You are correct; that simple experiment does not take into account all of the external effects. With regard to scaling, I am guessing that you refer to feedbac

You are correct; that simple experiment does not take into account all of the external effects. With regard to scaling, I am guessing that you refer to feedback effects produced by plant production of oxygen from the CO2. My assumption is that the rate plant growth on the planet will stay constant, or, at the rate we are going, vastly decrease (rainforests, etc) which will worsen the effect. Also, economic growth planet wide can only increase energy consumption, and therefore, CO2 production. I don't think there are any off-base assumptions there, but I am open to the evidence of some.