Regine Hock

• Hock, Regine; Huss, Matthias; Berthier, Etienne; Braun, Matthias; Gardner, Alex S. & Wouters, Bert [Vis alle 7 forfattere av denne artikkelen] (2026). Toward improved comparability of glacier mass-balance estimates: Challenges and recommendations. Journal of Glaciology. ISSN 0022-1430. 72. doi: 10.1017/jog.2026.10158. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Observing glacier mass changes is essential for understanding and projecting the impacts of climate change on sea-level rise, water resources and natural hazards, as well as providing data for developing, calibrating and validating glacier evolution models. The principal methods used to measure glacier mass changes — glaciological, geodetic (surface elevation differencing) and gravimetric — differ in the spatial and temporal scales at which they are most effectively applied. Here, we review these methods in the context of challenges that arise when comparing published mass-balance estimates. Compatibility can be hampered by (1) inconsistent reporting and lack of relevant information; (2) discrepancies in which mass-balance components are included; (3) differences in the time span analyzed; and (4) variations in the spatial domain of the reported mass balance. We provide recommendations for more rigorous and comprehensive reporting of mass-balance estimates to improve comparability and synthesis of reported glacier mass changes, and we emphasize open data and code sharing to enable full reproducibility and future reinterpretation. Our recommendations apply equally to both glacier and ice-sheet mass-balance reporting, and they are generally valid for mass balances simulated by numerical models.

• Cao, Bo; Hock, Regine; Geng, Haopeng; Wu, Guangjian & Pan, Baotian (2026). Glacier changes and their impact on water resources in the qilian mountains, China between 1970 and 2020. Frontiers in Earth Science. 14. doi: 10.3389/feart.2026.1708150. Fulltekst i vitenarkiv Vis sammendrag

  Changes in glacier meltwater runoff in the Qilian Mountains situated on the northeastern edge of the Tibetan Plateau are important for sustaining water resources in the arid regions of Northwest China. Combining multi-period remote sensing, historical data and modeling, we evaluate the glacier mass and area changes as well as associated runoff change of all glaciers in the area. Glacier area shrunk by 516.8 km 2 (∼26%, 0.53% ± 0.15% a −1 ) between 1970 and 2020 and glacier surface elevation change was −0.35 ± 0.04 m a −1 between 2000 and 2014. In general, glaciers in the eastern Qilian Mountains retreated faster than those in the western part. A mass balance model calibrated against geodetic estimates derived from DEM differencing was used to reconstruct annual glacier mass changes and runoff from 1990 to 2017. Across the 11 glacierized large-scale river basins (0.02%–2.5% glacierization), the index-based glacier runoff ratio relative to basin water input ranged from 0.1% to 6.2%. Results show an increase in glacier runoff volumes during 1990–2001, but no statistically significant trend thereafter (2002–2017) despite increasing glacier thinning. This slowdown is attributed to decreasing glacier area as the glaciers retreated. Overall, our findings highlight that while glacier runoff continues to play a critical role in sustaining river runoff in the Qilian Mountains, its buffering effect is weakening as glacier runoff approach peak water, implying increasing vulnerability of regional water resources to precipitation variability under future climate change.

• Frank, T.; Pelt, W. J.J. van; Rounce, D. R.; Jouvet, G. & Hock, Regine (2026). Global glacier-free topography reveals a large potential for future lakes in presently ice-covered terrain. Nature Communications. 17(1). doi: 10.1038/s41467-026-72548-9. Fulltekst i vitenarkiv
• Prusevich, A. A.; Lammers, R. B.; Grogan, D. S.; Zuidema, S.; Meko, D. M. & Rounce, D. R. [Vis alle 8 forfattere av denne artikkelen] (2025). Decomposing land surface total water storage in the Indus, Ganges, and Brahmaputra basins. Frontiers in Earth Science. 13. doi: 10.3389/feart.2025.1551218. Fulltekst i vitenarkiv Vis sammendrag

  Introduction The goal of this study is to decompose the influence of specific hydrologic reservoirs in the Earth’s critical zone that interact to create observed total water supply (TWS) anomalies in the highly altered and densely populated Indus, Ganges, and Brahmaputra drainage basins. Understanding the contributions to TWS anomalies can help find potential solutions for the sustainability of human water supply. Methods We compare changes in the macroscale hydrology of three important High Mountain Asian drainage basins through seasonal and long-term trends in TWS. Statistical time-series analysis of nine individual TWS components modeled by a hydrologic model are used to simulate water storage terms. Results Long-term TWS trends look similar across the study basins, we find that the drivers and causes of trends and their seasonal variability are fundamentally different in each basin. TWS declines in the Indus and Ganges watersheds are primarily driven by the depletion of aquifers (67% and 76%, respectively) due to irrigated land expansion and water overuse. The Brahmaputra lower aquifer water use stress, and its TWS drop is mostly due to the melting of glaciers, the highest rate over all three basins. The Ganges and Brahmaputra have a quasi-monotonic decline of TWS, and the Indus basin exhibits a non-monotonic trend line of TWS due to different stages of its aquifer depletion relevant to aquifer water accessibility limited by well depth thresholds. Seasonal variability is primarily controlled by soil moisture saturation, shallow groundwater levels, reservoir storage, and snow accumulation for the Ganges and Brahmaputra basins. The Indus is driven by high mountain storage of snow and glaciers. Discussion The combination of hydrologic modeling and gravity observations show the effectiveness of identifying the critical components that make up TWS. Understanding the spatially heterogeneous drivers of observed TWS decline allows us to translate satellite observations into policy-relevant information. Because this functionality is built within a process-based hydrological model, future projections can illuminate those aspects of the hydrological cycle that require additional attention by decision makers to ensure adequate water resources are available for all.

