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Greenland,
the world's largest island, extends over an area more than one quarter the size 
of the continental United States. Although sparsely populated,
it holds the potential to impact populations around the world.
The Greenland Ice Sheet, covering three quarters of the country 
in ice up to 3 kilometers thick, would increase global 
sea level by 7.2 meters if it were to melt completely.
Since the late 1970's, NASA
has been monitoring the changes in the Greenland Ice Sheet. 
Recent analysis of seven years of surface elevation readings from NASA's ICESat satellite
and four years of laser and ice-penetrating
radar data from NASA's airborne mission called Operation IceBridge 
show us how the surface elevation of the ice sheet has changed.
The colors shown here represent the accumulated 
change in elevation since 2003. 
The light yellow over the central region of the ice sheet indicates a slight thickening 
due to snow.This accumulation, along
with the weight of the ice sheet, pushes ice toward the coast.
Thinning near coastal regions, shown in green, blue and purple, 
has increased over time and now extends into the interior of the ice sheet 
where the bedrock topography permits.
As a result, there has been an average loss of 300 cubic kilometers of ice 
per year between 2003 and 2012.
The bedrock formations under the ice sheet 
affect the size of the basins being drained by outlet glaciers. 
The weight of the massive ice sheet has depressed the interior bedrock topography, 
shown here in shades of brown, but mountains along the coast, 
shown in green, confine the ice sheet along the margins.
In southeast Greenland, the ice sheet experienced fast thinning 
2004 to 2006, followed by brief periods of slower 
loss or even slight gain. 
Although significant loss has occurred, the glaciers that drain this region of 
Greenland’s ice sheet are short troughs hemmed in by coastal mountains.
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The topography of the north is quite different, where the Northeast Greenland 
Greenland Ice Stream has unfettered access to the large interior basin.
After a long period of stability, 
several large glaciers draining the region began thinning in 2000 
with increasing rates ever since.
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This thinning could result in increasing mass loss from the deep central portion
of the Greenland Ice Sheet, which would affect sea level
and coastlines worldwide.
The most dramatic mass loss has been observed since the 
late 1990s in the region feeding the Jakobshavn glacier on the central west coast.
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Increased glacier calving has continued
augmented by both an increase in surface melt, as well as 
melt caused by warming ocean temperatures.
The ice sheets’ response to climate change has been both more rapid and
much more complex than we would have thought a few decades ago. 
Over the last ten years, starting with the first ICESat satellite and 
continuing with Operation IceBridge, NASA missions have increased our understanding
of the ice sheets' response to environmental changes.
Future IceBridge flights and the launch of ICESat-2 will continue to help us better understand 
how the ice sheets respond to a changing climate
and ultimately, help us more accurately project how much they might contribute 
to sea level rise.
 
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