"it begs the question as to why plants flourished during the carboniferous.."
No, it doesn't... not the same plants that we have today... plants evolve, just like monkeys.. It does beg the question, "Why didn't you figure that out?", tho.
"But the people who own greenhouses LOVE CO2"
People in greenhouses control the environment. In the grain belt, not so much...despite higher CO2, we just had this

You can raise the CO2 as high as you wish, but if the winter is too warm, no fruit...
Chilling units or chilling hours Chilling unit in agriculture is a metric of a plant's exposure to chilling temperatures. Chilling temperatures extend from freezing point to, depending on the model, 45 °F (7 °C) or even 60 °F (16 °C). [3] Stone fruit trees and certain other plants of temperate climate develop next year's buds in the summer. In the autumn the buds go dormant, and the switch to proper, healthy dormancy is triggered by a certain minimum exposure to chilling temperatures. Lack of such exposure results in delayed and substandard foliation, flowering and fruiting. One chilling unit, in the simplest models, is equal to one hour's exposure to the chilling temperature; these units are summed up for a whole season. Advanced models assign different weights to different temperature bands.
en.wikipedia.org |