Western North American and Switzerland glaciers experience unprecedented mass loss over the last three years

Glaciers in western North America (WNA) and Switzerland represent important sources of freshwater, especially during times of drought. We employ extensive airborne laser altimetry campaigns in WNA coupled with in-situ surface mass balance measurements for both regions to quantify recent mass change. Over the last three years glaciers within these regions respectively lost mass at rates of -22.87.4and -1.70.3 Gt yr-1 which, for both regions, represents an approximate twofold increase in mass loss compared to the period 2010-2020. Based on the estimated glacier volume in the year 2020, total volume change in these regions was depleted by 9% (WNA) and 10% (Switzerland) over the last three years. The year 2023 represents the year of greatest common mass loss for both regions where glaciers in both WNA and Switzerland respectively lost -37.110.4 and -1.80.3 Gt yr-1. Meteorological conditions that favored high rates of mass loss included low winter snow accumulation, early-season heat waves, and prolonged warm, dry conditions. Loss of firn, high transient snow lines, and potential impurity loading due to wildfires (WNA) or Saharan dust (Switzerland) darkened glaciers and thereby accelerated melt via an increase in absorbed shortwave radiation available for melt. This ice-albedo feedback will lead to continued accelerated loss unless recently exposed dark firn and ice at high elevation can be buried by subsequent snowfall. Rates of mass loss for the years 2021-2023 exceed even those projected for unabated global emissions though the twenty-first century, signaling the need to rapidly mitigate greenhouse gas emissions if glaciers in both regions are to survive.