Here is the chemical equations behind the conclusions.
http://blueskymodel.org/gallon-gas
I personally believe that CO2, that we produce, is good for the environment and will spur more plant growth.
Electricity produced in U.S. average 1.4 pounds of CO2 per kWh
An electric car battery charge = 450 pounds of co2 per full charge. A gasoline powered car = 300 pounds of co2 per tank.