Set up by UNEP and the World Meteorological Organization, the Intergovernmental Panel on Climate Change (IPCC) brings together the best available science on climate change. In November 2007 it released its Fourth Assessment Report, comprising four sections: The Physical Science Basis, by Working Group I; Impacts, Adaptation and Vulnerability, by Working Group II; Mitigation of Climate Change, by Working Group III; and an overall Synthesis Report. It took six years to complete the report, which runs to several thousand pages. For this and its other work over the last 20 years, the IPCC was the joint winner of the 2007 Nobel Peace Prize.

The Summary for Policy Makers of the Synthesis Report of the IPCC Fourth Assessment Report highlights:

• Around 20 per cent to 30 per cent of the plant and animal species assessed are likely to be at increased risk of extinction if global average temperatures exceed 1.5 degree C to 2.5 degree C over late 20th century levels.
• The likelihood of "irreversible" impacts. For example if temperature increases exceed about 3.5 degrees C, between 40 per cent and 70 per cent of the species assessed might be at increased risk of extinction.
• Increases in sea surface temperatures of about one-three degrees C are projected to result in more "frequent coral bleaching events and widespread mortality".
• Concern over the oceans and seas becoming more acidic as they absorb rising levels of carbon dioxide and the impacts on "marine shell-forming organisms" like coral reefs.
• The risks of extreme weather events with higher confidence in the projected increases in droughts, heatwaves and floods as well as their adverse impacts.
• Concern that the poor and the elderly in low-latitude and less-developed areas including those in dry areas and living on mega-deltas are likely to suffer most.
• There is high confidence that by mid-century "many semi-arid areas, for example the Mediterranean basin, western United States, southern Africa and northeast Brazil, will suffer a decrease in water resources due to climate change".
• New observations linked with the Greenland and possibly Antarctic ice sheets may mean that the rate of ice loss will increase above previous forecasts.
• Concern that any benefits linked with climate change will be gone after more modest temperature rises.