• Rounce, David R.; Hock, Regine; Prusevich, Alexander A.; Grogan, Danielle S.; Lammers, Richard B. & Huss, Matthias [Vis alle 8 forfattere av denne artikkelen] (2025). Downstream Hydrology Reduces Glaciers' Direct Contribution to Sea‐Level Rise. Geophysical Research Letters. ISSN 0094-8276. 52(10). doi: 10.1029/2025gl114866. Fulltekst i vitenarkiv Vis sammendrag

  Glacier mass loss is a primary contributor to sea‐level rise. All prior assessments assume all glacial melt water reaches the ocean, but many mountain glaciers are located far from oceans and may be affected by the downstream systems. Here we track future glacier runoff through the hydrological system and estimate ∼95% directly reaches the ocean through the river systems for all emissions scenarios, while the remaining 5% is lost (consumed) via evapotranspiration or stored on land. Endorheic basins in High Mountain Asia account for 76%–82% of the glacier runoff that does not directly reach the ocean. The remaining 18%–24% is lost or stored in exorheic basins, including those with considerable anthropogenic water use like the Indus and Ganges. While the percentage of glacier runoff reaching the ocean differs between basins, the percentages are roughly constant over time for most basins.

• Covi, Federico; Hock, Regine; Rennermalm, Åsa; Fettweis, Xavier & Noël, Brice (2025). Spatiotemporal variability of air temperature biases in regional climate models over the Greenland ice sheet. Journal of Glaciology. ISSN 0022-1430. 71. doi: 10.1017/jog.2025.38. Fulltekst i vitenarkiv Vis sammendrag

  Regional climate models (RCMs) are fundamental tools in understanding and quantifying the contribution of the Greenland ice sheet to sea-level rise. We perform an extensive evaluation of the daily air temperature simulated by two RCMs, MARv3.12 and RACMO $2.3\text{p}2$ , and a global atmospheric reanalysis, ERA5, at 35 locations across the ice sheet over the period 1995–2020. We compare model results to weather station data from two climate networks, focusing on the spatial and temporal variability in mean biases (MBs). All three models perform well at low elevations (<1500 m a.s.l.) with an MB of 0.16 ∘ C (MAR), $0.36^{\circ}\mathrm{C}$ (RACMO) and $0.41^{\circ}\mathrm{C}$ (ERA5), while warm biases (>1.70 $^{\circ}\mathrm{C}$ ) are found at high elevations (>1500 m a.s.l.). Temperature biases exhibit a strong seasonality, being more pronounced during winter and much smaller during summer ranging from $0.11^{\circ}\mathrm{C}$ to $0.59^{\circ}\mathrm{C}$ . No interannual variability is found in the biases of all three datasets. Daily variability within each month is captured well by both climate models and the reanalysis at most locations. Finally, all three models perform overall better in the ablation zone during summer, i.e. where and when considerable melt production occurs.

• Zekollari, Harry; Schuster, Lilian; Maussion, Fabien; Hock, Regine; Marzeion, Ben & Rounce, David R. [Vis alle 21 forfattere av denne artikkelen] (2025). Glacier preservation doubled by limiting warming to 1.5°C versus 2.7°C. Science. ISSN 0036-8075. 388(6750), s. 979–983. doi: 10.1126/science.adu4675. Fulltekst i vitenarkiv Vis sammendrag

  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), s. 4023–4044. doi: 10.5194/gmd-18-4023-2025. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Siegert, Martin; Sevestre, Heïdi; Bentley, Michael J.; Brigham-Grette, Julie; Burgess, Henry & Buzzard, Sammie [Vis alle 42 forfattere av denne artikkelen] (2025). Safeguarding the polar regions from dangerous geoengineering: a critical assessment of proposed concepts and future prospects. Frontiers in Science. ISSN 2166-6083. 3. doi: 10.3389/fsci.2025.1527393. Fulltekst i vitenarkiv Vis sammendrag

