No, All Plantlife Doesn't Die at 150 ppm CO2
Frequently I'm told that the increase in CO2 from fossil fuel emissions is good for the planet because, before the industrial revolution, CO2 levels were dangerously low. Gregory Wrightstone, for instance, claims that "before we began adding CO2 to the atmosphere, we weren’t sure that we wouldn’t cross that critical 150-ppm threshold during the next glacial period" when nearly all "terrestrial plant life cannot exist." According to him, "advanced plant life could not survive without at least 150 ppm" CO2. He calls this a "line of death." [1] I've even read people claiming that currently the atmosphere is "starved" of CO2. It's hard to know where this 150 ppm value originates; I haven't been been able to find it anywhere in the scientific literature, but I did read once that in greenhouses, daytime photosynthesis can lower CO2 concentrations to about 150 ppm. However, that does not justify any conclusion that plants canno...