GLACIER NATIONAL PARK, Mont. — What will they call this place once the glaciers are gone?

A century ago, this sweep of mountains on the Canadian border boasted some 150 ice sheets, many of them scores of feet thick, plastered across summits and tucked into rocky fissures high above parabolic valleys. Today, perhaps 25 survive.

In 30 years, there may be none.

A warming climate is melting Glacier’s glaciers, an icy retreat that promises to change not just tourists’ vistas, but also the mountains and everything around them.

Streams fed by snowmelt are reaching peak spring flows weeks earlier than in the past, and low summer flows weeks before they used to. Some farmers who depend on irrigation in the parched days of late summer are no longer sure that enough water will be there. Bull trout, once pan-fried over anglers’ campfires, are now caught and released to protect a population that is shrinking as water temperatures rise.

Many of the mom-and-pop ski areas that once peppered these mountains have closed. Increasingly, the season is not long enough, nor the snows heavy enough, to justify staying open.