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CLIMATE
CHANGE & ENVIRONMENT
Global warming could cause oceans
to rise three times faster
Washington: 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.
-Sept
4, 2008
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