A consensus estimate for the ice thickness distribution of all glaciers on Earth

Abstract

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 ...

Ice Thickness and Bed Elevation of the Northern and Southern Patagonian Icefields

“…Time series of surface elevation data from satellite radar altimetry and optical imagery have shown that all the glaciers, except for Glaciares Pio XI and Moreno, have thinned rapidly in the last 40 years, with a contribution to sea level rise of 0.042 ± 0.002 mm /year between 1968/year between and 1975/year between -2000/year between (Rignot et al, 2003, 0.067±0.004 mm/year during 2000-2012 (Willis et al, 2012), and 0.059 ± 0.005 mm/year during 2011-2017 (Foresta et al, 2018). Other simple models, based on Glen's flow law and empirical relationships, estimated a total volume of the Patagonian Icefields of 4,607 ± 1.2 km 3 (Farinotti et al, 2019). Using a perfectly plastic model, Carrivick et al (2016) estimated a volume of ice of 4,326 ± 865 km 3 for SPI and 1,234 ± 247 km 3 for NPI.…”

Last Glacial Maximum glacier modelling in the Quemuqu Valley, southern Tibetan Plateau, and its climatic implications

“…To obtain subglacial bed topography, we adopted the modern glacier thickness data by Farinotti et al . (). The subglacial bed topography was described by subtracting the modern ice thickness from the 30×30 m DEM grids.…”

“…The DEM, trimmed to the watershed of the Quemuqu Valley with a 30930 m spatial resolution, was downloaded from the Geospatial Data Cloud (http://www.gscloud.cn/). To obtain subglacial bed topography, we adopted the modern glacier thickness data by Farinotti et al (2019). The subglacial bed topography was described by subtracting the modern ice thickness from the 30930 m DEM grids.…”

Detailed quantification of glacier elevation and mass changes in South Georgia

“…The ice thickness values of South Georgia are derived from the ensemble-based ice thickness estimation of Farinotti et al (2019), which is based on the RGI V6. Using our area changes at the front of the glaciers, the mean ice thickness on those area retreat (Farinotti et al 2019) ( figure S4), combined with the subaerial elevation changes, we obtain an average ice thickness of 130±40 m. The ice loss below sea or lake level is converted to volume-to mass assuming a density of 900±60 kg m −3 (scenario 2) (e.g.…”