China was the 3rd largest economy in the world. Their middle class was fine. If they wanted to add some environmental regulation it wouldnt have halted growth.
It is pointless to say "3rd largest" without mentioning the per capita data.
Per captia data is not useful because they have so many people who live rural lives without tech. Their urban class was doing well and causing a ton of pollution just like the US does. They then scaled up even more in the least emission efficient ways complete disregard for the damage it would do.