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The simulation of ice sheet‐climate interactions, such as surface mass balance fluxes, is sensitive to model grid resolution. Here we simulate the multi‐century evolution of the Greenland Ice Sheet (GrIS) and its interaction with the climate using the Community Earth System Model version 2.2 (CESM2.2) including an interactive GrIS component (the Community Ice Sheet Model v2.1 [CISM2.1]) under an idealized warming scenario (atmospheric CO2${\\text{CO}}_{2}$increases by 1% yr−1${\\text{yr}}^{-1}$until quadrupling the pre‐industrial level and then is held fixed). A variable‐resolution (VR) grid with 1/4°$4{}^{\\circ}$regional refinement over the broader Arctic and 1°$1{}^{\\circ}$resolution elsewhere is applied to the atmosphere and land components, and the results are compared with conventional 1°$1{}^{\\circ}$lat‐lon grid simulations to investigate the impact of grid refinement. Compared with the 1°$1{}^{\\circ}$runs, the VR run features a slower rate of surface melt, especially over the western and northern GrIS, where the ice surface slopes gently toward the periphery. This difference pattern originates primarily from higher snow albedo and, thus, weaker albedo feedback in the VR run. The VR grid better captures the CISM ice sheet topography by reducing elevation discrepancies between CAM and CISM and is, therefore, less reliant on the downscaling algorithm, which is known to underestimate albedo gradients. The sea level rise contribution from the GrIS in the VR run is 53 mm by year 150 and 831 mm by year 350, approximately 40% and 20% less than that of the 1°$1{}^{\\circ}$runs, respectively. Plain Language Summary As one of the main contributors to global sea level rise, the Greenland Ice Sheet (GrIS) has been losing mass at an accelerating rate in recent decades. A better understanding of the interactions between the GrIS and the climate can help us make more reliable future projections of GrIS mass loss. To simulate these interactions, a fully coupled model framework is necessary. The model resolution must also be high enough to resolve the surface topography and processes such as orographic precipitation. This study applies a 1/4°$4{}^{\\circ}$ ‐refined grid over the Arctic to an Earth System Model, which includes an interactive GrIS model, to simulate multi‐century GrIS evolution under an idealized warming scenario and compares the results with simulations using a lower‐resolution grid. We show that the refined grid results in a slower rate of surface melt and, thus, a smaller sea level rise contribution. This is mainly because the refined grid better captures GrIS topography, resulting in a more accurate solution. Key Points For the first time, a variable‐resolution atmosphere is coupled with the ocean and sea ice components in CESM with a dynamic Greenland Ice Sheet (GrIS) A slower rate of GrIS surface melt is detected in the Arctic‐refined simulation compared with simulations using a conventional 1°$1{}^{\\circ}$grid The refined grid better captures the CISM GrIS topography, resulting in less downscaling and a more accurate solution

The full history of ice sheet and climate interactions is recorded in the vertical profiles of geochemical tracers in polar ice sheets. Numerical simulations of these archives promise great advances both in the interpretation of these reconstructions and the validation of the models themselves. However, fundamental mathematical shortcomings of existing models subject tracers to spurious diffusion, thwarting straightforward solutions. Here, I propose a new vertical discretization for ice-sheet models that eliminates numerical diffusion entirely. Vertical motion through the model mesh is avoided by mimicking the real-world flow of ice as a thinning of underlying layers. A new layer is added to the surface at equidistant time intervals, isochronally, thus identifying each layer uniquely by its time of deposition and age. This new approach is implemented for a two-dimensional section through the summit of the Greenland ice sheet. The ability to directly compare simulations of vertical ice cores with reconstructed data is used to find optimal model parameters from a large ensemble of simulations. It is shown that because this tuning method uses information from all times included in the ice core, it constrains ice-sheet sensitivity more robustly than a realistic reproduction of the modern ice-sheet surface.

The ice sheet model developed by L.G. Shulyakovskii for calculating ice formation dates on water bodies is presented. A possibility of applying this model for predicting ice formation dates based on the information system of the Hydrometcenter of Russia is shown. The model is implemented in the Automated Operational Data Processing System for the large navigable rivers of northeastern Siberia. Forecast sites at which the morphometric parameters of the model were obtained from long-term observations are distinguished on these rivers. The analysis of the state of the information databases used to automate calculations revealed a possibility to increase the lead time of the forecasts of the ice phenomena onset up to 10 days. The verification of the floating ice formation date forecasts produced using the model in operational mode over 2014–2022 is performed.

Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to different climate scenarios and assess the mass loss that would contribute to future sea level rise. However, there is currently no consensus on estimates of the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes, forcings employed and initial states of ice sheet models. This study presents results from ice flow model simulations from 13 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015–2100 as part of the Ice Sheet Model Intercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climate model results. Simulations of the Antarctic ice sheet contribution to sea level rise in response to increased warming during this period varies between -7:8 and 30.0 cm of sea level equivalent (SLE) under Representative Concentration Pathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment with constant climate conditions and should therefore be added to the mass loss contribution under climate conditions similar to present-day conditions over the same period. The simulated evolution of the West Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica ass change varies between -6.1 and 8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional simulated mass loss of 28mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared to simulations done under present-day conditions for the two CMIP5 forcings used and display limited mass gain in East Antarctica.

To fulfil the strong need for monitoring seasonal difference of velocity over the Greenland ice sheet (GrIS), we developed an approach based on the fusion of multiple temporal and multi sensor remote sensing observations. We used spaceborne synthetic aperture radar (SAR) and optical data over the Russell glacier in southwestern Greenland. Firstly, offset tracking and InSAR time series analyses were employed for deriving the glacier's velocity in planimetric and line of sight (LOS) directions. Next, a three-dimensional (3D) decomposition was applied for estimating the 3D velocity vectors of the glacier. Once the reliability of the results was validated, a numerical ice sheet model (ISM) was further applied to derive the modelled basal friction in different seasons. We concluded that the overall data integration using multiple open-accessed satellite image employed in this study demonstrated a decent method to analyze seasonal velocity difference of the Russell glacier. Based on the proposed monitoring strategy, it is of great potential to further investigate other polar and inland glaciers with various remote sensed data.

To predict the future contributions of the Antarctic ice sheets to sea-level rise, numerical models use reconstructions of past ice-sheet retreat after the Last Glacial Maximum to tune model parameters 1 . Reconstructions of the West Antarctic Ice Sheet have assumed that it retreated progressively throughout the Holocene epoch (the past 11,500 years or so) 2 – 4 . Here we show, however, that over this period the grounding line of the West Antarctic Ice Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf) retreated several hundred kilometres inland of today’s grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the ice streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, ice-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating ice-shelf grounding. We explore the implications of these findings with an ice-sheet model. Modelled re-advance of the grounding line in the Holocene requires ice-shelf grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West Antarctica, and corroborate previous suggestions of ice-sheet re-advance 5 . Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated ice loss. Whether these processes can reverse present-day ice loss 6 on millennial timescales will depend on bedrock topography and mantle viscosity—parameters that are difficult to measure and to incorporate into ice-sheet models. Radiocarbon dating of sediment cores and ice-penetrating radar observations are used to demonstrate that the West Antarctic Ice Sheet has not retreated progressively during the Holocene epoch, but has instead showed periods of retreat and re-advance.

Geothermal heat flux (GHF) is one of the key thermal boundary conditions for ice-sheet models. We assess the sensitivity of the Lambert-Amery glacial system in East Antarctica to four different GHF datasets using a regional ice-sheet model. A control solution of the regional model is initialised by minimising the misfit to observations through an optimisation process. The Lambert-Amery glacial system simulation contains temperate ice up to 150 m thick and has an average basal melt of 1.3 mm a −1 , with maximum basal melting of 504 mm a −1 . The simulations which use a relatively high GHF compared to the control solution increase the volume and area of temperate ice, which causes higher surface velocities at higher elevations, which leads to the advance of the grounding line. The grounding line advance leads to changes in the local flow configuration, which dominates the changes within the glacial system. To investigate the difference in spatial patterns within the geothermal datasets, they were scaled to have the same median value. These scaled GHF simulations showed that the ice flow was most sensitive to the spatial variation in the underlying GHF near the ice divides and on the edges of the ice streams.

