Brazilian businessman Roberto Waack has told potential investors around the world about his sustainable forestry firm, explaining how it sells certified wood, conserves water, and protects forests. But at meeting after meeting, he gets the same question: Is there money to be made from trees absorbing fossil fuel emissions?

Waack says he has watched a wave of speculators edge in on Brazil, eyeing the world’s biggest tropical-forest country as the ideal place for polluters to pay off the wrongs they’ve done to the atmosphere. By paying to preserve a piece of the Amazon, they hope to “offset” the carbon dioxide they’ve released by burning coal, oil, and natural gas in factories and power plants across North America, Europe, and Japan.

Brazil’s sprawling