There is currently poor scientific agreement on whether the ice–bed interface is frozen or thawed beneath approximately one third of the Greenland ice sheet. This disagreement in basal thermal state results, at least partly, from differences in the subglacial geothermal heat-flow basal boundary condition used in different ice-flow models. Here, we employ seven widely used Greenland geothermal heat-flow maps in 10 000-year spin-ups of the Community Ice Sheet Model (CISM). We perform two spin-ups: one nudged toward thickness observations and the other unconstrained. Across the seven heat-flow maps, and regardless of unconstrained or nudged spin-up, the spread in basal ice temperatures exceeds 10 ^∘C over large areas of the ice–bed interface. For a given heat-flow map, the thawed-bed ice-sheet area is consistently larger under unconstrained spin-ups than nudged spin-ups. Under the unconstrained spin-up, thawed-bed area ranges from 33.5 % to 60.0 % across the seven heat-flow maps. Perhaps counterintuitively, the highest iceberg calving fluxes are associated with the lowest heat flows (and vice versa) for both unconstrained and nudged spin-ups. These results highlight the direct, and non-trivial, influence of the heat-flow boundary condition on the simulated equilibrium thermal state of the ice sheet. We suggest that future ice-flow model intercomparisons should employ a range of basal heat-flow maps, and limit direct intercomparisons with simulations using a common heat-flow map.

In this study, we investigate the differences between two transient, three-dimensional, thermomechanically coupled ice-sheet models, namely, a first-order approximation model (FOM) and a ‘full’ Stokes ice-sheet model (FSM) under the same numerical framework. For all numerical experiments, we take the FSM outputs as the reference values and calculate the mean relative errors in the velocity and temperature fields for the FOM over 100 years. Four different boundary conditions (ice slope, geothermal heat flux, basal topography and basal sliding) are tested, and by changing these parameters, we verify the thermomechanical behavior of the FOM and discover that the velocity and temperature biases of the FOM generally increase with increases in the ice slope, geothermal heat flux, undulation amplitude of the ice base, and with the existence of basal sliding. In addition, the model difference between the FOM and FSM may accumulate over time, and the spatial distribution patterns of the relative velocity and temperature errors are in good agreement.

To better understand the future evolution of Jiemayangzong Glacier (JMYZG), the headstream of the Yarlung Zangbo River, we simulated its future ice thickness evolution using a two-dimensional higher-order numerical flowline model. Due to the sparsity of in situ observational data, we used a combination of field observations and inversion models of velocity and ice thickness to initialize the model parameters. We validated the parametrizations of the calving scheme by comparing the modeled and observed glacier terminus retreats. To estimate the response of JMYZG to climate change, the ice flow model was forced with different climate scenarios. We found that the JMYZG will retreat under different climate scenarios. By 2100, the volume loss of JMYZG will be approximately 34%, 67% and 81% under SSP1-2.6, SSP3-7.0 and SSP5-8.5, respectively.

Glacier detachment is a severe natural hazard that can cause enormous damage in downstream regions. During detachment, a glacier will experience an abrupt change from slow-moving to high-speed flow within minutes. In this study, we investigate a massive glacier detachment event that occurred in 2018 in the Sedongpu Valley, southeastern Tibet, using a two-dimensional first-order ice flow model incorporating a positive feedback mechanism between ice stiffness and basal slip. In this model, detachment can be triggered if the ice stress exceeds the initial yield strength of glacier ice. By including this tipping mechanism, we simulate abrupt changes in the ice flow pattern of the Sedongpu Glacier. The transition from slow to abrupt flow occurs after most regions of the glacier reach a plastic state. The modeled duration of the 2018 Sedongpu detachment is comparable with observations. The abrupt weakening of ice strength during the transition from elastic to plastic deformation may be a primary cause of glacier detachment tipping processes.

Glacier detachment is a severe natural hazard that can cause enormous damage in downstream regions. During the detachment, glacier will experience an abrupt change from slow-moving to high-speed flow in just a few minutes. In this study, we investigate a massive glacier detachment event occurred in 2018 at the Sedongpu valley, Southeastern Tibet, using a two-dimensional first-order ice flow model by introducing an ice stiffness and basal slip positive feedback mechanism. In this model approach, ice detachment can be triggered if ice stress exceeds the initial yield strength of the glacier. By including this tipping mechanism, we simulate the abrupt changes in the ice flow pattern for the Sedongpu glacier. The transition process from slow to abrupt flow can occur within just several model time steps. The modeled duration time of the 2018 Sedongpu detachment is comparable with observation. The abrupt weakening of ice strength from elastic to plastic deformation may be one of the main causes of the tipping processes of glacier detachment. This numerical model approach could possibly be used for early warnings of glacier detachment hazards in the surrounding regions of the Sedongpu valley.