"There's been a lot of speculation about the stability of marine ice sheets, and many scientists suspected that this kind of behavior is under way," Ian Joughin, a glaciologist at the University of Washington, said in a statement about one of the studies. "This study provides a more quantitative idea of the rates at which the collapse could take place."
Joughin and colleagues reported in the U.S. journal Science that they used detailed topography maps and computer modeling to investigate a particularly unstable member of the West Antarctic Ice Sheet known as the Thwaites Glacier.
They found that in some places this glacier has been losing tens of feet, or several meters, of elevation per year. Further research showed that the Thwaites Glacier could disappear in an inevitable way in the next 200 to 1,000 years, raising sea levels by nearly 2 feet (about 60 centimeters).
The glacier also acts as a linchpin for the rest of the Ice Sheet, which could cause another 10 to 13 feet (3 to 4 meters) of global sea level rise if the glacier melts away, according to the researchers.
A second study, published in the U.S. journal Geophysical Research Letters, examined the retreat in the grounding lines, the point where the ice from the glacier reaches the ocean and goes afloat, of Thwaites and five other massive glaciers in the Amundsen Sea sector of West Antarctica, using radar observations captured between 1992 and 2011 by the European Earth Remote Sensing satellites, ERS-1 and ERS-2.
The glaciers "have passed the point of no return" and "will be a major contributor to sea level rise in the decades and centuries to come," said lead author of the study, Eric Rignot, a professor at the University of California at Irvine who is also with NASA's Jet Propulsion Laboratory.
"A conservative estimate is it could take several centuries for all of the ice to flow into the sea," Rignot said.
According to Rignot and colleagues, the six glaciers already contribute significantly to sea level rise, releasing almost as much ice into the ocean annually as the entire Greenland Ice Sheet.
The West Antarctic Ice Sheet has long been thought unstable, likely to lose ice and contribute to sea level rise at very high rates. Rignot said the fact that the retreat in glaciers' grounding lines is happening simultaneously over a large sector suggests it was triggered by a common cause, such as an increase in the amount of ocean heat beneath the floating sections of the glaciers.
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13/5/14
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Related:
- http://go.nasa.gov/1m6YZSf
- http://go.nasa.gov/1oIfSlO
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Antarctique : on sait maintenant que la fonte des glaces est bien irréversible...
ReplyDeleteDeux études montrent que la fonte des glaciers de l'ouest du continent austral va provoquer une montée du niveau des mers de 4 mètres dans les prochains siècles.
La fonte des glaces de la partie ouest de l'Antarctique est irréversible : telle est la conclusion d'une étude menée par des chercheurs de la Nasa et de l'université d'Irvine (Californie) et qu'ils viennent de publier dans la revue Geophysical Research Letters.
Même conclusion pour l'étude menée par des chercheurs de l'université de Washington, pour qui cette fonte pourrait s'étaler sur une échelle de temps allant de 200 ans à 1.000 ans pour l'hypothèse la plus optimiste.
Autant d'eau dans l'océan que le Groenland entier
Se basant sur 40 ans d'observation des glaciers dans la région de la mer d'Amundsen, dans l'ouest de l'Antarctique, les chercheurs californiens déduisent que ceux-ci ont dépassé le point de non retour. Il ne s'agit pas là de modélisations informatiques, mais bien de l'interprétation d'observations effectuées sur place, insiste le principal auteur de l'étude, Eric Rignot, glaciologue au Jet Propulsion Laboratory (Nasa) et professeur à l'université d'Irvine.
"Ces glaciers contribuent déjà de manière significative à la montée du niveau des mers, la fonte de leurs glaces produisant pratiquement autant d'eau dans les océans que le Groenland entier", expliquent les scientifiques. Et "ils contiennent assez de glace pour faire augmenter le niveau des mers de 1,2 mètres. Mais ce n'est pas tout : le professeur Rignot indique que ces prévisions peuvent être largement augmentée par l'influence qu'ont les glaciers étudiés sur trois autres bassins, ce qui porterait la fourchette de montée globale des eaux à entre 3 et 4,5 mètres......................empsreel.nouvelobs.com/sciences/20140512.OBS6867
12/5/14
West Antarctic Ice Sheet collapse is under way...
ReplyDeleteUniversity of Washington researchers used detailed topography maps and computer modeling to show that the collapse appears to have already begun. The fast-moving Thwaites Glacier will likely disappear in a matter of centuries, researchers say, raising sea level by nearly 2 feet. That glacier also acts as a linchpin on the rest of the ice sheet, which contains enough ice to cause another 10 to 13 feet (3 to 4 meters) of global sea level rise. The study will be published on May 16 in Science.
"There's been a lot of speculation about the stability of marine ice sheets, and many scientists suspected that this kind of behavior is under way," said Ian Joughin, a glaciologist at the UW's Applied Physics Laboratory. "This study provides a more quantitative idea of the rates at which the collapse could take place."
The good news is that while the word "collapse" implies a sudden change, the fastest scenario is 200 years, and the longest is more than 1,000 years. The bad news is that such a collapse may be inevitable...................Read more at: http://phys.org/news/2014-05-west-antarctic-ice-sheet-collapse.html#jCp