sierraclub.org - sierra magazine - sept/oct 2011 - grapple: woe is us

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WOE IS US
Ready, set, panic.

ATLANTIC CHILL

Hot and bothered about global warming? Your time to chill may come in the form of a cold snap that could bring summer frosts to Pennsylvania and icebergs to England.

Climate scientists are tracking a widening pool of freshwater in the Arctic Ocean that's already more than twice the size of Africa's Lake Victoria. Fed by melting permafrost, shrinking glaciers, and Siberian downpours, the freshwater is expected to flush from the Arctic into the Atlantic.

When it gets there, it could slow or even stop the Gulf Stream, the great oceanic conveyor belt that brings tropical waters, and temperate weather, to northern latitudes. Normally, these waters—cooled by winds and made increasingly dense and salty by evaporation and ice formation—plunge below lighter, less-saline water near Greenland, powering the cycle.

But according to Laura de Steur of the Royal Netherlands Institute for Sea Research, 1,800 cubic miles of meltwater pooling in the Arctic could throw the brakes on that system, rapidly ratcheting down temperatures in a way that we haven't experienced since the last ice age, 13,000 years ago.

Slowing of the Gulf Stream is expected to begin sometime this century. But with the Arctic melting far faster than predicted, the big chill could come sooner—and more suddenly—than anyone thought. If it does, stock up on earmuffs. The last time the Gulf Stream stalled, it took 1,300 years to start up again. —Dashka Slater

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