Global glacier modeling: Do non-linear feedbacks matter for century-scale projections? (GlacMod)

• Zekollari, Harry; Schuster, Lilian; Maussion, Fabien; Hock, Regine; Marzeion, Ben & Rounce, David R. [Show all 21 contributors for this article] (2025). Glacier preservation doubled by limiting warming to 1.5°C versus 2.7°C. Science. ISSN 0036-8075. 388(6750), p. 979–983. doi: 10.1126/science.adu4675. Full text in Research Archive Show summary

  Glaciers adapt slowly to changing climatic conditions, with long-term implications for sea-level rise and water supply. Using eight glacier models, we simulated global glacier evolution over multicentennial timescales, allowing glaciers to equilibrate with climate under various constant global temperature scenarios. We estimate that glaciers globally will lose 39 (range, 15 to 55)% of their mass relative to 2020, corresponding to a global mean sea-level rise of 113 (range, 43 to 204) mm even if temperatures stabilized at present-day conditions. Under the +1.5°C Paris Agreement goal, more than twice as much global glacier mass remains at equilibration (53% versus 24%) compared with the warming level resulting from current policies (+2.7°C by 2100 above preindustrial). Our findings stress the need for stringent mitigation policies to ensure the long-term preservation of glaciers.

• Dundovic, Davor; Wallwork, Joseph G.; Kramer, Stephan C.; Gillet-Chaulet, Fabien; Hock, Regine & Piggott, Matthew D. (2025). Anisotropic metric-based mesh adaptation for ice flow modelling in Firedrake. Geoscientific Model Development. ISSN 1991-959X. 18(13), p. 4023–4044. doi: 10.5194/gmd-18-4023-2025. Full text in Research Archive Show summary

  Glaciological modelling is a computationally challenging task due to its high cost and complexity associated with large spatial-scale and long timescale simulations. In this paper we propose feature-based anisotropic mesh adaptation methods and demonstrate their effectiveness for time-dependent glaciological modelling on a Marine Ice Sheet Model Intercomparison Project (MISMIP+) experiment. Our methods use the Python-based Firedrake finite element library and the mmg2d remeshing software. We show that we are able to achieve solution accuracy comparable to uniform 0.5 km resolution mesh simulations using a sequence of adapted meshes with, on average, 30 times fewer vertices when adapting meshes based on the basal stress and 8–12 times fewer when adapting based on ice thickness and velocity. We further introduce a novel hybrid time-dependent fixed-point mesh adaptation algorithm that reaches mesh convergence approximately twice as fast compared with the existing global fixed-point algorithm. Since the fixed-point algorithms require that the problem is solved multiple times, the reported reduction in the number of vertices ultimately translates into a 3–6 times lower overall computational cost compared to uniform mesh simulations.

• Innanen, Satu Karoliina; Hock, Regine; Schmidt, Louise Steffensen; Schuler, Thomas; Covi, Federico & Moholdt, Geir (2025). Witnessing the transition from cold to temperate firn on Austfonna ice cap, Svalbard, through observations and model simulations. Journal of Glaciology. ISSN 0022-1430. 71. doi: 10.1017/jog.2025.10072. Full text in Research Archive Show summary

  Refreezing is a critical component of the mass balance of glaciers in Svalbard, yet the processes and changes under a warming climate are not fully understood. Here, we investigate changes in firn properties of the Austfonna ice cap, Svalbard, using a combination of observations and model simulations. We analyze firn stratigraphy and density from five newly retrieved and 11 previously retrieved firn cores, collected at elevations ranging from 506 m a.s.l. to 791 m a.s.l. between 1958 and 2022. All cores exhibit frequent ice layers that indicate persistent refreezing of meltwater; however, no ice slabs (layers exceeding 1 m) were observed. A 13-year-long firn temperature time series from a site near the summit (773 m a.s.l.) shows that annual water percolation reaches depths of 7 m to over 13 m. A notable transition in the firn thermal regime occurred in 2013, transitioning from cold to temperate conditions above the firn-ice interface despite the seasonal cooling occurring in the upper firn layers. Simulations using the CryoGrid community model from 2009 to 2022 corroborate this thermal shift and suggest the development of a firn aquifer multiple times since 2013, with increasing duration and thickness over time.

• Petersen, Eric Ivan; Hock, Regine; Loso, Michael G.; Guo, Wanqin; Markovsky, Cameron & Yang, Ruitang [Show all 9 contributors for this article] (2025). Multi‐Year Glaciological and Meteorological Observations on Debris‐Covered Kennicott Glacier, Alaska, 2016–2023. Geoscience Data Journal. 12(4). doi: 10.1002/gdj3.70032. Full text in Research Archive Show summary

