...most plants alive today ALSO did not evolve to exist in such high CO2 levels? That such CO2 levels will cause dramatically higher temperatures and vastly different climatology, which will more than offset (ie: Kill the plants) any gains from higher CO2 levels? You also realize that CO2 is not "plant food" ? Plants use far more than just CO2? And plants are in general carbon nuetral, using and storing carbon while alive (in the form of growth), which then gets released back into the biosphere when they die?
Basic CO2 concentration guidelines:
The effects of increased CO2 levels on adults at good health can be summarized: normal outdoor level: 350 - 450 ppm acceptable levels: below 600 ppm complaints of stiffness and odors: 600 - 1000 ppm ASHRAE and OSHA standards: 1000 ppm general drowsiness: 1000 - 2500 ppm adverse health effects expected: 2500 - 5000 ppm maximum allowed concentration within a 8 hour working period: 5000 ppm
I'm too lazy to search the google:
... but wasn't there originally very high CO2 levels in earth's atmosphere, which kicked up temps. raised atmospheric moisture conc., therefore plant life went wild, eventually becoming so abundant as to drive down CO2 levels so that animal kingdom could thrive, as CO2 dropped plant life dropped off dramatically, eventually forming the goo in the ground that we now call oil, and burn to put the CO2 back.
A giant CO2 do loop