Huh? Theories that are backed up by enough evidence are generally regarded as "settled". That of course doesn't mean they can't be "unsettled" if some truly remarkable data shows up, but it's still a useful heuristic to concentrate on things that are more uncertain.
More so, the subject at hand is the evolution of a chaotic system with literally thousands of different influencing variables. This is not something as simple as gravity, electromagnetism, or even evolution. And the science of climatology is still very much an open debate. If the evidence of AGW actually was overwhelming then it'd be easy enough to present it and move on, as happened with the ozone hole. Instead the evidence is rather more subtle and has very significant error bars. If you believe that AGW requires bold action to avoid catastrophe then shutting down debate is an enormous mistake, because all it does is leave people who are unconvinced even less convinced while it forestalls the advancement of climate science and potentially the strengthening of evidence in support of that theory.
Gravity saw a heavy modification within the last 20 years with the discovery of the accelerating expansion of the Universe (dark energy forces).
The changes in our understanding of gravitation that have occurred in our generation do not make it advisable for you to walk off the edge of a building. That's what is meant by settled science.