Age has been unkind to Glacier National Park

But the same cannot be said for the park’s iconic glaciers, giant slabs of ancient ice that crawl slowly down the face of mountains, gouging spectacular landscapes.

Fagre said that based on geologic evidence, the park had about 150 glaciers in 1850, the end of the so-called Little Ice Age. Most would have still been around when the park was established in 1910.

Only about 25 named glaciers are left, and they could be gone by 2020, Fagre said.

Rising temperatures also mean spring is arriving about three weeks early, which causes winter snow to melt earlier and forests to become drier as the summer progresses, said Jack Potter, chief of science at the park.

That has led to bigger and more destructive fires, in part because insect infestations have weakened trees, Potter said. There are now fires at higher elevations, too, because the tree line is moving higher as temperatures rise, he said.

Less moisture means lower stream flows, which endanger fish species, he said. The vegetation is changing, providing less food and protective cover for animals.

The chance to see the glaciers that are now disappearing is what lures many visitors to the remote park.

But tourists won’t necessarily notice the glaciers are gone, because there will still be snow on the peaks of many mountains, Running said. And most of the remaining glaciers are located in the back country, far from visitors who stick to the main roads and lodges.

But it’s hard for people to imagine Glacier National Park without glaciers.

“The day that Glacier National Park officially announces there are no glaciers left, it will make worldwide headlines,” Running said. “When people find out I am from Montana, that is the first thing they ask me: ‘Is it true about Glacier National Park?’”