[1] A new physically based approach for calculating glacier ice thickness distribution and volume is presented and applied to all glaciers and ice caps worldwide. Combining glacier outlines of the globally complete Randolph Glacier Inventory with terrain elevation models (Shuttle Radar Topography Mission/Advanced Spaceborne Thermal Emission and Reflection Radiometer), we use a simple dynamic model to obtain spatially distributed thickness of individual glaciers by inverting their surface topography. Results are validated against a comprehensive set of thickness observations for 300 glaciers from most glacierized regions of the world. For all mountain glaciers and ice caps outside of the Antarctic and Greenland ice sheets we find a total ice volume of 170 Â 10 3 AE 21 Â 10 3 km 3 , or 0.43 AE 0.06 m of potential sea level rise.Citation: Huss, M., and D. Farinotti (2012), Distributed ice thickness and volume of all glaciers around the globe, J. Geophys.

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G laciers and ice caps outside the Greenland and Antarctic ice sheets ('glaciers' in the following) are changing rapidly in response to climate change 1 . Although they only contain a fraction of the worldwide ice volume 2 , the consequences of their mass loss are widespread and of global significance: glacier changes affect global trends in freshwater availability 3,4 , have dominated cryospheric contributions to recent sea level changes 5,6 and are anticipated to affect regional water resources over the twenty-first century 7,8 . Clearly, projections of such impacts require an estimate of the ice volume stored within present-day glaciers, and for regionalto local-scale projections the ice thickness distribution can also be essential 9,10 . Recent studies showed that even small features in the bedrock topography can cause decadal-scale variations in both ice dynamics response 11 and subglacial water discharge 12 .Despite far-reaching implications, knowledge of the ice thickness distributions of the world's glaciers is remarkably limited. The Glacier Thickness Database (GlaThiDa), which centralizes ice thickness measurements outside the two ice sheets, presently contains information for only about 1,000 out of the 215,000 glaciers worldwide 13 . This is despite important advances in the instrumentation used to measure ice thickness 14,15 , with airborne platforms now capable of operating in mountainous environments as well 16 .Owing to the lack of direct measurements, relations between glacier area and ice volume 17 have traditionally been used to estimate global glacier volumes 18-21 . For individual glaciers, instead, a suite of methods that infer the spatial ice thickness distribution from surface characteristics have been proposed [22][23][24][25][26][27] . Such methods use topographical information-typically extracted from digital elevation models (DEMs)-to estimate the distribution of the glacier's surface mass balance and, hence, its mass turnover. Knowledge of the ice thickness distribution of the world's glaciers is a fundamental prerequisite for a range of studies.Projections of future glacier change, estimates of the available freshwater resources or assessments of potential sea-level rise all need glacier ice thickness to be accurately constrained. Previous estimates of global glacier volumes are mostly based on scaling relations between glacier area and volume, and only one study provides global-scale information on the ice thickness distribution of individual glaciers. Here we use an ensemble of up to five models to provide a consensus estimate for the ice thickness distribution of all the about 215,000 glaciers outside the Greenland and Antarctic ice sheets. The models use principles of ice flow dynamics to invert for ice thickness from surface characteristics. We find a total volume of 158 ± 41 × 10 3 km 3 , which is equivalent to 0.32 ± 0.08 m of sea-level change when the fraction of ice located below present-day sea level (roughly 15%) is subtracted. Our results indicate that High Mountain Asia ...

Glaciers distinct from the Greenland and Antarctic ice sheets are shrinking rapidly, altering regional hydrology 1 , raising global sea-level 2 and elevating natural hazards 3 . Yet, due to the scarcity of constrained mass loss observations, glacier evolution during the satellite era is only known as a geographic and temporal patchwork 4,5 . Here we reveal the accelerated, albeit contrasted, patterns of glacier mass loss during the early twenty-first century. By leveraging 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 the first globally complete and consistent estimate of glacier mass change. We show that, during 2000-2019, glaciers lost 267 ± 16 Gt yr -1 , equivalent to 21 ± 3% of observed sea-level rise 6 . We identify a mass loss acceleration of 48 ± 16 Gt yr -1 per decade, explaining 6-19% of the observed acceleration of sea-level rise. Particularly, thinning rates of glaciers outside ice sheet peripheries doubled over the last two decades. Glaciers presently lose more mass, and at similar or larger accelerated rates, than the Greenland or Antarctic ice sheets taken separately [7][8][9] . Uncovering the patterns of mass change in many regions, we find contrasted glacier fluctuations that agree with decadal variability in precipitation and temperature. Those include a newly-identified 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 10 . We anticipate our highly-resolved estimates to foster 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 management of local water resources and cryospheric risks as well as for regional-to-global sea-level rise.About 200 million people live on land predicted to fall below the high-tide lines of rising sea levels by the end of the century 11 , while more than one billion could face water shortage and food insecurity within the next three decades 4 . Glaciers distinct from the ice sheets play a prominent role in these repercussions as the largest estimated contributor to twenty-first century sea-level rise after thermal expansion 2 , and as one of the most climate-sensitive constituents of the world's natural water towers 12,13 . Current glacier retreat temporarily mitigates water stress on populations reliant on ice reserves by increasing river runoff 1 , but this short-lived effect will eventually decline 14 . Understanding present-day and future glacier mass change is thus crucial to avoid water scarcity-induced socio-political instability 15 , to predict the alteration of coastal areas due to sea-level rise 4 , and to assess the impacts on ecosystems 16 as w...

