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America's three "benchmark" glaciers are melting and over the past two decades they have been shrinking at an accelerated rate because of global warming.

The glaciers in Alaska and Washington have undergone a "rapid and sustained" loss of mass since 1989. Scientists at the U.S. Geologic Survey think this "decline could be the result of recent climate changes" overcoming seasonal fluctuations that impact the glaciers' size.

These findings, "Fifty-Year Record of Glacier Change Reveals Shifting Climate in the Pacific Northwest and Alaska, USA", were released in a report by the USGS on Thursday.

The southern-most glacier in the study, South Cascade Glacier in the Cascade Mountains of Washington, has lost almost half of its volume and a quarter of its mass since the USGS began collecting data in 1957.

This picture sequence shows the retreat of the South Cascade Glacier during the 20th Century and the beginning of the 21st century. This glacier is melting at a rate that may cause it to disappear in 50 years.

The other two glaciers in the "benchmark" study are in Alaska. The Wolverine Glacier is on the Kenai Peninsula near Anchorage and Gulkana Glacier in the state's interior. Like the glacier in Washington, the two Alaskan glaciers are also melting rapidly. Each has lost nearly 15 percent of its mass.

While ocean-conditions effect glacier health, the USGS study found the correlation between seasonal conditions and glacier health "has weakened during the last two decades, as global average temperature has increased". The glaciers' accelerating decline are likely the result of "changes to warmer and (or) drier climate conditions that are affecting all three regions."

As the glaciers get smaller, their melting feeds into a vicious cycle of decline. The glaciers get smaller as they melt causing drier conditions in the region, which furthers accelerates their shrinking. Over the past 20 years, the study's data showed that each glacier's summer melt had increased while the winter snowpack had fallen.

Bloomberg interviewed Edward Josberger, the lead author of the study, and he explained this more clearly:

Glaciers in the Northwest have gained or lost mass from year to year since the agency began collecting data in 1957, because of changes in winter storm patterns tied to shifts in Pacific Ocean currents, Josberger said. The cumulative decline since 1989 suggests that global warming has overcome those seasonal variations.

"That's telling us something on a larger scale is happening," he said.

"The observations show that the melt rate has definitely increased over the past 10 or 15 years... This certainly is a very strong indicator that climate change is occurring and its effects on glaciers are virtually worldwide," Josberger is quoted saying in The Guardian.

What is happening to these three "benchmark" glaciers is indicative to what is happening to almost all American glaciers.

"In addition to these three glaciers, more than 99 percent of America's thousands of large glaciers have long documented records of an overall shrinkage as climate warms," said USGS scientist Bruce Molnia via a news release from the Department of the Interior. Aside from a few "unusual and unique" glaciers, "America's glaciers are shrinking".

Shrinking glaciers are dying glaciers. Glacier health directly impacts the health of all things living in the Pacific Northwest, including people. All water eventually flows to the sea and glacial melt adds to the rising sea level which endangers towns and cities along the coast.

In addition, some of the region's drinking water supply is glacial runoff. So shrinking glaciers mean less available drinking water, according to Shad O'Neel, another USGS scientist who worked on the study and interviewed by McClatchy.

Less glacial meltwater in mountain streams "means changes in water temperature for the creatures in the downstream ecosystem: insects, fish and the animals that eat them." Josberger said this will impact bull trout and salmon because "those fish prefer the colder, highly oxygenated water that runs off the glaciers in the spring and summer."

The Pacific Northwest salmon are already threatened by the region's large hydro-power dams, which in turn, will generate less electricity in the future due to less running water in the rivers.

The health of the Pacific Northwest is tied to the abundance of water. Losing our glaciers will have a long lasting and devastating impact on the health of all living in the region.

The USGS study indicates global warming has overwhelmed the normal fluctuations of the local climate. The phrase "glacial pace" doesn't apply to the melting of America's "benchmark" glaciers.

Maybe it is time for town halls on climate change? This slideshow of the South Cascade Glacier retreat makes me think so.

Originally posted to Magnifico on Thu Aug 06, 2009 at 09:00 PM PDT.

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