WASHINGTON - Climate change is shrinking three of the nation's most studied glaciers at an accelerated rate, a finding that government scientists say hastens global concerns about rising sea levels and the availability of fresh drinking water.
Known as "benchmark glaciers," the South Cascade Glacier in Washington state, 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," Ed Josberger, a USGS scientist based in Tacoma, Wash., said of the glaciers in the study. "We've crossed a threshold, and these glaciers, along with those globally, are shrinking."
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, begun as part of the International Geophysical Year, were part of the Cold War-era interest in polar science spurred by the threat of war with another polar nation, Russia.
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."
Although their data show a marked retreat in the size of glaciers, changes to Alaska's many glaciers are visible to the naked eye, O'Neel said. Gulkana Glacier is "markedly different than it was in the late 1980s," he said.
U.S. Sen. Mark Begich, D-Alaska, made the same point this week when he introduced a legislative package related to climate change and polar issues. Begich illustrated the effect of global warming in Alaska by showing a picture of himself as a child in front of Alaska's Portage Glacier in 1970. In 2005, his son Jacob stood in the exact same spot for a photo Begich displayed on the Senate floor -- but the glacier was "nowhere to be seen because it has dramatically receded due to global warming," Begich said. At the beginning of the 20th century, when glaciers were at their last peak in terms of size, the mass or volume of the remote South Cascade Glacier was estimated at one-half a cubic kilometer. In 1958 it had shrunk to half that size. The latest measurement, in 2004, found it had shrunk in half yet again, scientists said.
"We are getting warmer and glaciers are shrinking," Josberger 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 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.
It also means less available drinking water, O'Neel said, pointing out that in Anchorage, the drinking water comes from Eklutna Glacier runoff. There's little threat to Anchorage's water supply, but Bolivia's Chacaltaya Glacier disappeared this year, earlier than predicted. Its disappearance worries scientists that other glaciers in the region could be melting faster than expected, potentially threatening water supplies for millions of people in South America.
The long-term study is "exactly the kind of science we need to invest in to measure and mitigate the dangerous impacts of climate change," said Interior Secretary Ken Salazar.
Les Blumenthal of the McClatchy Washington Bureau contributed to this report.