According to a new NASA-funded study, Greenland and Antarctic ice sheets are losing mass at a much faster rate than previous model forecasts have predicted. The study, the longest of its kind—almost 20 years—used satellites to measure changes in polar ice sheet mass. Results suggest that the ice sheets, found only in Antarctica and Greenland, are melting faster than mountain glaciers and ice caps and are poised to become the dominant factor in global sea-level rise. The study’s findings will be published in this month’s Geophysical Research Letters, a journal of the American Geophysical Union.
Scientists conducting the study looked at the loss of ice mass from Greenland and Antarctic ice sheets—defined as being larger than 50,000 square kilometers, or 20,000 square miles—and found that the ice sheets lost a combined mass of an average of 475 gigatonnes a year. A gigatonne is one billion metric tons, or more than 2.2 trillion pounds, and the ice sheets’ combined mass loss is enough to raise the global sea level by about .05 inches or 1.3 millimeters a year. A separate study in 2006 showed that mountain glaciers and ice caps lost only 402 gigatonnes a year on average, with a yearly acceleration rate three times smaller than that of the ice sheets.
Quoted in an article in Science Daily, the study’s lead author, Eric Rignot, of NASA’s Jet Propulsion Laboratory, Pasadena, California, and the University of California, Irvine, said, “That ice sheets will dominate future sea level rise is not surprising—they hold a lot more ice mass than mountain glaciers. What is surprising is this increased contribution by the ice sheets is already happening. If present trends continue, sea level is likely to be significantly higher than levels projected by the United Nations Intergovernmental Panel on Climate Change in 2007.”
The researchers found that for each year during the 18-year-study, the Greenland ice sheet lost mass faster than the year before, and in Antarctica, the year-over-year acceleration in ice mass lost averaged 14.5 gigatonnes. The study’s authors conclude that if current ice sheet melting speeds continue for four more decades, their cumulative loss could raise sea level by 5.9 inches by 2050. The team cautions, however, that there are still several uncertainties in estimating the future ice loss acceleration.
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