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Tuesday, February 16, 2010

Kieran Mulvaney: A Farewell to Ice

A Farewell to Ice

Kieran Mulvaney
by Kieran Mulvaney, DiscoveryNews, February 7, 2010
Sea ice cover in the Arctic Ocean grew by an average of 13,000 square miles a day last month.

Great news, right? Well, not so much.

For one thing, it was January. Mid-winter. Sea ice cover is supposed to grow. For another, it ain't growing like it used to. In the 1980s, the average rate of ice growth was 35,000 square miles a day. According to the National Snow and Ice Data Center, average sea ice extent in the Arctic last month was 5.32 million square miles, which was 69,000 square miles above the record January low, set in 2006, but 417,000 square miles below the 1979-2000 average.

Now, nobody is predicting the disappearance of winter sea ice in the Arctic. Under even the most pessimistic of scenarios, the Arctic winter will be cold enough and dark enough that sea ice will continue to form, albeit at a reduced level. However, as NSIDC director Mark Serreze explained to Reuters, a reduction in winter sea ice extent -- and the fact that the ice that remains is younger and thinner -- sets up the Arctic for a summer "double whammy."

"We've grown back ice in the winter, but that ice tends to be thin and that's the problem," Serreze told Reuters. "You set yourself up for a world of hurt in summer. The ice that is there is also thinner than it was before and thinner ice simply takes less energy to melt out the next summer."

This thinner ice, in other words, is prone to melt earlier, and when it does, the heat-reflecting light-colored sea ice is replaced by heat-absorbing dark-colored ocean water, which causes the melting to increase.

The pace of the melt, and the consequent feedback loop as high-albedo ice yields to low-albedo water, has caused researchers to change their calculations about the Arctic's future. As David Barber of the University of Manitoba pointed out at a press conference on Friday to announce the initial findings of a two-year study involving 370 scientists from 27 countries, until recently, models predicted the Arctic would be sea ice-free in summer by the year 2100. Today, however, most researchers agree that, at present trends, a more likely date is 2030.

Climate change, said Barber, "is happening much faster than our most pessimistic models expected." 


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