More than 300 glaciers have vanished from the western United States since the middle of the 20th century, while the total area covered by glaciers across the country’s contiguous states has declined by 35%, according to a new scientific study highlighting the growing impact of rising temperatures on mountain ice.
The study, published in the *Proceedings of the National Academy of Sciences* on October 12, 2026, examined changes in glaciers across six western states and found that the number of glaciers has fallen substantially from more than 1,450 recorded in the mid-20th century. Their combined coverage, which stood at around 562 square kilometres, has also reduced considerably, with researchers warning that the remaining glaciers continue to shrink.
The findings point to the increasing vulnerability of mountain glaciers as warmer temperatures alter the landscapes of the American West. Although glaciers are commonly associated with vast ice formations in Alaska and Greenland, those in the contiguous United States are generally much smaller, making them particularly susceptible to changing climatic conditions.
Researchers found that the average glacier in the region covers approximately a quarter of a square kilometre. The largest, located on Mount Rainier in Washington state, spans around 11.24 square kilometres. The study also documented a substantial reduction in the overall area and volume of glaciers, with the losses varying considerably between mountain ranges.
The glaciers that continue to survive in the Rocky Mountains and California’s Sierra Nevada owe much of their persistence to the specific geographical features of their locations. Many are tucked into shaded mountain hollows, where surrounding terrain limits exposure to direct sunlight. Some also receive additional snow from avalanches, helping replenish their ice cover.
Scientists found that these local advantages allow certain glaciers to survive despite the broader regional conditions becoming increasingly unfavourable. Their continued existence, however, remains precarious, as changes in sunlight exposure, snowfall and temperatures could accelerate their decline.
The most rapid thinning has been recorded in the Beartooth-Absaroka Mountains of southern Montana, where glaciers are losing approximately half a metre of ice thickness annually. The findings underline the uneven impact of warming across the region, with glaciers in some mountain ranges deteriorating considerably faster than those in others.
Washington presents a different picture. Glaciers on Mount Rainier and Mount Baker are generally larger and benefit from cooler summers and heavier snowfall. Although these glaciers are also retreating, their ice thickness is declining at a slower rate of around half a foot annually. Mount Rainier alone contains more glacier-covered area than the combined total across the other states examined in the study. Researchers also observed that higher elevations in Washington generally experience less glacier loss, consistent with colder conditions at greater heights.
A similar relationship was not evident across the Rocky Mountains, indicating that the survival of glaciers there depends more heavily on local geographical conditions. The consequences of continued glacier loss extend beyond changes to the mountain landscape. Glaciers provide an important source of cold water for high-altitude ecosystems, particularly during late summer, when seasonal snow has melted and rainfall is limited.
Their meltwater helps maintain stream flows and supports fish and other aquatic species that depend on cold-water environments. In Washington, glacial meltwater also contributes to hydropower generation, adding to concerns about the long-term effects of shrinking ice reserves on regional water resources. Retreating glaciers may also increase the risk of landslides and debris flows in mountainous areas.
As glaciers recede, they leave behind accumulations of eroded rocks and sediment that are no longer supported by the ice. Heavy rainfall or increased meltwater can weaken these deposits, triggering flows of rocks and debris down mountain slopes. Similar incidents have previously disrupted transport routes near Mount Hood and Mount Rainier.
Earlier modelling by researchers suggested that most glaciers on Washington’s Olympic Peninsula could disappear by 2070 if current climate trends continue. While some glaciers on Mount Rainier and Mount Baker may survive beyond 2100, their long-term future remains uncertain.
The latest findings underline the scale of glacier loss already experienced across the American West and the potential consequences for mountain ecosystems, downstream waterways and communities that depend on these fragile ice reserves.
