Melting Ice Vanishing into Caves

A couple of hundred years from now, cities all over the world could disappear beneath the water that’s melted off the planet’s ice sheets. Jason Gulley is one of the few people on the earth who have been underneath Greenland's ice sheets, and he's seen the melting ice disappear somewhere into the ice caves known as moulins. Gulley is a professor of geology at the University of Southern Florida. (Segment produced by Haley Kendall)