> It seems likely we lend too much credence to experts ability to model complex systems over a long period of time.

You say "complex systems" but are actually referring to human behavior.

Humans are unique in that they change their behavior in light of predictions. You can't make a prediction, and publicize that prediction, without changing the system.

From what I've heard, many people are declining to have children precisely because of the environmental effects of overpopulation. There are of course other factors, but that's one factor.