That's what Tokyo is; increasing in population despite Japan as a whole falling. People in cities have smaller greenhouse gas emissions than people living rural

That's what Tokyo is; increasing in population despite Japan as a whole falling. People in cities have smaller greenhouse gas emissions than people living rural or suburbs; they don't need cars because things are close and mass transit is affordable and convenient because there are enough people sharing it. The US can't get there until they enforce standards of conduct in the public sphere and stop exclusionary zoning.