I believe that the earth self-regulates, that when it becomes too hot and gets a fever, it sweats just like a human body does in order to cool itself.
This sweating may come in the form of volcanic eruptions, such as the super volcano in the likes of the Yellowstone Caldera. Scientists have said that changes in atmospheric pressure can have an effect on fault lines or areas on the earth where there already is some tension. Where there is tension, atmospheric changes could work to release underground tensions resulting in earthquakes or volcanic eruptions.
If the earth becomes so hot that volcanos erupt, the volcanic eruptions would have a cooling effect. The ash in the air would effectively block out a hotter sun and thereby cool the earth.
An eruption of the magnitude of the Yellowstone Caldera could cause the entire North American continent to go into an ice age.
Alternatively, the earth could heat up without volcanic eruptions and earthquakes and simply cause areas near the equator to become uninhabitable and much of the United States to become a desert. In which case only the poles would be habitable and sustainable for agriculture and civilization.
One thing is sure, globla warming will certainly cause systemic and profound changes in the way civilazation may continue.
This is simply my opinion. Peace.