Scientific theories are always refutable---with better science. That element of self-correction is both the nature and the strength of the scientific method.
I quite frequently see scientists directly quoted in news reports as saying that man-made global warming is "established scientific fact". Very rarely do they ever strike me as being interested in debating the issue and very rarely do I ever hear them say things such as "I believe it's a fact, but it's possible that I'm wrong."
There are skeptics on the subject to be sure, but you have to admit that they usually tend to be ridiculed.