The primary reason EPA head Stephen Johnson rejected California’s waiver request is that the state did not face "extraordinary and compelling conditions" as defined under the Clean Air Act. The idea is that CO2 affects the entire atmosphere equally, so California didn’t face any particular dangers from it.
Turns out, not only is that shoddy legal reasoning, it’s straightforwardly false, at least if a new study out of Stanford holds up. Forthcoming in Geophysical Research Letters, research by engineering professor Mark Jacobson finds a direct causal link between increased CO2 in the atmosphere and increased morbidity from air pollution.
In other words: CO2 makes traditional air pollution — ozone, particulates, carcinogens — more deadly. It follows that states with the worst air pollution have more to fear from climate change.
As it happens, California faces particularly bad air pollution problems. In fact, that’s the whole reason there’s a provision in the CAA allowing waivers for California.
California’s latest request for a waiver is perfectly, almost paradigmatically, in line with the requirements of the act. Seems Johnson has no case.