Greenland's massive ice sheet is melting at a record pace this summer.
By Aug. 8, this year's summer melt had shattered the record set in 2010, according to a new analysis of satellite data by glaciologist Marco Tedesco of the City University of New York.
With four weeks to go before the end of Greenland's melt season, Tedesco said this year could end up being "a goliath," far outranking any other in the 30-year satellite record.
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Areas that don't normally melt or melt for just a few days each summer appear to have lost significant amounts of ice this year. That helped drive up this year's "cumulative melt index," a measure that takes into account the spatial extent and duration of thawing across the ice sheet.
"On the east coast, the west coast, at high elevations, in the north, there was a disproportionate amount of melting, both in terms of extent and duration, with respect to previous years," Tedesco said.
Thomas Mote, a climatologist at the University of Georgia, said his independent analysis of the same Air Force satellite data Tedesco used confirms that Greenland has broken its seasonal melt record this year.
The news comes on the heels of NASA's announcement that Greenland endured an unusually widespread, intense burst of surface melting for a few days in mid-July. During that brief period, an astonishing 97 percent of the surface of Greenland's ice sheet showed signs of thaw -- covering a larger area than any melting event since satellite records began 30 years ago (ClimateWire, July 25).
That was followed by a similar but shorter event in late July. While those incidents were unusual, their contributions to the record-breaking summer melt were small, Tedesco said.
"If you weigh an elephant with a leash and without a leash, the weight changes slightly, but it is still very heavy," he explained.
Warm temperatures not the only culprit
More important was persistent melting through June and July in areas that don't normally thaw much. Some high elevations in southern Greenland that usually melt for just a few days experienced 30, 40 or even 50 days of melting this summer.
Researchers believe that high temperatures kick-started that melting, but other factors helped intensify it. Warming removed layers of snow that covered the ice sheet's surface, leaving bare ice behind. Because that bare ice is less reflective that snow, it absorbs more heat from the sun, spurring even more melting.
According to Ohio State University glaciologist Jason Box, the Greenland ice sheet is less reflective this year than it has been since record-keeping began in 2000.
Still, researchers are hesitant to predict how Greenland's ice will fare over the remaining weeks of the summer melt season, which normally ends in mid-September.
"It's very hard to say what will happen within a month," Tedesco said. "If things keep going like this, melting will be considerable."
But Greenland's ice is not the only portion of the Arctic experiencing a record-breaking thaw this year. The region's sea ice cover is at a record low for this time of year, according to the National Snow and Ice Data Center -- on pace to set a new annual low in mid-September.
Just as removing snow from the surface of the ice sheet and exposing the bare ice below helps speed melting, replacing sea ice with dark ocean water helps trap heat. That warmth cycles back into the atmosphere each fall, when the amount of sunlight dips and sea ice reforms.
"It's a perfect storm in the Arctic," Tedesco said. "There are all these factors playing together in favor of continuous melting. It really stands out from other years."
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500
