The most comprehensive study of melting glaciers in North America released on Thursday shows a rapid and accelerating shrinkage during the past 50 years due to global warming. One of the glaciers, the South Cascade Glacier in Washington, has lost nearly half its volume and a quarter of its mass since 1958.
WASHINGTON — The federal government released the most comprehensive study of melting glaciers in North America on Thursday, and the results show a rapid and accelerating shrinkage during the past 50 years due to global warming.
One of the glaciers, the South Cascade Glacier in Washington, has lost nearly half its volume and a quarter of its mass since 1958, U.S. Geological Survey scientists said. The two others in the study — the Wolverine and Gulkana glaciers in Alaska — have both lost nearly 15 percent of their mass.
In all three cases, the melting has increased in the past 20 years. The acceleration is the result of warmer, drier climates in the Pacific Northwest and Alaska caused by global warming, the researchers said.
“By having a 50-year record, you can look over what’s going on, look over the meteorological, climatological record, and really get an idea of what’s going on in the mountains,” said Edward Josberger, a scientist with the USGS Washington Water Science Center in Tacoma, who has worked for a decade on the glacier study.
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“Climate-change effects are starting to become more and more noticeable,” he added, “and this is one of the effects that’s being displayed.” The three glaciers are known as “benchmark glaciers” because their varying climates and elevations are representative of thousands of other glaciers across the continent.
For 50 years, USGS researchers have periodically measured the glaciers’ size, with tools including measurement stakes and photographic surveys. Their data include tallies of winter-snow accumulation and summer melt.
In each case, the data show summer melting accelerated in the past 20 years. At the same time, winter snowpacks have fallen short of past levels. The reduced accumulations and increased melts add up to shrinking glaciers.
South Cascade Glacier, for example, had a volume of nearly 0.25 cubic kilometers of water in 1958, Josberger said. By 2008, it was down to 0.13 cubic kilometers.
When glaciers shrink, water runoff declines, setting the stage for drier conditions in the region, particularly at the end of summer, when other supplies of water dwindle.
In the past, shifting ocean conditions explained some of the shrinking trend, the USGS researchers report. But the latest acceleration suggests rising temperatures are “overwhelming” those natural cycles, the report concluded.