$$ per capita?  It's not as simple as that. The negotiators already thought of your odd math and moved to damage control. This global warming thing is overwhelmingly the fault of the US up to this point since the 1890's.

Per capita, a US citizen consumes far more carbon/oil than any other country in the world. We consume much, much more because we are the great consumers of the world. Look at what we drive and buy. Look at our homes and wealth. So yes we should pay more.