Here are some statistics from the U.S. Climate Action Report-2002 published by the EPA:
…In 1999, greenhouse gas emissions were ~12% above 1990 levels. [Under Kyoto they would have to in theory be reduced to like 7% below 1990 levels by 2012 although in reality, because of the various loopholes in the treaty for sinks and international emissions trading it would probably be something closer to even with 1990 levels.]
…Transportation accounted for 26% of the emissions.
…Passenger cars and light duty trucks together make up ~62% of the transportation emissions, with the breakdown reported as 40% for passenger cars and 22% for light trucks.
So, putting all that together: First, let’s say that by now we are probably ~15% above 1990 levels and given the Kyoto rules with the various loopholes, let’s then say we have to cut back by 15%. Since cars and light trucks alone account for 16% of the emissions, we clearly could not meet Kyoto by only dealing with them (without getting rid of them altogether!), let alone only dealing only with SUVs. I am a little confused whether “light trucks” includes all SUVs or if they are mixed in with both passenger cars and light trucks (because the numbers for emissions from light trucks seem a bit lower than I’d expect if they include SUVs). But assuming that “light trucks” includes SUVs, it looks like improving emissions of SUVs/light trucks to that of cars (or replacing them with cars) would get us maybe a 2% reduction in our emissions. Dramatically increasing the fuel efficiency of all passenger cars, light trucks, and SUVs (by a factor of, say, 1.7) would reduce emissions by about 6-7%.
So, the basic conclusion: SUVs are very far from the whole problem in meeting Kyoto. On the other hand, they are not a completely insignificant factor either: you get a couple percent emissions reductions here and a couple of percent of emissions reductions there and pretty soon you have met the target. It seems likely that we couldn’t easily meet the target by concentrating simply on one sector…We’d have to work on all the sectors (transportation, industrial, residential).