  ABSTRACT Despite increasing availability of satellite‐derived products, in situ glacier observations are pivotal to accurately monitor glacier change and to calibrate and validate glacier models. However, comprehensive multi‐variable field observations are especially rare on large glaciers and on debris‐covered glaciers. Here we present extensive field observations from Kennicott Glacier, a heavily debris‐covered glacier in central Alaska covering more than 400 km 2 . The multi‐year data set includes point glacier mass balances, meteorological data from several weather stations on and off the glacier, debris thickness and temperature, ice cliff back wasting derived from time‐lapse photography of horizontal stakes drilled into several cliffs, and bathymetry, water temperature, and water level of proglacial and supraglacial lakes. Cumulated summer melt of more than 8 m was observed at the lowest clean‐ice sites. Melt rates over clean ice correlate well with elevation, while the rates over debris‐covered ice lack any strong elevation dependence. Melt rates drop exponentially with increasing debris thickness and tend to be much lower than for clean ice at similar elevations. Melt rates determined for ice cliffs in areas of otherwise continuous debris cover were up to 10× those for debris‐covered ice, and even exceeded standard clean ice melt rates. Debris‐cover thickness measurements at 150 sites vary from < 1 to 69 cm with an average of 17 ± 11 cm (±standard deviation). Debris thickens down‐glacier, but with high spatial variability–thickness was observed to vary by tens of cm within a ~15 m radius. Depth‐averaged thermal heat conductivity derived from supraglacial debris temperature profiles at 12 sites ranges from 0.53 to 1.86 W m −1 K −1 . Interconnected proglacial lakes covered 1.61 km 2 in 2018 with observed water depths of more than 60 m in the two largest lakes. The dataset can be downloaded at https://doi.org/10.5281/zenodo.14625691 (Petersen, Hock, Loso, Guo, et al., 2024) and will be useful for glaciological and glacier meteorological studies.

• Yang, Ruitang; Hock, Regine; Rounce, David & Kang, Shichang (2025). Regional-Scale Response of Glacier Speed to Seasonal Runoff Variations on the Kenai Peninsula, Alaska. Geophysical Research Letters. ISSN 0094-8276. 52(8). doi: 10.1029/2025GL115248. Full text in Research Archive Show summary

  Seasonal variations in glacier motion are influenced by water supply and associated changes in subglacial drainage systems. Few studies have investigated how year-to-year variations in glacier runoff modify these seasonal speed patterns. We analyze more than 200 correlations between glacier surface speed and runoff for 77 glaciers (∼3,070 km2) on the Kenai Peninsula, Alaska, from 2015 to 2019. Correlations for the same-month or same-season were typically weak or insignificant. However, lower-than-average ice speeds in a given month or season often correspond with higher-than-average runoff in preceding months or seasons. Delays up to 9 months (e.g., correlations between April speed and preceding July runoff), suggest the impact of interannual runoff variations on ice speed lasts longer than previously documented. Unlike previous studies in the region and elsewhere, winter speed and summer runoff are weakly correlated or uncorrelated, while winter speed negatively correlates with October/November runoff.

• Hartl, Lea; Schmitt, Carl G.; Stuefer, Martin; Jenckes, Jordan; Page, Benjamin P. & Crawford, Christopher J. [Show all 9 contributors for this article] (2025). Leveraging airborne imaging spectroscopy and multispectral satellite imagery to map glacial sediment plumes in Kachemak Bay, Alaska. Journal of Hydrology Regional Studies. 57. doi: 10.1016/j.ejrh.2024.102121. Full text in Research Archive Show summary

  Study Region Kachemak Bay is a fjord-type estuary in the northern Gulf of Alaska. Water quality and habitat characteristics are strongly influenced by freshwater and sediment input from multiple glacierized catchments. Study Focus We present a new method combining imaging spectroscopy from an airborne survey with Landsat and Sentinel-2 imagery to map water surface turbidity originating from glacial runoff based on spectral abundance. We compare the spectral characteristics of turbid glacial water to clear water and generate a high resolution reference map of glacial turbidity in Kachemak Bay. This informs the subsequent analysis of a homogenized, Rayleigh corrected time series of Landsat and Sentinel-2 images and seasonal patterns of turbidity. New Hydrological Insights for the Region Our results provide the most comprehensive data set on water surface turbidity in Kachemak Bay to date and improve understanding of spatial and seasonal variability of glacial turbidity in a data sparse region. July and August have the largest plumes with median sizes around 150 km2, or around a quarter of Kachemak Bay. Plume sizes typically decrease with decreasing glacier runoff in September and October. We show that imaging spectroscopy aids assessments of turbid water in glacial marine catchments across scales. Leveraging high resolution spectral information allows for water color analyses that are customized to local conditions and catchment characteristics as well as scalable to wider regions.

• Hock, Regine & Truffer, Martin (2024). Glacier hazards: Will they change in the future? Arctic, Antarctic and Alpine research. ISSN 1523-0430. 56(1). doi: 10.1080/15230430.2024.2335991. Full text in Research Archive Show summary

  Glaciers can pose significant hazards (e.g., floods, landslides, ice falls) with disastrous consequences for people and infrastructure, especially as glaciers retreat in response to climate warming. Adverse potential risks are exacerbated as human activities increasingly expand into regions prone to glacier hazards.