More than half of Earth’s freshwater resources are held by the Antarctic Ice Sheet, which thus represents by far the largest potential source for global sea-level rise under future warming conditions 1 . Its long-term stability determines the fate of our coastal cities and cultural heritage. Feedbacks between ice, atmosphere, ocean, and the solid Earth give rise to potential nonlinearities in its response to temperature changes. So far, we are lacking a comprehensive stability analysis of the Antarctic Ice Sheet for different amounts of global warming. Here we show that the Antarctic Ice Sheet exhibits a multitude of temperature thresholds beyond which ice loss is irreversible. Consistent with palaeodata 2 we find, using the Parallel Ice Sheet Model 3 – 5 , that at global warming levels around 2 degrees Celsius above pre-industrial levels, West Antarctica is committed to long-term partial collapse owing to the marine ice-sheet instability. Between 6 and 9 degrees of warming above pre-industrial levels, the loss of more than 70 per cent of the present-day ice volume is triggered, mainly caused by the surface elevation feedback. At more than 10 degrees of warming above pre-industrial levels, Antarctica is committed to become virtually ice-free. The ice sheet’s temperature sensitivity is 1.3 metres of sea-level equivalent per degree of warming up to 2 degrees above pre-industrial levels, almost doubling to 2.4 metres per degree of warming between 2 and 6 degrees and increasing to about 10 metres per degree of warming between 6 and 9 degrees. Each of these thresholds gives rise to hysteresis behaviour: that is, the currently observed ice-sheet configuration is not regained even if temperatures are reversed to present-day levels. In particular, the West Antarctic Ice Sheet does not regrow to its modern extent until temperatures are at least one degree Celsius lower than pre-industrial levels. Our results show that if the Paris Agreement is not met, Antarctica’s long-term sea-level contribution will dramatically increase and exceed that of all other sources. Modelling shows that the Antarctic Ice Sheet exhibits multiple temperature thresholds beyond which ice loss would become irreversible, and once melted, the ice sheet can regain its previous mass only if the climate cools well below pre-industrial temperatures.

Understanding the causes of recent catastrophic ice shelf disintegrations is a crucial step towards improving coupled models of the Antarctic Ice Sheet and predicting its future state and contribution to sea-level rise. An overlooked climate-related causal factor is regional sea ice loss. Here we show that for the disintegration events observed (the collapse of the Larsen A and B and Wilkins ice shelves), the increased seasonal absence of a protective sea ice buffer enabled increased flexure of vulnerable outer ice shelf margins by ocean swells that probably weakened them to the point of calving. This outer-margin calving triggered wider-scale disintegration of ice shelves compromised by multiple factors in preceding years, with key prerequisites being extensive flooding and outer-margin fracturing. Wave-induced flexure is particularly effective in outermost ice shelf regions thinned by bottom crevassing. Our analysis of satellite and ocean-wave data and modelling of combined ice shelf, sea ice and wave properties highlights the need for ice sheet models to account for sea ice and ocean waves. Less sea ice allowed ocean swells to flex weakened ice shelves in Antarctica, contributing to their collapse.

The Greenland ice sheet is one of the largest contributors to global mean sea-level rise today and is expected to continue to lose mass as the Arctic continues to warm. The two predominant mass loss mechanisms are increased surface meltwater run-off and mass loss associated with the retreat of marine-terminating outlet glaciers. In this paper we use a large ensemble of Greenland ice sheet models forced by output from a representative subset of the Coupled Model Intercomparison Project (CMIP5) global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The simulations are part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We estimate the sea-level contribution together with uncertainties due to future climate forcing, ice sheet model formulations and ocean forcing for the two greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results indicate that the Greenland ice sheet will continue to lose mass in both scenarios until 2100, with contributions of 90±50 and 32±17 mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest mass loss is expected from the south-west of Greenland, which is governed by surface mass balance changes, continuing what is already observed today. Because the contributions are calculated against an unforced control experiment, these numbers do not include any committed mass loss, i.e. mass loss that would occur over the coming century if the climate forcing remained constant. Under RCP8.5 forcing, ice sheet model uncertainty explains an ensemble spread of 40 mm, while climate model uncertainty and ocean forcing uncertainty account for a spread of 36 and 19 mm, respectively. Apart from those formally derived uncertainty ranges, the largest gap in our knowledge is about the physical understanding and implementation of the calving process, i.e. the interaction of the ice sheet with the ocean.