Ice shelves, the floating margins of the Antarctic ice sheet, play an important role in the estimation of future sea-level rise. By their presence, they act as a brake on the flow from the grounded ice sheet to the ocean and therefore modulate how much of this ice is added to the ocean. As the atmosphere and ocean warm, melt is occurring at their surface and at their base, putting their existence under threat. In this context, the future of ice shelves looks grim. When can we expect them to disappear and what’s the main driver behind it? This is what we explored in a recent study…
[Note: As this paper was not published in open access (due to very high publication costs), we can unfortunately not share the figures in this blog post. Please check out the paper directly here if you have access to Nature or to its preprint version here.]
A climatic limit of viability for ice shelves?
The presence of ice shelves is governed by a fragile balance between mass gain and mass loss at their boundaries with the grounded ice sheet, the atmosphere and the ocean. If the mass loss exceeds mass gain, an ice shelf is bound to disappear on the long term. Based on the observation that ice shelves do not exist in the warmest parts of the Antarctic Peninsula, the idea of a climatic limit of viability linked to a given atmospheric threshold has been explored in the past 60 decades. This was reinforced by the collapse of the ice shelves Larsen A-B in 1995 and Larsen B in 2002, which were mainly driven by hydrofracturing. Hydrofracturing occurs when surface meltwater favours the propagation of crevasses and eventual disintegration of the ice shelf.
However, such a collapse can only occur if the ice shelf is weak enough. And this can be the result of (1) melt at the surface, through the atmosphere, (2) melt at the base, through the ocean and (3) mass loss and mass gain through ice dynamics (see Fig. 1 in the paper). In our study, we therefore decided to look beyond only the atmosphere-ice interface and also look at the other boundaries. We define the limit of viability as the moment when mass loss at the surface, at the base and at the front exceeds the maximum possible mass gain from the grounded ice sheet to the ice shelf (grounding-line flux for the experts). Our limit of viability therefore represents the ocean and atmosphere conditions for which it is almost impossible that an ice shelf maintains its current shape in the long term because it loses more mass than it gains.
Reaching non-viability
To investigate this limit of viability we inferred several estimates of (1) ice-shelf surface and basal conditions from several climate simulations (CMIP6) under a low and a high-emission scenario until 2300 and (2) a limit for the maximum mass gain from the grounded ice sheet from an ice-sheet model. Due to large uncertainties, we decided to set the calving flux (the icebergs) to zero (if you’re interested in their minimal effect on our results, check out the supplementary figures of our paper). This way, we could estimate a likelihood of reaching non-viability based on the whole group of simulations (across several climate models, and several methods to estimate basal conditions and ice-sheet bedrock conditions).
We find that the time of reaching likely non-viability strongly depends on the scenario (see Fig. 2 in the paper). Only 1 out of the 64 ice shelves becomes likely non-viable by 2300 in the low-emission scenario. By contrast, 38 out of 64 ice shelves become likely non-viable by 2300 in the high-emission scenario. While 2300 might seem far away, the number of ice shelves being likely non-viable by 2150 already reaches 26, showing that this is not necessarily a problem of the far-future.
Our results show that current choices to change emission pathways could significantly affect the likelihood of the long-term loss of most Antarctic ice shelves.
Drivers of non-viability
The next step of our analysis was to examine if the limit of viability is mainly linked to the atmosphere or if there is more at play behind the curtains. To do so, for each simulation, we looked at the proportion of mass loss to the atmosphere and to the ocean. We found that the ocean is by far the main driver for reaching non-viability (Fig. 4 in the paper). In both scenarios, ocean-induced melt at the base of the ice shelves explains more than half of the mass loss needed to reach non-viability for all ice shelves that reach non-viability.
Our results show that, while the final trigger for collapse might likely come from surface meltwater, long-term disappearance of ice shelves is mainly driven by ocean warming.
What now?
Once again, this study shows how vulnerable the icy environments of our planet are. Our current choices of greenhouse gas emissions impact the mighty ice sheets. Their loss represents several meters of global sea-level rise. The long response times of the ocean and ice should be a warning to act as fast as possible to avoid high-impact long-term consequences.
If you got curious, check out the whole paper here!
Burgard C., Jourdain, N.C., Mosbeux, C., Caillet, J., Mathiot, P., and Kittel, C. (2025): “Ocean warming threatens the viability of 60% of Antarctic ice shelves”, Nature, doi: 10.1038/s41586-025-09657-w.
