Yeah, it's 150ppm. Anything less than that and we're definitely heading towards mass extinction, as proven by history. Anything on the upper bound is theoretica

Yeah, it's 150ppm. Anything less than that and we're definitely heading towards mass extinction, as proven by history. Anything on the upper bound is theoretical and based on shaky models, whereas the lower bound is proven based on historical examples. Edit: Bring on the downvotes, but it won't change the science.