Is the marine ice cliff hypothesis collapsing

Marine margins, where ice sheets flow from land into the ocean, become exposed to environmental conditions and internally generated forces markedly different from those governing the flow of ice further inland. Prior research has suggested that if the retreat of such margins formed tall ice cliffs, they may become structurally unstable and collapse, leading to further retreat (1). Although the veracity and importance of the “marine ice-cliff instability” are still uncertain (2), increasing the accuracy of simulated ice cliff processes is a key challenge because the Greenland and Antarctic ice sheets could raise global sea level by 65 m. On page 1342 of this issue, Bassis et al. (3) developed a model that reliably captures the complex behavior of ice cliffs as they deform and fracture. In doing so, they find that marine-terminating parts of Antarctica may be less vulnerable than previously suggested to rapid and irreversible collapse (4, 5).