Climate change panel's 2007 predictions on Arctic ice loss too optimistic?

by Doug O'Harra, Alaska Dispatch, October 13, 2011

By now, the drumbeat of satellite observations, field reports and headlines have become a familiar rite of autumnal doom across the Far North:

Arctic sea ice shrinks again. Arctic sea ice has thinned faster than expected.Arctic sea lanes have opened sooner than thought possible.

The polar sea has been losing about 10% of its permanent ice every decade since 1980, with the 2011 melt season delivering the lowest volume seen during the modern age, and virtually matching the minimum record for the smallest extent set in 2007.

If the current trend continues, some scientists say, the polar ocean could become essentially ice free during summers within a decade or two. That outcome is about 80 years sooner than what the Intergovernmental Panel on Climate Change predicted in 2007.

So what gives? It turns out those IPCC supercomputing climate models, which conjured the once-unthinkable possibility of an ice-free Arctic Ocean by summer of 2100, all fumbled a key calculation. They underestimated just how fast thinning floes could exit south to the Atlantic Ocean where they would melt into slushy oblivion.

Arctic sea ice has been about thinning four times faster than previously forecast and is now at least 40 years ahead of some previous worst-case estimates for its summertime demise, according to new research by a French-American team of scientists published in the Journal of Geophysical Research.

"This strong underestimation of sea ice thinning and drift acceleration in models would imply that former projections for an ice‐free summer in the Arctic by 2100 ... are too conservative," wrote the four authors, including Jean-Marshal Campin at the Massachusetts Institute of Technology, along with three other scientists from French research institutions, the Centre National de Recherches Météorologiques and theLaboratoire de Glaciologie et Géophysique de l’Environnement.

"When this mechanism was taken into account to correct the discrepancy between simulations and observations, results from the new model suggested that there will be no Arctic sea ice in summer by the end of the century," the authors added in this story about the research.

The problem comes down to how the computer models envision the speed that ice will flow out of the Arctic through Fram Strait into the warmer waters of the Atlantic. Within the immensely complex computer models, this mass of sea ice drifts "freely" -- at the same speed, no matter the season or thickness.




But in the real world, the movement of sea ice out of the Arctic has been speeding up while the floes shrink and bust up. It makes sense that a soup of bits and pans would be able to drift much faster than a gridlocked jumble of island-sized bergs and growlers. 

"Sea ice has become thinner and more fragile," the scientists explained this story. "Because it breaks up more easily, its mobility is increased, as is its export from the Arctic Ocean through the Fram Strait between Greenland and the Svalbard archipelago, followed by its melting."

In the paper, the scientists tweaked the model estimates to take into account the acceleration of ice export. The results were chilling.

"This mechanism suggests that, well before the end of the century, the Arctic Ocean will be devoid of sea ice in late summer," they explained. "The disappearance of Arctic sea ice will probably occur in the next few decades, with far-reaching consequences for ecosystems, sea routes and off shore exploitation of resources."

Contact Doug O'Harra at doug(at)alaskadispatch.com


http://www.alaskadispatch.com/article/climate-change-panels-2007-predictions-arctic-ice-loss-too-optimistic