  Fossil-fuel burning is heating the planet with catastrophic consequences for its habitability and for the natural world on which our existence depends. Halting global warming requires rapid and deep decarbonization to “net zero” carbon dioxide (CO 2 ) emissions, which needs to be achieved by 2050 if warming is to remain within the limits set out by the 2015 Paris Agreement. However, some scientists and engineers claim that a mid-century decarbonization target will not be reached, and they propose that we should focus on technological geoengineering “fixes” or “climate interventions” that could delay or mask some of the impacts of global warming. They often cite the need to slow warming in polar regions because they are experiencing rates of warming higher than the global average, with severe and irreversible projected consequences both locally (e.g., on fragile ecosystems) and globally (e.g., on sea level). Several geoengineering concepts exist for polar regions, but they have not been fully examined by the polar science community, nor integrated with an understanding of polar dynamics and responses. Here, we evaluate five of those polar geoengineering concepts and highlight the significant issues and risks relating to technological availability, logistical feasibility, cost, predictable adverse consequences, environmental damage, scalability (in space and time), governance, and ethics. According to our expert assessment, none of these geoengineering ideas pass scrutiny regarding their use in the coming decades. Instead, we find that the proposed concepts would be environmentally dangerous. It is clear to us that the assessed approaches are not feasible, and that further research into these techniques would not be an effective use of limited time and resources. It is vital that these ideas do not distract from the priority to reduce greenhouse gas (GHG) emissions or from the critical need to conduct fundamental research in the polar regions.

• 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. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 9 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv Vis sammendrag

  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. [Vis alle 9 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• 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. Fulltekst i vitenarkiv Vis sammendrag

  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), s. 727–745. doi: 10.5194/esurf-12-727-2024. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Vandecrux, Baptiste; Fausto, Robert S.; Box, Jason E.; Covi, Federico; Hock, Regine & Rennermalm, Åsa K. [Vis alle 18 forfattere av denne artikkelen] (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), s. 609–631. doi: 10.5194/tc-18-609-2024. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Johnson, Andrew; Aschwanden, Andy; Albrecht, Torsten & Hock, Regine (2023). Range of 21st century ice mass changes in the Filchner-Ronne region of Antarctica. Journal of Glaciology. ISSN 0022-1430. 69(277), s. 1203–1213. doi: 10.1017/jog.2023.10. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Increases in ocean temperatures in the Filchner Ronne region of Antarctica are likely to result in increased ice mass loss and sea level rise. We constrain projections of the 21st century sea level contribution of this region using process-based ice-sheet modeling, with model parameters controlling ice dynamics calibrated using observed surface speeds and Markov-chain Monte Carlo sampling. We use climate forcing from Representative Concentration Pathway (RCP) scenarios as well as a set of hypothetical scenarios of deep ocean warming to evaluate the sensitivity of this region to ocean temperatures. Projected changes in regional ice mass correspond to a decrease in global mean sea level of 24±7 mm over 2015–2100 under RCP 2.6 and 28±9 mm under RCP 8.5. Increased regional inland surface accumulation related to higher warming levels in RCP 8.5 leads to more ice above flotation, offsetting increased ice shelf basal melt. The tests involving step changes in ocean temperatures with constant surface forcing show that one degree of ocean warming from present results in an additional +11 mm contribution to sea level by 2100 and 1% of the ice-covered area in the domain becomes ungrounded (23 200 km 2 ). The rate of mass loss with temperature increases at higher temperatures.

• Abdel-Fattah, Dina Tarek; Danielson, Mats; Ekenberg, Love; Hock, Regine & Trainor, Sarah (2023). Application of a structured decision-making process in cryospheric hazard planning: Case study of Bering Glacier surges on local state planning in Alaska. Journal of Multi-Criteria Decision Analysis. ISSN 1057-9214. 31(1-2). doi: 10.1002/mcda.1825. Fulltekst i vitenarkiv Vis sammendrag

  Surging glaciers are glaciers that experience rapidly accelerated glacier flow over a comparatively short period of time. Though relatively rare worldwide, Alaska is home to the largest number of surge-type glaciers globally. However, their impact on the broader socioecological system in the state is both poorly understood and underresearched, which poses a challenge in developing appropriate sustainability decisions in Alaska. We investigated how the surge patterns of the Bering Glacier in Alaska have potentially devastating effects on the local ecological biodiversity of its watershed via a structured decision-making analysis of the different possible consequences. Specifically, this analysis was conducted to explore the various outcomes of a Bering Glacier surge particularly if humans have an increased presence near the glacier due to the area potentially becoming a state park. This work explored the benefits of applying a risk and decision analytical framework in a cryosphere context, to better understand the socioeconomic impact of glacier surges. This is a novel approach in which a decision analysis tool was used to better understand an environmental sustainability challenge, offering an innovative method to support the achievement of the United Nations Sustainability Development Goals in Alaska. We therefore emphasise the need for integrated biophysical and socioeconomic analyses when it comes to understanding glacier hazards. Our research highlights the importance of understanding and researching biophysical changes as well as using a structured decision-making process for complicated hazard planning scenarios, exemplified via glaciated regions in Alaska, in order to create adaptation strategies that are sustainable and encompass the range of possible outcomes.

