Although major melts occur on the Greenland ice sheet every 150 years or so, scientists are still considering this an extreme event, and plan on closely monitoring the area for similar occurrences over the next ...
In an average summer, about half of Greenland’s ice sheet melts. This summer witnessed a substantially larger melt -- approximately 97 percent in only four days. This degree of melt monitored between July 8 and July 12 has not been witnessed in the 30 years of NASA observations. Even the Summit Station of the ice sheet at 2 miles above sea level displayed signs of melting.
Scientists said that on any typical day in July, an observer would expect to see at least 25 percent of the ice sheet intact. The large scale melt coincided with “ridges,” or areas of high pressure that occur between the Earth’s surface to the jet stream, of warm weather. These ridges had been observed moving across Greenland since late May. Thomas Mote, a climatologist at the University of Georgia, Athens, said that each ridge was stronger than the last.
While scientists are calling this an “extreme event,” they have also been careful to provide a fuller context for the melt. Ice core samples taken from the highest point of the ice sheet show that similar large scale melts occurred just about every 150 years, according to Lora Koenig, a glaciologist with NASA’s Goddard Space Flight Center who studies satellite imagery. The last major ice melt occurred in 1889, which makes this event timely according to that schedule. Koenig added that if similar events are observed in upcoming years, it would be “worrisome.”
The broader historical context aside, scientists still insist this melt is worthy of attention because rising ocean temperatures are causing a steady retreat of Greenland’s ice sheet. This event may actually be playing a major role, or help scientists better understand, global climate changes. Thomas P. Wagner, head of NASA’s cryosphere program, said, “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.”
Last week Greenland experienced another major ice sheet development: a chunk of ice the size of Manhattan broke off of the remote Petermann Glacier in the northwest of the country. A chunk of ice four times that size broke free from the glacier in 2010. This process, known as “ice calving” is a normal occurrence expected every 10 to 20 years.
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