People who wish to question the validity of climate science usually call themselves “sceptics”. Scientists object to this, since all good scientists are perennially sceptical (indeed, the motto of the Royal Society is Nullius in Verba i.e. “take no-one’s word for it”). The so-called “sceptics” object to being called “deniers”, although that is usually what they do (i.e. deny the validity of statements, despite the evidence that supports them). Perhaps this is understandable, given the association of the word with the unpleasant business of holocaust denial. To avoid accusations of bad faith, I therefore commend the term “dissenters” as preferable. It is not pejorative, and also accurately describes what they do, i.e. dissent from the consensus of mainstream scientific opinion.
By the way, there is an excellent iPhone app called Skeptical Science that has good answers to lots of controversial questions on climate science. It’s a nice complement to the excellent RealClimate web-site.