FAIRBANKS (AP) -- Alaska's glaciers have shrunk by an average total of about 50 cubic kilometers each year since the 1950s. But in the last decade, the rate of shrinkage has doubled, a team of scientists at the University of Alaska Fairbanks has found.
The accelerated melting has likely caused a rise in worldwide sea level of a few millimeters, they concluded.
Anthony Arendt, a graduate student in geophysics, and his supervisor Keith Echelmeyer, a professor of geology and geophysics, documented current glacial elevations by flying a small plane over the ice rivers and using laser instruments to record the location of the surface below them. Arendt then compared the current data with the elevations recorded on topographical maps made in the 1950s by the U.S. Geological Survey.
On 67 glaciers ranging from the western Alaska Range to southeast Alaska, the average rate of thinning was almost a half-meter each year from the 1950s to the mid-1990s. On 27 of the glaciers, Arendt also calculated ice losses for just the last half of the 1990s, the time when the project was being conducted. There, he found average annual ice thinning of about one meter.
For his work, Arendt won an award for excellence last week from the Arctic Research Consortium of the United States at the organization's annual meeting in Washington, D.C.
Arendt's work was one of four studies selected from more than 50 entries by students from around the world. ARCUS, based in Fairbanks, is a nonprofit group of research institutions, universities and agencies involved in Arctic science.
Extrapolating from the data on the 67 glaciers to all of Alaska's glaciers, Arendt and the other researchers figured the total loss at 52 cubic kilometers of water-equivalent ice annually since the mid-1950s, with an error of plus or minus seven cubic kilometers. From the mid-1990s through 2001, the glaciers lost 91 cubic kilometers annually, plus or minus 28 cubic kilometers.
The Alaska melting in recent years has added about a quarter-millimeter per year to ocean depths, Arendt said. Earlier studies had put Alaska's contribution at about two-tenths of a millimeter annually.
The Intergovernmental Panel on Climate Change has estimated the annual average sea level rise at 1.5 millimeters over the past century. Satellite studies have found a 3.22-millimeter rise recently, however, Arendt said.
If that's correct, Alaska's glaciers are contributing about 8 percent of the new ocean volume, he said.
Arendt said there are some obvious limitations to their method that introduce errors into the ice-loss estimates, which required the inclusion of plus-or-minus qualifications on their figures. The largest error probably comes from the old maps.
''The maps were made from aerial photographs and some of them have poor geodetic controls and some of them also have poor accuracy especially at the higher elevations where there is a lot of snow cover,'' Arendt told the Fairbanks Daily News-Miner.
Some error also arises from assuming that a single elevation profile along the center of a glacier holds true across the entire width of the ice, he said.
Arendt, who hails from Edmonton, Alberta, is in his second year as a graduate student at UAF. He expects the glacier project to continue for another few years. They will next look at why the glaciers are thinning.
The work is funded by the National Science Foundation, National Oceanic and Atmospheric Administration and National Aeronautics and Space Administration.
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