• 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. s. 1–13. doi: 10.1017/aog.2023.68. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 23 forfattere av denne artikkelen] (2023). Progress toward globally complete frontal ablation estimates of marine-terminating glaciers. Annals of Glaciology. ISSN 0260-3055. 63(87-89), s. 143–152. doi: 10.1017/aog.2023.35. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Debolskiy, Matvey; Hock, Regine; Alexeev, Vladimir A. & Romanovsky, Vladimir E. (2023). Topographic controls of water balance response to air temperature increase in permafrost-affected watersheds. Frontiers in Earth Science. 11. doi: 10.3389/feart.2023.1288680. Fulltekst i vitenarkiv Vis sammendrag

  Observed increases in runoff in permafrost regions have not only been associated with changes in air temperature and precipitation but also changes in hydrological pathways caused by permafrost thaw, however, the causes and detailed processes are still a matter of debate. In this study, we apply the physically-based hydrological model WaSIM to idealized small watersheds with permafrost to assess the response of total runoff and its components surface runoff, interflow, and baseflow to atmospheric warming. We use an idealized warming scenario defined by steady atmospheric warming (only in winter) over 100 years followed by 900 years of constant air temperatures leading to permafrost thaw. Sensitivity experiments include 12 watershed configurations with different assumptions on slope, profile curvature, and hydraulic conductivity. Results indicate that when subsurface conditions allow for faster lateral flow, at the end of the warming scenario the watersheds with steeper slopes or negative (convex) profile curvature, and thus larger unsaturated zones, experience delayed permafrost thaw due to decreased thermal conductivity and lower initial soil temperatures compared to watersheds with gentle slopes or positive (concave) curvature. However, in the long term, they exhibit a higher increase in annual runoff and baseflow (and subsequently winter runoff) than watersheds with lower hydraulic conductivity and/or more gentle terrain. Moreover, after the warming, for watersheds in which permeability at depth is lower than in near-surface soil, steeper slopes facilitate a significant reduction of the increase in baseflow (and winter runoff) and instead promote interflow generation compared to the watersheds with gentle slopes or lower near-surface permeability. For the watersheds with less permeable soil, a steeper slope facilitates a lesser decrease in interflow, and the increase in total runoff is delayed. In addition, water balance response to the warming has little sensitivity to profile curvature when hydraulic conductivity is low. On the other hand, in watersheds with high hydraulic conductivity, profile curvature can considerably alter water balance response to warming. Convex watersheds exhibit a larger (albeit delayed) increase in runoff and baseflow (and associated decrease in interflow generation) compared to those with zero or positive profile curvature.

• Rounce, David R.; Hock, Regine; Maussion, Fabien; Hugonnet, Romain; Kochtitzky, William & Huss, Matthias [Vis alle 13 forfattere av denne artikkelen] (2023). Global glacier change in the 21st century: Every increase in temperature matters. Science. ISSN 0036-8075. 379(6627), s. 78–83. doi: 10.1126/science.abo1324. Fulltekst i vitenarkiv Vis sammendrag

  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), s. 204–210. doi: 10.1017/jog.2023.1. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 10 forfattere av denne artikkelen] (2022). Winter accumulation drives the spatial variations in glacier mass balance in High Mountain Asia. Science Bulletin. ISSN 2095-9273. 67(19), s. 1967–1970. doi: 10.1016/j.scib.2022.08.019. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv Vis sammendrag

  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. [Vis alle 18 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 8 forfattere av denne artikkelen] (2022). Local-scale spatial variability in firn properties in Southwest Greenland. Frontiers in Earth Science. 10. doi: 10.3389/feart.2022.938246. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv Vis sammendrag

  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), s. 164–178. doi: 10.1017/jog.2022.54. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 7 forfattere av denne artikkelen] (2022). Which glaciers are the largest in the world? Journal of Glaciology. ISSN 0022-1430. 69(274), s. 301–310. doi: 10.1017/jog.2022.61. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 7 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Rounce, David; Hock, Regine; McNabb, Robert Whitfield; Millan, R; Sommer, C & Braun, M. H. [Vis alle 11 forfattere av denne artikkelen] (2021). Distributed global debris thickness estimates reveal debris significantly impacts glacier mass balance. Geophysical Research Letters. ISSN 0094-8276. 48(8). doi: 10.1029/2020GL091311. Fulltekst i vitenarkiv Vis sammendrag

  Supraglacial debris affects glacier mass balance as a thin layer enhances surface melting, while a thick layer reduces it. While many glaciers are debris-covered, global glacier models do not account for debris because its thickness is unknown. We provide the first globally distributed debris thickness estimates using a novel approach combining sub-debris melt and surface temperature inversion methods. Results are evaluated against observations from 22 glaciers. We find the median global debris thickness is ∼0.15 ± 0.06 m. In all regions, the net effect of accounting for debris is a reduction in sub-debris melt, on average, by 37%, which can impact regional mass balance by up to 0.40 m water equivalent (w.e.) yr-1. We also find recent observations of similar thinning rates over debris-covered and clean ice glacier tongues is primarily due to differences in ice dynamics. Our results demonstrate the importance of accounting for debris in glacier modeling efforts.

