melting + 1.1g: Sea Level + 1.2a: Anthropogenic Greenhouse Gas Emissions + 1.2c: Human Influence on Climate Change + 1.3a: Impacts of Climate Change + 1.4a: Extreme Events + 2.1b: Anthropogenic Emissions Causes and Projections + 2.1c: CO2 Correlation with Global Warming + 2.1d: Reducing Global Warming + 2.2e: Changes in Precipitations + 2.2f: Ocean Warming + 2.2g: Acidification + 2.2h: Ice Melting + 2.2m: Sea Level + 2.3a: Main Risks of Climate Change + 2.3b: Animal Extiction + 2.3c: Food Security + 2.3e: Economic Impact + 2.3f: Societal Impact + 2.4a: Surface Temperature + 2.4b: Stabilization + 2.4c: Sea Level + 2.4d: Overall Risks + 3.1a: Decision-making + 3.1b: Sustainable Development and Equity + 3.1c: Designing Climate Policies + 3.1d: Cooperation and Collective Action + 3.2b: Mitigation and Adaptation + 3.2d: Risks of Inaction + 3.2e: Actions for Mitigation + 3.2f: Mitigation Risks + 3.3a: Adaptation Advantages + 3.3b: Adaptation Implementation + 3.3c: Adaptation and Sciety + 3.3d: Adaptation Limits + 3.3f: Co-benefits + 3.3g: Transformational Change + 3.4a: Mitigation Pathways + 3.4b: Risks of Inaction + 3.4c: Emission Scenarios + 3.4d: Mitigation Scenarios + 3.4e: Reducing Emissions + 3.4f: Effects of Mitigation Delay + 3.4g: Economic Cost of Mitigation + 3.4h: Mitigation Technologies + 3.4i: Mitigation Co-benefits + 3.4l: Fossil Fuel + 4.1a: Enabling Mitigation and Adaptation + 4.1b: Innovation and Investments + 4.1c: Factors of Vulnerability + 4.2a: Adaptation Options + 4.2b: Adaptation Adoption + 4.2c: Need for Adaptation + 4.3a: Mitigation Options + 4.3b: Mitigation Scenarios + 4.3d: Impact of Behaviour + 4.4b: International Cooperation + 4.4g: National Strategies + 4.4l: Carbon Tax + 4.4m: Regulatory Approaches and Information Measures + 4.4n: Sector Policies + 4.4p: Co-benefits and Side Effects + 4.4q: Technological Solutions + 4.4r: Financial Solutions + 4.5a: Climate Change Projections + 4.5b: Tackling Climate Change +titles: + 1.1a: + - 'Atmosphere + + ' + 1.1b: + - 'Ocean + + ' + 1.1c: + - 'Atmosphere + + ' + - 'Ocean + + ' + 1.1d: + - 'Ocean + + ' + 1.1e: + - 'Cryosphere + + ' + 1.1g: + - 'Sea level + + ' + 1.2a: + - 'Natural and anthropogenic radiative forcings + + ' + - 'Human activities affecting emission drivers + + ' + 1.2c: + - 'Attribution of climate + + ' + 1.3a: + - 'Observed impacts attributed to climate change + + ' + 1.4a: + - 'Extreme events + + ' + 2.1b: + - 'Key drivers of future climate and the + + ' + - 'Response options for mitigation + + ' + 2.1c: + - 'Climate system responses + + ' + 2.1d: + - 'Climate system responses + + ' + 2.2e: + - 'Water cycle + + ' + 2.2f: + - 'Ocean, cryosphere and sea level + + ' + 2.2g: + - 'Carbon cycle and biogeochemistry + + ' + 2.2h: + - 'Ocean, cryosphere and sea level + + ' + 2.2m: + - 'Ocean, cryosphere and sea level + + ' + 2.3a: + - 'Exposure and vulnerability + + ' + - 'Future risks and impacts caused + + ' + - 'Climate change beyond 2100, + + ' + - 'Characteristics of adaptation pathways + + ' + 2.3b: + - 'Future risks and impacts caused + + ' + - 'Climate change beyond 2100, + + ' + 2.3c: + - 'Ecosystems and their services in the oceans, + + ' + - 'Water, food