The rapid collapse of some of the world’s biggest glaciers due to climate change will have devastating consequences for our planet’s coastlines due to sea level rise. Compounding this issue is the fact that many of these coastlines are heavily populated and developed. A recent proposal, first reported in The Atlantic, aims to avert potential catastrophe by turning to geoengineering through the construction of massive underwater walls, called sills, which would be built where glaciers meet the ocean in Antarctica and Greenland.