• Eric, Petersen,; Hock, Regine & G., Loso, Michael (2024). Stream hydrology controls on ice cliff evolution and survival on debris-covered glaciers. Earth Surface Dynamics. ISSN 2196-6311. doi: 10.5194/esurf-12-727-2024. Full text in Research Archive Show summary

  Abstract. Ice cliffs are melt hot spots that contribute disproportionately to melt on debris-covered glaciers. In this study, we investigate the impact of supraglacial stream hydrology on ice cliffs using in situ and remote sensing observations, streamflow measurements, and a conceptual geomorphic model of ice cliff backwasting applied to ice cliffs on Kennicott Glacier, Alaska. We found that 33 % of ice cliffs (accounting for 69 % of the ice cliff area) are actively influenced by streams, while half are nearer than 10 m from the nearest stream. Supraglacial streams contribute to ice cliff formation and maintenance by horizontal meandering, vertical incision, and debris transport. These processes produce an undercut lip at the ice cliff base and transport clasts up to tens of centimeters in diameter, preventing reburial of ice cliffs by debris. Stream meander morphology reminiscent of sedimentary river channel meanders and oxbow lakes produces sinuous and crescent ice cliff shapes. Stream avulsions result in rapid ice cliff collapse and local channel abandonment. Ice cliffs abandoned by streams are observed to be reburied by supraglacial debris, indicating a strong role played by streams in ice cliff persistence. We also report on a localized surge-like event at the glacier's western margin which drove the formation of ice cliffs from crevassing; these cliffs occur in sets with parallel linear morphologies contrasting with the crescent planform shape of stream-driven cliffs. The development of landscape evolution models may assist in quantifying the total net effect of these processes on steady-state ice cliff coverage and mass balance, contextualizing them with other drivers including supraglacial ponds, differential melt, ice dynamics, and collapse of englacial voids.

• Petersen, Eric; Hock, Regine & Loso, Michael G. (2024). Stream hydrology controls on ice cliff evolution and survival on debris-covered glaciers. Earth Surface Dynamics. ISSN 2196-6311. 12(3), p. 727–745. doi: 10.5194/esurf-12-727-2024. Full text in Research Archive Show summary

  Ice cliffs are melt hot spots that contribute disproportionately to melt on debris-covered glaciers. In this study, we investigate the impact of supraglacial stream hydrology on ice cliffs using in situ and remote sensing observations, streamflow measurements, and a conceptual geomorphic model of ice cliff backwasting applied to ice cliffs on Kennicott Glacier, Alaska. We found that 33 % of ice cliffs (accounting for 69 % of the ice cliff area) are actively influenced by streams, while half are nearer than 10 m from the nearest stream. Supraglacial streams contribute to ice cliff formation and maintenance by horizontal meandering, vertical incision, and debris transport. These processes produce an undercut lip at the ice cliff base and transport clasts up to tens of centimeters in diameter, preventing reburial of ice cliffs by debris. Stream meander morphology reminiscent of sedimentary river channel meanders and oxbow lakes produces sinuous and crescent ice cliff shapes. Stream avulsions result in rapid ice cliff collapse and local channel abandonment. Ice cliffs abandoned by streams are observed to be reburied by supraglacial debris, indicating a strong role played by streams in ice cliff persistence. We also report on a localized surge-like event at the glacier's western margin which drove the formation of ice cliffs from crevassing; these cliffs occur in sets with parallel linear morphologies contrasting with the crescent planform shape of stream-driven cliffs. The development of landscape evolution models may assist in quantifying the total net effect of these processes on steady-state ice cliff coverage and mass balance, contextualizing them with other drivers including supraglacial ponds, differential melt, ice dynamics, and collapse of englacial voids.

• Piermattei, Livia; Zemp, Michael; Sommer, Christian; Brun, Fanny; Braun, Matthias H. & Andreassen, Liss M. [Show all 35 contributors for this article] (2024). Observing glacier elevation changes from spaceborne optical and radar sensors - an inter-comparison experiment using ASTER and TanDEM-X data. The Cryosphere. ISSN 1994-0416. 18(7), p. 3195–3230. doi: 10.5194/tc-18-3195-2024. Full text in Research Archive Show summary

  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.

• Vandecrux, Baptiste; Fausto, Robert S.; Box, Jason E.; Covi, Federico; Hock, Regine & Rennermalm, Åsa K. [Show all 18 contributors for this article] (2024). Recent warming trends of the Greenland ice sheet documented by historical firn and ice temperature observations and machine learning. The Cryosphere. ISSN 1994-0416. 18(2), p. 609–631. doi: 10.5194/tc-18-609-2024. Full text in Research Archive Show summary

  Surface melt on the Greenland ice sheet has been increasing in intensity and extent over the last decades due to Arctic atmospheric warming. Surface melt depends on the surface energy balance, which includes the atmospheric forcing but also the thermal budget of the snow, firn and ice near the ice sheet surface. The temperature of the ice sheet subsurface has been used as an indicator of the thermal state of the ice sheet's surface. Here, we present a compilation of 4612 measurements of firn and ice temperature at 10 m below the surface (T10 m) across the ice sheet, spanning from 1912 to 2022. The measurements are either instantaneous or monthly averages. We train an artificial neural network model (ANN) on 4597 of these point observations, weighted by their relative representativity, and use it to reconstruct T10 m over the entire Greenland ice sheet for the period 1950–2022 at a monthly timescale. We use 10-year averages and mean annual values of air temperature and snowfall from the ERA5 reanalysis dataset as model input. The ANN indicates a Greenland-wide positive trend of T10 m at 0.2 ∘C per decade during the 1950–2022 period, with a cooling during 1950–1985 (−0.4 ∘C per decade) followed by a warming during 1985–2022 (+0.7 ∘ per decade). Regional climate models HIRHAM5, RACMO2.3p2 and MARv3.12 show mixed results compared to the observational T10 m dataset, with mean differences ranging from −0.4 ∘C (HIRHAM) to 1.2 ∘C (MAR) and root mean squared differences ranging from 2.8 ∘C (HIRHAM) to 4.7 ∘C (MAR). The observation-based ANN also reveals an underestimation of the subsurface warming trends in climate models for the bare-ice and dry-snow areas. The subsurface warming brings the Greenland ice sheet surface closer to the melting point, reducing the amount of energy input required for melting. Our compilation documents the response of the ice sheet subsurface to atmospheric warming and will enable further improvements of models used for ice sheet mass loss assessment and reduce the uncertainty in projections.

