for National Geographic News
Melting Greenland ice could cause oceans to rise by more than a foot (30 centimeters) over the next hundred years.
The resulting sea level rise, spurred by global warming, may also happen three times faster than previously predicted.
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.
(See a global warming interactive.)
The new estimates are based on disappearance rates of the ancient Laurentide ice sheet that long ago covered North America and melted 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," lead study author Anders Carlson, of the University of Wisconsin, said in a press release.
Carlson said 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."
The study appears this week in the journal Nature Geoscience.
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.
SOURCES AND RELATED WEB SITES