While reasonable skepticism is healthy, global warming is such a well sudied phenomenon by now that an unreasonable number of independent codebases must have identical bugs in order for it to be false.

There's also the fact that we have had a pretty solid grasp about the chemical reactions of greenhouse gases since long before computers, both theoretically and empirically, and we know roughly how much is put out in the atmosphere.

Where the models diverge is on far finer points than what is needed to make the basic policy changes that seems to be where we are stuck right now.