Thursday, April 26, 2012 2:32:12 AM
Antarctic Ice Melting From Below by Warming Ocean
First map of Antarctica's moving ice.
Image courtesy Eric Rignot, NASA Jet Propulsion Laboratory and University of California Irvine
[ http://earthobservatory.nasa.gov/IOTD/view.php?id=51781 ; related vid below via http://investorshub.advfn.com/boards/read_msg.aspx?message_id=66339379 ]
The Ronne-Filchner Ice Shelf in West Antarctica rapidly breaking up. Top image taken on the afternoon of 12 January 2010. Bottom image taken 24 hours later on the afternoon of 13 January 2010.
NASA images courtesy Jeff Schmaltz, MODIS Rapid Response Team at NASA GSFC
[ http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=42302 ]
By Julia Whitty
Wed Apr. 25, 2012 11:20 AM PDT
A paper [ http://www.nature.com/nature/journal/v484/n7395/full/nature10968.html ] published today in the science journal Nature reveals that the melting of Antarctica's ice sheet is being driven by a warming ocean more than a warming atmosphere.
Which means even though summer air temperatures have not yet warmed enough to substantially melt Antarctica's surface snows, the oceans are undermining the frozen continent from below—fueling a recent, widespread, and intensifying glacier acceleration and its accompanying rise in sea levels.
The results are based on 4.5 million measurements made by a laser instrument mounted on NASA's now defunct ICESat satellite [ http://icesat.gsfc.nasa.gov/ ] between 2003 and 2008, which mapped the thickness of most floating ice shelves around Antarctica. The results:
¦ Of 54 ice shelves mapped, 20 are being melted by warm ocean currents, most of those in West Antarctica.
¦ In all cases the inland glaciers that flow down to the coast and feed into these thinning ice shelves have accelerated, draining more ice into the sea and contributing to sea-level rise.
The melting is happening fastest where deep troughs cut through the underwater continental shelf, allowing warmer water access to the undersides of the ice shelves.
Lead author Hamish Pritchard [ http://www.antarctica.ac.uk/about_bas/contact/staff/profile/160e0ede4477bafd8a95351d411e9b6f/ ] at the British Antarctic Survey says:
"What’s really interesting is just how sensitive these glaciers seem to be. Some ice shelves are thinning by a few meters a year and in response the glaciers drain billions of tons of ice into the sea. This supports the idea that ice shelves are important in slowing down the glaciers that feed them, controlling the loss of ice from the Antarctic ice sheet... We think [the cause is] linked to changes in wind patterns. Studies have shown that Antarctic winds have changed because of changes in climate and that this has affected the strength and direction of ocean currents. As a result warm water is funnelled beneath the floating ice. These studies and our new results therefore suggest that Antarctica’s glaciers are responding rapidly to a changing climate.
The ice2sea project [ http://www.ice2sea.eu/ ] team behind the new paper [ http://www.nature.com/nature/journal/v484/n7395/full/nature10968.html ] will be releasing its projections on sea level rise into the 21st and 22nd centuries later this year.
Copyright ©2012 Mother Jones and the Foundation for National Progress
http://motherjones.com/blue-marble/2012/04/antarctic-ice-melting-below-warming-ocean [no comments yet]
===
Antarctic ice melting from warm water below: study
April 26, 2012 - 10:18AM
Antarctica's massive ice shelves are shrinking because they are being eaten away from below by warm water, a new study finds.
That suggests that future sea levels could rise faster than many scientists have been predicting.
The western chunk of Antarctica is losing 23 feet (seven metres) of its floating ice sheet each year. Until now, scientists weren't exactly sure how it was happening and whether or how man-made global warming might be a factor. The answer, according to a study published Wednesday in the journal Nature, is that climate change plays an indirect role — but one that has larger repercussions than if Antarctic ice were merely melting from warmer air.
Hamish Pritchard, a glaciologist at the British Antarctic Survey, said research using an ice-gazing NASA satellite showed that warmer air alone couldn't explain what was happening to Antarctica. A more detailed examination found a chain of events that explained the shrinking ice shelves.
