Okay, to work from what we know. And it's evidence is ample...
1. Atmosphere ingredients affect the temperatures we trap.
2. Earths surface affects radiation input.
3. Earths vegetation affects both.
For what we should know is that mankind affects all 3, noteably 2 & 3. The manner affected is most for warming effect, although there is some on the cooling effect. (dimming). So, we do not know exactly how much, but that's about it. No theory.