evidence: A third of Antarctic ice shelves could collapse at current pace of warming [...] A third of Antarctica's vast offshore ice shelves could collapse into the ocean if the world warms by 4 degrees Celsius (7.2 degrees Fahrenheit) above pre-industrial levels. These floating platforms of solid water wouldn't directly raise sea levels if they melted; they already sit in the ocean. But they're important barriers preventing the immense bulk of the frozen continent's glaciers from rolling out to sea. If those inland glaciers reached open water, sea level could rise catastrophically. [...] In other words, the world where climate change proceeds to the point where a third of Antarctic ice shelves are at risk would involve more major failures to curb greenhouse gas emissions or the discovery of some warming feedback mechanisms that haven't been discovered yet.