These undated handout images provided by NASA shows the extent of surface melt over...
WASHINGTON (AP) — Nearly all of Greenland's massive ice sheet suddenly started melting this month, a freak event that surprised scientists.
By SETH BORENSTEIN AP
Science Writer The Associated Press
Tuesday, July 24, 2012 5:54 PM EDT
Even Greenland's coldest and highest place, Summit station, showed melting. Ice core records show that last happened in 1889 and occurs about once every 150 years.
Three satellites show what NASA calls unprecedented melting of the ice sheet that blankets the island, starting on July 8 and lasting four days. Most of the thick ice remains. While some ice usually melts during the summer, what was unusual was that the melting happened in a flash and over a widespread area.
"You literally had this wave of warm air wash over the Greenland ice sheet and melt it," NASA ice scientist Tom Wagner said Tuesday.
The ice melt area went from 40 percent of the ice sheet to 97 percent in four days, according to NASA. Until now, the most extensive melt seen by satellites in the past three decades was about 55 percent.
Wagner said researchers don't know how much of Greenland's ice melted, but it seems to be freezing again.
"When we see melt in places that we haven't seen before, at least in a long period of time, it makes you sit up and ask what's happening?" NASA chief scientist Waleed Abdalati said. It's a big signal, the meaning of which we're going to sort out for years to come."
About the same time, a giant iceberg broke off from the Petermann Glacier in northern Greenland. And the National Snow and Ice Data Center on Tuesday announced that the area filled with Arctic sea ice continues near a record low.
Wagner and other scientists said because this Greenland-wide melting has happened before they can't yet determine if this is a natural rare event or one triggered by man-made global warming. But they do know that the edges of Greenland's ice sheets have already been thinning because of climate change.
Summer in Greenland has been freakishly warm so far. That's because of frequent high pressure systems that have parked over the island, bringing warm clear weather that melts ice and snow, explained University of Georgia climatologist Thomas Mote.
He and others say it's similar to the high pressure systems that have parked over the American Midwest bringing record-breaking warmth and drought.
Ohio State University ice scientist Jason Box, who returned Tuesday from a three-week visit, said he ditched his cold weather gear for the cotton pants that he normally dons in Nevada.
"It was sunny and warm and all the locals were talking about how sunny it was," Box said after getting off a plane. "Beyond T-shirt weather."
Greenland ice, it seems, can vanish in a flash, with new satellite images showing that over just a few days this month nearly all of the veneer of surface ice atop the island's massive ice sheet had thawed.
In Greenland, a glacier breaking off into the water causes a massive ice wave that collides with a boat filled with tourists. The tourists speed off, narrowly escaping the wave's full wrath.
That's a record for the largest area of surface melt on Greenland in more than 30 years of satellite observations, according to NASA and university scientists.
The images, snapped by three satellites, showed that about 40 percent of the ice sheet had thawed at or near the surface on July 8; just days later, on July 12, images showed a dramatic increase in melting with thawing across 97 percent of the ice sheet surface.
"This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?" said Son Nghiem of NASA's Jet Propulsion Laboratory inPasadena, Calif., referring to the July 12 images taken by the Indian Space Research Organisation's (ISRO) Oceansat-2 satellite.
Nghiem had reason to be baffled, as this record ice-melt is well above average: About half of Greenland's surface ice tends to melt every summer, with the meltwater at higher elevations quickly refreezing in place and the coastal meltwater either pooling on top of the ice or draining into the sea. [Giant Ice: Photos of Greenland's Glaciers]
Instruments on two other satellites proved out Nghiem's findings — the Moderate-resolution Imaging Spectroradiometer (MODIS) on NASA's Terra and Aqua satellites
Data from the Special Sensor Microwave Imager/Sounder on a U.S. Air Force meteorological satellite also confirmed the mind-blowing melt.
As for what caused the disappearing ice, University of Georgia, Athens climatologist Thomas Mote suggests it could be a ridge or dome of warm air hovering over Greenland that coincided with the extreme melt.
"Each successive ridge has been stronger than the previous one," Mote said in a NASA statement. The latest in a series of these heat domes, which have dominated Greenland weather since May, began to move over Greenland on July 8, before coming to a halt over the ice sheet some three days later. By July 16, the heat dome had started to dissipate.
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