"For some aquatic species, that's a threshold event," he said. "You only have to dry up once and you're history."

Not Cut-and-Dried

Andrew Fountain, a Portland State University professor of geography and geology, acknowledged that the glaciers of Glacier National Park shrank by 67 percent in the past hundred years.

"As a group, that is the fastest recession of any glaciated region in the lower 48 states" in the U.S., Fountain said.

But he's cautious about predicting the demise of any glacier.

In some situations, local topography can balance out climate change, he said.

"Take the Colorado Front Range, for example," he said.

"There is no reason for glaciers to inhabit Rocky Mountain National Park, climatically speaking. If it were not for … the drifting snow from the high plateau into the cirque basins"—valleys hollowed out by past glacial erosion—"you would not have glaciers there. But they are holding on fine."

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SOURCES AND RELATED WEB SITES U.S. Geological Survey Glacier National Park: Daniel Fagre Portland State University Glacier Research