Ar-Rehman

A quarter of the glaciers in the contiguous US have vanished since the mid-20th century

A new study compared the glaciers in the Lower 48 states against historical data from the mid-20th century. The results show the region’s vulnerabilities as temperatures rise. More than 300 glaciers have vanished from the American West since the mid-20th century, and the remaining glaciers share critical traits which allow them to endure. important points of the study are as follows:-

In the mid-20th century, over 1,450 glaciers spanned 217 square miles (562 square kilometers) across six western states in the contiguous US

300 glaciers have disappeared from the American West since the mid‑20th century, the survivors have a few things in common

The total area and volume of glaciers has dropped by about a third, and even more in California.

The decline of the glaciers, long a nourishing, and defining, fixture of the mountain West, is already having repercussions. Foremost, it’s robbing alpine ecosystems of needed moisture and squeezing water supplies for cities and farms.

Glacial melting in the Lower 48 states, a product of warming temperatures, is most severe in the Sierra Nevada and parts of the Rockies due to warmer, drier conditions and glaciers that are generally smaller and less resilient.

The research is a particularly comprehensive assessment of the bleak state of glaciers and a stark indictment of climate change.

If we look from an airplane, most of the glaciers of the Rocky Mountain West look like small patches of white nestled into rugged landscape where the topography folds. Scientists have taken measurements on Sperry Glacier, in Glacier National Park, Montana. The white is the snow cover, and lower down you can see the gray-blue bare ice. In the middle of the 20th century, over 1,450 glaciers could be found in the contiguous US Together, they covered 217 square miles (562 square km's) in six western states. A comprehensive review shows that their total area has shrunk by 35% and they are still shrinking, perhaps faster. Andrew Fountain took photos of glaciers in the Wind River Range in Wyoming while flying over the region in early October 2026. Most are located in protective niches. A little more than 300 glaciers have disappeared, way more than actually anticipated. Glaciers in the Beartooth-Absaroka Mountains of southern Montana are thinning the fastest, losing about 1.5 feet (half a meter) of ice thickness each year due to lower elevations and warmer conditions. Glaciers in Washington’s Cascade Range (such as on Mount Rainier and Mount Baker) shrink more slowly, about 0.5 feet per year, helped by higher elevations, cooler summers and heavier snowfall.

Few ones which survive reflect just how vulnerable mountain glaciers have become as global temperatures rise. Where glaciers once covered large expanses of the western mountains thousands of years ago, most of the remaining glaciers in the Rockies and Sierra Nevada are small and found in topographically protected places. When people think of glaciers, they often picture huge ice streams with icebergs calving off the front, like you’ll find in Alaska or Greenland. In the Lower 48 states, with the exception of a few large glaciers in Washington, they’re much smaller. The average glacier area is about one-tenth of a square mile (about a quarter of a square km) in size. The area of the largest glacier, found on Washington’s Mount Rainier, is about 4.3 square miles (11.24 square km's). Glaciers in the Rocky Mountains, those in Colorado, Montana and Wyoming and in the Sierra Nevada of California, subsist because of their unique position on the landscape, which somewhat insulates them from the otherwise less-favorable regional climate.

The surviving Rocky Mountain glaciers inhabit shaded niches less exposed to direct sunshine and gain additional snow from avalanches. If these glaciers were exposed to more sun and less snow accumulation, they likely wouldn’t exit at all. the fastest-thinning glaciers are in the Beartooth-Absaroka Mountains of the Rockies in southern Montana, which are losing about 1.5 feet (about half a meter) of ice thickness/year. It’s a different story in Washington, where the glaciers on Mount Rainier and Mount Baker are much larger, have cooler summers and get a lot more snowfall. Although they too are shrinking, they do so at a much slower rate, about half a foot of ice thickness/ year. The glacier area on Mount Rainier alone is greater than the total sum in all the other states. Satellite images of glaciers on Mount Shasta in Northern California, Mount Rainier in Washington and Sperry Glacier in Montana show how each has thinned, losing elevation over time.

In Washington, generally speaking, the higher you go, the less glacier loss you find. This makes sense; it’s cooler at higher elevations. But in the Rocky Mountain region there is no similar trend, suggesting the survivors are niche glaciers which depend on local topographic benefits. In an earlier study, scientists modeled the glaciers on Washington’s Olympic Peninsula and found most would disappear by 2070 under current climate trends. This indicates that glaciers elsewhere are probably not far behind. The Olympics are vulnerable because they’re close to the Pacific Ocean at somewhat lower elevation. The other Washington glaciers, particularly on Mount Rainier and Mount Baker, will likely survive past 2100, but how much longer is an open question." The principal importance of the glaciers is to provide water to high alpine ecosystems. The glaciers partially melt in late summer, providing cool water for cold-adapted fish and other stream life. They provide a water supply which otherwise absent in the dry late summer, after the seasonal snow disappears, when the region doesn’t get a lot of rain. While the glaciers of the Rockies are primarily important for ecosystems at this point, those in Washington also contribute to hydropower production.

An important hazard is also associated with the glaciers on the steep-sided volcanoes of the Cascade Range, which stretches from California to Washington. The moraines formed by these glaciers are large, partly due to the highly erodible volcanic rock beneath the ice. Moving ice deposits eroded rocks, forming aprons at their lower ends. As the glaciers retreat, they leave the accumulated rocks behind as steep-sided moraines that are no longer buttressed by the ice. High water flows from rain or glacier melt can undercut the moraines, triggering landslides and creating debris flows which go rocketing down the mountains. This happened in 2006 on Mount Hood and Mount Rainier and closed a number of highways. This might happen more often as the glaciers retreat. The shrinking and eventual loss of all of these glaciers will affect ecosystems across the West, as well as waterways humans and wildlife rely on. The survivors are mostly small and located in sheltered, shaded areas (such as deep cirques or north-facing slopes) which shield them from direct sunlight. Many surviving glaciers in the Rocky Mountains receive vital extra snow accumulation via avalanches from surrounding steep cliffs. Without these specific local shelters and extra snow drift/avalanche feeding, almost none of these remaining Lower 48 glaciers would still exist. Alpine glaciers act as natural water towers, storing winter snowpack and releasing water into streams and rivers during dry late-summer months. Shrinking ice masses reduce the buffering capacity against regional droughts and alter cold-water habitats for aquatic life.