Greenland and Antarctica’s ice sheets are shrinking more quickly, suggesting United Nations projections for sea-level rise are too conservative, a U.S. National Aeronautics and Space Administration-funded study said.
From 1992 to 2009, the two regions lost on average 36.3 billion tons more ice every year than the previous year, scientists led by Eric Rignot at NASA’s Jet Propulsion Laboratory in Pasadena, California, said in a study in the Geophysical Research Letters journal. The researchers said they linked two independent sets of measurements to validate them.
Continuing the trend may raise oceans 15 centimeters (6 inches) from 2010 to 2050, and by 56 centimeters by 2100, the study said. That’s more than what was factored into the 2007 projection by the UN’s Intergovernmental Panel on Climate Change for seas to rise 18 to 59 centimeters by 2100.
“If present trends continue, sea level is likely to be significantly higher than levels projected by the United Nations,” Rignot said in a statement e-mailed late yesterday by NASA. “Our study helps reduce uncertainties.”
The UN prediction also includes the expansion of water with warmer temperatures and the melting of mountain glaciers and smaller ice caps.
Rising Sea Levels
The researchers said their 2050 forecast has a margin of error of 2 centimeters. Melting from mountain glaciers and smaller ice caps would add 8 centimeters to the sea level increase. The expansion of water as temperatures rise would add 9 centimeters, the researchers said.
They warned their 2100 figure can’t be considered a projection because of “considerable uncertainty in future acceleration of ice sheet mass loss.”
The IPCC in 2007 said Greenland and Antarctica contributed a combined 0.42 millimeters a year to sea level rise from 1993 through 2003. That’s just over half the 0.77-millimeter contribution from mountain glaciers and smaller ice caps, and a quarter of the 1.6-millimeter rise as a result of water expanding with warmer temperatures.
Antarctica holds enough ice to raise sea levels by about 57 meters (187 feet), though melting isn’t likely for thousands of years, according to the UN. Greenland contains enough ice to raise sea levels by about 7 meters.
Glaciers and Ice Caps
The North Atlantic island and southern continent now contribute more than mountain glaciers and ice caps, according to the NASA study. The researchers cited another paper that put the ice loss of the glaciers and ice caps at 402 billion tons in 2006, compared with the 475 billion tons from Greenland and Antarctica in the same year -- equivalent to 1.3 millimeters of sea level rise. The acceleration in ice loss is three times greater than for mountain glaciers, they wrote.
“That ice sheets will dominate future sea level rise is not surprising -- they hold a lot more ice mass than mountain glaciers,” said Rignot, also a researcher at the University of California, Irvine. “What is surprising is this increased contribution by the ice sheets is already happening.”
Utrecht University in the Netherlands and the National Center for Atmospheric Research in Boulder, Colorado, also contributed to the research. The scientists correlated different sets of satellite, radar and climate modeling data to produce the study.