North America's Largest Glacier is Melting Away, Says

North America's Largest Glacier is Melting Away, Says Experienced ex-USGS Glaciologist Wendell Tangborn

Shrinkage of Bering Glacier attributed to Earth's rapidly warming climate

SEATTLE, Aug. 6, 2013 — (PRNewswire) — North America's largest glacier is rapidly wasting away. Bering Glacier, which flows from the vast ice fields of Alaska's St Elias and Chugach Mountains toward the Gulf of Alaska, covers 1700 square miles, an area larger than the state of Rhode Island. Indications are that the glacier has been there throughout the Wisconsin Glacial Epoch, which began over 100,000 years ago.

Bering Glacier surges every ten to twenty years. During each surge flow rates increase up to 100 times normal and transport large volumes of ice to lower elevations where it melts more rapidly. Based on temperature and precipitation data from nearby coastal weather stations in Yakutat and Cordova, Alaska, a computer model developed by Wendell Tangborn -- an 85-year-old retired US Geological Survey (USGS) glaciologist who works out of a small home office on Vashon Island, Washington -- has simulated the timing and magnitude of these surges using weather data that starts in 1951. Tangborn's model combines data that uses the glacier area as a function of the altitude of a glacier's surface with daily temperature and precipitation from coastal weather stations to simulate the glacier's "mass balance"; that is, whether it is gaining or losing ice. Tangborn says verifications of this model (called PTAA for precipitation-temperature-area-altitude) have shown that its accuracy equals field measurements, which are much more expensive and labor intensive. (An article describing his model and its application to Bering Glacier appeared recently in The Cryosphere, an open-access journal published by the European Geosciences Union). Some glaciologists doubt that the mass balance of a glacier can be simulated using only a computer model and data collected at low-altitude weather stations in lieu of traditional field measurements. However, Tangborn, who spent many years with the USGS measuring glaciers using traditional field methods, has made year by year comparisons of balances produced by his model with field measurements on a number of independently-measured glaciers. The PTAA model balances show excellent agreement with manual measurements. He currently monitors about forty glaciers worldwide. The results can be found here: www.ptaagmb.com.

Tangborn's model indicates Bering Glacier is now thinning at a rate of about 2 feet per year averaged over its entire area. This is a high rate of mass loss but insufficient historical data exist to determine whether Bering Glacier has ever lost mass this rapidly prior to 1951. Tangborn has found that the thinning of Bering Glacier is correlated with the dramatic reduction of Arctic sea ice during recent decades, suggesting both are responses to atmospheric warming.

"The rate at which Bering Glacier and most other glaciers worldwide are disappearing is irrefutable evidence of a rapidly warming climate," Tangborn points out.

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