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Glaciers distinct from the Greenland and Antarctic ice sheets are shrinking rapidly, altering regional hydrology1, raising global sea level2and elevating natural hazards3. Yet, owing to the scarcity of constrained mass loss observations, glacier evolution during the satellite era is known only partially, as a geographic and temporal patchwork4,5. Here we reveal the accelerated, albeit contrasting, patterns of glacier mass loss during the early twenty-first century. Using largely untapped satellite archives, we chart surface elevation changes at a high spatiotemporal resolution over all of Earth’s glaciers. We extensively validate our estimates against independent, high-precision measurements and present a globally complete and consistent estimate of glacier mass change. We show that during 2000–2019, glaciers lost a mass of 267 ± 16 gigatonnes per year, equivalent to 21 ± 3 per cent of the observed sea-level rise6. We identify a mass loss acceleration of 48 ± 16 gigatonnes per year per decade, explaining 6 to 19 per cent of the observed acceleration of sea-level rise. Particularly, thinning rates of glaciers outside ice sheet peripheries doubled over the past two decades. Glaciers currently lose more mass, and at similar or larger acceleration rates, than the Greenland or Antarctic ice sheets taken separately7–9. By uncovering the patterns of mass change in many regions, we find contrasting glacier fluctuations that agree with the decadal variability in precipitation and temperature. These include a North Atlantic anomaly of decelerated mass loss, a strongly accelerated loss from northwestern American glaciers, and the apparent end of the Karakoram anomaly of mass gain10. We anticipate our highly resolved estimates to advance the understanding of drivers that govern the distribution of glacier change, and to extend our capabilities of predicting these changes at all scales. Predictions robustly benchmarked against observations are critically needed to design adaptive policies for the local- and regional-scale management of water resources and cryospheric risks, as well as for the global-scale mitigation of sea-level rise.

Surges and glacier avalanches are expressions of glacier instability, and among the most dramatic phenomena in the mountain cryosphere. Until now, the catastrophic collapse of a glacier, combining the large volume of surges and mobility of ice avalanches, has been reported only for the 2002 130 × 106m3detachment of Kolka Glacier (Caucasus Mountains), which has been considered a globally singular event. Here, we report on the similar detachment of the entire lower parts of two adjacent glaciers in western Tibet in July and September 2016, leading to an unprecedented pair of giant low-angle ice avalanches with volumes of 68 ± 2 × 106m3and 83 ± 2 × 106m3. On the basis of satellite remote sensing, numerical modelling and field investigations, we find that the twin collapses were caused by climate- and weather-driven external forcing, acting on specific polythermal and soft-bed glacier properties. These factors converged to produce surge-like enhancement of driving stresses and massively reduced basal friction connected to subglacial water and fine-grained bed lithology, to eventually exceed collapse thresholds in resisting forces of the tongues frozen to their bed. Our findings show that large catastrophic instabilities of low-angle glaciers can happen under rare circumstances without historical precedent. Two catastrophic glacier collapse events in western Tibet in 2016 were caused by a convergence of weather and glacier-bed conditions, according to an analysis of observations and modelling.

High Mountain Asia hosts the largest glacier concentration outside the polar regions. These glaciers are important contributors to streamflow in one of the most populated areas of the world. Past studies have used methods that can provide only regionally averaged glacier mass balances to assess the glacier contribution to rivers and sea level rise. Here we compute the mass balance for about 92% of the glacierized area of High Mountain Asia using time series of digital elevation models derived from satellite stereo-imagery. We calculate a total mass change of −16.3 ± 3.5 Gt yr−1(−0.18 ± 0.04 m w.e. yr−1) between 2000 and 2016, which is less negative than most previous estimates. Region-wide mass balances vary from −4.0 ± 1.5 Gt yr−1(−0.62 ± 0.23 m w.e. yr−1) in Nyainqentanglha to +1.4 ± 0.8 Gt yr−1(+0.14 ± 0.08 m w.e. yr−1) in Kunlun, with large intra-regional variability of individual glacier mass balances (standard deviation within a region ∼0.20 m w.e. yr−1). Specifically, our results shed light on the Nyainqentanglha and Pamir glacier mass changes, for which contradictory estimates exist in the literature. They provide crucial information for the calibration of the models used for projecting glacier response to climatic change, as these models do not capture the pattern, magnitude and intra-regional variability of glacier changes at present.

