August 16, 2012
Greenland Summer Ice Melt Breaks Record Month Before Season Ends
April Flowers for redOrbit.com - Your Universe Online
The summer melting season in Greenland usually lasts from June when the first puddles of meltwater appear, to September when temperatures begin to cool again.Melting over the Greenland ice sheet shattered the seasonal record on August 8 this year — a full four weeks before the close of the melting season, reports Marco Tedesco, assistant professor of Earth and atmospheric sciences at The City College of New York. This year, cumulative melting in the first week of August exceeded the entire melting season of 2010, which had been a record setting melt.
"With more yet to come in August, this year's overall melting will fall way above the old records. That's a goliath year — the greatest melt since satellite recording began in 1979," said Professor Tedesco.
This could spell a change for the face of southern Greenland. The ice sheet is thinning at the edges and lakes are forming on the tops of glaciers. These changes are not surprising, they were predicted by weather and global warming models. The surprise is how quickly it seems to be happening.
Ice sheets, sometimes called continental glaciers, are massive land-based glaciers that are greater than 20,000 square miles. The Greenland ice sheet occupies about 81% of the surface of Greenland and contains so much water that if it were to completely melt, sea levels worldwide would rise by 23 feet.
Tedesco calculated the duration and extent of melting throughout the season across the entire ice sheet, using data collected by microwave satellite sensors to quantify the changes. The National Snow and Ice Data Center provided the satellite datasets.
The cumulative melting index, which is defined as the number of days when melting occurs multiplied by the total area subject to melting, can be seen as a measure of the strength of the melting season. The higher the index, the more melting has occurred.
Dr. Thomas Mote, Professor of Geography at the University of Georgia and colleague of Professor Tedesco, confirmed that the cumulative melt in 2012 had surpassed that of 2010 using a similar analysis.
The August 8th record differs from NASA's announcement of unprecedented melting in mid-July, reported by Professor Tedesco and other researchers. Then, they found that the Greenland ice sheet had melted over 97 percent of its surface.
"That event was exceptional in the sense that it was an extremely rare event," said Professor Tedesco. "Imagine Rio de Janeiro under a layer of snow and you get the idea."
The extreme melting detected in mid-July, on the other hand, generated liquid water that refroze after a few days. "This changed the physical properties of the snowpack — making a slushy layer that turned into an icy crust after refreezing — but very likely it did not add to the runoff of meltwater that makes sea levels rise."
In contrast, the index accounts for water flowing to the ocean. The same meltwater can affect ice dynamics by lubricating the base of the ice sheet and speeding it's slide toward the sea.
This year, Greenland experienced extreme melting in nearly every region, but especially at high elevations. Most years, the ice and snow at high elevations in southern Greenland melt for a few days at most, this year it has already exceeded two months.
Tedesco cautions against allowing this record setting season to cause doomsday thinking.
"We have to be careful because we are only talking about a couple of years and the history of Greenland happened over millennia," said Professor Tedesco. "But as far as we know now, the warming that we see in the Arctic is responsible for triggering processes that enhance melting and for the feedback mechanisms that keep it going. Looking over the past few years, the exception has become part of the norm."