The Paleolithic Era was marked by the advance of hunting/gathering and the spread of humanity over the globe. By burning millions of years’ production of hydrocarbons in a century or so, we’ve brought CO2 back to the “good old days”. You can bet changing the chemistry of the atmosphere will have some effect.
In the short term, increasing levels may stimulate growth of plants but we’ve cut down lots of trees and replaced them with feeble vegetables and cereals. The world is not in balance. The dynamics will cause an overshoot long before we cut our reliance on hydrocarbons. Spreading a CO2 tarpaulin over the globe will cause even more global warming and shift climates rapidly. At my age I won’t mind a bit of warming but drought is another matter. If the continental interiors warm even a bit we won’t be able to grow enough trees. They need rain not higher temperatures. I’ve done my share. TLW won’t allow me to plant any more trees. I’ll sneak in a few while she isn’t looking next year but I expect she will establish a census or other regulatory regime for the yard.
Further south, about 40% of USAians apparently support Trump and his denial of global warming so I expect it will take another generation suffering even larger effects before real action is taken. I know when I was a boy we had a lot more snow and lower temperatures. Last winter we had only ankle-deep snow here and I only ran the snow blower two or three times. I keep having to water my trees or the ground becomes cracked and dried all around my yard. That’s not normal. Having bigger and more severe storms year after year in USA along with rising sea-level is not normal either. Will enough of us take notice? Stay tuned. I’ll be checking out before the %#@! hits the fan most likely but my grandchildren and their children will suffer the consequences. Too bad.