• Schaffer, Nicole; Copland, Luke; Zdanowicz, Christian & Hock, Regine (2023). Modeling the surface mass balance of Penny Ice Cap, Baffin Island, 1959-2099. Annals of Glaciology. ISSN 0260-3055. p. 1–13. doi: 10.1017/aog.2023.68. Full text in Research Archive Show summary

  Abstract Glaciers of Baffin Island and nearby islands of Arctic Canada have experienced rapid mass losses over recent decades. However, projections of loss rates into the 21st century have so far been limited by the availability of model calibration and validation data. In this study, we model the surface mass balance of the largest ice cap on Baffin Island, Penny Ice Cap, since 1959, using an enhanced temperature index model calibrated with in situ data from 2006–2014. Subsequently, we project changes to 2099 based on the RCP4.5 climate scenario. Since the mid-1990s, the surface mass balance over Penny Ice Cap has become increasingly negative, particularly after 2005. Using volume–area scaling to account for glacier retreat, peak net mass loss is projected to occur between ~2040 and 2080, and the ice cap is expected to lose 22% (377.4 Gt or 60 m w.e.) of its 2014 ice mass by 2099, contributing 1.0 mm to sea level rise. Our 2015–2099 projections are approximately nine times more sensitive to changes in temperature than precipitation, with an absolute cumulative difference of 566 Gt (90 m w.e.) between +2 and −2°C scenarios, and 63 Gt (10 m w.e.) between +20% and −20% precipitation scenarios.

• Kochtitzky, William; Copland, Luke; Wychen, Wesley Van; Hock, Regine; Rounce, David R. & Jiskoot, Hester [Show all 23 contributors for this article] (2023). Progress toward globally complete frontal ablation estimates of marine-terminating glaciers. Annals of Glaciology. ISSN 0260-3055. 63(87-89), p. 143–152. doi: 10.1017/aog.2023.35. Full text in Research Archive Show summary

  Abstract 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.

• Rounce, David R.; Hock, Regine; Maussion, Fabien; Hugonnet, Romain; Kochtitzky, William & Huss, Matthias [Show all 13 contributors for this article] (2023). Global glacier change in the 21st century: Every increase in temperature matters. Science. ISSN 0036-8075. 379(6627), p. 78–83. doi: 10.1126/science.abo1324. Full text in Research Archive Show summary

  Glacier mass loss affects sea level rise, water resources, and natural hazards. We present global glacier projections, excluding the ice sheets, for shared socioeconomic pathways calibrated with data for each glacier. Glaciers are projected to lose 26 ± 6% (+1.5°C) to 41 ± 11% (+4°C) of their mass by 2100, relative to 2015, for global temperature change scenarios. This corresponds to 90 ± 26 to 154 ± 44 millimeters sea level equivalent and will cause 49 ± 9 to 83 ± 7% of glaciers to disappear. Mass loss is linearly related to temperature increase and thus reductions in temperature increase reduce mass loss. Based on climate pledges from the Conference of the Parties (COP26), global mean temperature is projected to increase by +2.7°C, which would lead to a sea level contribution of 115 ± 40 millimeters and cause widespread deglaciation in most mid-latitude regions by 2100.

• Hock, Regine; Maussion, Fabien; Marzeion, Benjamin & Nowicki, Sophie (2023). What is the global glacier ice volume outside the ice sheets? Journal of Glaciology. ISSN 0022-1430. 69(273), p. 204–210. doi: 10.1017/jog.2023.1. Full text in Research Archive Show summary

  Abstract A recent study (Millan and others, 2022 a , Nature Geoscience 15(2), 124–129) claims that ice volume contained in all glaciers outside the ice sheets and its potential contribution to sea level is 20% less than previously estimated. However, the apparent decrease is largely due to differences in choice of domain, as the study excludes 80% of the glacier area in the Antarctic periphery that was included in previous global glacier volume estimates. The issue highlights the difficulty in separating glaciers from the ice-sheet proper, especially in Antarctica, and the need for both the glacier and ice-sheet communities to develop standards and protocols to avoid double-counting in global ice volume and mass-change assessments and projections. Process-based inversion models have replaced earlier scaling methods, but large uncertainties in global glacier volume estimation remain due to the ill-posed nature of the inversion problem and poorly constrained parameters emphasizing the need for more direct ice thickness observations.

