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A HEADLINE-grabbing claim by climate scientists that they can see the hand of human activity in global warming will be contested at a meeting of the Intergovernmental Panel on Climate Change (IPCC) in Madrid later this month.

Press reports in recent weeks have highlighted a claim in the draft of the IPCC鈥檚 first full report for five years that the temperature rise over the past century is 鈥渦nlikely to be entirely due to natural causes, and that a pattern of responses to human activities is identifiable in the climate record鈥�.

The claim follows studies by climate modellers at Britain鈥檚 Meteorological Office in Bracknell and the Max Planck Institute for Meteorology in Hamburg. Earlier this year the two groups reported that their computer models of the world鈥檚 climate could, for the first time, mimic accurately the climatic trends of the past century. They did this by taking into account the shading effect of sulphate aerosols in Europe and elsewhere, as well as the general warming trend from increasing concentrations of greenhouse gases.

But some leading authors of the scientific chapters of the report are likely to push for the claim to be watered down when they meet in Madrid on 27 November. 鈥淢y concern is that the findings could be a fluke,鈥� Keith Shine of the University of Reading warned this week. 鈥淚t鈥檚 undoubtedly pioneering work, but we shouldn鈥檛 push it too far.鈥�

Elements not yet incorporated into the models include the effects of volcanic eruptions, soot in the atmosphere and tropospheric ozone. 鈥淭he danger is that when we add in other influences on climate we could find the models looking worse again 鈥� and then where would we be?鈥� Shine asks.

鈥淒ifferent parts of the report are in danger of becoming disconnected,鈥� says Shine. 鈥淚n the chapter I am mainly responsible for, we stress the great uncertainties in our understanding of influences on temperature. Then in others we say we can reproduce the climate of the past hundred years.鈥�

At earlier meetings there has been a clear consensus for a statement declaring that they have seen 鈥渁 pattern of responses to human activities鈥� 鈥� the current form of words. But some scientists feel they have been put under pressure to come up with a dramatic statement in time for the new IPCC report.

Bruce Callander of the Meteorological Office and a member of the IPCC鈥檚 science working group agrees that the text may be changed in Madrid. 鈥淭here will be a lot of debate,鈥� he says.