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Winter's freezing, so what's with Arctic sea ice?

An unusually warm January has limited the return of Arctic sea ice, whose extent set a record low for the month. The ice's ability to reflect sunlight back into space has a significant influence on climate worldwide.

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As February began the oscillation switched to a positive phase, which could speed ice growth for a period, according to the center.

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But the prognosis for ice extent during the upcoming melt season isn't good, according to Mark Serreze, who heads the NSIDC.

Even if the ice were to reach a winter expanse nearer normal, "a lot of that ice is thin, first-year stuff, and it's going to tend to melt out easily" come spring, he says.

Indeed, he adds, the thickness of the ice heading into the melt season is a bigger factor than overall winter extent in determining how severe the spring melt-back is likely to be. Researchers over the past several years have documented a decline in older ice and an increase in thinner ice at the start of the melt season.

"We know right now, that we'll be continuing that pattern" heading into the 2011 melt season, he says.

Nor is he looking for help from the Arctic Oscillation. While the strong negative this winter has kept things relatively toasty during an Arctic winter, it historically has tended to set up conditions that kept ice in the Arctic Ocean basin during the melt season. Winds also would spread the ice out, allowing more ice to grow in the wide cracks between floes.

Until last year, that is.

In a paper published Jan. 29 in the journal Geophysical Research Letters, a team led by Julienne Stroeve, also with the NSIDC, found that last winter's strongly negative Arctic Oscillation had its own unusual circulation pattern, which ultimately provided no help in retaining ice during the 2010 melt season. Instead, last melt season registered the third lowest summer-ice extent on record.

"It appears we're entering a new regime where old rules don't apply anyone," he says.

Since satellites began tracking Arctic sea-ice extend continuously in 1979, the maximum and minimum sea-ice extents have been steadily shrinking, when stacked against their 1979 to 2000 averages.

Researchers attribute the long-term to a self-reinforcing trend, or feedback, associated with global warming. As ice cover shrinks during the melt season, more of the ocean, darker than the ice, is exposed to absorb sunlight and retain it as heat. As fall arrives, the ocean releases the heat, slowing the return of sea ice.

Indeed, researchers are exploring the possibility that increases in ice loss could be driving the Arctic Oscillation into a negative phase more often than not. The jury is still out, Serreze says.

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