Any prediction, given enough time, will eventually be borne out, but maybe not in this universe. Runaway global warming is just not possible using the Three Laws of Thermodynamics.
- Energy can be changed from one form to another, but it cannot be created or destroyed.
- In all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state. (Entropy)
- Energy of any system can never be fully dissipated.
Or more succinctly and simply put:
1. You can’t win.
2. You can’t break even.
3. You are not allowed to get out of the game.
If the Sun puts more energy into the earth's thermodynamic domain than leaves the system, then the result is more energy likely in the form of heat. The earth has gone through warm and cold periods many times. I would venture a guess that the Sun had a variable input given changes in precession, orbital paths, and revolution inclination as well as cyclical solar activity. I would also venture a guess that ocean circulations, volcanic activity, and variations in atmospheric makeup resulting from the formation of life and subsequent changes has regulated output of energy from the earth. There is no violation of thermodynamic principle in changing earth temperatures.