• Huang, Lei; Hock, Regine; Li, Xin; Bolch, Tobias; Yang, Kun & Wang, Ninglian [Show all 10 contributors for this article] (2022). Winter accumulation drives the spatial variations in glacier mass balance in High Mountain Asia. Science Bulletin. ISSN 2095-9273. 67(19), p. 1967–1970. doi: 10.1016/j.scib.2022.08.019. Full text in Research Archive
• Petersen, Eric; Hock, Regine; Fochesatto, Gilberto J. & Anderson, Leif S. (2022). The Significance of Convection in Supraglacial Debris Revealed Through Novel Analysis of Thermistor Profiles. Journal of Geophysical Research (JGR): Earth Surface. ISSN 2169-9003. 127(9). doi: 10.1029/2021JF006520. Full text in Research Archive Show summary

  Melt from debris-covered glaciers represents a regionally important freshwater source, especially in high-relief settings as found in central Asia, Alaska, and South America. Sub-debris melt is traditionally predicted from surface energy balance models that determine heat conduction through the supraglacial debris layer. Convection is rarely addressed, despite the porous nature of debris. Here we provide the first constraints on convection in supraglacial debris, through the development of a novel method to calculate individual conductive and nonconductive heat flux components from debris temperature profile data. This method was applied to data from Kennicott Glacier, Alaska, spanning two weeks in the summer of 2011 and two months in the summer of 2020. Both heat flux components exhibit diurnal cycles, the amplitude of which is coupled to atmospheric conditions. Mean diurnal nonconductive heat flux peaks at up to 43% the value of conductive heat flux, indicating that failure to account for it may lead to an incorrect representation of melt rates and their drivers. We interpret this heat flux to be dominated by latent heat as debris moisture content changes on a diurnal cycle. A sharp afternoon drop-off in nonconductive heat flux is observed at shallow depths as debris dries. We expect these processes to be relevant for other debris-covered glaciers. Debris properties such as porosity and tortuosity may play a large role in modulating it. Based on the present analysis, we recommend further study of convection in supraglacial debris for glaciers across the globe with different debris properties.

• Kochtitzky, William; Copland, Luke; Wychen, Wesley Van; Hugonnet, Romain; Hock, Regine & Dowdeswell, Julian A. [Show all 18 contributors for this article] (2022). The unquantified mass loss of Northern Hemisphere marine-terminating glaciers from 2000–2020. Nature Communications. 13(1). doi: 10.1038/s41467-022-33231-x. Full text in Research Archive Show summary

  Abstract In the Northern Hemisphere, ~1500 glaciers, accounting for 28% of glacierized area outside the Greenland Ice Sheet, terminate in the ocean. Glacier mass loss at their ice-ocean interface, known as frontal ablation, has not yet been comprehensively quantified. Here, we estimate decadal frontal ablation from measurements of ice discharge and terminus position change from 2000 to 2020. We bias-correct and cross-validate estimates and uncertainties using independent sources. Frontal ablation of marine-terminating glaciers contributed an average of 44.47 ± 6.23 Gt a −1 of ice to the ocean from 2000 to 2010, and 51.98 ± 4.62 Gt a −1 from 2010 to 2020. Ice discharge from 2000 to 2020 was equivalent to 2.10 ± 0.22 mm of sea-level rise and comprised approximately 79% of frontal ablation, with the remainder from terminus retreat. Near-coastal areas most impacted include Austfonna, Svalbard, and central Severnaya Zemlya, the Russian Arctic, and a few Alaskan fjords.

• Xiao, Jing; Rennermalm, Åsa K.; Covi, Federico; Hock, Regine; Leidman, Sasha Z. & Miège, Clément [Show all 8 contributors for this article] (2022). Local-scale spatial variability in firn properties in Southwest Greenland. Frontiers in Earth Science. 10. doi: 10.3389/feart.2022.938246. Full text in Research Archive Show summary

  The increasing mass loss from the Greenland ice sheet is becoming growingly important to present-day global sea level rise. Meltwater export to the ocean may be amplified by near-surface ice layers in firn (i.e., snow that has survived at least one melt season) which prevent infiltration. Such ice layers have been documented at various sites in southwest Greenland, but little is known about the local-scale (less than 1 km) variability in firn and ice properties. Here we investigate the local variability in firn density and ice content (ice layer thickness fraction) by analyzing 45 shallow firn cores retrieved from 15 sites in southwest Greenland between 2012 and 2019. The core dataset contains groups of cores that were collected at the same site (1–632 m apart from each other) and in the same year (here referred to as same site/year cores). The two-sided Mann-Whitney U -tests suggest that most same site/year cores do not have statistically significant differences in median density or ice content over the upper 0–4.5, 4.5–9, and 9–13.5 m sections below the winter snow layer. That said, the same site/year cores still exhibit substantial density and ice content differences as well as variable ice layer stratigraphy (especially the distribution of centimeters-thick ice lenses) not explainable by measurement uncertainties. The local-scale variability in density and ice content (calculated from the same site/year cores) over the three 4.5-m sections is 4% and 19–29%, respectively. The variability is comparable to the regional gradient in our study area within an elevation difference of up to ∼200 m. The local variability is non-negligible particularly at mid- to high-elevation sites (&amp;gt;2,000 m a.s.l.), where firn structure changes such as ice layer formation are more recent phenomena compared to lower elevations. This study confirms that single cores can provide representative bulk statistics such as mean density and ice content of one site. However, these mean values mask substantial local variability which can compromise regional comparisons. Therefore, collection of same site/year cores and consideration of local variability are necessary for an in-depth analysis of regional variability.

