Antarctica holds about 27 million cubic kilometers of ice that is constantly flowing, pushed by its own weight and pulled by gravity. If just part of that ice – the West Antarctic Ice Sheet – were to melt into the ocean, it would raise global sea level by 6 meters. That’s more than a theoretical problem. West Antarctica is losing ice mass, and scientists are worried. Robin Bell, a glacialogist at Columbia University's Lamont-Doherty Earth Observatory, explains how the ice sheets are changing.