Greenland Ice Sheet Melted at Unprecedented Rate in July

By Chelsea Whyte on July 25, 2012 1:39 AM EDT

ice sheet melting
Extent of surface melt over Greenland’s ice sheet on July 8 (left) and July 12 (right). Measurements from three satellites showed that on July 8, about 40 percent of the ice sheet had undergone thawing at or near the surface. In just a few days, the melting had dramatically accelerated and an estimated 97 percent of the ice sheet surface had thawed by July 12. In the image, the areas classified as “probable melt” (light pink) correspond to those sites where at least one satellite detected surface melting. The areas classified as “melt” (dark pink) correspond to sites where two or three satellites detected surface melting. The satellites are measuring different physical properties at different scales and are passing over Greenland at different times. As a whole, they provide a picture of an extreme melt event about which scientists are very confident. (Photo: Nicolo E. DiGirolamo, SSAI/NAS)

Satellite images of Greenland's surface shows that for several days this month, the ice cover on the island melted over a larger area than at any time in more than 30 years of satellite observations.

Nearly the entire ice cover of Greenland - from the thin, low-lying coastal edges to the 2-mile thick center - experienced some degree of melting at its surface, which was confirmed by three independent satellites.

On average in the summer, about half of the surface of Greenland's ice sheet naturally melts. But this year, the ice sheet saw a dramatic jump in surface melting. Satellite data shows that an estimated 97 percent of the ice sheet surface thawed at some point in mid-July.

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"I started looking at the satellite imagery and saw something that was really unprecedented" since the advent of satellite imaging of the earth's frozen surface, or cryosphere, said Thomas L. Mote, a climate scientist at the University of Georgia who for 20 years has been studying ice changes on Greenland detected by satellite, according to The New York Times.

Son Nghiem of NASA's Jet Propulsion Laboratory in Pasadena, Calif., was analyzing radar data from the Indian Space Research Organisation's (ISRO) Oceansat-2 satellite last week when he noticed that most of Greenland appeared to have undergone surface melting on July 12.

Dorothy Hall at NASA's Goddard Space Flight Center in Greenbelt, Md., confirmed the melting with the Moderate-resolution Imaging Spectroradiometer (MODIS), which showed unusually high temperatures in the area.

And then Mote and Marco Tedesco of City University of New York also confirmed the melt seen by Oceansat-2 and MODIS with passive-microwave satellite data from the Special Sensor Microwave Imager/Sounder on a U.S. Air Force meteorological satellite.

The unusual amount of melt - coming on the heels of the Petermann glacier's loss of ice last week - has highlighted the extent to which warming temperatures are affecting the Arctic, reports The Washington Post. There has been an unusually strong ridge of warm air, or a heat dome, over Greenland, which is one of  a series of ridges that has plagued Greenland since the end of May.

 "Each successive ridge has been stronger than the previous one," said Mote. This latest heat dome started to move over Greenland on July 8, and then parked itself over the ice sheet about three days later. By July 16, it had begun to dissipate.

"Ice cores from Summit show that melting events of this type occur about once every 150 years on average. With the last one happening in 1889, this event is right on time," said Lora Koenig, a Goddard glaciologist and a member of the research team analyzing the satellite data. "But if we continue to observe melting events like this in upcoming years, it will be worrisome."

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