Ryan Avent makes a good point:

I think it’s worth pointing out that while it makes no sense to care much about the emission reductions in W-M independent of W-M’s effect on international emission reductions, it really makes no sense for other economies to care about their emission reductions independent of what America is doing. We’re richer than basically all of the other significant emitters, and our per capita emissions levels dwarf those of the other significant emitters. And we produce a fifth of global emissions. Why does it matter if we go first? Because what the hell is the point if we’re not involved?