GREENLAND ICE SHEET ON A DOWNWARD SLIDE

NASA
October 19, 2006

//www.nasa.gov/vision/earth/lookingatearth/greenland_slide.html

For the first time NASA scientists have analyzed data from direct, detailed satellite measurements to show that ice losses now far surpass ice gains in the shrinking Greenland ice sheet.

Using a novel technique that reveals regional changes in the weight of the massive ice sheet across the entire continent, scientists at NASA's Goddard Space Flight Center, Greenbelt, Md., report that Greenland's low coastal regions lost 155 gigatons (41 cubic miles) of ice per year between 2003 and 2005 from excess melting and icebergs, while the high-elevation interior gained 54 gigatons (14 cubic miles) annually from excess snowfall.

"With this new analysis we observe dramatic ice mass losses concentrated in the low-elevation coastal regions, with nearly half of the loss coming from southeast Greenland," said lead author Scott Luthcke of NASA Goddard's Planetary Geodynamics Laboratory. "In the 1990's the ice was very close to balance with gains at about the same level as losses. That situation has now changed significantly, with an annual net loss of ice equal to nearly six years of average water flow from the Colorado River."

The study is based on an innovative use of data from the Gravity Recovery and Climate Experiment (GRACE) satellite that reveals detailed information about where and when the Greenland ice mass has changed. Other recent studies using GRACE observations have reported continent-wide ice mass declines, but none has shown these changes in enough detail for scientists to investigate how much different areas of the ice sheet are losing.

To achieve this more-detailed view of the ice sheet's behavior, Luthcke and his colleagues used a technique that brings GRACE's global view of the Earth down to a more local and frequent view. The pair of GRACE satellites orbiting in close formation detect changes in the Earth's mass directly below them by measuring changes in the distance between the two satellites as the gravitational force of the mass causes each to speed up or slow down.

To achieve this more-detailed view of the ice sheet's behavior, Luthcke and his colleagues used a technique that brings GRACE's global view of the Earth down to a more local and frequent view. The pair of GRACE satellites orbiting in close formation detect changes in the Earth's mass directly below them by measuring changes in the distance between the two satellites as the gravitational force of the mass causes each to speed up or slow down.

Standard GRACE data products infer local mass changes from a global data set of these satellite measurements. The new study used only data from over the Greenland region.

"With this new detailed view of the Greenland ice sheet, we have come a long way toward resolving the differences among recent observations and what we know about how the ice sheet behaves," said co-author Waleed Abdalati, head of Goddard's Cryospheric Sciences Branch. "A consistent picture from the different data sets is emerging."

"The seasonal cycle of increased mass loss during the summer melt season and growth during winter is clearly captured," said co-author Jay Zwally, ICESat project scientist. The new results also capture more precisely where changes are taking place, showing that the losses of ice mass are occurring in the same three drainage systems where other studies have reported increased glacier flow and ice-quakes in outlet glaciers.

GRACE is a joint partnership between NASA and the German Aerospace Center, Deutsches Zentrum für Luft und Raumfahrt. The satellites, launched in 2002, are managed by the Jet Propulsion Laboratory.

Continued monitoring in the future is needed to determine whether this ice loss is a long-term trend, the authors point out. The new study appears in Science Express, the advance edition of the journal Science, on Oct. 19.


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