Post by Flash on Jan 14, 2008 13:14:41 GMT -5
Antarctic ice sheet shrinking at faster rate
New scientific study links melting to upwelling of warm waters along continent's coast
MARTIN MITTELSTAEDT
From Monday's Globe and Mail
January 14, 2008 at 6:00 AM EST
One of the biggest worries about global warming has been its potential to affect the stability of the Antarctic ice sheet, a vast storehouse of frozen water that would inundate the world's coastal regions if it were to melt because of a warming climate.
The southern continent contains enough ice to raise ocean levels by about 60 metres, a deluge that would put every major coastal city in the world deep under water and uproot hundreds of millions of people.
The huge implications posed by the health of the ice sheet have prompted major scientific interest into whether it is growing, shrinking, or stable, with no clear consensus among researchers about its overall trend.
But a new study released yesterday, based on some of the most extensive measurements to date of the continent's ice mass, presents a worrisome development: Antarctica's ice sheet is shrinking, at a rate that increased dramatically from 1996 to 2006.
A new study says the Antarctic ice sheet is melting at an even-faster rate than scientists expected.
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A new study says the Antarctic ice sheet is melting at an even-faster rate than scientists expected.
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The Globe and Mail
"Over the time period of our survey, the ice sheet as a whole was certainly losing mass, and the mass loss increased by 75 per cent in 10 years," the study said.
The results of the research project, led by Eric Rignot, principal scientist for the Radar Science and Engineering Section at NASA's Jet Propulsion Laboratory in Pasadena, Calif., are appearing in the current issue of Nature Geoscience.
In an e-mail, Dr. Rignot attributed the shrinkage in the ice sheet to an upwelling of warm waters along the Antarctic coast, which is causing some glaciers to flow more rapidly into the ocean.
He suspects the trend is due to global warming, and isn't part of a normal natural fluctuation.
"I see that as the main driver for the change in ice mass. And this means that we are not in a natural cycle, but in something that is related to global warming or global climate change, whichever you want to call it," he said.
The study said the continent had a net loss of about 196 billion tonnes of ice in 2006, an amount that is equal to more than a third of the water in Lake Erie, up from 112 billion tonnes in 1996.
The figures were calculated by deducting the amount of ice losses on the continent from the amount of snow that computer models indicate it receives.
The figures were based on satellite data on ice thickness and the speeds at which glaciers are flowing into the ocean.
Dr. Rignot said the Antarctic ice loss in 2006 raised sea levels about half a millimetre, putting it on par with the contribution to sea level rise from the recently observed melting of the Greenland ice sheet.
Within scientific circles, there is little doubt that Greenland's ice is melting, but there has been more uncertainty over the fate of the larger stores of ice on Antarctica.
The Intergovernmental Panel on Climate Change, the UN-sponsored scientific body that compiles information on global warming, said last year that studies on the subject have been all over the map.
Some have suggested the ice cap was expanding by 50 billion tonnes a year from 1993 to 2003, while others projected losses over the same period of up to 200 billion tonnes.
It said the wide range of estimates reflected such factors as the small number of ice measurements made on the continent and disagreements among scientists on what techniques best estimate trends there.
Some experts have even speculated that global warming might lead to increases in ice accumulation in Antarctic's interior due to more snowfall.
However, many experts say that this effect is unlikely to offset Antarctica's contribution to sea level rise because of the rapid melting of coastal glaciers.
"The concept that global warming will increase precipitation in Antarctica and mitigate sea level rise is a lullaby," Dr. Rignot said.
"Our [study] shows that the main driver for the mass balance is the rate of glacier flow to the sea, not the precipitation rate because other studies already showed recently that the precipitation rate has not changed significantly."
Another member of the research team, Curt Davis, director of the Centre for Geospatial Intelligence at the University of Missouri-Columbia, said the new study is the "most comprehensive" to date on the status of Antarctica's ice, and has zeroed in on exactly where the losses are occurring.
It found that the biggest losses are in West Antarctica, around the Amundsen Sea, and in the Antarctic Peninsula, the continent's distinctive long arm of land that points like a finger up at South America.
One encouraging finding from the study is that the largest ice sheet, the one covering East Antarctica, has remained relatively stable, showing a small net gain in size.