October
19, 2006
GREENLAND ICE SHEET ON A
DOWNWARD SLIDE
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.
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.
For
more information and
images, visit:
http://www.nasa.gov/vision/earth/lookingatearth/greenland_slide.html
For more
information about climate warming and polar ice sheets, visit:
http://www.nasa.gov/vision/earth/environment/ice_sheets.html
For more
information about the GRACE mission, visit:
http://www.csr.utexas.edu/grace/
For more
information about the ICESat mission, visit:
http://icesat.gsfc.nasa.gov/
##
Contact:
Steve Cole
NASA Goddard
Space Flight Center
301-286-3026
scole@pop600.gsfc.nasa.gov
This text is derived from:
http://www.nasa.gov/vision/earth/lookingatearth/greenland_slide.html
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