Nature and Man Jointly Cook Arctic (Nature study)

[jpak]

http://www.lasvegassun.com/sunbin/stories/tech/2008/jan/02/010200792.html

There's more to the recent dramatic and alarming thawing of the Arctic region than can be explained by man-made global warming alone, a new study found. Nature is pushing the Arctic to the edge, too.

There's a natural cause that may account for much of the Arctic warming, which has melted sea ice, ice sheets and glaciers, according to a study published Thursday in the journal Nature. New research points a finger at a natural and cyclical increase in the amount of energy in the atmosphere that moves from south to north around the Arctic Circle.

But that energy transfer, which comes with storms that head north because of ocean currents, is not acting alone either, scientists say. Another upcoming study concludes that the combination of both that natural energy transfer increase and man-made global warming serve as a one-two punch that is pushing the Arctic over the edge.

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

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Nature abstract...

http://www.nature.com/nature/journal/v451/n7174/abs/nature06502.html

Vertical structure of recent Arctic warming

Rune G. Graversen1, Thorsten Mauritsen1, Michael Tjernström1, Erland Källén1 & Gunilla Svensson1

Near-surface warming in the Arctic has been almost twice as large as the global average over recent decades1, 2, 3, 4, 5—a phenomenon that is known as the 'Arctic amplification'. The underlying causes of this temperature amplification remain uncertain. The reduction in snow and ice cover that has occurred over recent decades6, 7 may have played a role5, 8. Climate model experiments indicate that when global temperature rises, Arctic snow and ice cover retreats, causing excessive polar warming9, 10, 11. Reduction of the snow and ice cover causes albedo changes, and increased refreezing of sea ice during the cold season and decreases in sea-ice thickness both increase heat flux from the ocean to the atmosphere. Changes in oceanic and atmospheric circulation, as well as cloud cover, have also been proposed to cause Arctic temperature amplification12, 13, 14, 15, 16, 17. Here we examine the vertical structure of temperature change in the Arctic during the late twentieth century using reanalysis data. We find evidence for temperature amplification well above the surface. Snow and ice feedbacks cannot be the main cause of the warming aloft during the greater part of the year, because these feedbacks are expected to primarily affect temperatures in the lowermost part of the atmosphere, resulting in a pattern of warming that we only observe in spring. A significant proportion of the observed temperature amplification must therefore be explained by mechanisms that induce warming above the lowermost part of the atmosphere. We regress the Arctic temperature field on the atmospheric energy transport into the Arctic and find that, in the summer half-year, a significant proportion of the vertical structure of warming can be explained by changes in this variable. We conclude that changes in atmospheric heat transport may be an important cause of the recent Arctic temperature amplification.

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