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More than 300 glaciers have disappeared from the lower 48 United States since the middle of the 20th century, according to a 2026 report on a review published in Proceedings of the National Academy of Sciences. The losses represent more than a change in mountain scenery: the remaining western U.S. glacier area has fallen by about 35%, reducing a natural source of late-summer water.
How many glaciers have disappeared?
The review describes a western U.S. inventory of roughly 1,450 glaciers in the middle of the 20th century. More than 300 of those glaciers are now gone from the lower 48 states. The count is only part of the story. Glaciers that remain have also become smaller and thinner, so the region has lost substantially more ice than a disappearance count alone conveys.
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Glaciers occur across six western states. Washington contains the largest concentration, with about 114 square miles (295 square kilometers) of glacier area reported across the state. Many other ice bodies in the lower 48 are small, making them especially sensitive to warmer summers and winters that deliver more rain and less snow.
The key numbers at a glance
| Measure | Reported value | What it indicates |
|---|---|---|
| Glaciers in the western U.S. around the mid-20th century | About 1,450 | The historical reference point used in the report |
| Glaciers lost from the lower 48 | More than 300 | Permanent disappearance of documented ice bodies |
| Change in combined glacier area | Down 35% | Losses among glaciers that still remain, as well as vanished ice |
| Approximate shrinkage associated with warming air temperatures | About 8% per decade | A reported regional rate, not a prediction for every individual glacier |
| Washington glacier area | About 114 square miles (295 square kilometers) | The state’s extensive concentration of glacier ice |
How fast are western U.S. glaciers melting?
Rates vary sharply by mountain range, elevation, glacier size and local terrain. The review’s examples show why a single national melt rate would be misleading.
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Southern Montana: rapid thinning
Glaciers in Montana’s Beartooth–Absaroka Mountains are losing about 1.5 feet (0.5 meters) of thickness per year. That rate applies to the glaciers described in the report and should not be treated as a uniform value for every Montana ice body.
Washington’s larger volcano glaciers: slower, but still substantial
Glaciers on Mount Rainier and Mount Baker are shrinking by about 0.5 feet (15 centimeters) in thickness per year—roughly one-third of the Beartooth–Absaroka example. Their larger size and high, cold volcanic terrain provide more ice mass and can reduce exposure to the most intense seasonal melt, but the reported loss remains persistent.
Why neighboring glaciers can behave differently
Topography can shelter some glaciers from regional warming. The review identifies local landscape position as a reason certain glaciers in Colorado, Montana, Wyoming and California’s Sierra Nevada are less vulnerable than a regional average might suggest. Elevation, shading, slope orientation, wind redistribution of snow and the shape of surrounding ridges can all affect how much snow accumulates and how much ice is exposed to summer heat.
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Why small glaciers disappear first
Small glaciers have less stored ice to buffer a run of hot summers or a sequence of winters with poor snowfall. As air temperatures rise, summer melting increases. At the same time, warmer winters shift precipitation from snow to rain. That combination reduces the snowpack that normally replenishes a glacier and exposes more bare ice to sunlight.
Once annual melting consistently exceeds snowfall, a small ice body can retreat beyond recovery. A glacier does not need to vanish completely to lose much of its hydrologic importance: thinning and shrinking reduce the volume available for release during the warm season.
What happens to rivers when glaciers disappear?
Glaciers act as natural water storage. Cold-season precipitation is held as snow and ice, then released as meltwater during warmer months. This timing matters because late summer is often when mountain snowpack has largely melted and streams face their greatest water stress.
The short-term effect: a temporary runoff increase
During an early phase of rapid melt, a shrinking glacier can contribute more runoff than it did previously. Extra ice loss temporarily increases summer discharge, even as the glacier’s stored volume declines.
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The long-term effect: less late-summer water
After enough ice has been depleted, there is less glacier mass available to melt. Late-summer flows then fall because the natural reservoir is smaller. The transition can make water supplies less predictable for cold-water streams, wildlife, ecosystems and communities downstream.
Why stream temperature and ecology matter
Glacier-fed runoff is cold. Losing that contribution can alter the thermal conditions of rivers and streams, with consequences for organisms that depend on cold water. The report links the changing seasonal pattern to uncertainty for ecosystems and communities, rather than assigning one identical outcome to every watershed.
Which western states still have glaciers?
The review reports glaciers across six western states and identifies Washington as the state with the most extensive concentration. It also discusses glaciers in Colorado, Montana, Wyoming and California’s Sierra Nevada when describing differences in local vulnerability. The supplied report does not provide a complete state-by-state inventory or a current glacier count for each state, so those details cannot be inferred from the headline total.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to interpret the 35% area decline
The 35% figure describes the reduction in combined western U.S. glacier area. It should not be read as meaning that every glacier has lost exactly 35% of its surface, or that the remaining ice will decline at a fixed rate indefinitely. Glaciers respond to local climate and terrain, and the report gives markedly different thinning examples for Montana and Washington.
The reported association of about 8% shrinkage per decade likewise describes a regional relationship with warming air temperatures. It is a useful measure of the broad direction and pace of change, not a schedule that determines when any particular glacier will disappear.
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What the review establishes—and what remains unspecified
The public account establishes the scale of disappearance, the 35% area loss, the approximate decade-scale shrinkage rate and representative thinning rates. It does not, in the available report, provide the review’s full methods, author list, inventory definitions or additional watershed statistics. Those limits matter when comparing the figures with other glacier inventories, whose counting rules and observation dates may differ.
What is clear is the physical sequence: warming increases melt, warmer winters reduce snow accumulation, small glaciers lose mass fastest, and a depleted glacier eventually supplies less water when rivers need it most.
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