The problem isn't just reducing the emissions produced by people who already have cars (though that would of course help); it's limiting the future emissions of

The problem isn't just reducing the emissions produced by people who already have cars (though that would of course help); it's limiting the future emissions of the huge numbers of people who don't yet have cars, but want them. Hence the reason China and India won't agree to limit their citizens to current per-capita levels of emissions that are a fraction of those in countries with higher levels of car ownership.