3-4x the current level of CO2 is far far past runaway environmental catastrophe. A plant can have all the CO2 it wants but it would have to attempt to eke out a

3-4x the current level of CO2 is far far past runaway environmental catastrophe. A plant can have all the CO2 it wants but it would have to attempt to eke out an existence in a far drier climate that is multiple degrees hotter.