Greenland’s surface ice cover has melted over a larger area than at any time in more than 30 years of satellite observations several times this month.
Almost 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 the 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.”
Based on the satellite data, around 97 percent of the whole ice sheet surface melted 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.”
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