The Earth's temperature could rise under the impact of global warming to levels far higher than previously predicted, according to the United Nations' team of climate experts. A draft of the next influential Intergovernmental Panel on Climate Change (IPCC) report will tell politicians that scientists are now unable to place a reliable upper limit on how quickly the atmosphere will warm as carbon dioxide levels increase. The report draws together research over the past five years and will be presented to national governments in April and made public next year. It raises the possibility of the Earth's temperature rising well above the ceiling quoted in earlier accounts.
Such an outcome would have severe consequences, such as the collapse of the Greenland ice sheet and disruption of the Gulf Stream ocean current. The shift in position comes as Tony Blair is expected to pledge today to work towards a date for stabilising international greenhouse gas emissions when he meets Stop Climate Chaos, the climate change equivalent of Make Poverty History. The group is campaigning for a target date of 2015 for stabilisation, saying a later date would endanger the planet.
The new IPCC report will underpin international talks on how to cut greenhouse gas emissions when the first phase of the Kyoto protocol expires in 2012. Set up in 1988 by the UN, the IPCC brings together hundreds of experts to summarise the state of climate science for policymakers. It has produced three reports since 1990, each of which has been instrumental in establishing national and international strategies to address global warming. Government officials have until June to comment on the new draft, when scientists will gather in Bergen, Norway, to produce a final version.
The IPCC's removal of the upper temperature estimation is posited on new predictions about how the atmosphere would react to the carbon blanket wrapped around it. The three previous reports assumed that a doubling of carbon dioxide in the atmosphere would increase average global temperature by between 1.5 and 4.5C. Since then, computer models have foreseen increases as high as 11C, and some scientists wanted the naturally conservative IPCC to raise the upper end of the range. Others said such a move would be increase would be misleading and alarmist. According to sources who have seen it, the draft now assumes a doubling of carbon dioxide would cause a likely temperature rise of between 2 and 4.5C, but says higher increases are possible.
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http://www.guardian.co.uk/climatechange/story/0,,1719606,00.html
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