An astute reader might well ask why I write "septic" where you might expect me to write "skeptic" (e.g. here). Its not a mistake of course. And its not just because I can never remember whether its a c or a k. No, its deeper than that... read on, though I warn you that this post is mostly meanings-of-words, not science.
So: the people who, for one reason or another, disbelieve the standard global warming consenus (if they know enough they will know its the IPCC they disagree with; if they are ignorant they will rant about enviro's or somesuch) are usually called skeptics. Or sceptics (I tend to use the k version, when I'm being polite). But there is a problem with this: the true definition of skeptic in this context is something like:
skeptic [Gr. skeptiko`s thoughtful, reflective, fr. ske`ptesqai to look carefully or about, to view, consider] 1. One who is yet undecided as to what is true; one who is looking or inquiring for what is true; an inquirer after facts or reasons.
(I got that from here and edited it lightly (update 2004/12/11: but! they've changed the page. Argh. OK, so for the moment you can get the version I saw from googles cache, and if that fails, the original source is Webster's Revised Unabridged Dictionary. I've also created an entry at wictionary in frustration; and the same defn is also available from BrainyDictionary. Anyway you know what I mean...)).
This defn of skeptic applies to all scientists: who amongst us is not thoughtful? who does not look carefully? who is not an inquirer after facts? There is a danger of the unthinking saying "aha! these folks call themselves skeptics. Therefore the other side must be careless enthusiasts". And indeed, thats the sort of level of logic that the septics themselves usually operate at. Its like saying "aha! one of the parties in the US are called Democrats. That means the other ones must be totalitatians!" (err, well, whether or not you agree with the conclusion you have to admit the logic is poor).
Which is why I prefer septic. Its close enough that you recognise the term. And it describes their style of debate quite accurately.
While we're here, there are another two terms worth noting, "denialist" (in the sense of global warming denialist) and "contrarian". Neither has really caught on because they carry the wrong associations. The first one is fairly accurate (they define themselves in opposition, rather than having anything of their own to say. See a comment by Eli Rabett on Deltoid) but has perhaps unfortunate connotations of holocaust denial. Contrarian is OK too: they are speaking out against the established consensus. OTOH they tend not to like this themselves, since as far as they are concerned there either is no consensus or (if they are pushing their luck in a forum where they think they might get away with it) they think they are the consensus.