SMITH: Two million dollars and 40 years of coal plant emissions would go away. The project got a lot ofpress.Oh, this is a Time magazine.STURGES: This is Time magazine from October 24, 1988.SMITH: Oh, my gosh, there's a cigarette ad.STURGES: Yeah (laughter) here it is. "Antidote For A Smokestack" it's called - is the title. Guatemalanseedlings will be planted to combat the greenhouse effect.SMITH: And this is the moment that launched a thousand carbon offsets because all around the country,CEOs were sitting, reading their Time magazine and going wait a minute here. It's easy, it's simple, I lovetrees, my company loves trees, you know, it's great PR and we don't even have to look at the trees. Wecan have someone plant them halfway around the world. It was a great deal. And car rental companies,airlines, travel sites, Dell computer, HSBC - they've all paid to plant millions of trees. They've all usedSheryl's idea.SMITH: I think you might've been the first person to look at carbon as, like, a - I don't want to say acurrency, but you know what I mean?STURGES: No, it is. It's a commodity. We were trying to commoditize carbon so that you could trade itand conserve it and, like, sell the non-production of it.SMITH: So after talking to Sheryl and Paul, I was ready to call up our reporters and say that, yes, carbonoffsets seem legit. In theory, you can pay someone to plant trees that will undo the carbon emissions fromyour trip. But the more I looked into it the more I started reading about the other side of carbon offsets.Hannah Wittman is a professor at the University of British Columbia. She actually did a study on AES'streeplanting program in Guatemala, and she said she saw a lot of problems.HANNAH WITTMAN: There was conflicts over land use. The farmers didn't have a sense that it was theirobligation to offset carbon for North American consumers.SMITH: Hannah says when all of those farmers in the region started planting trees, it meant less room forfood. There were actually food shortages in the area. Then some of the farmers decided they didn't wantto plant those weird Leucaena leucocepholia trees. They wanted to plant fruit trees. That was great for thefood supply, but fruit trees don't suck up carbon like the Leucaena leucocepholia trees. And Hannah saysby her calculations the program with the Guatemalan farmers only offset about 10 percent of the coal