We do not have a Chinese or an American atmosphere. We have a global atmosphere. We cannot run independent experiments upon it. We have instead been running a joint experiment. This was not a conscious decision: it happened as a result of the industrial revolution. But we are consciously deciding not to stop.
Conducting irreversible experiments with the only planet we have is irresponsible. It would only be rational to refuse to do anything to mitigate the risks if we were certain the science of man-made climate change is bogus. Since it rests on well-established science, it would be ludicrous to claim any such certainty.
On the contrary, any reasonably open-minded reader of the Summary for Policymakers from the Intergovernmental Panel on Climate Change would reach the conclusion that any such certainty on the science would be ludicrous. It is rational to ask if the benefits of mitigation outweigh the costs. It is irrational to deny the plausibility of man-made climate change.