> I said nothing about a monotonic relationship.

You made a scale-free claim about increasing greenness with increasing CO2 concentration. That implies a monotonic relationship.

> The only debate is over what might happen in the future, which, again, is fortune telling

The idea that using models of physical systems to predict their future evolution is "fortune telling" will surprise many scientists. Indeed, you yourself have proposed a simple model and used it to make a prediction about the future ("the world will be greener in a high-CO2 environment"), and used linear extrapolation of the past to justify the adequacy of your model.

That's not necessarily a bad starting point, but when actual studies with more complex models show different behaviours you should consider there's a possibility you're over-confident in your predictions.

Anyway, I suspect this conversation has become rather pointless. It's always unclear online to what extent people are engaging in good faith, but if it was then I'm rather sure you've now mentally pigeonholed me as a "doomer" who can't be reasoned with.