The one child policy worked though. The 70s 2 child and 80s-2000s 1 child policies prevented 400-600m births. Almost all the consequences were a fallout of sexist cultures in China against women killing or abandoning their female children.

They don't need the policy in place anymore today because they got over the observable demographic hump where an industrializing economy goes through a population boom before social infrastructure and education lead women to drop their reproduction rates naturally.

The environmental impacts of 25-35% more people existing in China today would have been palpable. Even if, like most impoverished nations, the "lost" population would only have contributed the equivalent CO2 and environmental drain of a tenth of an American thats still the equivalent of 40-60 million Americans less. It was one of the most effective environmentalist policies in history.