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

Scientists take measurements on Sperry Glacier, in Glacier National Park, Montana. USGS

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. 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 U.S. Together, they covered 217 square miles (562 square kilometers) in six western states. Today, a comprehensive review my colleagues and I just published in the Proceedings of the National Academy of Sciences shows their total area has shrunk by 35% and they are still shrinking, perhaps faster.