• Luo, L; Zhang, Jing; Hock, Regine & Yao, Y (2021). Case study of blowing snow impacts on the Antarctic Peninsula low atmosphere and surface simulated over with a snow/ice enhanced WRF model. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 126(2). doi: 10.1029/2020JD033936. Fulltekst i vitenarkiv Vis sammendrag

  To better capture the air-snow-ice interaction, a snow/ice enhanced Weather Research and Forecasting (WRF-ice) model has been developed. This study examines the performance of WRF-ice and its blowing snow component during a strong cyclone event from October 23 to 27, 2017 over the Antarctic Peninsula, which is characterized by a synoptic cyclone crossing the northern part of the Peninsula and an embodied mesoscale cyclone over the Weddell Sea. Evolution of the cyclone is accurately reproduced in the 5-km resolution WRF-ice simulation, and the simulated near-surface conditions agree well with station and satellite observations. Numerical simulations show that the process of blowing snow sublimation can be prominent within the lower atmosphere when the air is dry, and produces moistening and cooling effects. Over relatively warm and humid areas, cloud enhancement by blowing snow can lead to either colder or warmer surfaces because of competing effects of longwave and shortwave cloud radiative forcings. In particular, additional moisture from blowing snow sublimation can slightly intensify precipitation over the mountains. Surface energy budget analysis indicates that absorbed shortwave (Sa), incoming longwave (Ld), and outgoing longwave (Lu) are dominant components of surface energy budget. When increases in Ld, Lu, and sensible heat flux are combined with decreases in Sa and latent heat flux due to blowing snow effects, a negative surface net heat flux (∼0.5 W/m2) occurs during daytime. A positive domain-total surface mass balance (∼0.43 Gt) is generated during the simulated cyclone event due to increases in precipitation, decreases in runoff, and decreases in sublimation.

• Rennermalm, Åsa; Hock, Regine; Covi, Federico; Xiao, Jing; Corti, Giovanni & Kingslake, Johnny [Vis alle 13 forfattere av denne artikkelen] (2021). Shallow firn cores 1989-2019 in southwest Greenland's percolation zone reveal decreasing density and ice layer thickness after 2012. Journal of Glaciology. ISSN 0022-1430. 68(269), s. 431–442. doi: 10.1017/jog.2021.102. Fulltekst i vitenarkiv
• Debolskiy, Matvey; Alexeev, Vladimir; Hock, Regine; Lammers, Richard; Shiklomanov, Alexander & Schulla, Joerg [Vis alle 9 forfattere av denne artikkelen] (2021). Water balance response of permafrost-affected watersheds to changes in air temperatures. Environmental Research Letters. 16(8). doi: 10.1088/1748-9326/ac12f3. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Observations show increases in river discharge to the Arctic Ocean especially in winter over the last decades but the physical mechanisms driving these changes are not yet fully understood. We hypothesize that even in the absence of a precipitation increase, permafrost degradation alone can lead to increased annual river runoff. To test this hypothesis we perform 12 millennium-long simulations over an idealized hypothetical watershed (1 km 2 ) using a distributed, physically based water balance model (Water flow and Balance Simulation Model, WaSiM). The model is forced by both a hypothetical warming defined by an air temperature increase of 7.5 ∘ C over 100 years, and a corresponding cooling scenario. To assess model sensitivity we vary soil saturated hydraulic conductivity and lateral subsurface flow configuration. Under the warming scenario, changes in subsurface water transport due to ground temperature changes result in a 7%–14% increase in annual runoff accompanied by a 6%–20% decrease in evapotranspiration. The increase in runoff is most pronounced in winter. Hence, the simulations demonstrate that changes in permafrost characteristics due to climate warming and associated changes in evapotranspiration provide a plausible mechanism for the observed runoff increases in Arctic watersheds. In addition, our experiments show that when lateral subsurface moisture transport is not included, as commonly done in global-scale Earth System Models, the equilibrium water balance in response to the warming or cooling is similar to the water balance in simulations where lateral subsurface transport is included. However, the transient changes in water balance components prior to reaching equilibrium differ greatly between the two. For example, for high saturated hydraulic conductivity only when lateral subsurface transport is considered, a period of decreased runoff occurs immediately after the warming. This period is characterized by a positive change in soil moisture storage caused by the soil moisture deficit developed during prior cooling.

• Edwards, Tamsin L.; Nowicki, Sophie; Marzeion, Ben; Hock, Regine; Goelzer, Heiko & Seroussi, Helene [Vis alle 84 forfattere av denne artikkelen] (2021). Projected land ice contributions to 21st century sea level rise. Nature. ISSN 0028-0836. 593, s. 74–82. doi: 10.1038/s41586-021-03302-y. Fulltekst i vitenarkiv Vis sammendrag

  The land ice contribution to global mean sea level rise has not yet been predicted1 using ice sheet and glacier models for the latest set of socio-economic scenarios, nor using coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects generated a large suite of projections using multiple models, but primarily used previous-generation scenarios and climate models, and could not fully explore known uncertainties. Here we estimate probability distributions for these projections under the new scenarios using statistical emulation of the ice sheet and glacier models. We find that limiting global warming to 1.5 degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. The median decreases from 25 to 13 centimetres sea level equivalent (SLE) by 2100, with glaciers responsible for half the sea level contribution. The projected Antarctic contribution does not show a clear response to the emissions scenario, owing to uncertainties in the competing processes of increasing ice loss and snowfall accumulation in a warming climate. However, under risk-averse (pessimistic) assumptions, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42 centimetres SLE under current policies and pledges, with the 95th percentile projection exceeding half a metre even under 1.5 degrees Celsius warming. This would severely limit the possibility of mitigating future coastal flooding. Given this large range (between 13 centimetres SLE using the main projections under 1.5 degrees Celsius warming and 42 centimetres SLE using risk-averse projections under current pledges), adaptation planning for twenty-first-century sea level rise must account for a factor-of-three uncertainty in the land ice contribution until climate policies and the Antarctic response are further constrained.

