Ancient Arctic Melts

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German-led team of scientists said on Thursday that the Arctic went through ice-free periods of extreme warmth over the past 2.8 million years, based on a new analysis of deep sediment in Russia.

The international team, headed by Martin Melles of the University of Cologne, Germany, drilled into an iced-over lake formed by a meteorite impact on the Chukchi Peninsula in Siberia for the longest sediment core ever collected in the terrestrial Arctic.

Since the meteorite struck an area of Lake El'gygytgyn that was not eroded by glaciers, the sediment record reaches back nearly 30 times further in time than ice cores from Greenland that cover the past 110,000 years.

The sediment reveals periods of extreme warmth that show the polar regions are much more vulnerable to change than previously thought, and are difficult to explain by greenhouse gases alone, said the study in the journal Science.

Scientists have long known that the Arctic went through climate cycles, but the latest research shows some of these warm phases were "exceptional," with temperatures four to five degrees Celsius warmer and 12 inches wetter than during normal interglacials, the study said.

So much for man-made global warming.