10 Oct 2023
 | 10 Oct 2023
Status: this preprint is currently under review for the journal TC.

A topographically-controlled tipping point for complete Greenland ice-sheet melt

Michele Petrini, Meike Scherrenberg, Laura Muntjewerf, Miren Vizcaino, Raymond Sellevold, Gunter Leguy, William Lipscomb, and Heiko Goelzer

Abstract. A major impact of anthropogenic climate change is the triggering of tipping points, such as the complete mass loss of the Greenland ice sheet (GrIS). At present, the GrIS is losing mass at an accelerated rate, largely due to a steep decrease in its surface mass balance (SMB, the balance between snow accumulation and surface ablation from melt and associated runoff). Previous work on the magnitude and nature of a threshold for GrIS complete melt remains controversial. Here, we explore a potential SMB threshold for GrIS complete melt, and the processes controlling the nature of this threshold. To this end, we use the Community Ice Sheet Model v.2 (CISM2) forced with different levels of SMB previously calculated with the full-complexity Community Earth System Model v.2 (CESM2). The SMB calculation in CESM2 has been evaluated with contemporary observations and high-resolution modelling, and includes an advanced representation of surface melt and snow/firn processes.

We find a positive SMB threshold for complete GrIS melt of 230±84 Gt/yr, corresponding to a 60 % decrease from the GrIS pre-industrial SMB. The ice-sheet response to sustained melt is highly non-linear, and determined by the effect of the SMB-height feedback in response to surface melt and Glacial Isostatic Adjustment (GIA). While the former process increases melt and promote runaway retreat, GIA-induced bedrock uplift stabilises the ice margin and delays deglaciation. The GrIS is tipping from ~50 % mass towards complete melt when the melt-induced surface lowering outweighs the GIA-induced bedrock uplift and the initially positive SMB becomes and remains negative for at least a few thousand years. We also find that the GrIS is tipping towards complete melt when the ice margin in the central west unpins from a coastal region with high bedrock elevation and SMB. Based on the minimum ice-sheet configuration in modelling studies of the GrIS during the last interglacial, we suggest that a stabilising effect of this midwestern topographic pinning point might have occurred in the past.

Michele Petrini et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2023-154', Anonymous Referee #1, 31 Oct 2023
  • RC2: 'Comment on tc-2023-154', Anonymous Referee #2, 10 Nov 2023
  • RC3: 'Comment on tc-2023-154', Anonymous Referee #3, 30 Nov 2023

Michele Petrini et al.

Michele Petrini et al.


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Short summary
In this study, we investigate with a numerical model the stability of the Greenland ice-sheet under prolonged sustained warming and ice melt. We show that there is a threshold beyond which the ice-sheet will lose more than 80 % of its mass over tens of thousand of years. The point of no return is reached when the ice-sheet disconnects from a region of high topography in western Greenland. This threshold is determined by the interaction of surface and solid-Earth processes.