Below hard‐bedded glaciers, both basal friction and distributed subglacial drainage are thought to be controlled by a network of cavities. Previous coupled hydro‐mechanical models, however, describe cavity‐driven friction and hydraulic transmissivity independently, resulting in a physically inconsistent cavity evolution between the two components of the models. Here, we overcome this issue by describing the hydro‐mechanical system using a common cavity‐evolution description, that governs both transient friction and hydraulic transmissivity. We show that our coupling approach is superior to previous formulations in explaining a unique observation record of glacier sliding speed from the French Alps. We find that, at multi‐day to multi‐decadal timescales, sliding speed can be expressed as a direct function of basal shear stress and water discharge, without accounting for water pressure, which simply adjusts to maintain the cavitation ratio needed to accommodate the water supply. Predicting the sliding speed of glaciers and ice sheets is challenged by the difficulties of assessing the water pressure at the glacier base. Here, we improve the coupling between existing theories about basal friction and subglacial hydrology by introducing a consistent description of roughness and hydraulic transmissivity. Our work breaks with the common view on the subglacial environment that water pressure drives the sliding speed by modulating friction at the glacier base. Instead, our findings show that at multi‐day and longer timescales sliding speed and water pressure are imposed by the water discharge along the glacier base that needs to be accommodated. Our results open new perspectives for understanding contemporary glacier and ice sheet sliding and predicting its future behavior under changing climate. We introduce a consistent framework to describe the effect of cavitation on both friction and hydraulic transmissivityThis approach reduces the number of parameters of the coupled hydro‐mechanical problem and shows better performance in explaining our dataWe find that seasonal sliding variations are well captured assuming cavities in equilibrium with their average discharge We introduce a consistent framework to describe the effect of cavitation on both friction and hydraulic transmissivity This approach reduces the number of parameters of the coupled hydro‐mechanical problem and shows better performance in explaining our data We find that seasonal sliding variations are well captured assuming cavities in equilibrium with their average discharge

Concerns over greenhouse-gas forcing and global temperatures have initiated research into understanding climate forcing and associated Earth-system responses. A significant component is the Earth's cryosphere, as glacier-related, feedback mechanisms govern atmospheric, hydrospheric and lithospheric response. Predicting the human and natural dimensions of climate-induced environmental change requires global, regional and local information about ice-mass distribution, volumes, and fluctuations. The Global Land-Ice Measurements from Space (GLIMS) project is specifically designed to produce and augment baseline information to facilitate glacier-change studies. This requires addressing numerous issues, including the generation of topographic information, anisotropic-reflectance correction of satellite imagery, data fusion and spatial analysis, and GIS-based modeling. Field and satellite investigations indicate that many small glaciers and glaciers in temperate regions are downwasting and retreating, although detailed mapping and assessment are still required to ascertain regional and global patterns of ice-mass variations. Such remote sensing/GIS studies, coupled with field investigations, are vital for producing baseline information on glacier changes, and improving our understanding of the complex linkages between atmospheric, lithospheric, and glaciological processes.

In the version of this Article originally published, the symbols for ‘greater than’ and ‘less than or equal to’ were inverted in the equation that defines σΔz. The original (1) and corrected (2) versions of the equation are shown below. This error did not affect the calculation of the uncertainties. In addition, erroneous values that were a remnant of an earlier version of the authors’ work and higher than the final values calculated were reported for the uncertainties on ASTER estimates in Supplementary Table 4. Table 1 below shows the corrected values in bold font. These errors have now been corrected in the online versions of the Article.