An annual mass balance estimate for each of the world’s glaciers based on observations.

The geodetic method has become a popular tool to measure glacier elevation changes over large glacierized regions with high accuracy for multiannual/decadal time periods. In contrast, the glaciological method provides annually to seasonally resolved information on glacier mass balance, but only for a small sample of the world’s glaciers (less than 1%). Various methods have been proposed to bridge the gap regarding the spatio-temporal coverage of glacier change observations and provide annually resolved glacier mass balances using the geodetic sample as calibration. Thanks to a new globally near-complete (96% of the world’s glaciers) dataset of geodetic mass balance between 2000 and 2020, a global-scale assessment of annual mass changes at glacier-specific level has now become feasible. Inspired by previous methodological frameworks, we developed a new approach to combine the glacier outlines from the globally complete Randolph Glacier Inventory with the mass balance and elevation change observations from the Fluctuation of Glaciers database of the World Glacier Monitoring Service (WGMS). Our results provide a global assessment of annual glacier mass change and related uncertainties for every individual glacier since 1976. The glacier-specific time series can then be integrated into an annually-resolved gridded global glacier change product at any user-requested spatial resolution, useful for comparison with, for example, gravity-based products, calibration or validation of glacier mass balance models operating at a global scale and to improve assessments of glacier contribution to regional hydrology and global sea-level rise. These developments additionally open a new door of opportunity to keep on pushing the frontiers of glacier change observations towards future assessments of global glacier mass changes at increased temporal resolutions.