July 25, 2012
Greenland Ice Melt Is “Unprecedented”
Lee Rannals for redOrbit.com - Your Universe Online
Satellites have revealed that Greenland's surface ice cover has melted this month more than any time in over 30 years of satellite observations.
NASA said that nearly the entire ice cover of Greenland experienced some degree of melting at its surface this past month.
Measurements from three independent satellites were analyzed by NASA and university scientists, who found that 97 percent of the ice sheet surface in Greenland thawed at some point in mid-July.
"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," Tom Wagner, NASA's cryosphere program manager in Washington, said. "Satellite observations are helping us understand how events like these may relate to one another as well as to the broader climate system."
During an average summer, about half of the surface of Greenland's ice sheet naturally melts, and at high elevations, most of that melt water quickly freezes in place.
NASA said researchers haven't determined whether this extensive ice melt will affect the overall volume of ice loss this summer and contribute to sea level rise.
"This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?" Son Nghiem of NASA's Jet Propulsion Laboratory in Pasadena, California said.
He consulted with Dorothy Hall at NASA's Goddard Space Flight Center in Greenbelt, Maryland about the results. She confirmed that Moderate-resolution Imaging Spectroradiometer (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, and Marco Tedesco of City University of New York also confirmed the findings through data from the Special Sensor Microwave Imager/Sounder on a U.S. Air Force meteorological satellite.
The melt maps showed that on July 8, about 40 percent of the ice sheet's surface had melted, and by July 12, 97 percent had thawed out.
The melting coincided with an unusually strong ridge of warm air over Greenland. A series of these heat ridges have been encompassing Greenland since the end of May.
"Each successive ridge has been stronger than the previous one," Mote said.
The most recent surge of warm air moved over Greenland on July 8, and stood over an ice sheet for about three days.
Even Summit Station in central Greenland, the highest point of the ice sheet, showed signs of melting. Melting at Summit and across the ice sheet has not taken place since 1889.
"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," Lora Koenig, a Goddard glaciologist and a member of the research team analyzing the satellite data, said. "But if we continue to observe melting events like this in upcoming years, it will be worrisome."
Image 2 (below): Extent of surface melt over Greenland's ice sheet on July 8, 2012 (left) and July 12, 2012 (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. Image credit: Jesse Allen, NASA Earth Observatory and Nicolo E. DiGirolamo, SSAI and Cryospheric Sciences Laboratory