and urban systems, human + + ' + 2.3e: + - 'Water, food and urban systems, human + + ' + 2.3f: + - 'Water, food and urban systems, human + + ' + 2.4a: + - 'Climate change beyond 2100, + + ' + 2.4b: + - 'Climate change beyond 2100, + + ' + 2.4c: + - 'Climate change beyond 2100, + + ' + 2.4d: + - 'Climate change beyond 2100, + + ' + 3.1a: + - 'Foundations of decision-making + + ' + 3.1b: + - 'Foundations of decision-making + + ' + - 'Interaction among mitigation, adaptation + + ' + 3.1c: + - 'Foundations of decision-making + + ' + 3.1d: + - 'Foundations of decision-making + + ' + 3.2b: + - 'Climate change risks reduced by + + ' + - 'Trade-offs, synergies and integrated responses + + ' + 3.2d: + - 'Future risks and impacts caused + + ' + - 'Climate change risks reduced by + + ' + - 'Characteristics of mitigation pathways + + ' + 3.2e: + - 'Climate system responses + + ' + - 'Climate change risks reduced by + + ' + - 'Characteristics of mitigation pathways + + ' + 3.2f: + - 'Climate change risks reduced by + + ' + - 'Characteristics of mitigation pathways + + ' + 3.3a: + - 'Characteristics of adaptation pathways + + ' + 3.3b: + - 'Characteristics of adaptation pathways + + ' + 3.3c: + - 'Characteristics of adaptation pathways + + ' + 3.3d: + - 'Characteristics of adaptation pathways + + ' + 3.3f: + - 'Characteristics of adaptation pathways + + ' + 3.3g: + - 'Characteristics of adaptation pathways + + ' + 3.4a: + - 'Characteristics of mitigation pathways + + ' + 3.4b: + - 'Characteristics of mitigation pathways + + ' + 3.4c: + - 'Characteristics of mitigation pathways + + ' + 3.4d: + - 'Characteristics of mitigation pathways + + ' + 3.4e: + - 'Characteristics of mitigation pathways + + ' + 3.4f: + - 'Characteristics of mitigation pathways + + ' + 3.4g: + - 'Characteristics of mitigation pathways + + ' + 3.4h: + - 'Characteristics of mitigation pathways + + ' + 3.4i: + - 'Mitigation + + ' + 3.4l: + - 'Mitigation + + ' + 4.1a: + - 'Common enabling factors and constraints + + ' + 4.1b: + - 'Common enabling factors and constraints + + ' + 4.1c: + - 'Common enabling factors and constraints + + ' + 4.2a: + - 'Response options for adaptation + + ' + 4.2b: + - 'Human responses to climate change: + + ' + - 'Response options for adaptation + + ' + - 'Adaptation + + ' + 4.2c: + - 'Response options for adaptation + + ' + 4.3a: + - 'Response options for mitigation + + ' + 4.3b: + - 'Response options for mitigation + + ' + 4.3d: + - 'Common enabling factors and constraints + + ' + - 'Response options for mitigation + + ' + 4.4b: + - 'International and regional cooperation + + ' + 4.4g: + - 'Adaptation + + ' + - 'Mitigation + + ' + 4.4l: + - 'Mitigation + + ' + 4.4m: + - 'Mitigation + + ' + 4.4n: + - 'Mitigation + + ' + 4.4p: + - 'Response options for mitigation + + ' + - 'Mitigation + + ' + 4.4q: + - 'Technology development and transfer + + ' + 4.4r: + - 'Investment and finance + + ' + 4.5a: + - 'Interaction among mitigation, adaptation + + ' + - 'Trade-offs, synergies and integrated responses + + ' + 4.5b: + - 'Foundations of decision-making + + ' + - 'Interaction among mitigation, adaptation + + ' + - 'Trade-offs, synergies and integrated responses + + '