• Autin, P.; Sicart, J.E.; Rabatel, A.; Soruco, A. & Hock, Regine (2022). Climate Controls on the Interseasonal and Interannual Variability of the Surface Mass and Energy Balances of a Tropical Glacier (Zongo Glacier, Bolivia, 16°S): New Insights From the Multi-Year Application of a Distributed Energy Balance Model. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 127(7). doi: 10.1029/2021JD035410. Full text in Research Archive Show summary

  The application of a distributed energy balance model over nine years at an hourly time step to a 20 × 20 m grid cell over Glacier Zongo (Bolivia, 16°S) enabled assessment of the climate factors that control the interseasonal and interannual variability of its surface mass balance. The model was validated by comparing the measured and simulated discharge at the outlet, albedo at the Automatic Weather Station, surface state and annual mass balance both glacier-wide and as a function of altitude. Analysis of the mean monthly energy fluxes highlighted the importance of the meteorological conditions over October and November on the variability of the annual surface mass balance. Two sensitivity analyses are presented, one of the distribution of precipitation over time which maintains a physical coherence between the different meteorological variables and one of the impact of prolonged periods of intense cloud radiative forcing on the surface mass balance. The distribution of precipitation events over time and their associated amounts are the main drivers of the interannual variability of the surface mass balance via an albedo feedback effect. Additionally, prolonged periods of negative cloud radiative forcing, specifically over the month of November, notably reduce the melt rate.

• Covi, Federico; Hock, Regine & Reijmer, Carleen H. (2022). Challenges in modeling the energy balance and melt in the percolation zone of the Greenland ice sheet. Journal of Glaciology. ISSN 0022-1430. 69(273), p. 164–178. doi: 10.1017/jog.2022.54. Full text in Research Archive Show summary

  Increased surface melt in the percolation zone of the Greenland ice sheet causes significant changes in the firn structure, directly affecting the amount and timing of meltwater runoff. Here we force an energy-balance model with automatic weather stations data at two sites in the percolation zone of southwest Greenland (2040 and 2360 m a.s.l.) between spring and fall 2019. Extensive model validation and sensitivity analysis reveal that the skin layer formulation used to compute the surface temperature by closing the energy balance leads to a consistent overestimation of melt by more than a factor of two or three depending on the site. In contrast, model results match the observations well when the model is forced by observed surface temperatures; however, unexplained residuals in the energy balance occur. The sensible and ground heat flux differ markedly in the two simulations accounting largely for the difference in modeled melt amounts. This indicates that the energy available for melt is highly sensitive to small changes in surface temperature. Thus, regional climate models that also use the skin layer formulation may have a bias in surface temperature and melt energy in the percolation zone of the ice sheet.

• Windnagel, Ann; Hock, Regine; Maussion, Fabien; Paul, Frank; Rastner, Philipp & Raup, Bruce [Show all 7 contributors for this article] (2022). Which glaciers are the largest in the world? Journal of Glaciology. ISSN 0022-1430. 69(274), p. 301–310. doi: 10.1017/jog.2022.61. Full text in Research Archive Show summary

  Abstract Glacier monitoring has been internationally coordinated for more than 125 years. Despite this long history, there is no authoritative answer to the popular question: ‘Which glaciers are the largest in the world?’ Here, we present the first systematic assessment of this question and identify the largest glaciers in the world – distinct from the two ice sheets in Greenland and Antarctica but including the glaciers on the Antarctic Peninsula. We identify the largest glaciers in two domains: on each of the seven geographical continents and in the 19 first-order glacier regions defined by the Global Terrestrial Network for Glaciers. Ranking glaciers by area is non-trivial. It depends on how a glacier is defined and mapped and also requires differentiating between a glacier and a glacier complex, i.e. glaciers that meet at ice divides such as ice caps and icefields. It also depends on the availability of a homogenized global glacier inventory. Using separate rankings for glaciers and glacier complexes, we find that the largest glacier complexes have areas on the order of tens of thousands of square kilometers whereas the largest glaciers are several thousands of square kilometers. The world's largest glaciers and glacier complexes are located in the Antarctic, Arctic and Patagonia.

• Yang, Ruitang; Hock, Regine; Kang, Shichang; Guo, Wanqin; Shangguan, Donghui & Jiang, Zongli [Show all 7 contributors for this article] (2022). Glacier Surface Speed Variations on the Kenai Peninsula, Alaska, 2014–2019. Journal of Geophysical Research (JGR): Earth Surface. ISSN 2169-9003. 127(3). doi: 10.1029/2022JF006599. Full text in Research Archive Show summary

