Three Colorado glaciers lose ice at twice their prior five-year rate

St. Mary’s Glacier melts completely as record heat follows record-low snowpack

Three prominent Colorado glaciers thinned sharply in 2026: the Andrews Glacier lost more than 12 feet (3.7 meters), the Arapaho Glacier lost nearly 10 feet (3 meters), and the Isabelle Glacier lost about 6.5 feet (2 meters), according to research by Colorado State University glaciologist Dan McGrath. McGrath said the losses doubled the glaciers’ thinning rate from the prior five years; in the decade before that, their 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.”

While glaciologists typically measure changes over longer intervals, McGrath examined what happened over 2026 because it was an exceptional year. The new research attributes the dramatic thinning to record-low mountain snow and record-warm temperatures; Colorado’s worst snowpack on record was followed by record summer heat, leaving the year-round ice masses in the Rocky Mountains exposed.

The report placed Colorado’s shrinking on par with recent observations of glacier loss across the planet. Warmer temperatures accelerate melting while less snow falls to replenish glaciers’ ice, threatening water sources, increasing mountain hazards and contributing to sea-level rise. The report also said glacial runoff supplies water to high-alpine and downstream ecosystems across the western United States.

More than 7 trillion tons of ice (6.5 trillion metric tons) has been lost worldwide since 2000, according to research cited in the report. The report called worldwide ice loss “a slow-motion disaster that sometimes provokes sudden devastation.” It also said more than 1,300 people were killed in August after a massive section of rock and an overlying glacier collapsed near Nepal’s border with China.

A new study co-authored by Brian Menounos, an earth sciences professor at the University of Northern British Columbia, found that 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, the study found.

Menounos said those high-alpine and downstream areas may eventually become more vulnerable to extreme drought as the glaciers disappear. He also said wildfires are hastening the melting by darkening glacier surfaces with soot and dust, making the ice more vulnerable to absorbing sunlight. He described the combination as a “one-two punch.”

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.

Researchers with the North Cascade Glacier Climate Project surveyed six glaciers on Mount Baker during an annual summer trip. Director Mauri Pelto said this year’s survey showed the fastest average retreat since 1950, with the collapse of several large ice caves that form as warm air circulates in retreating glaciers. McDermott reported from Providence, Rhode Island.

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, Menounos said. The process may take several hundred years, he said.

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 was sad to see their decline but important to record the changes. “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.”