I've seen several other companies that were doing this overseas, but now there's one based in the US on the West Coast.
let's you do is to buy certificates for the C02 emissions produced by your car. You simply look up your car's model and year and the number of miles you drive annually on their website, and then purchase the appropriately priced TerraPass for your car.The funds are then used to directly offset the amount of C02 your car produces.
It's actually pretty reasonable; for example, my 5500 pound Suburban diesel only costs $29.95/year. Terrapass uses these funds to buy market traded carbon certificates or finance clean energy projects,
TerraPass eventually plans to offer certificates for air travel and household utility emissions too.
This is a very simple and convenient way for anyone to directly pay for the environmental cost of their vehicle's carbon output and in essence, zero out it's effect.