Twenty ice shelves showed signs that they were melting from warm water below. Changes in wind currents pushed that relatively warmer water closer to and beneath the floating ice shelves. The wind change is likely caused by a combination of factors, including natural weather variation, the ozone hole and man-made greenhouse gases, Pritchard said in a phone interview.
As the floating ice shelves melt and thin, that in turn triggers snow and ice on land glaciers to slide down to the floating shelves and eventually into the sea, causing sea level rise, Pritchard said. Thicker floating ice shelves usually keep much of the land snow and ice from shedding to sea, but that's not happening now.
That whole process causes larger and faster sea level rise than simply warmer air melting snow on land-locked glaciers, Pritchard said.
"It means the ice sheets are highly sensitive to relatively subtle changes in climate through the effects of the wind," he said.
What's happening in Antarctica "may have already triggered a period of unstable glacier retreat", the study concludes. If the entire Western Antarctic Ice Sheet were to melt — something that would take many decades if not centuries — scientists have estimated it would lift global sea levels by about 16 feet (4.87 metres).
NASA chief scientist Waleed Abdalati, an expert in Earth's ice systems who wasn't involved in the research, said Pritchard's study "makes an important advance" and provides key information about how Antarctica will contribute to global sea level rise.
Another outside expert, Ted Scambos of the National Snow and Ice Data Centre, said the paper will change the way scientists think about melt in Antarctica. Seeing more warm water encircling the continent, he worries that with "a further push from the wind" newer areas could start shrinking.
Copyright 2012 The Associated Press
http://www.smh.com.au/environment/climate-change/antarctic-ice-melting-from-warm-water-below-study-20120426-1xmiy.html [has the new NASA video in the item above embedded]
===
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First map of Antarctica's moving ice.
Image courtesy Eric Rignot, NASA Jet Propulsion Laboratory and University of California Irvine
[ http://earthobservatory.nasa.gov/IOTD/view.php?id=51781 ; related vid below via http://investorshub.advfn.com/boards/read_msg.aspx?message_id=66339379 ]
The Ronne-Filchner Ice Shelf in West Antarctica rapidly breaking up. Top image taken on the afternoon of 12 January 2010. Bottom image taken 24 hours later on the afternoon of 13 January 2010.
NASA images courtesy Jeff Schmaltz, MODIS Rapid Response Team at NASA GSFC
[ http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=42302 ]
By Julia Whitty
Wed Apr. 25, 2012 11:20 AM PDT
A paper [ http://www.nature.com/nature/journal/v484/n7395/full/nature10968.html ] published today in the science journal Nature reveals that the melting of Antarctica's ice sheet is being driven by a warming ocean more than a warming atmosphere.
Which means even though summer air temperatures have not yet warmed enough to substantially melt Antarctica's surface snows, the oceans are undermining the frozen continent from below—fueling a recent, widespread, and intensifying glacier acceleration and its accompanying rise in sea levels.
The results are based on 4.5 million measurements made by a laser instrument mounted on NASA's now defunct ICESat satellite [ http://icesat.gsfc.nasa.gov/ ] between 2003 and 2008, which mapped the thickness of most floating ice shelves around Antarctica. The results:
¦ Of 54 ice shelves mapped, 20 are being melted by warm ocean currents, most of those in West Antarctica.
¦ In all cases the inland glaciers that flow down to the coast and feed into these thinning ice shelves have accelerated, draining more ice into the sea and contributing to sea-level rise.
The melting is happening fastest where deep troughs cut through the underwater continental shelf, allowing warmer water access to the undersides of the ice shelves.