  To characterize the spatiotemporal variations of glacier surface speed on the Kenai Peninsula, Alaska (∼3,900 km2), we derived 92 surface speed fields between October 2014 and December 2019 using intensity offset tracking on Sentinel-1 data. On average, speeds are 50% greater in spring (March-May) than the annual mean (69 m a−1) while winter speeds are close to the annual mean. While marine-terminating glaciers have their maximum speed near the terminus, both land- and lake-terminating glaciers flow fastest around the median glacier elevation. On average, the lake-terminating and tidewater glaciers flow 1.7 and 2.3 times faster than the land-terminating glaciers, respectively. Monthly variations over the 5-year period are strikingly synchronous regardless of terminus type suggesting that regional-scale meteorological drivers govern the temporal variability. Mean annual speeds fluctuate roughly ±10% of the period mean without an apparent trend. At lake-terminating Bear Glacier, a short-term tripling in ice speed in fall 2019 over the area below an ice-dammed lake coincides with an observed glacier lake outburst flood (GLOF). An earlier GLOF caused a persistent breach of the beach barrier between the proglacial lake and ocean which likely led to overall speed-up of the lower glacier part throughout 2019. A significant speedup was also observed at the lower part of the lake-terminating Ellsworth Glacier and attributed to rapid glacier retreat and lake expansion, probably further amplified by the terminus area becoming buoyant and a large tabular iceberg breaking off. Our results highlight the impact of GLOFs and proglacial characteristics in spatial and temporal glacier speed variations.

• Autin, Philémon; Sicart, Jean Emmanuel; Rabatel, Antoine; Hock, Regine & Jomelli, Vincent (2022). Climate reconstruction of the Little Ice Age maximum extent of the tropical Zongo Glacier using a distributed energy balancemodel. Comptes rendus Geoscience. ISSN 1631-0713. 355(S1). doi: 10.5802/crgeos.145. Full text in Research Archive Show summary

  This study assessed the climate conditions that caused the tropical Zongo Glacier (16° S, Bolivia) to reach its Little Ice Age (LIA) maximum extent in the late 17th century. We carried out sensitivity analyses of the annual surface mass balance to different physically coherent climate scenarios constrained by information taken from paleoclimate proxies and sensitivity studies of past glacier advances. These scenarios were constrained by a 1.1 K cooling and a 20% increase in annual precipitation compared to the current climate. Seasonal precipitation changes were constructed using shuffled input data for the model: measurements of air temperature and relative humidity, precipitation, wind speed, incoming short and longwave radiation fluxes, and assessed using a distributed energy balance model. They were considered plausible if conditions close to equilibrium glacier-wide mass balance were obtained. Results suggest that on top of a 1.1 K cooling and 20% increase in annual precipitation, only two seasonal precipitation patterns allow LIA equilibrium: evenly distributed precipitation events across the year and an early wet season onset.

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• Hock, Regine (2025). Density and ice layer stratigraphy in 16 firn cores from Austfonna, Svalbard, 1958-2022. Full text in Research Archive
• Hock, Regine (2025). Global glacier modeling – Recent progress and projections. Full text in Research Archive
• Hock, Regine (2025). Can we geo-engineer a way out of climate change and sea-level rise? Full text in Research Archive
• Yang, Ruitang (2025). Frontal ablation modeling in the global glacier model. Full text in Research Archive
• Hock, Regine (2025). Interview. [TV]. French National TV (TF1). Full text in Research Archive
• Hock, Regine (2025). Interview glacier melt. [Radio]. BBC. Full text in Research Archive
• Hock, Regine (2025). Glacier hazards - Will they change in the future ? Full text in Research Archive
• Hock, Regine (2025). Global glacier meltdown - Every degree temperature increase matters. Full text in Research Archive
• Aalstad, Kristoffer; Guillet, Gregoire; Yang, Ruitang; Yilmaz, Yeliz & Hock, Regine (2025). Glacier reanalysis using hierarchical data assimilation. Full text in Research Archive
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Guillet, Gregoire & Hock, Regine (2025). Strategies for Future Projections with PyGEM. Full text in Research Archive
• Hock, Regine (2024). Stream hydrology controls on ice cliff generation, evolution, and survival on debris-covered glaciers. Full text in Research Archive
• Hock, Regine (2024). The SUMup collaborative database: Surface mass balance, subsurface temperature and density measurements from the Greenland and Antarctic ice sheets. doi: https:/arcticdata.io/catalog/view/doi:10.18739/A2M61BR5M. Full text in Research Archive
• Vandecrux, Baptiste; Amory, Charles; Ahlstrøm, Andreas P.; Akers, Pete D.; Albert, Mary & Alley, Richard B. [Show all 103 contributors for this article] (2024). The SUMup collaborative database: Surface mass balance, subsurface temperature and density measurements from the Greenland and Antarctic ice sheets (2025 release). doi: 10.18739/A2M61BR5M. Full text in Research Archive
• Hock, Regine (2024). Glaciers and sea-level rise. Full text in Research Archive
• Hock, Regine (2024). Global glacier projections and Paris Limits. Full text in Research Archive
• Hock, Regine (2024). Response of high mountain glaciers to climate change - Every increase in temperature matters ! Full text in Research Archive
• Hock, Regine (2024). How much global glacier mass loss is committed under policy-relevant global warming scenarios? Full text in Research Archive
• Hock, Regine (2024). Complex pattern of subsurface water flow at the rising limit of runoff in Greenland firn. Full text in Research Archive
• Yang, Ruitang; Hock, Regine; Rounce, David & Kang, Shichang (2024). Regional scale response of glacier speed to seasonal runoff variations on the Kenai Peninsula, Alaska. Full text in Research Archive
• Yang, Ruitang; Ultee, Lizz; Hock, Regine; Debolskiy, Matvey V. & Rounce, David (2024). Modeling frontal ablation in a global glacier evolution model. Full text in Research Archive
• Hock, Regine & Truffer, Martin (2024). Glacier hazards: Will they change in the future? Arctic, Antarctic and Alpine research. ISSN 1523-0430. 56(1). doi: 10.1080/15230430.2024.2335991. Full text in Research Archive
• Yang, Ruitang (2024). Modeling frontal ablation in a global glacier evolution model. Full text in Research Archive
• Aalstad, Kristoffer; Hock, Regine; Mazzolini, Marco; Pirk, Norbert; Treichler, Désirée & Westermann, Sebastian [Show all 9 contributors for this article] (2024). Ensemble-Based Reanalysis of the Terrestrial Cryosphere. Full text in Research Archive Show summary

