El Niño Southern Oscillation (ENSO) and Health: An Overview for Climate and Health Researchers <s> Climate Change and ENSO <s> The 1998 flood in Bangladesh ravaged approximately 60% of the land and affected over 30 million people. The aim of this study is to examine the impact of the flood on the health of the communities affected and to explore factors associated with episodes of diarrhoea. We conducted structured interviews with 517 people in two districts that had been affected in October 1998, when the flood water level was at its peak. Of the 517 respondents, 98.3% developed health problems or found that existing health problems were exacerbated. Many perceived that their general health condition was 'much worse' (16.9%) or 'worse' (64.3%). The most prevalent condition was fever (63.6%), followed by respiratory problems (46.8%), diarrhoea (44.3%), and skin problems (41.0%). Only 1.0% and 6.7% of the respondents treated water before drinking, by boiling and chlorination, respectively, although water collected from tube-wells (93.2%) and rivers (6.0%) was perceived by 75.0% of the respondents to be contaminated. Factors associated with developing or worsening diarrhoea were as follows; the number of family members, poor economic status, a lack of distribution of water purification tablets, the type of water storage vessels, not putting a lid on the vessel, no use of latrines, perceived change of drinking water, food scarcity, and worries about the future. In logistic regression analysis, men, poor economic status, lack of distribution of water purification tablets, and the type of water storage vessels had a significant association with diarrhoea. The 1998 Bangladesh flood had a substantial impact on the health of communities. Diarrhoea was associated with socioeconomic status, water handling and household sanitation. There ought to be more emphasis on health education in the pre-disaster period in order to empower communities against floods. <s> BIB001 </s> El Niño Southern Oscillation (ENSO) and Health: An Overview for Climate and Health Researchers <s> Climate Change and ENSO <s> Every year floods cause enormous damage all over the world. This study investigates loss of human life statistics for different types of floods and different regions on a global scale. The OFDA/CRED Database contains data on international disasters and is maintained by the Centre for Research on the Epidemiology of Disasters in Brussels (CRED) in cooperation with United States Office for Foreign Disaster Assistance (OFDA). Information from this source on a large number of flood events, which occurred between January 1975 and June 2002, is evaluated with respect to flood location and flood type. Due to the limited availability of information on coastal flood events, the scope of this study is limited to three types of freshwater flooding: river floods, flash floods and drainage problems. First, the development of loss of life statistics over time is discussed. Second, the dataset is analysed by region, by flood type and by the combination of type and region. The study shows that flash floods result in the highest average mortality per event (the number of fatalities divided by the number of affected persons). A cross analysis by flood type and location shows that average mortality is relatively constant for the different types over various continents, while the magnitude of the impacts (numbers of killed) and affected for a certain type varies between the different continents. On a worldwide scale Asian river floods are most significant in terms of number of persons killed and affected. Finally, a comparison with figures for other types of natural disasters shows that floods are the most significant disaster type in terms of the number of persons affected. <s> BIB002 </s> El Niño Southern Oscillation (ENSO) and Health: An Overview for Climate and Health Researchers <s> Climate Change and ENSO <s> During the warm early Pliocene (approximately 4.5 to 3.0 million years ago), the most recent interval with a climate warmer than today, the eastern Pacific thermocline was deep and the average west-to-east sea surface temperature difference across the equatorial Pacific was only 1.5 +/- 0.9 degrees C, much like it is during a modern El Niño event. Thus, the modern strong sea surface temperature gradient across the equatorial Pacific is not a stable and permanent feature. Sustained El Niño-like conditions, including relatively weak zonal atmospheric (Walker) circulation, could be a consequence of, and play an important role in determining, global warmth. <s> BIB003 </s> El Niño Southern Oscillation (ENSO) and Health: An Overview for Climate and Health Researchers <s> Climate Change and ENSO <s> The El Nino–Southern Oscillation (ENSO) drives large changes in global climate patterns from year to year, yet its sensitivity to continued anthropogenic greenhouse