Reviewing five decades of data on three 'benchmark glaciers,' researchers say that shrinking glaciers clearly result from global warming.
Jim Tankersley, LA Times 7 Aug 09;
Reporting from Washington -- The federal government Thursday released the most comprehensive study of melting glaciers in North America -- and the results show a rapid and accelerating shrinkage over the last half a century because of global warming.
One of the glaciers in the study, the South Cascade Glacier in Washington state, has lost nearly half of its volume and a quarter of its mass since 1958, scientists from the U.S. Geological Survey said. The two others in the study, the Wolverine and Gulkana glaciers in Alaska, have both lost nearly 15% of their mass.
In all three cases, the melting has increased over the last two decades. 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, Wash., who has worked for a decade on the study.
"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 in the study are known as "benchmark glaciers" because their varying climates and elevations are representative of thousands of other glaciers across the continent.
For five decades, 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 that summer melting accelerated in the last 20 years. At the same time, winter snowpacks have tapered off. The reduced accumulations and increased melts have resulted in shrinking glaciers.
South Cascade Glacier, for example, had a volume of nearly 0.06 cubic mile of water in 1958, Josberger said. By 2008, it was down to 0.03 cubic mile.
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 reported. But the latest acceleration suggests rising temperatures are "overwhelming" those natural cycles, the report concluded.
Alaska glaciers shrinking fast: survey
Yereth Rosen, Reuters 6 Aug 09;
ANCHORAGE, Alaska (Reuters) - Three major glaciers in Alaska and Washington state have thinned and shrunk dramatically, clear signs of a warming climate, according to a study released Thursday by the U.S. Geological Survey.
The three glaciers -- Gulkana and Wolverine in Alaska and South Cascade in Washington -- are considered benchmarks for those in alpine and maritime climates because they closely parallel other glaciers in their regions. They have also been the subject of close scientific scrutiny since 1957.
"These are the three glaciers in North America that have the longest record of mass change," said Shad O'Neel, a United States Geological Survey glaciologist in Anchorage who was one of the study authors.
"All three of them have a different climate from the other two, yet all three are showing a similar pattern of behavior, and that behavior is mass loss."
Scientists are keeping a close watch on melting glaciers, as a rise in sea-levels would threaten coastal and low-lying areas around the world.
The latest study compares records of snow and ice thickness and densities over the years, the factors used to calculate mass. The glaciers have lost mass as melting outpaced new snow and ice accumulation, and for all three, the losses were especially dramatic over the past 15 years, according to the USGS study.
By themselves, the glaciers and their changes are not proof of global warming, he said. But their behavior fits with a pattern of warmer weather or drier weather or both.
"It certainly says that the place where these glaciers are, the climate is not supportive of healthy glaciers anymore," he said.
Ed Josberger, the Tacoma, Washington-based USGS hydrologist who coordinated the study, said the results from the Gulkana, Wolverine and South Cascade glaciers mirror worldwide trends.
"There is no doubt that most mountain glaciers are shrinking worldwide in response to a warming climate," Josberger said in a statement released by the Department of Interior.
Climate change melting US glaciers at faster rate, study finds
US geological survey commissioned by Obama administration indicates a sharp rise in the melt rate of key American glaciers over the last 10-15 years
Suzanne Goldenberg, guardian.co.uk 6 Aug 09;
Climate change is melting America's glaciers at the fastest rate in recorded history, exposing the country to higher risks of drought and rising sea levels, a US government study of glaciers said today.
The long-running study of three "benchmark" glaciers in Alaska and Washington state by the US geological survey (USGS) indicated a sharp rise in the melt rate over the last 10 or 15 years.
Scientists see the three - Wolverine and Gulkana in Alaska and South Cascade in Washington - as representative of thousands of other glaciers in North America.
"The observations show that the melt rate has definitely increased over the past 10 or 15 years," said Ed Josberger, a USGS scientist. "This certainly is a very strong indicator that climate change is occurring and its effects on glaciers are virtually worldwide."
The survey also found that all three glaciers had begun melting at the same higher rate - although they are in different climate regimes and some 1,500 miles apart.
For South Cascade, the average surface loss rate grew to 1.75 to 2m a year from about 1m a year.
USGS researchers have been measuring the three glaciers for more than 50 years, drawing on photographs and a network of stakes driven into the glaciers to gauge the accumulation of snow during winter, and the resulting melt each spring. It is the oldest such record of glacier activity.
In a sign of the Obama administration's focus on climate change, this year's survey was promoted by the interior secretary, Ken Salazar, who called it an important contribution to dealing with climate change. "This information is helpful in tackling the effects of climate change and it is exactly the kind of science we need to invest in to measure and mitigate the dangers impacts of climate change," he said.
Shrinking glaciers have led to a reduction in spring run-off which is intensifying the effects of drought in California and other states, especially later in the summer when other water sources dry up.
Glacier loss has also contributed to rising sea levels, which has put low-lying coastal areas - such as New Orleans - at greater risk of storm surges.
