AGW is happening now, so unfortunately we're getting the opportunity to test the models. And carbon levels, and climate, have both varied in the past, albeit a lot more slowly. Those variations can be used to tune some aspects of our current models.

It's a valid point of discussion, but unfortunately almost everyone opposed to climate action is anti-scientific and political in their motivations, and usually duplicitous about it. Which causes people to lose their cool.

Most actual climate scientists, on the other hand, are more than happy to entertain honest skepticism. It's integral to science.