DENVER (AP) — The most prominent glaciers in Colorado thinned dramatically over the past year due to record low mountain snow and record warm temperatures, according to new research.
Their shrinking is on par with recent observations of glacier loss across the planet as warmer temperatures accelerate melting and less snow falls to replenish their ice, threatening water sources, increasing mountain hazards and contributing to sea level rise.
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While glaciologists typically measure changes over longer intervals, glaciologist Dan McGrath at Colorado State University sought to find out what happened over 2026 since it was such an exceptional year. The state’s worst snowpack on record, followed by record summer heat, left the year-round ice masses in the Rocky Mountains exposed.
The Andrews Glacier thinned by more than 12 feet (3.7 meters) in this single year, the Arapaho Glacier lost nearly 10 feet (3 meters), and the Isabelle Glacier lost about 6.5 feet (2 meters) — doubling their rate of thinning from the prior five years, McGrath said. In the decade before that, the thinning measured a foot or less per year.
St. Mary's Glacier, a perennial snowfield popular among hikers and skiers, melted completely in September.
“What we’re witnessing is the loss of that part of Colorado’s identity. And it’s not just Colorado,” said McGrath, who specializes in glacier dynamics. “Obviously we see it in the Alps and we’re seeing it in other mountain ranges in the western U.S., the European Alps and globally. There are very clear, consistent patterns across these ranges.”
More than 7 trillion tons of ice (6.5 trillion metric tons) has been lost worldwide since 2000, according to research, a slow-motion disaster that sometimes provokes sudden devastation: More than 1,300 people were killed in August after a massive section of rock and overlying glacier collapsed near Nepal’s border with China.
Glaciers in Switzerland lost 5.5% of their ice volume this year, the second-biggest percentage drop on record, due to heat waves and low winter snowfall. The GLAMOS Swiss glacier monitoring service and Swiss Academy of Sciences said this month that alpine glaciers have no chance of surviving long-term under such conditions. Switzerland is home to the most glaciers in the Alps.
In Washington state, researchers with the North Cascade Glacier Climate Project have surveyed six glaciers on Mount Baker during an annual summer trip. Director Mauri Pelto said this year's survey shows the fastest average retreat since 1950 with the collapse of several large ice caves, which form as warm air circulates in retreating glaciers.
Mountain glaciers in the contiguous United States average just 0.16 square miles (0.41 square kilometers), or about 100 acres (about 40 hectares), and are widely distributed at high elevations. Since the mid-1900s, about one-quarter of them have disappeared and the remnants have lost a third of their area and volume, according to a new study co-authored by Brian Menounos, an earth sciences professor at the University of Northern British Columbia.
The runoff supplies water to high alpine and downstream ecosystems across the western United States, and eventually these areas may become more vulnerable to extreme drought as the glaciers disappear, he added.
And in a “one-two punch,” wildfires also are hastening the melting by darkening the surfaces of glaciers with soot and dust, Menounos said, making them more vulnerable to absorbing sunlight.
Glaciers could re-form if carbon pollution declines substantially and temperatures drop enough to enable snowfall to build year-round, eventually compressing again into glacial ice, but that may take several hundred years, Menounos added.
Looking at how much ice Colorado's remaining glaciers have lost, McGrath thinks they could soon disappear. The Andrews Glacier has already lost half of its ice since 2017, he said.
“This past decade has showed us that these glaciers are out of balance with the climate here in Colorado, in the western U.S., and they’re thinning at a rate that could lead to their demise in the next 20 years,” he said.
Harlan Ulmer, 20, is a student at Colorado State University who has photographed the glaciers annually since 2022 and volunteers with McGrath’s research project. He said it's sad to see their decline, but important to record.
“Being Gen Z, I came in too late to ever see the glaciers at their largest,” he said. “But I think we have the opportunity, I have the opportunity, to sort of document the changes that are taking place in my time to preserve them for future generations and for posterity.”
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McDermott reported from Providence, Rhode Island.
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