Greenlands 1,600-foot ice dome vanished 7,000 years ago when temperatures were several degrees warmer than today. Now, scientists have found the buried evidence beneath Prudhoe Dome. The discovery raises a difficult question about Greenlands future. Similar warmth could return by the end of this century. If that happens, the ancient melt record could offer a rare clue to how quickly Greenlands ice may respond and what it could mean for global sea levels.