It isn't all about population either, it's also affluence - you've no doubt heard that the average American consumes ~30 times as much energy as the average Indian. In other words, the fact that most of the world is (comparatively) poor is what is allowing us to get by with our current population. So what happens as developing countries develop?
Usually whenever this topic comes up, some yokel will say, "As populations become more affluent, their birthrate goes down. Problem solved." Conveniently overlooking the fact that as populations become more affluent they also consume more, at a faster rate than the birth rate reduction. This is what I meant by something which won't be acted on until it can no longer be denied. There's a lot of denial out there on this subject.