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Glaciers, distinct from the Greenland and Antarctic ice sheets, play a crucial role in Earth's climate system by affecting global sea levels, freshwater availability, nutrient and energy budgets and regional climate patterns. Accurate measurements of glacier mass changes are needed to understand and project glacier evolution and its related impacts on the climate system. Two distinct methods allow to measure glacier mass changes at high spatial resolution. Remotely sensed surface elevation data provides volume change estimates over large glacierized regions for multi-annual to decadal time periods. Field glaciological measurements provide annually to seasonally resolved information on glacier mass change for a small sample of the world's glaciers. By combining the two methods we provide annual time series of individual glacier mass changes and related uncertainties spanning the hydrological years from 1976 to 2023. The per-glacier time series can then be seamlessly integrated into annually resolved global regular grids of glacier mass changes at user-specified spatial resolution. Our results undergo a leave-one-out cross-validation confirming uncertainty estimates at the glacier level to be in the conservative side. Our dataset provides a new baseline for future glacier change modelling assessments and their impact on the world's energy, water, and sea-level budget. The present annual mass change time-series for the individual glaciers and the derived global gridded annual mass change product at a spatial resolution of 0.5° latitude and longitude will be made available from the WGMS webpage. During the review process, the dataset is temporarily available from URL: https://user.geo.uzh.ch/idussa/Dussaillant_etal_ESSD_data/. [ABSTRACT FROM AUTHOR]

Observations of glacier mass changes are key to understanding the response of glaciers to climate change and related impacts, such as regional runoff, ecosystem changes, and global sea level rise. Spaceborne optical and radar sensors make it possible to quantify glacier elevation changes, and thus multi-annual mass changes, on a regional and global scale. However, estimates from a growing number of studies show a wide range of results with differences often beyond uncertainty bounds. Here, we present the outcome of a community-based inter-comparison experiment using spaceborne optical stereo (ASTER) and synthetic aperture radar interferometry (TanDEM-X) data to estimate elevation changes for defined glaciers and target periods that pose different assessment challenges. Using provided or self-processed digital elevation models (DEMs) for five test sites, 12 research groups provided a total of 97 spaceborne elevation-change datasets using various processing approaches. Validation with airborne data showed that using an ensemble estimate is promising to reduce random errors from different instruments and processing methods but still requires a more comprehensive investigation and correction of systematic errors. We found that scene selection, DEM processing, and co-registration have the biggest impact on the results. Other processing steps, such as treating spatial data voids, differences in survey periods, or radar penetration, can still be important for individual cases. Future research should focus on testing different implementations of individual processing steps (e.g. co-registration) and addressing issues related to temporal corrections, radar penetration, glacier area changes, and density conversion. Finally, there is a clear need for our community to develop best practices, use open, reproducible software, and assess overall uncertainty to enhance inter-comparison and empower physical process insights across glacier elevation-change studies. [ABSTRACT FROM AUTHOR]

Glaciers distinct from the Greenland and Antarctic ice sheets are shrinking rapidly, altering regional hydrology.sup.1, raising global sea level.sup.2 and elevating natural hazards.sup.3. 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 patchwork.sup.4,5. 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 [plus or minus] 16 gigatonnes per year, equivalent to 21 [plus or minus] 3 per cent of the observed sea-level rise.sup.6. We identify a mass loss acceleration of 48 [plus or minus] 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 separately.sup.7-9. 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 gain.sup.10. 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. Analysis of satellite stereo imagery uncovers two decades of mass change for all of Earth's glaciers, revealing accelerated glacier shrinkage and regionally contrasting changes consistent with decadal climate variability., Author(s): Romain Hugonnet [sup.1] [sup.2] [sup.3] , Robert McNabb [sup.4] [sup.5] , Etienne Berthier [sup.1] , Brian Menounos [sup.6] [sup.7] , Christopher Nuth [sup.5] [sup.8] , Luc Girod [sup.5] , [...]

Observations of glacier mass changes are key to understanding the response of glaciers to climate change and related impacts, such as regional runoff, ecosystem changes, and global sea-level rise. Spaceborne optical and radar sensors make it possible to quantify glacier elevation changes, and thus multi-annual mass changes, on a regional and global scale. However, estimates from a growing number of studies show a wide range of results with differences often beyond uncertainty bounds. Here, we present the outcome of a community-based inter-comparison experiment using spaceborne optical stereo (ASTER) and synthetic aperture radar interferometry (TanDEM-X) data to estimate elevation changes for defined glaciers and target periods that pose different assessment challenges. Using provided or self-processed digital elevation models (DEMs) for five test sites, 12 research groups provided a total of 97 spaceborne elevation-change datasets using various processing strategies. Validation with airborne data showed that using an ensemble estimate is promising to reduce random errors from different instruments and processing methods, but still requires a more comprehensive investigation and correction of systematic errors. We found that scene selection, DEM processing, and co-registration have the biggest impact on the results. Other processing steps, such as treating spatial data voids, differences in survey periods, or radar penetration, can still be important for individual cases. Future research should focus on testing different implementations of individual processing steps (e.g. co-registration) and addressing issues related to temporal corrections, radar penetration, glacier area changes, and density conversion. Finally, there is a clear need for our community to develop best practices, use open, reproducible software, and assess overall uncertainty in order to enhance inter-comparison and empower physical process insights across glacier elevation-change studies. [ABSTRACT FROM AUTHOR]

