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Greenland,

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the world's largest island, extends over an area more than one quarter the size

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of the continental United States. Although sparsely populated,

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it holds the potential to impact populations around the world.

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The Greenland Ice Sheet, covering three quarters of the country

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in ice up to 3 kilometers thick, would increase global

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sea level by 7.2 meters if it were to melt completely.

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Since the late 1970's, NASA

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has been monitoring the changes in the Greenland Ice Sheet.

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Recent analysis of seven years of surface elevation readings from NASA's ICESat satellite

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and four years of laser and ice-penetrating

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radar data from NASA's airborne mission called Operation IceBridge

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show us how the surface elevation of the ice sheet has changed.

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The colors shown here represent the accumulated

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change in elevation since 2003.

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The light yellow over the central region of the ice sheet indicates a slight thickening

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due to snow.This accumulation, along

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with the weight of the ice sheet, pushes ice toward the coast.

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Thinning near coastal regions, shown in green, blue and purple,

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has increased over time and now extends into the interior of the ice sheet

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where the bedrock topography permits.

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As a result, there has been an average loss of 300 cubic kilometers of ice

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per year between 2003 and 2012.

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The bedrock formations under the ice sheet

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affect the size of the basins being drained by outlet glaciers.

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The weight of the massive ice sheet has depressed the interior bedrock topography,

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shown here in shades of brown, but mountains along the coast,

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shown in green, confine the ice sheet along the margins.

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In southeast Greenland, the ice sheet experienced fast thinning

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2004 to 2006. followed by brief periods of slower

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loss or even slight gain.

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Although significant loss has occurred, the glaciers that drain this region of

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Greenland’s ice sheet are short troughs hemmed in by coastal mountains.

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[music]

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The topography of the north is quite different, where the Northeast Greenland

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Greenland Ice Stream has unfettered access to the large interior basin.

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After a long period of stability,

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several large glaciers draining the region began thinning in 2000

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with increasing rates ever since.

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[music]

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This thinning could result in increasing mass loss from the deep central portion

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of the Greenland Ice Sheet, which would affect sea level

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and coastlines worldwide.

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The most dramatic mass loss has been observed since the

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late 1990s in the region feeding the Jakobshavn glacier on the central west coast.

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[music]

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Increased glacier calving has continued

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augmented by both an increase in surface melt, as well as

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melt caused by warming ocean temperatures.

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The ice sheets’ response to climate change has been both more rapid and

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much more complex than we would have thought a few decades ago.

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Over the last ten years, starting with the first ICESat satellite and

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continuing with Operation IceBridge, NASA missions have increased our understanding

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of the ice sheets' response to environmental changes.

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Future IceBridge flights and the launch of ICESat-2 will continue to help us better understand

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how the ice sheets respond to a changing climate

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and ultimately, help us more accurately project how much they might contribute

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to sea level rise.

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