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article imageGreenland Ice Sheet Melt Accelerates

By Bob Ewing     Dec 11, 2007 in Environment
The 2007 melting rate of the Greenland ice sheet broke the 2005 summer melt record by 10 per cent, making it the largest ever decrease since satellite measurements began in 1979.
A recent study indicates that the 2007 melt extent on the Greenland ice sheet broke the 2005 summer melt record by 10 percent. The study was conducted by Professor Konrad Steffen, the director of the Cooperative Institute for Research in Environmental Sciences at the University of Buffalo.
This makes it the largest melt ever recorded there since satellite measurements began in 1979.
Between 1979 and 2006 the melting increased by about 30 per cent for the western part of Greenland and there were record melt years in 1987, 1991, 1998, 2002, 2005 and 2007, according to Steffen.
The study states that the air temperatures on the Greenland ice sheet have increased by about 7 degrees Fahrenheit since 1991. This is primarily a result of the build-up of greenhouse gases in Earth's atmosphere.
Steffen’s team developed their information using data from the Defense Meteorology Satellite Program's Special Sensor Microwave Imager aboard several military and weather satellites to chart the area of melt, including rapid thinning and acceleration of ice into the ocean at Greenland's margins.
Steffen maintains an extensive climate-monitoring network of 22 stations on the Greenland ice sheet known as the Greenland Climate Network, transmitting hourly data via satellites to CU-Boulder to study ice-sheet processes.
Greenland has been experiencing a thickening at higher elevations because of increased snowfall; however, the gain is more than offset by an accelerating mass loss, primarily from rapidly thinning and accelerating outlet glaciers.
Steffen said. "The amount of ice lost by Greenland over the last year is the equivalent of two times all the ice in the Alps, or a layer of water more than one-half mile deep covering Washington, D.C."
The Jacobshavn Glacier on the west coast of the ice sheet has sped up nearly two-fold in the last decade. While glaciers nearby have shown an increase in flow velocities of up to 50 per cent during the summer melt period as a result of melt water draining to the ice-sheet bed.
"The more lubrication there is under the ice, the faster that ice moves to the coast," said Steffen. "Those glaciers with floating ice 'tongues' also will increase in iceberg production."
Approximately 80 per cent of the surface of Greenland is covered by a massive ice sheet and Greenland hosts about one-twentieth of the world's ice which is the equivalent of about 21 feet of global sea rise. The current contribution of Greenland ice melt to global sea levels is about 0.5 millimeters annually.
"Inclusion of the dynamic processes of these glaciers in models will likely demonstrate that the 2007 Intergovernmental Panel on Climate Change assessment underestimated sea-level projections for the end of the 21st century," Steffen said.
Helicopter surveys have shown that an increase in cylindrical, vertical shafts in Greenland's ice known as moulins, which drain melt water from surface ponds down to bedrock, has occurred.
"These melt-water drains seem to allow the ice sheet to respond more rapidly than expected to temperature spikes at the beginning of the annual warm season," Steffen said. "In recent years the melting has begun earlier than normal."
The team has used a rotating laser and a sophisticated digital camera and high-definition camera system provided by NASA's Jet Propulsion Laboratory to map the volume and geometry of moulins on the Greenland ice sheet to a depth of more than 1,500 feet.
"We know the number of moulins is increasing," said Steffen. "The bigger question is how much water is reaching the bed of the ice sheet, and how quickly it gets there."
The ice loss trend in Greenland is somewhat similar to the trend of Arctic sea ice in recent decades. Last October, the CU-Boulder's National Snow and Ice Data Center reported that the 2007 Arctic sea-ice extent had dropped to the lowest levels since satellite measurements began in 1979 and was now 39 per cent below the long-term average tracked from 1979 to 2007.
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