The anticipated retreat of glaciers around the globe will pose far-reaching challenges to the management of fresh water resources and significantly contribute to sea-level rise within the coming decades. Here, we present a new model for calculating the twenty-first century mass changes of all glaciers on Earth outside the ice sheets. The Global Glacier Evolution Model (GloGEM) includes mass loss due to frontal ablation at marine-terminating glacier fronts and accounts for glacier advance/retreat and surface elevation changes. Simulations are driven with monthly near-surface air temperature and precipitation from 14 Global Circulation Models forced by RCP2.6, RCP4.5, and RCP8.5 emission scenarios. Depending on the scenario, the model yields a global glacier volume loss of 25-48% between 2010 and 2100. For calculating glacier contribution to sea-level rise, we account for ice located below sea-level presently displacing ocean water. This effect reduces the glacier contribution by 11-14%, so that our model predicts a sea-level equivalent (multi-model mean ±1 standard deviation) of 79±24 mm (RCP2.6), 108±28 mm (RCP4.5), and 157±31 mm (RCP8.5). Mass losses by frontal ablation account for 10% of total ablation globally, and up to ∼30% regionally. Regional equilibrium line altitudes are projected to rise by ∼100-800 m until 2100, but the effect on ice wastage depends on initial glacier hypsometries.

Glaciers distinct from the Greenland and Antarctic ice sheets cover an area of approximately 706,000 square kilometres globally 1 , with an estimated total volume of 170,000 cubic kilometres, or 0.4 metres of potential sea-level-rise equivalent 2. Retreating and thinning glaciers are icons of climate change 3 and affect regional runoff 4 as well as global sea level 5,6. In past reports from the Intergovernmental Panel on Climate Change, estimates of changes in glacier mass were based on the multiplication of averaged or interpolated results from available observations of a few hundred glaciers by defined regional glacier areas 7-10. For data-scarce regions, these results had to be complemented with estimates based on satellite altimetry and gravimetry 11. These past approaches were challenged by the small number and heterogeneous spatiotemporal distribution of in situ measurement series and their often unknown ability to represent their respective mountain ranges, as well as by the spatial limitations of satellite altimetry (for which only point data are available) and gravimetry (with its coarse resolution). Here we use an extrapolation of glaciological and geodetic observations to show that glaciers contributed 27 ± 22 millimetres to global mean sea-level rise from 1961 to 2016. Regional specific-mass-change rates for 2006-2016 range from −0.1 metres to −1.2 metres of water equivalent per year, resulting in a global sea-level contribution of 335 ± 144 gigatonnes, or 0.92 ± 0.39 millimetres, per year. Although statistical uncertainty ranges overlap, our conclusions suggest that glacier mass loss may be larger than previously reported 11. The present glacier mass loss is equivalent to the sea-level contribution of the Greenland Ice Sheet 12 , clearly exceeds the loss from the Antarctic Ice Sheet 13 , and accounts for 25 to 30 per cent of the total observed sea-level rise 14. Present mass-loss rates indicate that glaciers could almost disappear in some mountain ranges in this century, while heavily glacierized regions will continue to contribute to sea-level rise beyond 2100. Changes in glacier volume and mass are observed by geodetic and glaciological methods 15. The glaciological method provides glacier-wide mass changes by using point measurements from seasonal or annual in situ campaigns, extrapolated to unmeasured regions of the glacier. The geodetic method determines glacier-wide volume changes by repeated mapping and differencing of glacier surface elevations from in situ, airborne and spaceborne surveys, usually over multiyear to decadal periods. In this study, we used glaciological and geodetic data from the World Glacier Monitoring Service (WGMS) 16 , complemented by new and as-yet-unpublished geodetic assessments for glaciers in Africa,

Abstract. The geodetic method is widely used for assessing changes in the mass balance of mountain glaciers. However, comparison of repeated digital elevation models only provides a glacier volume change that must be converted to a change in mass using a density assumption or model. This study investigates the use of a constant factor for the volumeto-mass conversion based on a firn compaction model applied to simplified glacier geometries with idealized climate forcing, and two glaciers with long-term mass balance series. It is shown that the "density" of geodetic volume change is not a constant factor and is systematically smaller than ice density in most cases. This is explained by the accretion/removal of low-density firn layers, and changes in the firn density profile with positive/negative mass balance. Assuming a value of 850 ± 60 kg m −3 to convert volume change to mass change is appropriate for a wide range of conditions. For short time intervals (≤ 3 yr), periods with limited volume change, and/or changing mass balance gradients, the conversion factor can however vary from 0-2000 kg m −3 and beyond, which requires caution when interpreting glacier mass changes based on geodetic surveys.

Abstract:The future runoff from three highly glacierized alpine catchments is assessed for the period 2007-2100 using a glaciohydrological model including the change in glacier coverage. We apply scenarios for the seasonal change in temperature and precipitation derived from regional climate models. Glacier surface mass balance and runoff are calculated in daily time-steps using a distributed temperature-index melt and accumulation model. Model components account for changes in glacier extent and surface elevation, evaporation and runoff routing. The model is calibrated and validated using decadal ice volume changes derived from four digital elevation models (DEMs) between 1962 and 2006, and monthly runoff measured at a gauging station . Annual runoff from the drainage basins shows an initial increase which is due to the release of water from glacial storage. After some decades, depending on catchment characteristics and the applied climate change scenario, runoff stabilizes and then drops below the current level. In all climate projections, the glacier area shrinks dramatically. There is an increase in runoff during spring and early summer, whereas the runoff in July and August decreases significantly. This study highlights the impact of glaciers and their future changes on runoff from high alpine drainage basins.