BILLINGS, Mont. — Glacier National Park has lost two more of its namesake moving icefields to climate change, which is shrinking the rivers of ice until they grind to a halt, the U.S. Geological Survey said Wednesday.
Warmer temperatures have reduced the number of named glaciers in the northwestern Montana park to 25, said Dan Fagre, an ecologist with the agency.
He warned the rest of the glaciers may be gone by the end of the decade.
"When we're measuring glacier margins, by the time we go home the glacier is already smaller than what we've measured," Fagre said.
The latest two to fall below the 25 acre threshold were Miche Wabun and Shepard. Each had shrunk by roughly 55 percent since the mid-1960s. The largest remaining glacier in the park is Harrison Glacier, at about 465 acres.
On a local scale, fewer glaciers means less water in streams for fish and a higher risk for forest fires. More broadly, Fagre said the fate of the glaciers offers a climate barometer, indicating dramatic changes to some ecosystems already under way.
While the meltoff shows the climate is changing, it does not show exactly what is causing temperatures to rise.
In alpine regions around the world, glacier melting has accelerated in recent decades as temperatures increased. Most scientists tie that warming directly to higher atmospheric concentrations of greenhouse gases such as carbon dioxide.
Some glaciers, such as in the Himalayas, could hold out for centuries in a warmer world. But more than 90 percent of glaciers worldwide are in retreat, with major losses already seen across much of Alaska, the Alps, the Andes and numerous other ranges, according to researchers in the United States and Europe.
In some areas of the Alps, ski resorts set atop glaciers have taken drastic measures to stave off the decline, such as draping glaciers in plastic sheeting to keep them cooler.
It could prove a losing battle: Scientists working for the United Nations say the last period of widespread glacial growth was more than three decades ago, lasting only for a few years.
Since about 1850, when the Little Ice Age ended, the trend has been steadily downward.
The area of the Rocky Mountains now within Glacier National Park once boasted about 150 glaciers, of which 37 were eventually named.
Fagre said a handful of the park's largest glaciers could survive past 2020 or even 2030, but by that point the ecosystem would already be irreversibly altered.
Fagre said geological evidence points to the continual presence of glaciers in the area since at least 5000 B.C.
"They've been on this landscape continually for 7,000 years, and we're looking at them disappear in a couple of decades," he said.
A glacier needs to be 25 acres to qualify for the title. If it shrinks more, it does not always stop moving right away. A smaller mass of ice on a steep slope would continue to grind its way through the mountains, but eventually could disappear completely.
Smaller glaciers and warmer temperatures could lower stream flows, which in turn prompt fishing restrictions and hobble whitewater rafting businesses, said Denny Gignoux, who runs an outfitting business in West Glacier. Tourism is a $1 billion-a-year industry in the area.
"What happens when all these threats increase?" Gignoux asked. "We're losing a draw to Glacier."
A report released Wednesday by two environmental groups highlighted the threat to tourism of fewer glaciers. The study by the Rocky Mountain Climate Organization and Natural Resources Defense Council included an analysis of weather records that showed Glacier was 2 degrees hotter on average from 2000 to 2009, compared with 1950 to 1979.