IPCC reports more climate change certainty

There is now a 'very high confidence' that human actions have caused a warming of the Earth, according to the Intergovernmental Panel on Climate Change (IPCC). Global temperatures are predicted to rise by between 1.8-4.0 degrees C by 2100. Sea levels are most likely to rise by 28-43cm.

The IPCC, who advise the UN on the scientific understanding of climate change, published these findings in Climate Change 2007: The Physical Science Basis, the first part of the IPCC’s Fourth Assessment Report.

The main differences between this new report and the Third Assessment Report, published in 2001, are greater certainty that an increase in temperature due to human influences has occurred and a higher level of confidence in predictions of climatic changes by 2100. In 2001 the IPCC would only say it was likely that temperature rises were associated with human actions, 'likely' meaning a 66-90% probability. In the 2007 report this link is now at least 90% certain.

The Fourth Assessment Report also concluded that it was probable that Arctic summer sea ice would disappear in second half of century. It was also very likely that there would be an increase in heatwaves and likely that there would be an increase in tropical storm intensity.

The headline temperature and sea level rises predicted in the fourth report cover a narrower range than those in the third, which predicted temperature increases of 1.4-5.8 degrees C and sea level rises of up to 88cm by 2100. However, the two reports are not directly comparable, because of changes in the methodologies used. The minimum and maximum figures reflect the most probable temperature increase associated with two different emissions scenarios. If the likely ranges for those two scenarios were included the temperature range would be 1.1-6.4 degrees C.

The IPCC have also chosen not to include possible sea level rise due to melting of the Greenland Ice Sheet. One source told WNN that this choice had rendered the report 'already out of date'.

Further reports on the impact of these changes and ways of mitigating the effects will be published later in the year.

Further Information

IPCC Climate Change 2007: The Physical Science Basis

WNA's Global Warming - The Science information paper