"Deniers" believe that climate change is a normal and natural process that would occur with or without the participation of man. Man certainly is a variable that effects that change but a far less significant variable than what some would have us believe. Computer models that predict dire consequences have not proven to be accurate (at all!) indicating flaws in those models and the theories upon which they are based.
There is extremism on both sides of this issue. I suggest that a rational skepticism is the middle ground.
I think it's better to overestimating man's ability to impact the global climate than underestimating. The latter could be very expensive to fix and it could be too late. Why not be proactive rather than reactive?