Hummm... Its not normally reported that way. First you need to determine how many miles you are getting per gallon. A good estimate is that you will discharge 19.6 pounds of CO2 from burning 1 gallon of gasoline. This does not depend on the power or configuration of the engine. Of course if the car gets more miles per gallon of gasoline, you will get less CO2 per unit of service rendered (that is, less CO2 per mile traveled).
Once you determine how many miles per gallon you are getting then divide that by 19.6 and that should give you the pounds of Carbon dioxide produced per mile.
The U.S. Department of Energy and the U.S. Environmental Protection Agency recently launched a new Fuel Economy Web Site designed to help the public factor energy efficiency into their car buying decisions. This site offers information on the connection between fuel economy, advanced technology, and the environment.
