Unprecedented 21st century glacier loss on Mt. Hood, Oregon, USA

Abstract. As part of the southern Cascades, Mt. Hood is the tallest and most glacierized peak in Oregon, USA. 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 at the ground level. Here we directly measure changes in the extents of Mt. Hood's glaciers from 2003 to 2023 and find dramatic retreat of all glaciers, with one glacier ceasing to flow (joining another glacier that ceased flowing before 2003) and another three glaciers retreating towards this status. By 2023, Mt. Hood glaciers had lost ∼17 % of their 2015–2016 area and ∼39 % of their 1981 area. The rate of area loss from 2015–2016 to 2023 (∼2.10 % yr−1) was ∼2.6 times faster than the rate from 1981 to 2015–2016 (∼0.81 % yr−1). The seven largest glaciers on the volcano lost ∼25 % of their area between 2000 and 2023. Comparison to historic records of glacier area back to 1907 shows that this 21st century retreat is unprecedented relative to the previous century. The rate of area loss over the last 23 years (∼1.07 % yr−1) was ∼1.9 times faster than the fastest rate documented in the last century from 1907 to 1946 (∼0.56 % yr−1) and ∼3.5 times faster than the 20th century average (∼0.31 % yr−1). This unprecedented rate of retreat corresponds to regional summer warmth reaching 1.7–1.8 °C (2013–2023 average) relative to the early 1900s, but not with regional changes in winter 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.