Monday, December 22, 2014

Great Lakes nearly frozen

CHEBOYGAN, Mich.—From the bridge of the U.S. Coast Guard cutter Mackinaw, northern Lake Huron looks like a vast, snow-covered field dotted with ice slabs as big as boulders—a battleground for the icebreaker’s 58-member crew during one of the roughest winters in memory.
It’s been so bitterly cold for so long in the Upper Midwest that the Great Lakes are almost completely covered with ice.

The last time they came this close was in 1994, when 94 percent of the lakes’ surface was frozen.
As of yesterday, ice cover extended across 88 percent, according to the federal government’s Great Lakes Environmental Research Laboratory in Ann Arbor, Mich.
Sections of the lakes, which hold nearly one-fifth of the freshwater on the world’s surface, harden almost every winter.
But over the past four decades, the average ice cover has receded 70 percent, scientists say, probably in part because of climate change.
Still, as this season shows, short-term weather patterns can trump multi-year trends. Winter arrived early and with a vengeance—and refuses to loosen its grip.
“That Arctic vortex came down and the ice just kept going,” noted George Leshkevich, a physical scientist with the federal lab.
The deep freeze is more than a novelty. By limiting evaporation, it may help replenish lake water levels—a process that began last year after a record-breaking slump dating to the late 1990s.

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