SCIENCE: Man’s climate fingerprints clear — U.K. Met Office (03/05/2010)

The possibility that human activity is not the prime cause of climate change is becoming “increasingly remote,” according to a major review of climate science released by Britain’s national weather service, the Met Office.

The study used computer models of different possible climate change drivers — including solar output, volcanic eruptions, El Niño and the release of greenhouse gases — matched against tangible climate changes over the past decades to air and sea temperature and Arctic sea ice. This technique, called “optimal detection,” showed clear fingerprints of man-caused warming, said Peter Stott, who led the project.

“This wealth of evidence shows that there is an increasingly remote possibility that climate change is being dominated by natural factors rather than human factors,” he said.

According to NASA, average atmospheric temperatures have risen by 0.8 degrees centigrade since 1880. But much of the recent warming trends have been found instead in the world’s oceans, Stott said.

“Over 80 percent of the heat that’s trapped in the climate system as a result of the greenhouse gases is exported into the ocean, and we can see that happening,” Stott said.

One possibility frequently cited by critics of global warming is that warming could be driven by increased activity from the sun. However, if that was the case, the Earth’s atmosphere would have warmed more evenly and temperatures would have increased early in the 20th century, rather than later.

“There hasn’t been an increase in solar output for the last 50 years,” Stott said. “And solar output would not have caused cooling of the higher atmosphere and the warming of the lower atmosphere that we have seen.”

The review was published in Wiley Interdisciplinary Reviews: Climate Change (Alok Jha, London Guardian, March 5). – PV