December 16, 2010
No ‘Tipping Point’ For Arctic Icecap Melting
According to a new study released Wednesday, there is no "tipping point" beyond which climate change will eventually push the Arctic icecap into a total melt off.
Over the past 30 years the polar icecap has shrunk between 15 and 20 percent causing much concern that with current trends -- with regional temperatures increasing two to three times the global average -- it could disappear entirely during the summer months by the end of this century.
One factor in this calculation is a so-called positive feedback, in which a reduced area of floating ice helps fuel global warming. As ice cover recedes decade by decade, more of the Sun's radiative force is absorbed by dark-blue sea rather than reflected back into space by ice and snow.
But according to the new study, published in the British journal Nature, there is nothing inevitable about this process, and that it can be stopped or even reversed.
"There is no 'tipping point' that would result in unstoppable loss of summer sea ice when greenhouse gas-driven warming rose above a certain threshold," said Professor Steven Amstrup of the University of Washington and lead author of the study.
Many scientists have worried that there was an as yet unidentified temperature threshold which would eventually doom the icecap.
But the study indicates that if annual emission of greenhouse gases are greatly reduced over the next 20 years, an initial phase of rapid loss would be followed by a period of stability and, eventually, partial recovery.
If computer models are accurate, that could mean a reprieve for polar bears, which rely on floating ice shelves as staging areas for stalking and hunting its seal prey. Many of the majestic beasts are already teetering on the edge of starvation because the ice melts sooner in springtime and forms later in the fall, shortening their hunting season.
The new research "offers a very promising, hopeful message," said co-author and University of Washington professor Cecilia Blitz. "But it's also an incentive for mitigating greenhouse gas emissions," she said in a statement to AFP.
In previous research, Amstrup and colleagues had calculated that only a third of the world's 22,000 polar bears would still be alive by 2050, and that even those surviving animals would most likely disappear.
Washington listed polar bears under the Endangered Species Act in 2008.
More than 150 biologists and climatologists called on President Barack Obama earlier this week to step up action to save the polar bears.
The US Department of the Interior faces a court-imposed deadline next week on whether the Arctic's top predators should continue to be classified as "threatened" or be given maximum protection under US law as "endangered."
A separate study, also published in Nature on Wednesday, warned that melting sea ice was pushing Arctic mammals to breed with cousin species, a trend that could further push the polar bear and other iconic animals toward extinction.
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