posted by gutI agree with everything else you posted, but the above is ridiculous. We were @ 280ppm BEFORE industrialization.
I have no idea what "optimal" CO2 concentrations are and no one does. It's just assumed that "more CO2 = bad", but the science is pretty suspect. My guess is the true "goldilocks" zone is somewhere between 400-800ppm, but the speed we get there is potentially a problem.
We DO KNOW at @ 160ppm the planet dies. The last million years or so has cycled several times between about 190-300, so several times the planet has come perilously close to extinction long before modern man came on the scene.
250-300 is the ideal zone for humans since we have leveled much of the old growth forest we'll have to keep it lower than the pre-industrialization number to keep our crops going. 280 was ideal for 7ft plus diameter white oak and ash trees. them some bitches are long dead.