One of the main sources in Pelley's piece was glaciologist Gino Casassa, who's been scrutinizing Patagonia's O'Higgins glacier for years. The rate it's shrinking -- both in area and thickness -- is alarming. At one point in the story, he discovers that what had been glacial ice in 2004 is now a lake. Casassa used to be skeptical about climate change. "I just didn’t believe in global warming; I mean, in global warming being produced by mankind, by us contaminating the atmosphere. I just refused to believe that,” he says.He's not a skeptic now. The evidence of the O'Higgins glacier changed that. . . . . . . . . . .THIS NEWS ITEM WAS AIRED ON" 60 MINUTES"RECENTLY.