Greenland Ice Sheet
on a Downward Slide
(19 October 2006) For the first time NASA scientists have analysed data from direct, detailed satellite measurements to show that ice losses now far surpass ice gains in the shrinking Greenland ice sheet.
Greenland's massive ice sheet has lost nearly 100 gigatons of ice annually recently, much of it in low-elevation regions along the continent's southeastern coast, including the southern tip (pictured here). (courtesy: NASA MODIS Land Rapid Response Team)
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.
NASA satellite data has revealed regional changes in the weight of the Greenland ice sheet between 2003 and 2005. Low coastal regions (blue) lost three times as much ice per year from excess melting and icebergs than the high-elevation interior (orange/red) gained from excess snowfall. (courtesy: Scott Luthcke, NASA Goddard)
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.
The changes in the ice sheet's mass were measured from space by the GRACE mission. GRACE is a pair of satellites orbiting in close formation that can detect changes in the Earth's mass directly below them by measuring changes in the distance between the two spacecraft as the gravitational force of the mass causes each to speed up or slow down. (courtesy: NASA)
"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.
(source: NASA)