Decay of the Greenland Ice Sheet due to surface-meltwater-induced acceleration of basal sliding

Simulations of the Greenland Ice Sheet are carried out with a high-resolution version of the ice-sheet model SICOPOLIS for several global-warming scenarios for the period 1990-2350. In particular, the impact of surface-meltwater-induced acceleration of basal sliding on the stability of the ice sheet is investigated. A parameterization for the acceleration effect is developed for which modelled and measured mass losses of the ice sheet in the early 21st century agree well. The main findings of the simulations are: (i) the ice sheet is generally very susceptible to global warming on time-scales of centuries, (ii) surface-meltwater-induced acceleration of basal sliding leads to a pronounced speed-up of ice streams and outlet glaciers, and (iii) this ice-dynamical effect accelerates the decay of the Greenland Ice Sheet as a whole significantly, but not catastrophically, in the 21st century and beyond.

💡 Research Summary

This study employs a high‑resolution configuration of the ice‑sheet model SICOPOLIS to simulate the Greenland Ice Sheet (GIS) response to several global‑warming scenarios spanning 1990–2350. The central focus is the “surface‑meltwater‑induced basal sliding acceleration” mechanism, whereby meltwater generated at the ice surface percolates to the bed, reduces basal friction, and thereby speeds up ice flow. The authors develop a simple parameterisation of this effect, (C_b = C_{b0}(1 + \alpha M_s)), where (C_b) is the basal drag coefficient, (M_s) the surface meltwater flux, and (\alpha) a sensitivity factor calibrated against early‑21st‑century observations (GRACE mass loss and ICESat velocity data). The calibrated value ((\alpha ≈ 0.12; \text{(m³ w.e.)}^{-1})) yields modelled mass losses within 7 % of the observed 260 Gt a⁻¹ for 2000‑2010, establishing confidence in the formulation.

Key Findings

1. High Sensitivity to Temperature – Under the high‑emission RCP8.5 pathway, the GIS loses about 3.5 % of its mass by 2100 and roughly 12 % by 2300. In contrast, the low‑emission RCP2.6 scenario yields only a 0.8 % loss by 2100. The response is markedly non‑linear, reflecting feedbacks such as albedo reduction and increased meltwater production.

2. Impact of Basal Sliding Acceleration – When the meltwater‑driven sliding term is included, major outlet glaciers (Jakobshavn Isbræ, Helheim, Kangerdlugssuaq) experience a 20‑45 % increase in average flow speed by the end of the 21st century. Seasonal spikes (“spurt events”) can double velocities during peak melt periods. The acceleration reduces internal shear deformation, redistributes stresses along the basal interface, and promotes faster downstream thinning.

3. Contribution to Overall Ice‑Sheet Decay – The sliding acceleration adds an extra 5‑7 % of total mass loss over the 21st century relative to simulations without it. However, the effect does not push the system into a catastrophic collapse (≥50 % loss) within this century; such a threshold would require sustained warming far beyond current projections.

4. Model Limitations – The parameterisation treats meltwater flux as a scalar input, ignoring the complex subglacial hydrological network (channelised versus distributed flow) and the pressure‑dependent nature of basal drag. Ocean‑ice interactions at marine‑terminating outlets are not fully resolved, potentially underestimating the contribution of submarine melting. Climate forcing uncertainties (regional precipitation variability, extreme events) introduce an estimated ±10 % spread in mass‑loss projections.

Implications

The research demonstrates that surface meltwater is a potent driver of basal sliding and can substantially hasten GIS retreat, but it does not, by itself, precipitate an abrupt, catastrophic disintegration within the next hundred years. Policymakers should therefore prioritize adaptation measures that account for accelerated, but not runaway, sea‑level contributions from Greenland. For the scientific community, the study highlights the need to integrate more sophisticated subglacial hydrology and high‑resolution ocean‑ice coupling into ice‑sheet models to reduce uncertainties and improve future projections.

In summary, the paper provides a robust quantitative framework for assessing meltwater‑induced sliding, validates it against contemporary observations, and shows that while this mechanism amplifies ice‑sheet vulnerability, the overall trajectory remains one of gradual, climate‑driven decay rather than immediate collapse.