> per passenger-mile, flying is much less polluting than driving a car, even after you account for the fact that pollution in the stratosphere is more damaging. If getting rid of air travel results in more people driving across the country, that makes the greenhouse worse.

Flying enables burning more fuel to go farther in the same amount of time.

Your comparison is simply bogus and structured to favor flying.

In a world without flying, those travel miles don't get replaced by automobile miles. They simply don't occur for the most part.

For such comparisons you should really hold the travel time constant, not the distance.