Global warming could cause oceans to rise three times faster than previously predicted

September 4th, 2008 - 1:08 pm ICT by ANI  

National Geographic

Washington, September 4 (ANI): New estimates have indicated that the melting Greenland ice, spurred by global warming, could cause oceans to rise three times faster than previously predicted, by more than a foot (30 centimeters) over the next hundred years.
When all other sources of melting ice are also factored in, such as the Antarctic ice sheet and smaller glaciers, the sea level has been predicted to increase by several more feet by 2100, according to previous studies.
According to a report in National Geographic News, the new estimates are based on disappearance rates of the ancient Laurentide ice sheet that covered North America between 9,000 and 6,000 years ago.
“We have never seen an ice sheet retreat significantly or even disappear before, yet this may happen for the Greenland ice sheet in the coming centuries to millennia,” said lead study author Anders Carlson, of the University of Wisconsin.
Carlson said that his team’’s research on the Laurentide ice sheet “gives us a window into how fast these large blocks of ice can melt and raise sea level.”
At its peak, the Laurentide ice sheet was more than 5,000,000 square miles (13,000,000 square kilometers) across, with a thickness of up to 10,000 feet (3,000 meters) in some places, according to previous estimates.
To determine the demise of the massive sheet, Carlson and his team estimated the ages of boulders left in its wake based on how long they had been exposed to cosmic rays.
The geologists also obtained radiocarbon dates of trees and other organic materials that couldn”t have existed until after the ice was gone.
Finally, they measured oxygen atoms in plankton fossils in Labrador Bay, which is adjacent to the site of the historic ice sheet.
The atoms-oxygen isotopes indicate the contribution of fresh water from the melting glacier, and therefore independently confirm the land-fossil measurements, according to Carlson.
The authors said that there were two major Laurentide melting pulses - 9,000 years ago and 7,500 years ago - that added a total of almost 40 feet (12 meters) of depth to the world’’s oceans.
They said that the entire Laurentide ice sheet was gone by about 6,500 years ago. It was exposed to direct solar heat because Earth’’s tilt had it angling closer to the sun.
The concentration of heat caused by greenhouse gases is having a similar effect on today’’s Greenland ice sheet.
The new findings have also suggested that the Greenland ice sheet will melt faster than the United Nations Intergovernmental Panel on Climate Change (IPCC) predicted last year.
Any rise at all could threaten U.S. cities that are built, at least in part, at sea level. These cities include New York, Boston, Los Angeles, Philadelphia, New Orleans.
Large swaths of entire countries, including Bangladesh and the Maldives, would also be vulnerable to flooding. (ANI)

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