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McClatchy Washington Bureau

Posted on Thursday, Sep. 03, 2009

Study: More evidence Arctic's rapid warming isn't natural

By Renee Schoof

WASHINGTON — The Arctic was cooling for 1,900 years because of a natural change in Earth's orbit until greenhouse gas accumulation from the use of fossil fuels reversed the trend in recent decades, according to a study published Thursday in Science magazine.

Scientists reconstructed the temperature record of the past 2,000 years using evidence from tree rings, ice cores and lake sediment, and found a steady cooling trend in Arctic summer temperatures of about 0.5 degrees Celsius — 0.9 degrees Fahrenheit — during the first 1,900 years. The cooling was caused by a slow natural cycle in Earth orbit that continues in this century.

"The summer cooling would likely be continuing today were it not for the increase of greenhouse gases from fossil fuel burning," said David Schneider, a scientist at the National Center for Atmospheric Research and one of the authors of the study. "The results are important in showing that the dramatic changes happening today — and particularly the rapidity of the changes — are not natural."

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