In Greenland, 87% of the glacierized area terminates in the ocean, but mass lost at the ice‐ocean interface, or frontal ablation, has not yet been fully quantified. Using measurements and models we calculate frontal ablation of Greenland's 213 outlet and 537 peripheral glaciers and find a total frontal ablation of 481.8 ± 24.0 for 2000–2010 and 510.2 ± 18.6 Gt a−1 for 2010–2020. Ice discharge accounted for ∼90% of frontal ablation during both periods, while mass loss due to terminus retreat comprised the remainder. Only 16 glaciers were responsible for the majority (>50%) of frontal ablation from 2010 to 2020. These estimates, along with the climatic‐basal balance, allow for a more complete accounting of Greenland Ice Sheet and peripheral glacier mass balance. In total, Greenland accounted for ∼90% of Northern Hemisphere frontal ablation for 2000–2010 and 2010–2020. Plain Language Summary: We estimate the mass of ice lost from all Greenland glaciers that entered the ocean during each of the last two decades. This ice loss at the front of these marine‐terminating glaciers is called frontal ablation and is approximately equal to the mass of icebergs entering the ocean. Frontal ablation is important because 87% of glacier area in Greenland ends in the ocean, through 750 outlets, and previous work has only approximated frontal ablation. This study quantifies it for the first time, helping to close the mass budget for the Greenland Ice Sheet and better partition its mass balance into components. We find that Greenland accounts for ∼90% of all Northern Hemisphere frontal ablation and, of that contribution, just 17 glaciers for 2000–2010 and 16 glaciers for 2010–2020 account for more than half of total Greenland frontal ablation. Key Points: Frontal ablation of the Greenland Ice Sheet averaged 510.2 ± 18.6 Gt a−1 for 2010–2020, ∼90% of which came from ice dischargeThe frontal ablation we measured is larger than the total mass loss from the ice sheet, indicating a positive climatic‐basal balanceOnly 16 glaciers account for 50% of the total frontal ablation from the Greenland Ice Sheet [ABSTRACT FROM AUTHOR]

Knowledge of frontal ablation from marine-terminating glaciers (i.e., mass lost at the calving face) is critical for constraining glacier mass balance, improving projections of mass change, and identifying the processes that govern frontal mass loss. Here, we discuss the challenges involved in computing frontal ablation and the unique issues pertaining to both glaciers and ice sheets. Frontal ablation estimates require numerous datasets, including glacier terminus area change, thickness, surface velocity, density, and climatic mass balance. Observations and models of these variables have improved over the past decade, but significant gaps and regional discrepancies remain, and better quantification of temporal variability in frontal ablation is needed. Despite major advances in satellite-derived large-scale datasets, large uncertainties remain with respect to ice thickness, depth-averaged velocities, and the bulk density of glacier ice close to calving termini or grounding lines. We suggest ways in which we can move toward globally complete frontal ablation estimates, highlighting areas where we need improved datasets and increased collaboration. [ABSTRACT FROM AUTHOR]

Western North American (WNA) glaciers straddle the Alaska/Canada border and cover14,384 km2 of mountainous terrain. To better quantify the response of these glaciers to early21st century climate variability we generated over 15,000 multi-sensor digital elevationmodels from spaceborne optical imagery. Over the period 2000-2018, WNA glaciers lost 117± 42 Gigatons (Gt) of mass, which accounts for up to 0.32 ± 0.11 mm of sea level rise overthe full period of study. Using existing surface mass balance measurements for 14glaciers in WNA we estimate that these glaciers experienced an average mass changeof -874 ± 100 kg m−2 yr−1 over the period 2000-2017. When multiplied by thetotal glacierized area of WNA, this value yields an annual mass loss of 13.6 ±4.3 Gt yr−1, close to the value [14 ± 3 Gt yr−1] calculated previously for WNAglaciers. Both of these values are twice as large as those based on our trend analysis.The discrepancy between surface mass balance measurements and those obtainedfrom our geodetic surveys suggests that glaciers chosen for long-term monitoringprograms are losing mass more rapidly than the region as a whole. We also note afour-fold increase in mass loss rates between 2000-2009 [-2.9 ± 3.1 Gt yr−1] and2009-2018 [-12.3 ± 4.6 Gt yr−1] which we attribute to a shift in regional meteorologicalconditions driven by the location and strength of upper level zonal wind. Undermoderate emission scenarios, glaciers in both the conterminous US and westernCanada are expected to undergo continued mass loss throughout this century. Theseprojected changes will affect thermal- and flow-buffering capacity provided by glacierrunoff for many watersheds, with implications for downstream ecosystems and waterresources. Although an increase in thermal energy caused by increased greenhouse gasconcentration will drive widespread mass loss throughout the century decadal scaleclimate variability will likely modulate this long-term change in the years ahead. [ABSTRACT FROM AUTHOR]

Nowadays, geodetic methods are frequently used as a reference for local, regional or global glacier mass balances estimates, especially in remote areas of the globe. Data gaps in digital elevation models derived from remote sensing data are a very common occurrence over glacierized terrain. These can be due to clouds, failure of stereoscopic correlation where images lack contrast (snowfield, shadows,...), or simply out of instrument swath. These data gaps propagate in maps of elevation change and need to be filled when computing glacier volume change and, ultimately, glacier-wide and region-wide mass balances.Thus, the robustness of interpolation methods and their uncertainty for volume change estimates are key to an improved assessment of glacier mass change by allowing optimal use of limited coverage data. However, the dependence of these methods on the spatial distribution of data gaps has been studied to a limited extent.In this study, we simulate gaps over numerous glacier elevation change maps of different regions and with various characteristics to assess and improve the robustness of existing methods of void interpolation. We also investigate formal uncertainties related to these interpolation methods which are poorly known and conservatively estimated in the literature.While depending strongly on the distribution of data voids, glacier-wide hypsometric interpolation methods yield satisfying results given their simplicity. Other methods and related uncertainties are also investigated. [ABSTRACT FROM AUTHOR]