A method and system for estimating CO2 produced by an internal combustion engine disposed in a vehicle and transmitting the CO2 produced to a display device within the vehicle are disclosed. Estimated CO2 produced is based on amount of fuel consumed and fuel composition, e.g., alcohol content in a gasoline-alcohol blend. The amount of fuel consumed is computed based on fuel pulse width commanded to fuel injectors disposed in the engine, the pressure drop across the fuel injectors, and fuel injector nozzle cross-section. Instantaneous CO2 produced and/or average CO2 produced can be computed and displayed. Instantaneous CO2 produced is averaged over a short interval with the display updated regularly. Average CO2 produced is averaged over a typically longer interval, being reset, in one embodiment, by an operator of the vehicle depressing a reset button.