Colorado Glaciers Shrink Dramatically Amid Record Heat and Low Snowfall

Colorado's most prominent glaciers experienced dramatic thinning over the past year, a consequence of record low mountain snowpack and unusually warm temperatures, according to new research.

Glaciologist Dan McGrath of Colorado State University documented the significant ice loss in 2026, a year characterized by the state's worst snowpack on record followed by intense summer heat. This combination left the year-round ice masses in the Rocky Mountains exposed and vulnerable.

Specifically, the Andrews Glacier thinned by more than 12 feet (3.7 meters) in this single year, while the Arapaho Glacier lost nearly 10 feet (3 meters), and the Isabelle Glacier receded by about 6.5 feet (2 meters). This rate of thinning represents a doubling compared to the average over the preceding five years. In the decade prior to that, these glaciers thinned by a foot or less annually.

St. Mary's Glacier, a popular perennial snowfield, melted away entirely in September.

McGrath noted that this phenomenon is not unique to Colorado. "What we’re witnessing is the loss of that part of Colorado’s identity. And it’s not just Colorado," he stated. "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."

This trend aligns with global observations of glacier loss, where warming temperatures accelerate melting and reduced snowfall fails to replenish ice reserves. This has broader implications, threatening water sources, increasing mountain hazards, and contributing to sea level rise.

Globally, over 7 trillion tons of ice have been lost since 2000. In Switzerland, glaciers lost 5.5% of their ice volume in the past year, the second-largest percentage drop on record, attributed to heat waves and minimal winter snowfall. The GLAMOS Swiss glacier monitoring service has indicated that alpine glaciers have little chance of long-term survival under current conditions.

In Washington state, researchers observed the fastest average retreat of glaciers on Mount Baker since 1950, marked by the collapse of several large ice caves that form within receding glaciers. Mountain glaciers in the contiguous United States, averaging about 100 acres each, have seen about a quarter disappear since the mid-1900s, with remaining glaciers losing a third of their area and volume.

The meltwater from these glaciers is a crucial water supply for high alpine and downstream ecosystems across the western United States. Their disappearance could leave these areas more vulnerable to extreme drought.

Furthermore, wildfires contribute to accelerated melting by darkening glacier surfaces with soot and dust, enhancing sunlight absorption. While glaciers could eventually reform if carbon pollution significantly decreases and temperatures drop enough for year-round snowfall to accumulate and compress into ice, this process could take several hundred years.

McGrath estimates that Colorado's remaining glaciers could disappear within the next 20 years, citing the Andrews Glacier's loss of half its ice since 2017 as an example. "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, a student at Colorado State University who volunteers with McGrath's research, has photographed the glaciers annually since 2022. He expressed sadness at their decline but emphasized the importance of documenting the changes for future generations.