Natural causes behind Arctic warming 

World news
6th January 2008, 5:09 WST

A natural cause may account for much of the recent dramatic thawing of the Arctic region, in addition to man-made global warming, a new study finds.
New research indicates a natural and cyclical increase in the amount of energy in the atmosphere that moves from south to north around the Arctic Circle, according to the study published in the journal Nature.

But that energy transfer, which comes with storms that head north because of ocean currents, is not acting alone, scientists say.

Another upcoming study concludes that the combination of that natural energy transfer increase and man-made global warming serves as a one-two punch that is pushing the Arctic over the edge, with melting sea ice, ice sheets and glaciers.

Scientists are trying to figure out why the Arctic is warming and melting faster than computer models predict.

The summer of 2007, like the summer of 2005, smashed all records for loss of summer sea ice in the Arctic Ocean and ice sheet in Greenland. In September, the Arctic Ocean had 23 per cent less sea ice than the previous record low. Greenland's ice sheet melted 19 billion tons more than its previous record.

The Nature study suggests there is more behind the change than global warming because the air a couple miles above the ground is warming more than calculated by the climate models.

Climate change theory concentrates on warming of surface temperatures and explains an Arctic that is warming faster than the rest of the world as mostly because reduced sea ice and ice sheets means less reflecting solar rays.

Rune Graversen, the Nature study co-author and a meteorology researcher at Stockholm University in Sweden, said a shift in energy transfer explains the thawing more, including what is happening in the atmosphere, but does not contradict consensus global warming science.

Oceanographer James Overland, who reviewed Graversen's study for Nature, said the research dovetails with an upcoming article of his which concludes that the Arctic thawing is a combination of the two.

"If we didn't have the little extra kick from global warming then we wouldn't have gone past the threshold for the change in sea ice," said Overland, of the National Oceanic and Atmospheric Administration's lab in Seattle.

Other researchers said Graversen's study underestimates the effect of global warming because it relied on older data that stopped at 2001 and was not the most accurate.

Overland and scientist Mark Serreze disagree over which effect - man-made or natural - was the big shove that pushed the Arctic over the edge, but they agreed that overall it is a combined effort.

AP