The Earth’s climate has changed throughout history. In the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era — and of human civilization. Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives.
The current warming trend is of particular significance because most of it is very likely human-induced and proceeding at a rate that is unprecedented in the past 1,300 years.
Carbon dioxide (CO2) is an important heat-trapping (greenhouse) gas, which is released through human activities such as deforestation and burning fossil fuels, as well as natural processes such as respiration and volcanic eruptions.
The Earth’s average temperature has increased about 1 degree Fahrenheit during the 20th century. One degree may sound like a small amount, but it’s an
unusual event in our planet’s recent history. Earth’s climate record, preserved in tree rings, ice cores, and coral reefs, shows that the global average temperature is stable over long periods of time. Small changes in temperature correspond to enormous changes in the environment.
The rise in the planet’s temperature has mostly occurred since the 1970. The 20 warmest years have occurred since 1981 and all 10 of the warmest years have occurred in the past 12 years. Even though the 2000s witnessed a solar output decline resulting in an unusually deep solar minimum in 2007-2009, surface temperatures continue to increase.
Sea level rise
Click to view infographic on sea level rise.
IPCC 4 key findings
1. There is 95 percent certainty that human activities are responsible for global warming
2. Carbon dioxide is at an “unprecedented” level not seen for at least the last 800,000 years
3. Sea level is set to continue to rise at a faster rate than over the past 40 years
4. Over the last two decades, the Greenland and Antarctic ice sheets have been melting and glaciers have receded in most parts of the world.
These key findings emerged from the Intergovernmental Panel on Climate Change’s (IPCC) Fifth Assessment Report Summary for Policy Makers, released September 27, 2013, which more than 25 NASA scientists helped author and review.
The report is the work of 209 lead authors and 50 review editors from 39 countries, and over 600 contributing authors from 32 countries.
Source: Information above comes from NASA’s climate research center: climate.nasa.gov/