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.
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