Annual mass change of the world's glaciers from 1976 to 2024 by temporal downscaling of satellite data with in situ observations

Abstract. Glaciers, distinct from the Greenland and Antarctic ice sheets, play a crucial role in Earth's climate system by affecting global sea levels, regional freshwater availability, nutrient and energy budgets, and local geohazards. Past assessments of regional to global glacier mass changes were limited in spatial coverage, temporal resolution, and/or temporal coverage. Here, we present a new observation-based dataset of glacier mass changes with global coverage and annual resolution from 1976 to 2024. We use geostatistical modeling for the temporal downscaling of decadal glacier-wide elevation change estimates derived from satellite and airborne geodetic data, with glaciological annual in situ observations. In more detail, we spatially interpolate the annual mass balance anomalies from sparse in situ observations and calibrate them to glacier-wide long-term trends from elevation change observations available for individual glaciers for varying time periods and with global glacier coverage from 2000 to 2019. We then extrapolate the results to yearly time series starting between 1915 and 1976, depending on the regional data availability, and extending to 2024. The time series are calculated separately for each of the world's glaciers and then aggregated to gridded (0.5° latitude and longitude), regional, and global estimates of annual glacier mass changes. Since 1976, Earth's glaciers have lost 9179 ± 621 Gt (187 ± 20 Gt per year) of water, contributing 25.3 ± 1.7 mm (0.5 ± 0.2 mm per year) to the global mean sea level rise. About 41 % (∼ 10 mm) of this loss occurred in the last decade, with 6 % (∼ 1.5 mm) occurring in 2023 alone, the record-breaking year of glacier mass loss. We review the strengths and limitations of our new dataset, validate and discuss related uncertainty estimates in a leave-one-out/block-out cross-validation exercise, and compare our results to earlier assessments. The annual mass change time series for individual glaciers and the derived global gridded annual mass change product are available from the World Glacier Monitoring Service (WGMS) at https://doi.org/10.5904/wgms-amce-2025-02 (Dussaillant et al., 2025).