In a nutshell: Take all the pollution your car is generating, add it up, and fund programs to cut the equivalent amount of pollution in more cost-effective places. (They point out that a hybrid car costs around $3000 more, and over the course of five years cuts about 15 tons of carbon from the atmosphere. On the Chicago Climate Exchange, 15 tons of carbon pollution costs about $30. I don't know how accurate their numbers are, but if they're anywhere close to reality, that's a damn inefficient way of eliminating pollution.)
What I don't know is what kind of efficiency TerraPass has. How much of the money that they get goes into actual climate work, and how efficiently is that spent? Are there better ways to spend the money?
Does anyone have info on this that I haven't been able to dig out? CNN says they've vowed to cap their profits at 10 percent of revenues (apparently they're not non-profit because they felt they could get off the ground faster as a for-profit), but I'm not sure how much that means or even if it's official.