Greenland is about one-quarter as big as the continental United States, and 80 percent of it is covered by a massive ice sheet. It got its name because, from about A.D. 1000 to 1300, during the so-called “Medieval Warm Period,” it was warm enough to support forests and thriving colonies of Viking settlers.

This year’s melt lifted global sea levels by about two one-hundredths of an inch, Steffen said. If the entire ice cap melted, it could raise the sea by 21 feet, swamping coastal cities and low-lying islands, but such a catastrophe isn’t expected for at least a thousand years, if ever.

Steffen, who’s spent 18 seasons working on the Greenland ice cap, attributed the accelerated melting to an air temperature increase of about 7 degrees Fahrenheit since 1991.

Ten percent more ice melted this year than in 2005, the previous record year. Since 1979, when satellite data over Greenland began, melting has increased by a total of 30 percent, he said.
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