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U.S. scientists back claim on climate change

David Adam

A 1999 study showed that humans are altering the climate.

U.S. SCIENTISTS have endorsed the contentious findings of a global warming study that showed humans are drastically altering the climate. The U.S. National Academies of Science said the last few decades of the 20th century were the warmest for 400 years. It adds that many parts of the globe were warmer during the past 25 years than during any comparable period over the last 1,000 years. But it had less confidence in more specific claims that the 1990s were the warmest decade, and 1998 the warmest year.

The new report, published on Thursday, focussed on the "hockey stick" graph — a reconstruction of average global temperatures over the last 1,000 years that shows a sharp upswing in the late 20th century. The image was produced in 1999 by a team led by climate expert Michael Mann who estimated past temperatures using centuries-old sediments and tree rings.

It seemed to show the rise in global temperatures since the industrial revolution. It became a main factor in the climate change debate but critics said Dr. Mann's techniques were flawed.

Thursday's report, prepared by the National Academies' national research council, said: "The committee found the Mann team's conclusion that warming in the last few decades of the 20th century was unprecedented over the last 1,000 years to be plausible." —

© Guardian Newspapers Limited 2006

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