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Dramatic Summer Surface Melt of Greenland Ice Sheet


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Report this Jul. 27 2012, 9:37 am


Extent of surface melt over Greenland's ice sheet on July 8, left, and July 12. right.



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. Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory


For several days this month, Greenland's surface ice cover 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 its thin, low-lying coastal edges to its two-mile-thick center, experienced some degree of melting at its surface, according to measurements from three independent satellites analyzed by NASA and university scientists.

On average in the summer, about half of the surface of Greenland's ice sheet naturally melts. At high elevations, most of that melt water quickly refreezes in place. Near the coast, some of the melt water is retained by the ice sheet and the rest is lost to the ocean. But this year the extent of ice melting at or near the surface jumped dramatically. According to satellite data, an estimated 97 percent of the ice sheet surface thawed at some point in mid-July.

Researchers have not yet determined whether this extensive melt event will affect the overall volume of ice loss this summer and contribute to sea level rise.

"The Greenland ice sheet is a vast area with a varied history of change. This event, combined with other natural but uncommon phenomena, such as the large calving event last week on Petermann Glacier, are part of a complex story," said Tom Wagner, NASA's cryosphere program manager in Washington. "Satellite observations are helping us understand how events like these may relate to one another as well as to the broader climate system."

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. Nghiem said, "This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?"

Nghiem consulted with Dorothy Hall at NASA's Goddard Space Flight Center in Greenbelt, Md. Hall studies the surface temperature of Greenland using the Moderate-resolution Imaging Spectroradiometer (MODIS) on NASA's Terra and Aqua satellites. She confirmed that MODIS showed unusually high temperatures and that melt was extensive over the ice sheet surface.

Thomas Mote, a climatologist at the University of Georgia, Athens, Ga; 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 melting spread quickly. Melt maps derived from the three satellites showed that on July 8, about 40 percent of the ice sheet's surface had melted. By July 12, 97 percent had melted.

This extreme melt event coincided with an unusually strong ridge of warm air, or a heat dome, over Greenland. The ridge was one of a series that has dominated Greenland's weather 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.

Even the area around Summit Station in central Greenland, which at 2 miles above sea level is near the highest point of the ice sheet, showed signs of melting. Such pronounced melting at Summit and across the ice sheet has not occurred since 1889, according to ice cores analyzed by Kaitlin Keegan at Dartmouth College in Hanover, N.H. A National Oceanic and Atmospheric Administration weather station at Summit confirmed air temperatures hovered above or within a degree of freezing for several hours July 11-12.

"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," says 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."

Nghiem's finding while analyzing Oceansat-2 data was the kind of benefit that NASA and ISRO had hoped to stimulate when they signed an agreement in March 2012 to cooperate on Oceansat-2 by sharing data.


Maria-José Viñas
NASA's Earth Science News Team


caltrek: What is truly shocking is not only the dramatic extent of the melt, but the fact that aside form a scientific journal or two (and a short story on NPR), so little media attention is being paid to this.


As Americans, we sometimes suffer from too much pluribus and not enough unum. - Arthur Schelsinger, Jr.


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Report this Jul. 27 2012, 1:37 pm

It is disheartening. I do not understand why this is not front page news either. 

"Ten thousand dollars for me by myself. For that you get the head, the tail, the whole damn thing."


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Report this Jul. 29 2012, 6:38 am

One reason it is not front page news relates to how the modern media functions. News is increasingly dominated by personalities. Fewer and fewer resources are being given to investigative reporting. Nobody wants to spend money on even simple things like traveling to Greenland or picking up the phone to arrange an interview with a knowlegdeable scientist.

Then there is the notion of "fairness". If they do talk to a scientist who represents the consensus of the scientific community, then they feel compelled to interview somebody who represent the "other side" of the story. In the case of global warming, this turns out to be hacks who are hired by the carbon emmissions based industries to spread propoganda and junk science to "balance" the claims of responsible scientists.  Unlike peer reviewed journals, no need is seen to vet such views for obvious flaws in logic, reason, and use of evidence. This is seen as being in confromance with the "Fairness Doctrine".

Even if a reporter is willing to go through all of that effort, he or she must then explain to his or her editor why the news outlet should run stories that may antagonize advertisers such as oil companies.    

Then there is the fact that such stories are becoming more and more commonplace, and thus not "news" any more. So like the proverbial frog in the pot of water, we are simply left to boil to death instead of jumping out of the water.

Even my experiences here at the Science and Technology forum demonstrate the problem. Discussions such as the one I have just initiated are considered to be "political" even by those who acknowledge the problems of global warming. They prefer strictly science oriented stories that do not create political animus.

Over at Ten Forwrd, you can always count on somebody heavily into denial to come forth and spread their absurd conspiracy theories about how scientists are just trying to justify grant funding. The carbon industry funded points made in the conservative media are dragged out to justify their paranoia, even as they ignore the real conspiratorial forces at work. Aggravation caused by all this leads to spammer attacks. Hard to say what the spammers feel about global warming, but they simply get worked up about other personality related clashes related to arguing controversial topics and dealing with people of a different philosophical orientation.  

If you are interested in this topic from the perspective of how the carbon fuel based industry has warped our thinking on all of this, I suggest The Carbon War by Jerremy Legget and Merchants of Doubt by Naomi Oreskes & Erik M. Conway.


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Report this Jul. 29 2012, 12:40 pm

anti-spam bump

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