I can't think of a single time in history that humanity responded to a threat in a fully coordinated manner. Maybe this is the first time, but the incentive stack from the individual voter all the way up to geopolitical grand strategy argues against it.

Trying to tell poor nations to remain poor -- or telling rich nations to consume less -- is a losing game. There's evidence that as societies get richer, their populations demand cleaner air, water, etc. And, as another commenter mentioned, a realistic hope is that the whole green-tech stack matures to the point where it can compete on price.

We'll either make lower-carbon/lower-warming solutions work at near-market rates, in a way that allows personal and national economies to grow, or it'll just be talk for the next 50 years as well.