Since the late 1970’s, NASA has been monitoring changes in the Greenland Ice Sheet. An analysis of seven years of surface elevation readings from the agency’s ICESat satellite and four years of laser and ice-penetrating radar data from the Operation IceBridge airborne mission provides the first comprehensive picture of how Greenland’s ice is vanishing.
This image shows the change in the surface elevation of the Greenland ice sheet between 2003 and 2012; thinning near coastal regions is shown in green, blue and purple; blue/white flows indicate the direction and speed of the ice movement. Image credit: NASA’s Goddard Space Flight Center.
“The great importance of our data is that for the first time, we have a comprehensive picture of how all of Greenland’s glaciers have changed over the past decade,” said Dr Beata Csatho of the University at Buffalo, who is the lead author of a paper published in the Proceedings of the National Academy of Sciences.
“This information is crucial for developing and validating numerical models that predict how the ice sheet may change and contribute to global sea level over the next few hundred years,” said co-author Prof Cornelis J. van der Veen of the University of Kansas.
Dr Csatho, Prof van der Veen and their colleagues produced the first comprehensive study of how the Greenland Ice Sheet is losing mass based on satellite and airborne data at nearly 100,000 locations across Greenland.
Previous ice sheet simulations used the activity of four well-studied glaciers – Jakobshavn, Helheim, Kangerlussuaq and Petermann – to forecast how the entire ice sheet will dump ice into the oceans.
But the current study shows that activity at these four locations may not be representative of what is happening with glaciers across the ice sheet.
Dr Csatho’s team identified areas of rapid shrinkage in southeast Greenland that today’s models don’t acknowledge.
“The ice sheet could lose ice faster in the future than today’s simulations would suggest,” Dr Csatho said.
To analyze how the height of the ice sheet was changing, the scientists developed a new computational technique to fuse together data from NASA satellite and aerial missions.
Their analysis found that the Greenland Ice Sheet shed about 243 gigatons of ice per year – equivalent to about 277 cubic kilometers – from 2003-09.
This loss is estimated to have added about 0.68 mm of water to the oceans annually.
The figures are averages, and ice loss varied from year to year, and from region to region.
The team also found that some of Greenland’s glaciers thickened even when the temperature rose. Others exhibited accelerated thinning. Some displayed both thinning and thickening, with sudden reversals.
As a step toward building better models of sea level rise, the research team divided Greenland’s 242 glaciers into 7 major groups based on their behavior from 2003-09.
“Understanding the groupings will help us pick out examples of glaciers that are representative of the whole,” Dr Csatho said.
“We can then use data from these representative glaciers in models to provide a more complete picture of what is happening.”
This study was a massive undertaking, using satellite and aerial data from the ICESat spacecraft, which measured the elevation of the ice sheet starting in 2003, and the Operation IceBridge mission that has flown annually since 2009. Additional airborne data from 1993-2008, collected by NASA’s Program for Arctic Regional Climate Assessment, were also included to extend the timeline of the study.
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Beata M. Csatho et al. Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics. PNAS, published online before print December 15, 2014; doi: 10.1073/pnas.1411680112
