Keep in mind that one of the dimensions is, of course, that the definition of toxicity in the existing act is quite broad and was actually drafted for the specific purpose of being able to capture something that doesn't have a direct toxic effect at the level of individuals or people, but at a systemic environmental level. That's the basis on which it was declared toxic.
Indeed, when that definition was originally drafted, they weren't thinking about CO2. They were actually thinking about CFCs and ozone-depleting substances. They wanted to be sure that the definition was broad enough to capture those sorts of global threats. I think the classification of the Kyoto six substances under CEPA demonstrates that there is breadth and flexibility within that definition to capture these very serious threats.