• Johnson, Andrew; Hock, Regine & Fahnestock, Mark (2021). Spatial variability and regional trends of Antarctic ice shelf surface melt duration over 1979 - 2020 derived from passive microwave data. Journal of Glaciology. ISSN 0022-1430. s. 1–14. doi: 10.1017/jog.2021.112. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Passive microwave satellite observations are used to identify the presence of surface meltwater across Antarctica at daily intervals from July 1979 to June 2020, with a focus on ice shelves. Antarctic Peninsula ice shelves have the highest number of annual days of melt, with a maximum of 89 days. Over the entire time period, there are few significant linear trends in days of melt per year. High melt years can be split into two distinct categories, those with high melt days in Dronning Maud Land and Wilkes Land, and those with high melt days in the Antarctic Peninsula and the Bellingshausen Sea sector of West Antarctica. The first pattern coincides with significant negative correlations between melt days and spring and summer Southern Annular Mode. Both patterns also form the primary modes of spatial and annual variability in the dataset observed by Principal Component Analysis. Areas experiencing extended melt for the first time in years tend to show large decreases in subsequent winter microwave emissions due to structural changes in the firn. We use this to identify the impact of novel melt events, particularly over the austral summers of 1991/92 and 2015/16 on the Ross Ice Shelf.

• Abdel-Fattah, Dina; Trainor, Sarah; Hood, Eran; Hock, Regine & Kienholz, Christian (2021). User Engagement in Developing Use-Inspired Glacial Lake Outburst Flood Decision Support Tools in Juneau and the Kenai Peninsula, Alaska. Frontiers in Earth Science. 9. doi: 10.3389/feart.2021.635163. Fulltekst i vitenarkiv Vis sammendrag

  Glacial lake outburst floods (GLOFs) significantly affect downstream communities in Alaska. Notably, GLOFs originating from Suicide Basin, adjacent to Mendenhall Glacier, have impacted populated areas in Juneau, Alaska since 2011. On the Kenai Peninsula, records of GLOFs from Snow Glacier date as far back as 1949, affecting downstream communities and infrastructure along the Kenai and Snow river systems. The US National Weather Service, US Geological Survey, and University of Alaska Southeast (for Suicide Basin) provide informational products to aid the public in monitoring both glacial dammed lakes as well as the ensuing GLOFs. This 2 year study (2018–2019) analyzed how communities affected by the aforementioned GLOFs utilize these various products. The participants in this project represented a variety of different sectors and backgrounds to capture a diverse set of perspectives and insights, including those of homeowners, emergency responders, tour operators, and staff at federal and state agencies. In addition, feedback and suggestions were collected from interviewees to facilitate improvements or modifications by the relevant entities to make the informational products more usable. Findings from this study were also used to inform changes to the US National Weather Service monitoring websites for both Suicide Basin and Snow Glacier. This paper’s findings on GLOF information use are relevant for other GLOF-affected communities, from both an information user and information developer perspective.

• Geck, Jason; Hock, Regine; Loso, Mike; Ostman, J & Dial, R (2021). Modeling the impacts of climate change on mass balance and discharge of Eklutna Glacier, Alaska, 1985-2019. Journal of Glaciology. ISSN 0022-1430. 67(265). doi: 10.1017/jog.2021.41. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Alaska's largest city, Anchorage, depends on Eklutna Glacier meltwater for drinking water and hydropower generation; however, the 29 km 2 glacier is rapidly retreating. We used a temperature-index model forced with local weather station data to reconstruct the glacier's mass balance for the period 1985–2019 and quantify the impacts of glacier change on discharge. Model calibration involved a novel combination of in situ, geodetic mass-balance measurements and observed snowlines from satellite imagery. A resulting ensemble of 250 best-fitting model parameters was used to model mass balance and discharge. Eklutna Glacier experienced a significant negative trend (−0.31 m w.e. decade −1 ) in annual mean surface mass balance (mean: −0.62 ± 0.06 m w.e.). The day of the year when 95% of annual melt occurs was five days later in 2011–19 than in 1985–93, demonstrating a prolongation of melt season (May–September). Modeled mean specific discharge increased at 0.14 m decade −1 , indicating peak water, the year when annual discharge reaches a maximum due to glacier retreat, has not been reached. Four of the five highest discharge years occurred since 2000. Increases in discharge quantity and melt season length require water resource managers consider future decreased discharge as the glacier continues to shrink.

