Glacier mass change gridded data from 1976 to present derived from the Fluctuations of Glaciers Database - A new product in the Copernicus Service Climate Data Store

Glaciers play a fundamental role in the Earths water cycles. They are one of the most important freshwater resources for societies and ecosystems and the recent increase in ice melt contributes directly to the rise of ocean levels. For this reasons, they have been declared as an Essential Climate Variable (ECV) by the Global Climate Observing System (GCOS). Within the Copernicus Climate Change Services (C3S), the global gridded annual glacier mass change dataset provides information on changing glacier resources for the last five decades by combining 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). The glacier change product provides a global assessment of annual glacier mass change and related uncertainties (in m w.e. and Gt) and gridded area changes (km2) since the hydrological year 1975/76 to present, provided in a 0.5x0.5 (latitude-longitude) global regular grid and in netcdf file format. The new product bridges the gap on spatio-temporal coverage of glacier change observations, providing for the first time in the CDS an annually resolved glacier mass change product using the glacier elevation change sample as calibration. This goal has become feasible at the global scale only recently and thanks to a new globally near-complete (96% of the worlds glaciers) dataset of glacier elevation changes between 2000 and 2020. The global gridded annual glacier mass change product integrates nicely into the family of the gridded ECV products provided by the C3S CDS. It provides new insights into regional to global glacier mass changes and, hence, has a great potential for contributing to the various state of the climate reports as well as to assessments of the global sea-level budget, the global energy cycle or the global water cycle. Continuation and expansion of the glaciological in-situ observation network is essential for providing the temporal variability of the glacier mass change product. Ensuring the continuation of open source spaceborne datasets with extensive acquisitions tasking planned over glaciated regions is crucial for ensuring the good quality of future glacier products, and one of the greatest gaps in the quality and continuation of the glacier services delivered to C3S.