  The terrestrial cryosphere in the form of glaciers, permafrost, and seasonal snow, plays a vital role in the climate system by regulating the global cycles of energy, carbon, and water. As a result, these components of the cryosphere are considered essential climate variables (ECVs) by the Global Climate Observing System. At the same time, these ECVs are only partially observable by Earth observing satellites due to gaps, noise, and indirect retrieval algorithms. The statistical fusion of uncertain models and noisy observations referred to as data assimilation in geoscience represents a natural solution to this problem of partial observability. Nonetheless, beyond the confines of weather prediction and atmospheric reanalyses, data assimilation has received relatively little attention in broader Earth system science despite its potential for adding value to observations by filling gaps and inferring latent ECVs with uncertainty quantification. In this contribution, we present ongoing efforts in several projects applying ensemble-based (probabilistic) data assimilation techniques to carry out long term and large scale reanalyses of the terrestrial cryosphere. Our lofty goals in these projects are to generate global high resolution multi-decadal ensemble-based reanalyses of glacier mass balance, the thermal state of permafrost, and seasonal snow mass. In doing so, we are leveraging a plethora of emerging data from Earth observing satellites, global atmospheric reanalyses, and in-situ observations. Herein, we will focus mainly on the general implementation of the novel ensemble-based methods that we are using to solve the reanalysis (or reconstruction) problem as opposed to the structure of the specific cryospheric models and data that they are applied to. Considerable emphasis is placed on how these methods can be deployed at unprecedented spatio-temporal scales while retaining uncertainty quantification that is crucial in guiding decisions. Looking further ahead, we will highlight the challenges that remain in pushing the boundaries of terrestrial reanalysis efforts towards the hillslope (100 m) scale and making use of the largely untapped and continuously growing stream of Earth observation data.

• Hock, Regine (2023). Radio interview. [Radio]. BBC. Full text in Research Archive
• Hock, Regine (2023). Radio interview. [Radio]. Hessischer Rundfunk Germany. Full text in Research Archive
• Hock, Regine (2023). Global glacier melt. Full text in Research Archive
• Hock, Regine (2023). Glacier meltdown - Every increase in temperature matters ! Full text in Research Archive
• Rounce, David; Hock, Regine & Maussion, Fabien (2023). The loss of our glaciers over the 21st century: a future we can control. TheScienceBreaker. ISSN 2571-9262. doi: 10.25250/thescbr.brk749. Full text in Research Archive
• Hock, Regine (2023). World-wide glacier meltdown and how it impacts hazards. Full text in Research Archive
• Hock, Regine (2023). World-wide glacier meltdown - Why should we care? Full text in Research Archive
• Hock, Regine (2023). World-wide glacier meltdown: Implications for global sea level and streamflow. Full text in Research Archive
• Yang, Ruitang (2023). Towards more physical modeling of frontal ablation of marine- and lake-terminating glaciers in a global glacier evolution model. Full text in Research Archive
• Hock, Regine (2022). fmaussion/global_glacier_volume_paper: v1.1 (v1.1) [Data set]. Full text in Research Archive
• Maussion, Fabien & Hock, Regine (2022). fmaussion/global_glacier_volume_paper: v1.1. doi: 10.5281/ZENODO.7492152. Full text in Research Archive
• Hock, Regine (2022). High Mountain Asia PyGEM Glacier Projections with RCP Scenarios, Version 1. Full text in Research Archive
• Hock, Regine (2022). Resampled density in 48 shallow firn cores from Southwest Greenland, 2012–2019. Full text in Research Archive
• Hock, Regine (2022). Global PyGEM-OGGM Glacier Projections with RCP and SSP Scenarios, Version 1. Full text in Research Archive
• Yang, Ruitang (2022). Influence of glacier runoff on seasonal ice-speed variations on the Kenai Peninsula, Alaska. Full text in Research Archive
• Hock, Regine (2022). Future global glacier mass changes and their impact on sea level and streamflow. Full text in Research Archive
• Hock, Regine (2022). Glacier mass and surface speed
 variations on the Kenai Peninsula, Alaska. Full text in Research Archive
• Hock, Regine (2022). Every degree of temperature increase matters for future global glacier change. Full text in Research Archive

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