Buried below the ice sheet that covers most of Greenland, there's an abandoned U.S. Army base. Camp Century had trucks, tunnels, even a nuclear reactor. It was also a test site for deploying nuclear missiles. The camp was abandoned almost 50 years ago. But serious pollutants were left behind. Now a team of scientists says that as climate warming melts the ice sheet, those pollutants could spread. [Researcher William Colgan] found unclassified records that described what was left behind there - for example, the nuclear reactor was removed, but low-level radioactive cooling water used in it was not. There were very likely PCBs, which are toxic compounds in electrical equipment. There's no record of how much remained. Colgan says the Army figured all of it would be entombed forever. They thought it would snow in perpetuity," he says, "and the phrase they used was that the waste would be preserved for eternity by perpetually accumulating snow." Except now, the climate has changed. Greenland's ice sheet is melting. Computer models say the camp could be uncovered by the end of this century. Meltwater could easily end up in the buried camp and then carry contamination through under-ice channels to the ocean. Colgan says it's unclear who owns this waste. The Army built the camp under a treaty between the U.S. and Denmark, which had jurisdiction over Greenland. It's a legal dilemma that's likely to start cropping up more often.