This didn't happen purely because Western countries became more aware of their impact on the environment. As countries develop, their population growth rate slows. Their technology improves and they can spend energy more efficiently.

In the US's case, there was a large gain from switching from coal to natural gas for power generation. Not because it was better environmentally, but because it was cheaper. It's disingenuous for the US to go "Look at all we've done" when half the country is in firm denial that there's even a problem.