Obviously, but having US onboard opens up possibilities to create incentives that credible international accords are built on. Or the other way around, without

Obviously, but having US onboard opens up possibilities to create incentives that credible international accords are built on. Or the other way around, without the US, China and Australia, even if the rest of the world does everything right, global carbon dioxide levels will not only keep increasing, but do so in an accelerating manner. And before you ask why not China could create credible incentives for the US, the answer is that they do not have the institutions for it, which the US has. At least in theory.