The ruggedly stunning landscape of Montana's Glacier National Park will still be stunning and rugged in 50 years, but the glaciers the park was named for will be harder to spot—if they exist at all.

As global temperatures have warmed over the past half-century, the park's major "named" glaciers have receded, shrinking by an average of 39 percent since 1966, according a study released Wednesday by the U.S. Geological Survey (USGS) and Portland State University.

"Over the past 50 years, some of the glaciers have shrunk about 82 percent, so they won't be with us soon," said Daniel Fagre, the lead USGS scientist on the project. "For others, shrinkage has been more modest — about 13 percent. But the amount of ice in all cases is diminished, so the long-term prospects for our glaciers are not good."

Fagre and his colleagues analyzed measurements, taken over the past five decades, of the park's 37 major glaciers and two others on adjacent U.S. Forest Service land. They found that of those 39 glaciers, only 26 still meet a 25-acre threshold. Glaciologists consider that amount of mass a convenient cut-off point to distinguish between a glacier (a perennial wedge of ice and snow that moves) and stagnant ice or a perennial snowfield (a wedge of ice and snow that doesn't).

Before its founding in 1910, Glacier National Park was home to about 150 glaciers.

"The glaciers were not shrinking very much from the end of the Little Ice Age to the park's founding," Fagre said, referring to the global cooling period that ended around 1715. "Most of the loss has occurred since then."

Geologists with the USGS and at universities have found similar glacial downsizing across the West, where they're trying to understand the impact of larger climate patterns on different mountain environments.

"We've been working in the Sierra of California. We've been working up in the Olympics. We're going to start on the North Cascades this summer. This is emblematic of what's happening all over the West," said Andrew Fountain, a professor of geology and geography at Portland State University and co-author of the study.

The impacts of climate change on glaciers could be especially potent in the Rocky Mountains, where warming trends are 1.8 times the global average. The region is increasingly prone to drought and wildfires, a scenario that's both a symptom of glacier loss and a cause.

"Locally speaking, smaller glaciers don't produce as much meltwater, which threatens local ecosystems, especially in the late summer. They have less capacity to buffer droughts or contribute water during droughts," Fountain said. "But all this water is going someplace, and it's going to oceans, so even though it's happening in the mountains, Florida is feeling the effects."

Within Glacier National Park, the impacts go beyond the scenery, too. Some aquatic species, including an insect called the meltwater stonefly, are threatened by the changing conditions.

"These glaciers are instrumental in maintaining cold water for certain aquatic organisms. The safety net will be gone for those organisms," Fagre said. "It's an early warning signal of broader ecosystem change."

A record 2.9 million visitors were drawn to the nearly 1,600-square mile park last summer, Fagre said.

"Clearly the park is not going to have these glaciers past a few more decades," Fagre added. "But it's a beautiful landscape, and it will continue to be so after the glaciers are gone."