Posted on 02/16/2006 4:54:22 PM PST by blam
Greenland ice swells ocean rise
By Paul Rincon
BBC News science reporter, St Louis
Kangerdlussuaq Glacier "drains" about 4% of the ice sheet
Greenland's glaciers are sliding towards the sea much faster than previously believed, scientists have told a conference in St Louis, US.
It was thought the entire Greenland ice sheet could melt in about 1,000 years, but the latest evidence suggests that could happen much sooner.
It implies that sea levels will rise a great deal faster as well.
Details of the study, by Nasa and University of Kansas researchers, are also reported in the journal Science.
The comprehensive analysis found that the amount of ice dumped into the Atlantic Ocean has doubled in the last five years.
If the Greenland ice sheet melted completely, it would raise global sea levels by about 7m.
Greenland's contribution to global sea level rise today is two to three times greater than it was in 1996.
Sleeping giant
"We are concerned because we know that sea levels have been able to rise much faster in the past - 10 times faster. This is a big gorilla. If sea level rise is multiplied by 10 or more, I'm not sure we can deal with that," co-author Eric Rignot, from the US space agency's (Nasa) Jet Propulsion Laboratory in California, told the BBC News website.
Previous estimates suggested it would take many hundreds of years for the Greenland ice sheet to melt completely. The new data will cut this timescale, but by how much is uncertain.
It takes a long time to build and melt an ice sheet, but glaciers can react quickly to temperature changes
Dr Eric Rignot, Nasa "It depends on how fast the glaciers can go and how sustainable the acceleration can be," said Dr Rignot.
He added: "It takes a long time to build and melt an ice sheet, but glaciers can react quickly to temperature changes."
In 1996, Greenland was losing about 100 cubic km per year in mass from its ice sheet. In 2005, this had increased to about 220 cubic km. By comparison, the city of Los Angeles uses about one cubic km of water per year.
Rising surface air-temperatures seem to be behind the increases in glacier speed in the southern half of Greenland since 1996; but the northward spread of warmer temperatures may be responsible for a rapid increase in glacier speed further north after 2000.
Satellite monitoring
Over the past 20 years, the air temperature in south-east Greenland has risen by 3C.
Warmer temperatures cause more surface melt water to reach the base of the ice sheet where it meets the rock. This is thought to serve as a lubricant, easing the glaciers' march to the sea.
Helheim Glacier loses the equivalent of about half a football field a day
The study's results come from satellites that monitor glacier movement from space.
Rignot and colleague Pannir Kanagaratnam, from the University of Kansas, built up a glacier speed map from the data for 2000 and then used measurements from 1996-2005 to determine how glacier velocity had changed in the last decade.
The researchers plan to continue their monitoring of the Greenland glaciers using satellite data.
The Greenland ice sheet covers 1.7 million sq km and is up to 3km thick.
The scientists described their results at the annual meeting of the American Association for the Advancement of Science.
Parts of California's "Central Valley" are already BELOW SEA LEVEL.
Thanks, I'll check it out.
Please post your figures and the URL for their source.
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Couple of reality points here:
First: NOT ALL of the Greenland ice cap is that thick: It is basically a bowl made by mountains surrounding a deeper center. The center may be that thick, but even the majority of the center of Greenland is NOT covered by ice that thick. You CANNOT multiply "ice 2 miles thick" x Area of Greenland = Amount of water released by melting the ice!
Second: The "bowl" is an deep hollow: example: TWO MILES of ice = 10,000 FEET (plus) in elevation IF (bit IF) all of the ice were actually above sea level. Now, what is the maximum elevation of the top of the ICE PACK in Greenland? (Don't know offhand, and will try to look it up later.)
NASA reports (in the following) that little of the icepack is actually above 2000 meters (7000 feet), so obviously, ANY assumption that the top of entire ice mass is above 10,000 feet is foolish.
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Science 21 July 2000:
Vol. 289. no. 5478, pp. 428 - 430
DOI: 10.1126/science.289.5478.428
Prev | Table of Contents | Next
Reports
Greenland Ice Sheet: High-Elevation Balance and Peripheral Thinning
W. Krabill,1* W. Abdalati,2 E. Frederick,3 S. Manizade,3 C. Martin,3 J. Sonntag,3 R. Swift,3 R. Thomas,3 W. Wright,1 J. Yungel3
Aircraft laser-altimeter surveys over northern Greenland in 1994 and 1999 have been coupled with previously reported data from southern Greenland to analyze the recent mass-balance of the Greenland Ice Sheet. Above 2000 meters elevation, the ice sheet is in balance on average but has some regions of local thickening or thinning. Thinning predominates at lower elevations, with rates exceeding 1 meter per year close to the coast. Interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet, sufficient to raise sea level by 0.13 millimeter per year--approximately 7% of the observed rise.
1 Laboratory for Hydrospheric Processes, NASA Goddard Space Flight Center and
3 EG&G Services, Wallops Flight Facility, Building N-159, Wallops Island, VA 23337, USA.
2 Laboratory for Hydrospheric Processes, NASA Goddard Space Flight Center, Building 33, Room A225, Greenbelt, MD 20771, USA.
* To whom correspondence should be addressed. E-mail: krabill@osb1.wff.nasa.gov
#
3. The total surface of the Greenland ice sheet is approximately 1.7 million square km;
4. The average depth of the Greenland ice sheet is approximately 1.5 km.
Justify those two assumptions please. The ice pack doesn't cover all of Greenland, and most of its depth is much shallower than 1.7 km.
3. The total surface of the Greenland ice sheet is approximately 1.7 million square km;
4. The average depth of the Greenland ice sheet is approximately 1.5 km.Justify those two assumptions please. The ice pack doesn't cover all of Greenland, and most of its depth is much shallower than 1.7 km.
Reasonable requests...I posted hurriedly, without providing references.
Justification of #3, from an Encyclopædia Britannica page (my underline):
The Greenland Ice Sheet, though subcontinental in size, is huge compared with other glaciers in the world except that of Antarctica. Greenland is mostly covered by this single large ice sheet (1,730,000 square kilometres)...
Justification of #4, from another Encyclopædia Britannica page (my underline):
[The Greenland Ice Sheet] extends 1,570 miles (2,530 km) north-south, has a maximum width of 680 miles (1,094 km) near its northern margin, and has an average thickness of about 5,000 feet (1,500 m).
http://www.awi-bremerhaven.de/ATM/asood/route.html
But the outer rim of the mountains surrounding the ice cap is 700 meters to 900 meters. The ice cap within this area has a very small region at ELEVATION 3200 meters, (not thickness of 3200 meters!). Then the ice slopes down towards the mountains, with only a few valleys as an outlet to the sea.
Thus, the ICE is NOT 1.7 km thick. Nor 1.5 km, despite the Encyclopædia Britannica. They are not allowing for the "bowl" effect of the rock under under ice.
Its volume is estimated to be 2.600.000 km³, or about 8% of the ice supplies of the earth.
That's pretty close to the 2.55 million cubic kilometers that I used, basing it on a surface area of about 1.7 million square kilometers and an average depth of 1.5 kilometers. Interesting. I guess the sheet does have a volume somewhere in that vicinity.
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