Post-industrial civilzations are already at negative population growth, they still produce a great deal of pollution and urban bloat.

There's no magic bullet to fix the issues we face, it takes a lot of smaller solutions in addition to some bigger fixes to tie it all together. And most of all it needs to be adaptable, to allow for new fixes to be folded into the plan as a whole as it goes along.

Most importantly: it takes time. Like, lots of time. No real, effective, solution is going to make everything better immediately.