Thanks for the explanation. I do think it's misleading to say that "CO2 exhaust production goes up the more efficient an internal combustion engine runs" - this implies that less efficient engines are desirable!
An IC engine gains energy from two elements, Carbon and Hydrogen. At optimum efficiency these two elements are completely combusted into CO2 and H2O. If the engine is running rich, lower CO2 will be emitted from the engine because some of the carbon is being exhausted as CO and some as unburnt HC. Those products will be burnt in the catalytic converter as wasted CO2. So the net CO2 emissions for the engine-CAT system will be the same for the same fuel input. However since the engine is less efficient, more fuel will be used to do the same amount of work (mile-hours) and hence more net CO2 will be produced from a less efficient engine. Think of it this way - if the cat is working properly all carbon going into the engine will be turned into CO2, the more that is burnt in the engine and not in the cat, the further the car will go per gram of carbon. No matter whether the fuel is burnt in the engine or in the cat, ten litres of fuel burned over 100 km (23.5 mpg) equates to 238 grams of CO2 per km.
In Europe cars are already including the CO2 grams/100 km in their specifications. The
EC has set up a monitoring program for new cars. That's because they have taken their Kyoto targets seriously. This chart shows the improvements in car efficiency (measures in grams CO2/100Km) for European Automobile Manufacturers Association (ACEA), Japanese (JAMA) and Korean (KAMA) carmakers over the last few years
http://www.transportenvironment.org/doc ... lation.pdf
