China managed it
China "managed" it thanks to a policy that, in part, involved forced abortions. No, thanks, I'd rather not take the Chinese path.
Look, if we aren't talking about dragging people off to prison camps and forced-sterilization centers (which I hope we're not) then we're talking about a system of fines or other (probably financial) disincentives for people to have children. In which case we develop a two-tiered system in which the rich can afford to pay the consequences and do as they please, while the poor would be the ones really restricted. "Fine," I can hear some people saying, "the poor are the ones who shouldn't be breeding so much anyway." And that sort of eugenics argument is really chilling. Extend it out to brown people, those who practice a certain religion, etc.... Sorry, I can't envision a way in which enforcing such restrictions wouldn't be a nightmare.
It comes down to this - either you enforce birth control, humanely if at all possible, or a lot of people die of starvation and war.
I suppose it sorts itself one way or another, but humans at this stage are pretty much one big roiling ball of stupid, and expecting sensible behaviour doesn't seem very realistic.
Or rather - if all the sensible people got together and decided to stage simultaneous coups in many countries, resulting in some kind of decentralised but unified world government, and they really were sensible enough not to allow that to turn into the usual bloodbath that follows coups, and civil wars didn't break out everywhere, then some kind of sustainable planning might be possible.
But otherwise - where is the leadership going to come from? Western governments are rotten through with an infestation of free market and security-state drones. Eastern governments suffer from the same problems, with an added dose of violent authoritarianism.
We can have our intelligent conversations here, but we have to remember that most of the population doesn't agree with us, even in the West, and the leaders believe we're entertaining idiots - to the extent that they take environmentalism seriously at all, sui generis, without seeing it as an exercise in marketista droning.
Aside from a few windmills here and there, and some tentative edging into other sustainables, not only is no one doing the right thing, but our beloved leaders are aggressively doing exactly the wrong thing, combining a 19th century resource war with a 12th century crusade.
Turning this around is not going to be easy.