forcing is uncertain. We analyzed fossil coral reconstructions of ENSO spanning the past 7000 years from the Northern Line Islands, located in the center of action for ENSO. The corals document highly variable ENSO activity, with no evidence for a systematic trend in ENSO variance, which is contrary to some models that exhibit a response to insolation forcing over this same period. Twentieth-century ENSO variance is significantly higher than average fossil coral ENSO variance but is not unprecedented. Our results suggest that forced changes in ENSO, whether natural or anthropogenic, may be difficult to detect against a background of large internal variability. <s> BIB004 </s> El Niño Southern Oscillation (ENSO) and Health: An Overview for Climate and Health Researchers <s> Climate Change and ENSO <s> The El Nino/Southern Oscillation exhibits considerable natural variability on interdecadal to centennial timescales making it difficult to understand how climate change affects it. A reconstruction now shows there has been anomalously high activity in the late twentieth century, relative to the past seven centuries. This is suggestive of a response to global warming, and will provide constraints to improve climate models and projections. <s> BIB005 </s> El Niño Southern Oscillation (ENSO) and Health: An Overview for Climate and Health Researchers <s> Climate Change and ENSO <s> Abstract. It is vital to understand how the El Nino–Southern Oscillation (ENSO) has responded to past changes in natural and anthropogenic forcings, in order to better understand and predict its response to future greenhouse warming. To date, however, the instrumental record is too brief to fully characterize natural ENSO variability, while large discrepancies exist amongst paleo-proxy reconstructions of ENSO. These paleo-proxy reconstructions have typically attempted to reconstruct ENSO's temporal evolution, rather than the variance of these temporal changes. Here a new approach is developed that synthesizes the variance changes from various proxy data sets to provide a unified and updated estimate of past ENSO variance. The method is tested using surrogate data from two coupled general circulation model (CGCM) simulations. It is shown that in the presence of dating uncertainties, synthesizing variance information provides a more robust estimate of ENSO variance than synthesizing the raw data and then identifying its running variance. We also examine whether good temporal correspondence between proxy data and instrumental ENSO records implies a good representation of ENSO variance. In the climate modeling framework we show that a significant improvement in reconstructing ENSO variance changes is found when combining information from diverse ENSO-teleconnected source regions, rather than by relying on a single well-correlated location. This suggests that ENSO variance estimates derived from a single site should be viewed with caution. Finally, synthesizing existing ENSO reconstructions to arrive at a better estimate of past ENSO variance changes, we find robust evidence that the ENSO variance for any 30 yr period during the interval 1590–1880 was considerably lower than that observed during 1979–2009. <s> BIB006 </s> El Niño Southern Oscillation (ENSO) and Health: An Overview for Climate and Health Researchers <s> Climate Change and ENSO <s> We analyse the ability of CMIP3 and CMIP5 coupled ocean–atmosphere general circulation models (CGCMs) to simulate the tropical Pacific mean state and El Nino-Southern Oscillation (ENSO). The CMIP5 multi-model ensemble displays an encouraging 30 % reduction of the pervasive cold bias in the western Pacific, but no quantum leap in ENSO performance compared to CMIP3. CMIP3 and CMIP5 can thus be considered as one large ensemble (CMIP3 + CMIP5) for multi-model ENSO analysis. The too large diversity in CMIP3 ENSO amplitude is however reduced by a factor of two in CMIP5 and the ENSO life cycle (location of surface temperature anomalies, seasonal phase locking) is modestly improved. Other fundamental ENSO characteristics such as central Pacific precipitation anomalies however remain poorly represented. The sea surface temperature (SST)-latent heat flux feedback is slightly improved in the CMIP5 ensemble but the wind-SST feedback is still underestimated by 20–50 % and the shortwave-SST feedbacks remain underestimated by a factor of two. The improvement in ENSO amplitudes might therefore result from error compensations. The ability of CMIP models to simulate the SST-shortwave feedback, a major source of erroneous ENSO in CGCMs, is further detailed. In observations, this feedback is strongly nonlinear because the real atmosphere switches from subsident (positive feedback) to convective (negative feedback) regimes under the effect of seasonal and interannual variations. Only one-third of CMIP3 + CMIP5 models reproduce this regime