Se alle arbeider i NVA

• Hock, Regine & Huss, Matthias (2021). Glaciers and climate change. Elsevier. ISBN 9780128215753. 29 s. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Hock, Regine (2026). Interview American Scientific. [Journal]. American Scientific. doi: https:/www.scientificamerican.com/article/nepals-deadly-debris-avalanche-is-a-warning-for-the-rest-of-the-world/. Fulltekst i vitenarkiv
• Hock, Regine (2026). A glimpse in the IPCC: An Overview Through a Glaciology Lead Author’s Lens. doi: https:/oggm.org/2025/12/08/10th-workshop-announcement/. Fulltekst i vitenarkiv
• Hock, Regine (2026). Reviewing the IPCC Report. Fulltekst i vitenarkiv
• Yılmaz, Yeliz A.; Aalstad, Kristoffer; Guillet, Gregoire; Rounce, David; Tober, Brandon & Yang, Ruitang [Vis alle 8 forfattere av denne artikkelen] (2026). Probabilistic calibration of glacier projections using data assimilation. doi: 10.5194/egusphere-egu26-14845. Fulltekst i vitenarkiv Vis sammendrag

  Global glacier mass loss is accelerating, yet considerable spread in projected glacier changes remains due to model structure, forcing, and parameter uncertainty. Most global glacier projections rely on relatively simple models where calibration approaches are essential to constrain uncertainty by using scarce observations. Probabilistic calibration strategies that help with quantifying uncertainities have recently incorporated into a limited number of global glacier models. As a next step, we suggest employing Bayesian data assimilation methods with untapped potential to integrate multi source observations (in-situ, satellite, reanalysis) when calibrating global glacier model projections.Here, we present a probabilistic calibration framework for the Python Glacier Evolution Model (PyGEM) based on ensemble-based data assimilation. Two data assimilation techniques (PBS and AdaPBS) are used to calibrate mass balance parameters to constrain future projections of glacio-hydrological variables (surface mass balance and runoff) between 2015 and 2100 under four SSP climate scenarios across the Scandinavian region. In this work, we compare our calibration results with commonly used deterministic and probabilistic glacier model calibration algorithms which are already in use in PyGEM. Our probabilistic calibration framework based on data assimilation has the potential to quantify and disentangle uncertainties from climate forcing, model structure, and parameters. Better constrained and uncertainty-aware glacier models increases confidence in projections of future glacier change and their relevant impacts. This work paves the way for producing policy relevant global glacier projections and scenarios with their uncertainty estimates within the ERC-AdG GLACMASS project.

• Hock, Regine & Pelt, Ward van (2026). IASC Workshop on the dynamics and mass budget of Arctic glaciers. doi: https:/nag.iasc.info/images/publications/abstracts/IASC_NAG_2026_abstractbook.pdf. Fulltekst i vitenarkiv
• Hock, Regine (2026). Interview. [Journal]. Aventine. Fulltekst i vitenarkiv
• Hock, Regine (2026). Comparing Glacier Mass-Balance Estimates: Challenges and Recommendations. Fulltekst i vitenarkiv
• Hock, Regine (2025). Density and ice layer stratigraphy in 16 firn cores from Austfonna, Svalbard, 1958-2022. Fulltekst i vitenarkiv
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Mazzolini, Marco; Guillet, Gregoire; Yang, Ruitang & Hock, Regine (2025). Data assimilation for snow and glacier modeling in climate applications. Fulltekst i vitenarkiv
• Hock, Regine (2025). Global glacier modeling – Recent progress and projections. Fulltekst i vitenarkiv
• Hock, Regine (2025). Can we geo-engineer a way out of climate change and sea-level rise? Fulltekst i vitenarkiv
• Hock, Regine (2025). Interview. [TV]. French National TV (TF1). Fulltekst i vitenarkiv
• Hock, Regine (2025). Interview glacier melt. [Radio]. BBC. Fulltekst i vitenarkiv
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Guillet, Gregoire; Rounce, David; Tober, Brandon & Yang, Ruitang [Vis alle 7 forfattere av denne artikkelen] (2025). Calibrating future glacier projections using data assimilation. doi: https:/imc2025.info/imc25/abstract/calibrating-future-glacier-projections-using-data-assimilation/. Fulltekst i vitenarkiv Vis sammendrag

  Global glacier mass is changing rapidly, and projections of global glacier mass balance under changing climatic conditions are crucial for informed decision-making. Existing glacier projections use relatively simple glacier models constrained by sparse observations. In these projections, model calibration plays a key role in constraining uncertainty. The use of Bayesian data assimilation methods for calibration by integrating multiple emerging observational data sets (in-situ mass balance measurements, climate reanalyses, and satellite remote sensing) to constrain model parameters and their dynamics remains relatively unexplored. Such a probabilistic calibration strategy could enable us to quantify and disentangle uncertainties related to the glacier model, the selected climate model forcing, and internal climate variability. The Python Glacier Evolution Model (PyGEM) is one of a handful of global glacier models that allow us to simulate the evolution of the mass balance of all glaciers in the world. In this work, we adopt ensemble-based data assimilation methods to calibrate PyGEM model parameters and thus constrain future projections of glacier mass balance across Scandinavia. We compare our results with traditional glacier model calibration algorithms and the Bayesian gold standard Markov Chain Monte Carlo (MCMC) method in PyGEM for glacio-hydrological indicators (surface mass balance and runoff projections) between 2015 and 2100 with four SSP scenarios. This work serves as the kernel for a scalable glacier data assimilation framework to produce policy relevant global glacier projections and scenarios within the recently funded ERC-AdG GLACMASS project. The probabilistic calibration framework developed in this study can in principle be adapted for a wide range of cryospheric applications.

