Melting and retreating glaciers are generating meltwater and creating space for new glacial lakes in Earth’s high mountains. These glacial lakes become increasingly important freshwater reservoirs, but their value for hydropower, drinking water supply, tourism and ecosystem services over decades depends on their storage capacity and sedimentation-dependent lifespan. Here we estimate the volumes and sediment storage capacities for ~71,000 glacial lakes globally as of 2020. Combined, these lakes impound a water volume of \({\mathrm{2,048}}_{{-}296}^{+218}\) km³ (median and 68% highest density interval), representing a \({+12.7}_{{-}13.2}^{+9.1} \%\) change compared with 1990. Half of the 2020 glacial lake water volume is located within 63 km of a coastline and below 200 m above sea level, mostly in sparsely populated, high-latitude regions such as Greenland, Arctic Canada, Patagonia and Alaska, where use of, and demand for, freshwater remains limited. The smallest lakes (<0.1 km2; ~80% of all) could lose 10% of their storage capacity within a century owing to sedimentation, while the 40 largest lakes, holding half of the global glacial lake volume, could endure for tens of thousands of years. These differing lifespans put pressure on a sustainable use of meltwater impounded within lakes, particularly in High Mountain Asia, where small glacial lakes could help serve the basic needs of millions of people, while unstable dams might rapidly remove some of this capacity. Overall, we offer regional and local baseline data of lake longevity to constrain a window of opportunity, in which growing demands for water security must be balanced with hazard mitigation and protection of rapidly evolving high-mountain ecosystems.
