Unprecedented Twenty-First Century Glacier Loss on Mt. Hood, Oregon, U.S.A.

Abstract. As part of the southern Cascades, Mt. Hood is the tallest and most glaciated peak in Oregon, U.S.A. Despite alpine glaciers being one the clearest indicators of human-caused climate change, the 21st century behavior of glaciers on Mt. Hood has not been directly documented. Here we directly measure changes in Mt. Hood’s glacier extents from 2003 to 2023 and find dramatic retreat of all glaciers, with one glacier disappearing, another two nearing this status, and a third retreating towards this status. The seven largest glaciers on the volcano lost ~2.8 km², or ~40 % of their area in the 21st century. Comparison to historic records of glacier area back to 1907 shows that this 21st-century retreat is unprecedented with respect to the previous century and has outpaced modeled glacier changes. The rate of retreat over the last 23 years is more than double the fastest rate documented in the last century from 1907 to 1946. We demonstrate that this century-scale retreat strongly correlates with regional 30-year-average climate warming of ~1.1 ºC since the early 1900s, but not with regional changes in precipitation. We conclude that Mt. Hood’s glaciers are retreating in response to a warming climate and that this recession has accelerated in the 21st century, with attendant consequences for water resources.