Study: Arctic hit its warmest in '07

Temperatures in the Arctic last fall hit an all-time high – more than 9 degrees Fahrenheit above normal – and are almost as high this year, an international team of scientists reported Thursday.

“The year 2007 was the warmest year on record in the Arctic,” said Jackie Richter-Menge, a climate expert at the Cold Regions Research and Engineering Laboratory in Hanover, N.H., and editor of the latest annual Arctic Report Card.

“These are dynamic and dramatic times in the Arctic,” she said. “The outlook isn't good.”

Arctic temperatures naturally peak in October and November, after sea ice shrinks during the summer. The shrinkage lets more of the sun's rays heat the ocean rather than be reflected back into space.

As a result, the ocean is warming and causing global sea levels to rise even faster than predicted, according to the Arctic Report Card, the product of 46 scientists from 10 countries.

Summer 2007 set a record low for sea ice in the Arctic, threatening reindeer, walruses and polar bears, and opening shipping lanes above the Arctic Circle, the report said. This summer's ice melt was slightly smaller.

“There has been a massive loss of sea ice starting in the 1990s,” said one of the authors, James Overland, an Arctic expert at the Pacific Marine Environmental Laboratory in Seattle. “In 2008, we've lost so much multi-year-old ice, it's very difficult for the ice cover to go back to where it was 20 years ago.”

The Arctic Report Card's authors attributed the temperature spike to a combination of long-term global warming and short-term natural variations in ocean currents and winds above the Arctic Circle.

“Global warming by itself wouldn't cause this much sea ice loss,” Overland said. Nor would changes in wind and ocean currents alone.

“Changes in the Arctic show a domino effect of both natural variation and the emerging global warming signal,” he said. “Both are necessary to put us in this strange new world. Once we're in this place, it's very hard to go back.”

Although the Arctic is warming overall, its effects vary from place to place. The Bering Sea, for example, is in a cooling spell, and an unusually severe winter has bulked up Alaska's glaciers.

At the same time, the huge Greenland ice cap shrank by 88 square miles as a result of an unusually warm spring and summer, a source said.

Greenland dumped at least 24 cubic miles of melted ice into the ocean. The report said the result was an “unprecedented” rise of nearly 0.1 inch per year.