BILLINGS, Mont. - Glacier National Park has lost two more of its namesake moving ice fields to climate change, which is shrinking the rivers of ice until they grind to a halt, the U.S. Geological Survey said Wednesday. Higher 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 might be gone by decade's end. "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 each had shrunk by roughly 55 percent since the mid-1960s. The largest glacier left in the park is Harrison Glacier, at about 465 acres. Fewer glaciers means less water in streams for fish and a higher risk for forest fires. Fagre said the fate of the glaciers offers a climate barometer, indicating that dramatic changes to some ecosystems are already under way. 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.