We have a runaway population explosion, as well as the CO2 explosion
we cannot feed the population we have now, 7.5bn, and we are forecast to have 10bn plus by mid century.
Clearly this cannot happen, so something is going to act rapidly to prevent it and reduce our numbers to pre-oil levels. (about 1 or 2 Bn)
Disease can’t do it, we usually find cures
nuclear war won’t kill enough of us quickly enough
so it seems C02 release is the only killer factor that will do the job.
I’ve expanded on it here