Arctique: la fonte accélère

Economist. Climate change in the Arctic

Arctic sea ice is melting far faster than climate models predict. Why?

ON SEPTEMBER 9th, at the height of its summertime shrinkage, ice covered 4.33m square km, or 1.67m square miles, of the Arctic Ocean, according to America’s National Snow and Ice Data Centre (NSIDC). That is not a record low—not quite. But the actual record, 4.17m square km in 2007, was the product of an unusual combination of sunny days, cloudless skies and warm currents flowing up from mid-latitudes. This year has seen no such opposite of a perfect storm, yet the summer sea-ice minimum is a mere 4% bigger than that record. Add in the fact that the thickness of the ice, which is much harder to measure, is estimated to have fallen by half since 1979, when satellite records began, and there is probably less ice floating on the Arctic Ocean now than at any time since a particularly warm period 8,000 years ago, soon after the last ice age.

That Arctic sea ice is disappearing has been known for decades. The underlying cause is believed by all but a handful of climatologists to be global warming brought about by greenhouse-gas emissions. Yet the rate the ice is vanishing confounds these climatologists’ models. These predict that if the level of carbon dioxide, methane and so on in the atmosphere continues to rise, then the Arctic Ocean will be free of floating summer ice by the end of the century. At current rates of shrinkage, by contrast, this looks likely to happen some time between 2020 and 2050.

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