Conor here: While the Colorado River often takes center stage in discussions about water challenges in the West, it’s essential to remember that other climate change-related issues are emerging on the horizon.
By Andrew Fountain, Professor of Geography at Portland State University. Originally published at The Conversation.
The breathtaking glaciers of the Rocky Mountain West may seem like small patches of white from an airplane, dotting the rugged terrain where the landscape undulates. This snow cover, along with the gray-blue bare ice below, tells a story of climatic change and vulnerability.
Back in the mid-20th century, the contiguous United States boasted over 1,450 glaciers, covering an area of 217 square miles (562 square kilometers) across six western states. Current research that my colleagues and I published in the Proceedings of the National Academy of Sciences reveals a sobering reality: these glaciers have experienced a 35% reduction in total area, with the alarming possibility of even faster shrinkage.
Photos of glaciers in the Wind River Range, Wyoming, taken by Andrew Fountain during an October 2026 flight. These glaciers are primarily located in protective niches.
Surprisingly, more than 300 glaciers have vanished, a figure that exceeded my expectations.
The glaciers that remain are a testament to the fragility of these ice formations amid rising global temperatures. Once vast glaciers that blanketed the western mountains thousands of years ago have dwindled to smaller remnants often tucked away in sheltered areas favorable for survival, such as the Rockies and the Sierra Nevada.
Where U.S. Glaciers Are Disappearing Most Rapidly
When people envision glaciers, they often think of massive ice flows and calving icebergs, like those found in Alaska or Greenland. However, in the contiguous United States—apart from a few sizable glaciers in Washington—most are considerably smaller.
Our findings revealed that the average glacier size in the Lower 48 states is only one-tenth of a square mile (approximately a quarter of a square kilometer). The largest glacier, located on Mount Rainier in Washington, spans roughly 4.3 square miles (11.24 square kilometers).
I was taken aback to discover that glaciers in the Rocky Mountains—specifically those in Colorado, Montana, and Wyoming, along with those in the Sierra Nevada—thrive due to their unique placements within the landscape. This positioning affords them some protection from the harsher regional climate.
The surviving Rocky Mountain glaciers rest in shaded niches, minimizing exposure to direct sunlight, and benefit from snow accumulation through avalanches. If these glaciers faced more sunlight and less snowfall, they would likely cease to exist.
Our review identified the quickest thinning glaciers in the Beartooth-Absaroka Mountains of southern Montana, experiencing an annual loss of about 1.5 feet (roughly half a meter) in ice thickness.
Conversely, glaciers on Mount Rainier and Mount Baker in Washington, which are considerably larger and located in cooler summer conditions, are also diminishing but at a much slower pace—about half a foot of ice thickness each year. Notably, the glacier area on Mount Rainier alone surpasses the total of all other states combined.
Satellite images reveal how glaciers on Mount Shasta, Mount Rainier, and Sperry Glacier in Montana have thinned over time. Redder hues indicate the most significant loss. Andrew Fountain, et al., PNAS, 2026
In Washington, a general trend shows that at higher altitudes, glacier loss decreases, which is logical since cooler temperatures predominate at elevated elevations. However, in the Rocky Mountain region, no parallel trend exists, indicating that the surviving glaciers depend on specific local geographic factors.
What Lies Ahead
In previous research, my colleagues and I modeled the glaciers on Washington’s Olympic Peninsula and found that most are likely to vanish by 2070 if current climate trends continue. This suggests that glaciers in other regions may not be far behind.
The glaciers on the Olympics are particularly vulnerable due to their proximity to the Pacific Ocean and their lower elevation. In contrast, glaciers on Mount Rainier and Mount Baker in Washington may endure beyond 2100, but their long-term fate remains uncertain.
This uncertainty raises several concerns.
Glaciers play a crucial role in supplying water to high alpine ecosystems. Their late-summer melt provides essential cool water for cold-adapted fish and other aquatic life, serving as a vital water source when seasonal snow recedes and the area tends to be dry.
While the glaciers in the Rockies primarily support ecosystems, those in Washington also play a significant role in hydropower generation.
Water accumulating behind moraines created by glaciers can lead to significant debris flows down the mountain. This image depicts a debris flow originating from the White River Glacier on Mount Hood in Oregon. William Scott/USGS
There is also a considerable risk associated with glaciers situated on the steep slopes of the Cascade Range, stretching from California to Washington. The large moraines formed by these glaciers are influenced by the highly erodible volcanic rock beneath the ice. As glaciers retreat, they leave behind steep-sided moraines that have lost their support from ice.
High flows from rain or glacier melt can erode these moraines, leading to landslides and debris flows that rush down the mountains. Such events were recorded in 2006 on both Mount Hood and Mount Rainier, causing major road closures. We should expect to see more of these incidents as glaciers continue to recede.
The decline and anticipated extinction of these glaciers will have profound implications for ecosystems throughout the West and the water sources that both wildlife and humans depend on.
