Greenland’s ice loss occurring rapidly: study

Washington – Ice loss from the Greenland ice sheet, which has
been increasing during the past decade over its southern region, is now
moving up its northwest coast, according to a new international study.

The
research indicates the ice-loss acceleration began moving up the
northwest coast of Greenland staring in late 2005. The team drew their
conclusions by comparing data from NASA’s Gravity and Recovery Climate Experiment
satellite system, or GRACE, with continuous GPS measurements made from
long-term sites on bedrock on the edges of the ice sheet.

The data from the GPS and GRACE provided the researchers with monthly
averages of crustal uplift caused by ice-mass loss. The team, which
includes researchers from Denmark’s Technical Institute’s National
Space Institute in Copenhagen and University of Colorado at Boulder,
combined the uplift measured by GRACE over United Kingdom-sized chunks
of Greenland, while the GPS receivers monitored crustal uplift on
scales of just tens of miles.

“Our results show that the ice
loss, which has been well documented over southern portions of
Greenland, is now spreading up along the northwest coast,” says Shfaqat
Abbas Khan, lead author on a paper that was published March 19, in Geophysical Research Letters, a publication of the American Geophysical Union (AGU).

Although
the low resolution of GRACE — a swath of about 250 kilometers across —
is not precise enough to pinpoint the source of the ice loss, the fact
that the ice sheet is losing mass nearer to the ice sheet margins
suggests the flows of Greenland outlet glaciers there are increasing in
velocity, said the study authors.

“When we look at the monthly
values from GRACE, the ice mass loss has been very dramatic along the
northwest coast of Greenland,” says CU-Boulder physics professor and
study co-author John Wahr, also a fellow at CU-Boulder’s Cooperative
Institute for Research in Environmental Sciences.

“This is a
phenomenon that was undocumented before this study,” Wahr says. “Our
speculation is that some of the big glaciers in this region are sliding
downhill faster and dumping more ice in the ocean.”

Other
co-authors on the new study are Michael Bevis and Eric Kendrick from
Ohio State University, Columbus, and Isabella Velicogna of the
University of California-Irvine, who also is a scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

A 2009 study by Velicogna, published also in Geophysical Research Letters,
showed that between April 2002 and February 2009, the Greenland ice
sheet shed roughly 1,605 cubic kilometers of ice. The mass loss is
equivalent to about 0.5 millimeters of global sea-level rise per year.

“These
changes on the Greenland ice sheet are happening fast, and we are
definitely losing more ice mass than we had anticipated,” says
Velicogna. “We also are seeing this trend in Antarctica, a sign that
warming temperatures really are having an effect on ice in Earth’s cold
regions.”

Researchers have been gathering data from GRACE since
NASA launched the system in 2002. Two GRACE satellites whip around
Earth 16 times a day separated by 220 kilometers and measure changes in
Earth’s gravity field caused by regional shifts in the planet’s mass,
including ice sheets, oceans and water stored in the soil and in
underground aquifers. “GRACE is unique in that it allows us see changes
in the ice mass in almost real time,” says Velicogna. “Combining GRACE
data with the separate signals from GPS stations gives us a very
powerful tool that improves our resolution and allows us to better
understand the changes that are occurring.”

“If this activity in
northwest Greenland continues and really accelerates some of the major
glaciers in the area — like the Humboldt Glacier and the Peterman
Glacier — Greenland’s total ice loss could easily be increased by
additional 50 to 100 cubic kilometers, within a few years,” Khan says.

The study was funded by NASA and the National Science Foundation.

Greenland’s
massive ice sheet covers about 80 percent of its surface. It holds
about 20 percent of the world’s ice, the equivalent of about 6.4 meters
of global sea rise. Air temperatures over the Greenland ice sheet have
increased by about 2.2 degrees Celsius since 1991, which most
scientists attribute to a build-up of greenhouse gases in the
atmosphere.

A 2006 study by Wahr and Velicogna using the GRACE
satellite indicated that Greenland lost roughly 684 cubic kilometers of
ice from April 2004 to April 2006 — more than the volume of water in
Lake Erie.

View an animation of the Greenland melting on the NASA homepage.