The majority of Antarctic ice shelves are set to disappear if greenhouse gas emissions keep increasing
A group of researchers from Grenoble, including OCEAN ICE participants, estimated dates, in given anthropogenic emission scenarios, beyond which individual ice shelves can no longer exist as they presently are. The authors took into account most uncertainties related to the future of the ice, atmosphere, and ocean, including deep uncertainties about poorly understood processes such as ice fracturing and calving.
The disappearance of floating ice shelves may unleash a strong contribution of the Antarctic Ice Sheet to global sea level rise. Yet, predicting their evolution in future climate scenarios remains a major challenge. Since the 1960s, scientists have attempted to predict their limit of viability from the evolution of local air temperatures. However, the break-up of ice shelves observed in a few regions of Antarctica since the mid 1990s has revealed a complex picture in which melting by the ocean and fracturing can play key roles. The problem is that many of these processes are poorly observed and therefore understood. This limits the scientific community's ability to simulate the fate of ice shelves in plausible futures.
In this study, the researchers took a step back and considered all the ocean atmosphere and ice processes that have the potential to change the mass of individual ice shelves. The fact that many aspects are poorly understood motivated the exploration of the full range of possibilities. This range was then reduced by giving more importance to the cases where the present-day estimates were close to observations. The authors also gave more importance to climate models simulating a plausible response to increased greenhouse gases. They had no confidence in their ability to estimate the evolution of a few key aspects like ice fracturing and calving. For these, they adopted a conservative approach, to be sure that their estimates remain valid regardless the future progress in the understanding of these processes. In the end, they were able to estimate dates beyond which there is high confidence that ice shelves can no longer exist in their current shape.
For a scenario of reduced greenhouse gases emissions, in which the global mean temperature remains within 2°C of the pre-industrial conditions, nearly all ice shelves have some chance of survival in a similar state as today. In contrast, a scenario in which emissions keep increasing would let no chance to a majority of ice shelves. Many of them are set to drastically shrink or disappear once the global mean temperature surpasses pre-industrial conditions by 5°C. By the end of the 23rd century, in such warming conditions, the authors are confident that a majority of ice shelves would drastically shrink or disappear. These results point to ocean warming as the main driver of such a fatal fate.
These results show that the measures taken or not taken to limit greenhouse gas emissions around the World will directly determine the future of Antarctic ice shelves. For a scenario in which emissions of greenhouse gas keep increasing throughout the 21st century, the disappearance of many Antarctic ice shelves would unleash a potential contribution to sea level rise of 10 meters. The estimation of when an ice shelf is set to drastically shrink or disappear reflects the author's high confidence that this ice shelf can no longer exist in given climatic conditions. They therefore provide ultimate dates for the possible existence of ice shelves. The break-up of ice shelves should therefore occur before these ultimate dates, in particular due to possible increase in rates of ice calving, rifting and fracturing. The authors nonetheless suggest that the latter are preconditioned by ice-shelf thinning due to ocean warming.
The obvious next step is to refine these estimates and move from an ultimate date of possible ice-shelf existence to a most probable date of ice-shelf breakup. Simulating the yearly evolution of ice shelves together with the evolution of the grounded ice sheet and of the entire climate system would be the pinnacle.
The author of the article - Nicolas Jourdain(Universite Grenoble Alpes)
Photo Credit: Fig. 1: Schematic of the processes that contribute to the Antarctic ice-shelf mass balance. (https://doi.org/10.1038/s41586-025-09657-w)