March 4, 2010 10:16 pm

Review says global warming is man-made

The case for man-made global warming is even stronger than the Intergovernmental Panel on Climate Change maintained in its official assessments, according to the first scientific review published since December’s Copenhagen conference and subsequent attacks on the IPCC’s credibility.

An international research team led by the UK Met Office spent the past year analysing more than 100 recent scientific papers to update the last IPCC assessment, released in 2007.

Although the review itself preceded the sceptics’ assault on climate science over the past three months, its launch in London on Thursday marks a resumption of the campaign by mainstream scientists to show that man-made releases of greenhouse gases are causing potentially dangerous global warming.

“The fingerprint of human influence has been detected in many different aspects of observed climate changes,” said Peter Stott, head of climate monitoring at the Met Office Hadley Centre for Climate Research. “Natural variability, from the sun, volcanic eruptions or natural cycles, cannot explain recent warming.”

The review, published in the journal Wiley Interdisciplinary Reviews: Climate Change, found several “fingerprints” of warming that had not been established by the time of the last IPCC assessment but were now unambiguously present.

One is human-induced climate in the Antarctic, the last continent where regional warming has been demonstrated.

There is also new evidence of warming in the oceans, which is having several effects. The subtropical Atlantic is becoming saltier; the extra salinity could in turn alter ocean currents.

Another effect of ocean warming is increasing evaporation, leading to more humidity in the atmosphere and changing rainfall patterns.

“The whole water cycle is changing,” said Mr Stott. “The wet regions are tending to get wetter and the dry regions are getting dryer.”

Globally, this means less rainfall in the tropics and more at higher latitudes, although Mr Stott said there was much regional variation in the pattern, which scientists were still working to make sense of.

The review is based on a forensic comparison of the pattern of changes expected from man-made warming with those that would result from other factors such as changing solar radiation and purely natural variations.

A separate study by Russian and US scientists, published today in the journal Science, shows that methane, a powerful greenhouse gas, is escaping from the seafloor of the warming Arctic Ocean more rapidly than had been suspected.

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