shift, with the other models remaining locked in one of the two regimes. The modelled shortwave feedback nonlinearity increases with ENSO amplitude and the amplitude of this feedback in the spring strongly relates with the models ability to simulate ENSO phase locking. In a final stage, a subset of metrics is proposed in order to synthesize the ability of each CMIP3 and CMIP5 models to simulate ENSO main characteristics and key atmospheric feedbacks. <s> BIB007 </s> El Niño Southern Oscillation (ENSO) and Health: An Overview for Climate and Health Researchers <s> Climate Change and ENSO <s> Tropical Pacific Ocean dynamics during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) are poorly characterized due to a lack of evidence from the eastern equatorial Pacific. We reconstructed sea surface temperature, El Nino–Southern Oscillation (ENSO) activity, and the tropical Pacific zonal gradient for the past millennium from Galapagos ocean sediments. We document a mid-millennium shift (MMS) in ocean-atmosphere circulation around 1500–1650 CE, from a state with dampened ENSO and strong zonal gradient to one with amplified ENSO and weak gradient. The MMS coincided with the deepest LIA cooling and was probably caused by a southward shift of the intertropical convergence zone. The peak of the MCA (900–1150 CE) was a warm period in the eastern Pacific, contradicting the paradigm of a persistent La Nina pattern. <s> BIB008 </s> El Niño Southern Oscillation (ENSO) and Health: An Overview for Climate and Health Researchers <s> Climate Change and ENSO <s> Editor’s note: For easy download the posted pdf of the State of the Climate for 2016 is a very low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download. <s> BIB009 </s> El Niño Southern Oscillation (ENSO) and Health: An Overview for Climate and Health Researchers <s> Climate Change and ENSO <s> We investigate the dependence of ENSO atmospheric feedbacks on the mean-state in a perturbed atmospheric physics ensemble with the Kiel Climate Model (KCM) and in CMIP5 models. Additionally, uncoupled simulations are conducted with the atmospheric component of the KCM to obtain further insight into the mean-state dependence. It is found that the positive zonal wind feedback and the negative heat flux feedback, with the short-wave flux as dominant component, are strongly linearly related through sea surface temperature (SST) and differences in model physics are less important. In observations, strong zonal wind and heat flux feedbacks are caused by a convective response in the western central equatorial Pacific (Nino4 region), resulting from an eastward (westward) shift of the rising branch of the Walker Circulation (WC) during El Nino (La Nina). Many state-of-the-art climate models exhibit an equatorial cold SST bias in the Nino4 region, i.e. are in a La Nina-like mean-state. Therefore they simulate a too westward located rising branch of the WC (by up to 30°) and only a weak convective response. Thus, the position of the WC determines the strength of both the amplifying wind and usually damping heat flux feedback, which also explains why biases in these two feedbacks partly compensate in many climate models. Furthermore, too weak atmospheric feedbacks can cause quite different ENSO dynamics than observed, while enhanced atmospheric feedbacks lead to a substantial improvement of important ENSO properties such as seasonal ENSO phase locking and asymmetry between El Nino and La Nina. Differences in the mean-state SST are suggested to be a major source of ENSO diversity in current climate models. <s> BIB010
The recent 2015-16 El Niño event is a timely reminder of the mammoth impacts that ENSO events can have on ecosystems and society. For instance, extensive forest fires in Indonesia and an associated haze hazard across the wider region, devastating floods in Peru, severe coral bleaching in a number of places across the Pacific and widespread health issues throughout the Pacific and elsewhere over the course of the 2015-16 El Niño are similar to the type of impacts that occurred during previous El Niño episodes such as in 1982-83 and 1997-98 BIB009  . Although attention is often directed to El Niño impacts, intense La Niña events can be equally impactful as is evidenced for the 1998-99 La Niña event that spawned catastrophic flooding in Bangladesh, Venezuela, and China, with a large number of lives lost BIB002 BIB001 . Understandably consternation associated with such impacts, twinned with the worrisome spectre of anthropogenic climate change precipitated an immense interest in establishing how ENSO might respond to climate change and the implication this holds for future population health. Two broad approaches were applied to establish ENSO responses to a warmer world: the analysis of paleoclimate records and the conduct of numerical climate modelling experiments  117] . That inter-annual climate