WASHINGTON – Three of the nation’s most studied glaciers, including one in Washington state’s remote north Cascades, are shrinking at an accelerating pace, a report based on 50 years of measurements released by the Interior Department concluded Thursday.

Known as “benchmark glaciers,” the South Cascade Glacier, along with the Wolverine Glacier on Alaska’s Kenai Peninsula and the Gulkana Glacier in interior Alaska, have all shown a “rapid and sustained” retreat, the report said.

For years scientists have reported glaciers around the world were melting, but the study, conducted by the U.S. Geological Survey, offers some of the most definitive findings to date. Because the three glaciers represent different climates and elevations, they can be used to understand thousands of other North American glaciers.

“They are living on the edge,” Tacoma based USGS scientist Ed Josberger said of the glaciers. “We’ve crossed a threshold and these glaciers along with those globally are shrinking.”

At the beginning of the 20th century, when glaciers were at their last peak in terms of size, the mass or volume of the South Cascade Glacier was estimated at one-half a cubic kilometer. In 1958, it had shrunk to roughly half that size. The latest measurement, in 2004, found is shrunk nearly in half again.

“We are getting warmer and glaciers are shrinking,” Josberger said.

Scientists with the USGS have been taking measurements and detailed pictures of the three glaciers since 1957, including using ice-penetrating radar to map the bedrock underneath them. The studies were part of the Cold War-era interest in polar science spurred by the threat of war with another polar nation, what was then the Soviet Union.

The result is a half century’s worth of data to use for modeling future changes, said Shad O’Neel, one of the Anchorage-based USGS scientists who worked on the study.

“These three glaciers have been losing mass since they’ve been studied, and that mass loss has gotten more rapid in the past 15 years,” O’Neel said. “The most important thing about having a long record like this is that we can use these records to verify and validate models out into the future.”

In some years, the South Cascade Glacier has actually grown because of heavy snowpack. But melting caused by warmer temperatures has wiped out any gains, Josberger said.

The study also suggests that while ocean phenomena can affect glaciers, global warming has emerged as a more dominant factor.

The Pacific Decadal Oscillation is an ocean-related climate condition in the North Pacific similar to El Niño in the South Pacific. When the PDO is in its warm phase, Pacific storms head north into Alaska. In its cool phase, the Pacific Northwest is stormier, Josberger said.

But regardless of what cycle the PDO might be in, all three glaciers in the study are shrinking at an accelerating pace, he said.

With some exceptions caused by unique or unusual local conditions – the glaciers on California’s Mount Shasta, for example – more than 99 percent of the country’s thousands of glaciers are shrinking, Bruce Molnia, another USGS scientist, said.

Worldwide, most glaciers are losing mass and some are disappearing altogether. Glacier National Park’s namesake glaciers in Montana decreased from 150 to 26 over the past 99 years. If current warming trends continue, scientists predict they will disappear entirely by 2030. And scientists have predicted that the famed snows of Africa’s Mount Kilimanjaro could retreat by 2015.

Scientists at the U.S. Geological Survey’s Northern Rocky Mountain Science Center, who study the glaciers in Montana, point out that a drop in runoff means changes in water temperature for the creatures in the downstream ecosystem: insects, fish and the animals that eat them.