Greenland Ice Sheet Rapidly Melting

GREENBELT, Maryland, October 20, 2006 (ENS) - Ice losses now far surpass ice gains in the shrinking Greenland ice sheet, NASA scientists reported Thursday. The researchers estimate the annual net loss from the ice sheet equals six years of water flow from the Colorado River, but found the ice sheet may not be melting quite as quickly as other studies have found.

The research team reported 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. During the same period the high-elevation interior gained 54 gigatons, or 14 cubic miles, annually from excess snowfall.

Meltwater stream in the ablation zone (area below the equilibrium line) of the Greenland ice sheet.(Photo by Roger J. Braithwaite courtesy NASA)

"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 1990s the ice was very close to balance with gains at about the same level as losses. That situation has now changed significantly."

Continued monitoring in the future is needed to determine whether this ice loss is a long-term trend, the research team said. The study was published Thursday in "Science Express", the advance edition of the journal "Science."

The study details a dramatic acceleration in the rate of ice mass loss since the late 1990s that is nearly identical to reports earlier this year based on radar measurements of glacier acceleration.

Although the ice mass loss observed in the new study is less than half of what other recent research has reported, Greenland is now losing 20 percent more mass than it receives from new snowfall each year, the researchers concluded.

"This is a very large change in a very short time," said coauthor Jay Zwally, a project scientist with ICESat, a NASA Earth observing system mission. "In the 1990s, the ice sheet was growing inland and shrinking significantly at the edges, which is what climate models predicted as a result of global warming. Now the processes of mass loss are clearly beginning to dominate the inland growth, and we are only in the early stages of the climate warming predicted for this century."

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)(Photo courtesy NASA)

The new results also capture more precisely where changes are taking place, the researchers said, 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.

"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 coauthor Waleed Abdalati, head of Goddard's Cryospheric Sciences Branch. "A consistent picture from the different data sets is emerging."

Research released last month suggested the ice sheet is melting faster than scientists thought.

The rate of loss accelerated from 2004 to 2006, with the massive ice sheet melting two and one-half times faster than the previous two-year period, according to a study by researchers at the University of Colorado at Boulder.

The UC-Boulder study, published in "Nature," presented analysis of satellite observations that show Greenland lost roughly 164 cubic miles of ice from April 2004 to April 2006 - more than the volume of water in Lake Erie.

There is growing interest about the fate of the Greenland ice sheet, which has the potential to dramatically affect sea levels. Greenland harbors about 10 percent of the world's freshwater in its ice sheet, which is up to two miles thick in places.

Scientists estimate that if the Greenland ice sheet melted completely, the world's oceans would rise more than 20 feet.