variability similar to that associated with ENSO has been a characteristic of the Pacific Basin for millennia is borne out by a number of paleoclimate studies. These revealed not only that strong east to west Pacific contrasts in ocean temperatures, similar to the current climatological difference of 2 o C, existed in the past BIB003 , but that ENSO frequency has not changed significantly since the Pliocene (5.333 to 2.58 million years BP) when global temperatures were 2-3 o C higher than present  . Similarly there is evidence for ENSO events and associated inter-annual climate variability during the last glacial maximum  and the Medieval Climate Anomaly and the Little Ice Age [ BIB008 . Paleoclimate studies have also revealed that, compared to previous centuries and millennia, twentieth-century ENSO activity has been considerably stronger BIB004 BIB005 BIB006 , which has been interpreted as possible evidence for a link between global warming and ENSO response [117] . In brief, the upshot of most paleoclimate studies is that ENSO and marked inter-annual climate variability originating in the Pacific Basin is a characteristic of the global climate system whether it be in a cooler or warmer state than present. While it is likely that ENSO will be a feature of a warmer world  , the question remains as to whether the intensity and frequency of El Niño/La Niña events might change with anthropogenic climate change. About the only way to answer this question is by performing climate model experiments using a range of greenhouse gas concentration scenarios, currently codified as Representative Concentration Pathways (RCP). Cai et al. [117] and Wang et al.  provided useful summaries of the current thinking on how ENSO climatology might respond to greenhouse warming based on a review of results from climate models in the Coupled Model Inter-comparison Project phases 3 (CMIP3) and 5 (CMIP5) BIB007 and the work of others. They concluded that there is some modelling-based evidence for increases in the frequency of ENSO events with global warming. However, in relation to whether future El Niño/La Niña events will become stronger or weaker, Wang et al.  were far more cautionary in their conclusions than Cai et al. [117] , with the former concluding that evidence for a stronger or weaker El Niño/La Niña under global warming is unclear in contrast to the latter who confidently stated there will be an increased frequency of extreme El Niño and La Niña events. That an unequivocal greenhouse warming response of ENSO in climate models is not apparent stems from a range of factors. These include complex competing ocean-atmosphere feedback processes that have a negating effect on some of the key elements of the ENSO system  BIB010 plus general uncertainties related to the ability of climate models to simulate the current ENSO state, the sensitivity of ENSO onset and cessation to global warming, difficulties with parameterizing climate processes that occur at scales less than that resolved in models and how climate change related distant influences from the Atlantic and Indian Oceans will affect ENSO  . Clearly the equivocal findings regarding the possible impacts of climate change on ENSO hold important implications for future ENSO -health associations. Given the state of the science, perhaps all that can ventured at this point is that ENSO will be influenced in some way by climate change, with associated implications for health. The direction of such an alteration will depend on a number of climate and non-climate related drivers. The climate drivers include ENSO-related variability in rainfall, temperature and storm activity, layered upon changes to the mean climate state attributable to climate change. Moreover, a factor that makes speculation about the health risks of an altered ENSO phenomenon challenging is the significant inter-event variability of ENSO climate outcomes -is there a canonical El Niño/La Niña -and the decadal scale non-stationary relationship between ENSO and climate and thus health risks. While these generalities might seem inconsequential in terms of furthering our understanding of climate change, ENSO and health relationships, they serve as a reminder that caution is required when telescoping current ENSO health associations into the future in the absence of a firm understanding of how ENSO related climate variability may respond to further greenhouse warming. Lastly and notwithstanding issues associated with a non-stationary and highly variable ENSO climate system and associated implications for health impacts, if the probability of future ENSO events can be constrained as a result of the convergence of climate modelling results then estimating future ENSO-related health risks will largely be conditioned on non-climate factors such as the efficacy of early warning systems embedded in wider disaster risk reduction strategies.