For anyone who may be interested, there is a program called Drive Neutral that "neutralizes" carbon dioxide emissions.
Brief synopsis from website: Drive Neutral purchases and retires greenhouse gas emissions credits on your behalf through the Chicago Climate Exchange (CCX) greenhouse gas market. DriveNeutral is a non-profit enterprise of the non-profit Presidio World College’s Presidio School of Management.
Their website: http://driveneutral.com/
I had a Drive Neutral certificate for my old Honda, and just got one for my new Versa.
Overall I think that Versa is a good car for the environment with the better gas mileage and low emissions.
