The cliff face of Thrym glacier in Skjoldungen fjord, Greenland, in August 2025Caroline Needell The world’s thickest glaciers may “calve” icebergs up to three times faster than previously predicted. However, such rapid retreat may not be sustained over long periods. Instead, the large bodies of ice – which include Antarctica’s Thwaites glacier – may collapse in bursts, with intervening periods of stability. The behaviour of tall ice cliffs is one of the biggest sources of uncertainty in predicting future sea level rise. Several of the world’s largest glaciers in Greenland and Antarctica extend out to sea, with their bases resting on the sea floor. Their coastal edges can form ice cliffs loom...