Hot Report: IPCC Report on the Physical Science of Climate Change

OLR Report 2013-R-0388 summarizes the recent Intergovernmental Panel on Climate Change (IPCC) report on the physical science basis of climate change. 2013-R0388 is based on the report's Summary for Policymakers and Technical Summary, which are both available at http://www.ipcc.ch/. The report was accepted, but not approved in detail, by the IPCC's Working Group I on September 26, 2013. As a result, it should be considered a draft, rather than final, product.

2013-R-0388 focuses on the aspects of the report that are most relevant to Connecticut, global warming and changes in sea level and precipitation patterns. Other issues addressed in the report include climate modeling and changes in ocean chemistry, glaciers and Arctic and Antarctic ice sheets, and climate phenomena such as monsoons.

Among the report's key findings are:

1. Climate warming is unequivocal. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of carbon dioxide (CO2) and other greenhouse gases have increased.
2. Each of the last three decades has been successively warmer at the earth's surface than any preceding decade since 1850. In the northern hemisphere, 1983–2012 was very likely the warmest 30-year period of the last 800 years.
3. It is extremely likely that human influence has been the dominant cause of the warming observed since the mid-20th century.
4. Continued emissions of greenhouse gases will cause further warming. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.
5. Global surface warming for the end of the 21st century is likely to exceed 1.5°C relative to the 1850 to 1900 baseline and will continue beyond 2100.
6. More than 90% of the energy accumulated between 1971 and 2010 has been stored in the oceans.
7. The oceans' volume has increased due to this warming and this, combined with melting of glaciers and ice sheets, has caused sea levels to rise.
8. The rate of sea level rise since the mid-19th century has been larger than the mean (average) rate during the previous two thousand years. From 1901 to 2010, global mean sea level rose by 0.19 meters (7.4 inches).
9. Global mean sea level will continue to rise during the 21st century at a rate that will very likely exceed that observed during 1971–2010.
10. Extreme precipitation events (e.g., downpours) over most of the mid-latitudes (e.g., Connecticut) will very likely become more intense and more frequent by the end of this century.

According to the report, most aspects of climate change will persist for many centuries even if emissions of CO2 are stopped.

On the other hand, there are variables where the data are not clear. For example, the report notes that there are no clear trends in annual numbers of tropical storms, hurricanes, and major hurricanes over the past 100 years in the North Atlantic basin. It expresses low confidence, on a global scale, that climate change will increase the intensity or duration of droughts. In addition, warming has varied and, according to the report, will continue to vary from year to year and decade to decade and will not be uniform across regions.

The report's findings and projections are generally similar to those in IPCC's last assessment of the climate. This report is more confident that climate change is largely due to anthropogenic (human-made) forces. On the other hand, it projects that a doubling of CO2 concentrations may have less impact on temperature than IPCC previously projected.

For more information, read the full report.