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PASADENA, Calif. – In the first
comprehensive satellite study of its kind, a
University of Colorado at Boulder-led team used NASA
data to calculate how much Earth's melting land ice
is adding to global sea level rise.
Using satellite measurements from the
NASA/German Aerospace Center Gravity Recovery and
Climate Experiment (GRACE), the researchers measured
ice loss in all of Earth's land ice between 2003 and
2010, with particular emphasis on glaciers and ice
caps outside of Greenland and Antarctica.
The total global ice mass lost from
Greenland, Antarctica and Earth's glaciers and ice
caps during the study period was about 4.3 trillion
tons (1,000 cubic miles), adding about 0.5 inches
(12 millimeters) to global sea level. That's enough
ice to cover the United States 1.5 feet (0.5 meters)
deep.
"Earth is losing a huge amount of ice
to the ocean annually, and these new results will
help us answer important questions in terms of both
sea rise and how the planet's cold regions are
responding to global change," said University of
Colorado Boulder physics professor John Wahr, who
helped lead the study. "The strength of GRACE is it
sees all the mass in the system, even though its
resolution is not high enough to allow us to
determine separate contributions from each
individual glacier."
About a quarter of the average annual
ice loss came from glaciers and ice caps outside of
Greenland and Antarctica (roughly 148 billion tons,
or 39 cubic miles). Ice loss from Greenland and
Antarctica and their peripheral ice caps and
glaciers averaged 385 billion tons (100 cubic miles)
a year. Results of the study will be published
online Feb. 8 in the journal Nature.
Traditional estimates of Earth's ice
caps and glaciers have been made using ground
measurements from relatively few glaciers to infer
what all the world's unmonitored glaciers were
doing. Only a few hundred of the roughly 200,000
glaciers worldwide have been monitored for longer
than a decade.
One unexpected study result from
GRACE was that the estimated ice loss from high
Asian mountain ranges like the Himalaya, the Pamir
and the Tien Shan was only about 4 billion tons of
ice annually. Some previous ground-based estimates
of ice loss in these high Asian mountains have
ranged up to 50 billion tons annually.
"The GRACE results in this region
really were a surprise," said Wahr, who is also a
fellow at the University of Colorado-headquartered
Cooperative Institute for Research in Environmental
Sciences. "One possible explanation is that previous
estimates were based on measurements taken primarily
from some of the lower, more accessible glaciers in
Asia and extrapolated to infer the behavior of
higher glaciers. But unlike the lower glaciers, most
of the high glaciers are located in very cold
environments and require greater amounts of
atmospheric warming before local temperatures rise
enough to cause significant melting. This makes it
difficult to use low-elevation, ground-based
measurements to estimate results from the entire
system."
"This study finds that the world's
small glaciers and ice caps in places like Alaska,
South America and the Himalayas contribute about
0.02 inches per year to sea level rise," said Tom
Wagner, cryosphere program scientist at NASA
Headquarters in Washington. "While this is lower
than previous estimates, it confirms that ice is
being lost from around the globe, with just a few
areas in precarious balance. The results sharpen our
view of land-ice melting, which poses the biggest,
most threatening factor in future sea level rise."
The twin GRACE satellites track
changes in Earth's gravity field by noting minute
changes in gravitational pull caused by regional
variations in Earth's mass, which for periods of
months to years is typically because of movements of
water on Earth's surface. It does this by measuring
changes in the distance between its two identical
spacecraft to one-hundredth the width of a human
hair.
The GRACE spacecraft, developed by
NASA's Jet Propulsion Laboratory, Pasadena, Calif.,
and launched in 2002, are in the same orbit
approximately 137 miles (220 kilometers) apart. The
California Institute of Technology manages JPL for
NASA.
For more on GRACE, visit:
http://www.csr.utexas.edu/grace and http://grace.jpl.nasa.gov .
For more information about NASA and
agency programs, visit:
http://www.nasa.gov .
JPL is managed for NASA by the
California Institute of Technology in Pasadena.
Additional media contact: Jim Scott,
CU-Boulder, 303-492-3114,
jim.scott@colorado.edu .
Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov
Steve Cole 202-358-0918
NASA Headquarters, Washington
Stephen.e.cole@nasa.gov
Source: Nasa |
