I remember an audio book/course by an economist 20 years ago where he did back of the envelope calculations for the cost/benefits of all sorts of policies (deregulating trains, etc) and he got to carbon. And he said no matter how you cut it, getting rid of the carbon dioxide (unlike CFC) costs bazillions.
I'd also add that it is an uncoordinated game. So anyone stops burning the fossils, someone else will burn them.