• Hock, Regine (2025). Glacier hazards - Will they change in the future ? Fulltekst i vitenarkiv
• Hock, Regine (2025). Global glacier meltdown - Every degree temperature increase matters. Fulltekst i vitenarkiv
• Aalstad, Kristoffer; Guillet, Gregoire; Yang, Ruitang; Yilmaz, Yeliz & Hock, Regine (2025). Glacier reanalysis using hierarchical data assimilation. Fulltekst i vitenarkiv
• Yilmaz, Yeliz A.; Aalstad, Kristoffer; Guillet, Gregoire & Hock, Regine (2025). Strategies for Future Projections with PyGEM. Fulltekst i vitenarkiv
• Moudgil, Pragay Shourya; Vaate, Inger Bij de; Hock, Regine & Guillet, Gregoire (2025). Mass balance modeling of glaciers in Switzerland using machine learning. Fulltekst i vitenarkiv
• Hock, Regine (2024). Stream hydrology controls on ice cliff generation, evolution, and survival on debris-covered glaciers. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• Hock, Regine (2024). Glaciers and sea-level rise. Fulltekst i vitenarkiv
• Hock, Regine (2024). Global glacier projections and Paris Limits. Fulltekst i vitenarkiv
• Hock, Regine (2024). Response of high mountain glaciers to climate change - Every increase in temperature matters ! Fulltekst i vitenarkiv
• Hock, Regine (2024). How much global glacier mass loss is committed under policy-relevant global warming scenarios? Fulltekst i vitenarkiv
• Hock, Regine (2024). Complex pattern of subsurface water flow at the rising limit of runoff in Greenland firn. Fulltekst i vitenarkiv
• Yang, Ruitang; Hock, Regine; Rounce, David & Kang, Shichang (2024). Regional scale response of glacier speed to seasonal runoff variations on the Kenai Peninsula, Alaska. Fulltekst i vitenarkiv
• Yang, Ruitang; Ultee, Lizz; Hock, Regine; Debolskiy, Matvey V. & Rounce, David (2024). Modeling frontal ablation in a global glacier evolution model. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• Aalstad, Kristoffer; Hock, Regine; Mazzolini, Marco; Pirk, Norbert; Treichler, Désirée & Westermann, Sebastian [Vis alle 9 forfattere av denne artikkelen] (2024). Ensemble-Based Reanalysis of the Terrestrial Cryosphere. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv
• Hock, Regine (2023). Radio interview. [Radio]. Hessischer Rundfunk Germany. Fulltekst i vitenarkiv
• Hock, Regine (2023). Global glacier melt. Fulltekst i vitenarkiv
• Hock, Regine (2023). Glacier meltdown - Every increase in temperature matters ! Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• Hock, Regine (2023). World-wide glacier meltdown and how it impacts hazards. Fulltekst i vitenarkiv
• Hock, Regine (2023). World-wide glacier meltdown - Why should we care? Fulltekst i vitenarkiv
• Hock, Regine (2023). World-wide glacier meltdown: Implications for global sea level and streamflow. Fulltekst i vitenarkiv
• Hock, Regine (2022). fmaussion/global_glacier_volume_paper: v1.1 (v1.1) [Data set]. Fulltekst i vitenarkiv
• Hock, Regine (2022). High Mountain Asia PyGEM Glacier Projections with RCP Scenarios, Version 1. Fulltekst i vitenarkiv
• Hock, Regine (2022). Resampled density in 48 shallow firn cores from Southwest Greenland, 2012–2019. Fulltekst i vitenarkiv
• Hock, Regine (2022). Global PyGEM-OGGM Glacier Projections with RCP and SSP Scenarios, Version 1. Fulltekst i vitenarkiv
• Hock, Regine (2022). Future global glacier mass changes and their impact on sea level and streamflow. Fulltekst i vitenarkiv
• Hock, Regine (2022). Glacier mass and surface speed
 variations on the Kenai Peninsula, Alaska. Fulltekst i vitenarkiv
• Hock, Regine (2022). Every degree of temperature increase matters for future global glacier change. Fulltekst i vitenarkiv
• Hock, Regine (2021). Disappearing glaciers - Every degree of warming matters ! Fulltekst i vitenarkiv
• Hock, Regine & Truffer, Martin (2021). Book review: A. Fowler and F. Ng (Eds.), 2020. Glaciers and Ice Sheets in the Climate System: The Karthaus Summer School Lecture Notes. Journal of Glaciology. ISSN 0022-1430. s. 1–2. doi: 10.1017/jog.2021.129. Fulltekst i vitenarkiv

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