Satellites See Unprecedented Greenland Ice Sheet Melt

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Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
alan.d.buis@jpl.nasa.gov

Steve Cole 202-358-0918
NASA Headquarters, Washington
Stephen.e.cole@nasa.gov

News release: 2012-217 July 24 2012

Satellites see Unprecedented Greenland Ice Sheet Melt

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2012-217&cid=release_2012-217

PASADENA, Calif. – 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 2-mile-thick (3.2-kilometer) 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; 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 (3.2 kilometers) 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 to 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," 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."

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.

For more information about NASA programs, visit: http://www.nasa.gov .

The California Institute of Technology in Pasadena manages JPL for NASA.

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