Lead author Hamish Pritchard [ http://www.antarctica.ac.uk/about_bas/contact/staff/profile/160e0ede4477bafd8a95351d411e9b6f/ ] at the British Antarctic Survey says:
"What’s really interesting is just how sensitive these glaciers seem to be. Some ice shelves are thinning by a few meters a year and in response the glaciers drain billions of tons of ice into the sea. This supports the idea that ice shelves are important in slowing down the glaciers that feed them, controlling the loss of ice from the Antarctic ice sheet... We think [the cause is] linked to changes in wind patterns. Studies have shown that Antarctic winds have changed because of changes in climate and that this has affected the strength and direction of ocean currents. As a result warm water is funnelled beneath the floating ice. These studies and our new results therefore suggest that Antarctica’s glaciers are responding rapidly to a changing climate.
You can see that happening in this NASA video [ http://www.youtube.com/watch?v=08sDlxhNEHQ (above)] which shows warm ocean currents attacking the underside of ice shelves. Ice shelves colored red are thicker (greater than 1,800 feet / 550 meters). Those colored blue are thinner (less than 650 feet / 200 meters).
The ice2sea project [ http://www.ice2sea.eu/ ] team behind the new paper [ http://www.nature.com/nature/journal/v484/n7395/full/nature10968.html ] will be releasing its projections on sea level rise into the 21st and 22nd centuries later this year.
Copyright ©2012 Mother Jones and the Foundation for National Progress
http://motherjones.com/blue-marble/2012/04/antarctic-ice-melting-below-warming-ocean [no comments yet]
===
Antarctic ice melting from warm water below: study
April 26, 2012 - 10:18AM
Antarctica's massive ice shelves are shrinking because they are being eaten away from below by warm water, a new study finds.
That suggests that future sea levels could rise faster than many scientists have been predicting.
The western chunk of Antarctica is losing 23 feet (seven metres) of its floating ice sheet each year. Until now, scientists weren't exactly sure how it was happening and whether or how man-made global warming might be a factor. The answer, according to a study published Wednesday in the journal Nature, is that climate change plays an indirect role — but one that has larger repercussions than if Antarctic ice were merely melting from warmer air.
Hamish Pritchard, a glaciologist at the British Antarctic Survey, said research using an ice-gazing NASA satellite showed that warmer air alone couldn't explain what was happening to Antarctica. A more detailed examination found a chain of events that explained the shrinking ice shelves.
Twenty ice shelves showed signs that they were melting from warm water below. Changes in wind currents pushed that relatively warmer water closer to and beneath the floating ice shelves. The wind change is likely caused by a combination of factors, including natural weather variation, the ozone hole and man-made greenhouse gases, Pritchard said in a phone interview.
As the floating ice shelves melt and thin, that in turn triggers snow and ice on land glaciers to slide down to the floating shelves and eventually into the sea, causing sea level rise, Pritchard said. Thicker floating ice shelves usually keep much of the land snow and ice from shedding to sea, but that's not happening now.
That whole process causes larger and faster sea level rise than simply warmer air melting snow on land-locked glaciers, Pritchard said.
"It means the ice sheets are highly sensitive to relatively subtle changes in climate through the effects of the wind," he said.
What's happening in Antarctica "may have already triggered a period of unstable glacier retreat", the study concludes. If the entire Western Antarctic Ice Sheet were to melt — something that would take many decades if not centuries — scientists have estimated it would lift global sea levels by about 16 feet (4.87 metres).
NASA chief scientist Waleed Abdalati, an expert in Earth's ice systems who wasn't involved in the research, said Pritchard's study "makes an important advance" and provides key information about how Antarctica will contribute to global sea level rise.
Another outside expert, Ted Scambos of the National Snow and Ice Data Centre, said the paper will change the way scientists think about melt in Antarctica. Seeing more warm water encircling the continent, he worries that with "a further push from the wind" newer areas could start shrinking.
Copyright 2012 The Associated Press
http://www.smh.com.au/environment/climate-change/antarctic-ice-melting-from-warm-water-below-study-20120426-1xmiy.html [has the new NASA video in the item above embedded]
===
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http://investorshub.advfn.com/boards/read_msg.aspx?message_id=69632569 and preceding and following
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Greensburg, KS - 5/4/07
"Eternal vigilance is the price of Liberty."
from John Philpot Curran, Speech
upon the Right of Election, 1790
F6
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