Gliders on the storm

IN NOVEMBER 2016 a large crack appeared in the Larsen C ice shelf off Antarctica (pictured). By July 2017 a chunk a quarter of the size of Wales, weighing one trillion tonnes, broke off from the main body of the shelf and started drifting away into the Southern Ocean. The shelf is already floating, so even such a large iceberg detaching itself did not affect sea levels. But Larsen C buttresses a much larger mass of ice that sits upon the Antarctic continent. If it breaks up completely, as its two smaller siblings (Larsens A and B) have done over the past 20 years, that ice on shore could flow much more easily into the ocean. If it did so—and scientists believe it would—that ice alone could account for 10cm of sea-level rise, more than half of the total rise seen in the 20th century.