Wednesday, March 21, 2007

Arctic could have iceless summers by 2100

Writing for the Los Angeles Times, Alan Zarembo reports that the Arctic could have iceless summers by 2100:

Climate models show a complete melting down to open ocean in warmer weather, maybe as early as 2040.

A review of existing computer climate models suggests that global warming could transform the North Pole into an ice-free expanse of ocean at the end of each summer by 2100, scientists reported today.

The researchers said that out of the 15 models they looked at, about half forecast that the sea-ice cover — a continent-sized expanse that shrinks and grows with the seasons — would seasonally vanish by the turn of the century.

"That may be conservative," said lead author Mark Serreze, a senior research scientist at the National Snow and Ice Data Center in Boulder, Colo.

One model predicted the Arctic would be ice-free each September as early as 2040, according to the article in the journal Science.

The remaining models showed the presence of some ice beyond 2100, although they agreed there would be significant ice loss if greenhouse gas emissions continue to grow at the current rate.

The computer models were included in a landmark United Nations report last month that blamed human activities for the "runaway train" of global warming.

The disappearance of the ice would lead to a dramatic reshaping of the Arctic that would accelerate warming of the oceans and potentially change precipitation patterns worldwide.

The Arctic's end-of-summer ice expanses already have been declining by about 9% each decade since the 1970s.

It is possible to see the difference from an airplane heading north from Alaska. "You have to fly a lot longer to get to the ice edge than you used to," said Josefino Comiso, a satellite imaging expert at NASA's Goddard Space Flight Center who was not connected to the report.

He and other experts believe the melting will accelerate as more ice disappears and exposes the open ocean, which absorbs heat and melts more ice from below.

"With less and less ice, you have more and more heat," eventually contributing to further warming around the globe, Comiso said.

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