Comparing calving laws at Greenland's three largest ice shelves

Abstract. The retreat of Greenlandic glaciers through calving has major implications for the ice sheet's mass balance and future sea-level rise contributions. Despite its importance, the implementation of calving in ice sheet models remains contested, with several calving laws suggested to parametrise this process. While the performance of some of these calving laws has been tested for Antarctic ice shelves and Greenland's grounded outlet glaciers, it is unclear which calving law would best capture the observed behaviour of Greenland's ice shelves. Petermann, Ryder, and Nioghalvfjerdsbræ (79N) glaciers terminate as Greenland's three largest ice shelves, accounting for 90 % of the remaining floating ice and buttressing ∼ 15 % of the ice sheet's mass. Here we build on other systematic calving studies by comparing five calving laws at Greenland's three largest ice shelves using the Ice-sheet and Sea-level System Model (ISSM). We begin by constraining the performance of each law against observed terminus fluctuations between 2008 and 2024, and continue with projections to 2300 under various climate forcings. When evaluated against observed terminus changes, we recommend the use of a von Mises or Crevasse Depth calving law owing to their consistent performance and similar tuning parameters across the three ice shelves. However, in our extended projection runs, we find that calving parametrisations have little influence on grounding line discharge rates, which are instead driven by the choice of climate forcings. Large ice shelf calving or collapse events are scarce, and only in these rare cases do we find any pronounced increase in ice discharge. Our results indicate either continued buttressing potential from Greenland's ice shelves into the coming centuries or fundamental flaws in the current set of calving laws when calibrated to contemporary ice-shelf behaviour.