Rapid contemporary shrinking and loss of ice-capped summits in the western United States

Ice-capped summits exist when the highest point of a mountain in late summer comprises ice and snow. For the last century, there have been five ice-capped summits in the contiguous United States, all in Washington State. In this study, we measured the contemporary elevations of these ice-capped summits and compared our findings to historical surveys and photographs to assess whether their elevations have changed and whether their ice caps are still intact. We hypothesized that ongoing impacts of climate change are altering even the highest elevation mountains in the western United States. Indeed, all five of these historically ice-capped summits have shrunk since ~1980, with four of the five shrinking by at least 6 m (20 ft) due to loss of snow and ice. As of 2024, only two of the five summits still had perennial ice as their highest point. Free-air temperatures for the ice-capped summits indicate significant late summer warming of 2.75°C since 1950 and increases in summer melt days, with most of the change occurring since the late 1990s. Given the synchronous trends, we offer climate-induced loss of summit ice as the most likely explanation for the observed changes to ice-capped summits in the western United States.