Extinction of humans is not a possible result of global warming. Such a result is only put forward by people without political or scientific understanding. Worst case global warming (as in we continue to pump out and put every bit of buried accessible CO2 that's in the ground into the atmosphere) only returns us to an age of tremendous amounts of vegetation and coastal cities being flooded. It also causes wars and massive population movements, but it does not cause extinction. It might also cause advanced civilization to revert to an earlier stage of development, but Earth cannot become a Venus-like planet or anything close to it with current levels of buried CO2.

Granted this is a very bad experiment to run, and we should not do this, but it's not an existential crisis.