This post is really a question. Over the past few years, ever since the climate change debate, well, heated up, the words "skeptic" and "denier" have been thrown around on countless websites and blogs, usually accompanied by much frothing at the mouth. This has left me wondering; is there anything bordering on a consensus among the climaterati that recognizes a difference between the two?

Now I understand of course that the words lie on an often too slippery continuum. I also realize that true deniers often conveniently cloak themselves with a veneer of polite skepticism. But it strikes me that my own perception of both groups is akin to Potter Stewart's famous take on pornography; I can't (and won't) always define them, but I can usually recognize bonafide cases, at least extreme ones. So for instance, in my dictionary Senator James Inhofe is squarely in the "denier" camp but Freeman Dyson is squarely in the "skeptic" camp.

In addition I firmly believe that being a skeptic is not just a good thing but a great thing; skepticism is what all of science is founded on after all. So I respect true skeptics as much as I detest true deniers. I am still undecided on someone like Bjorn Lomborg who seems to have started out as a firm denier but gradually gravitated toward the skeptic camp. There's the additional problem that people like Lomborg sometimes pitch a mix of denial and bonafide skepticism and it can be hard to distinguish between the two.

I also seem to have developed my own rough, somewhat well-defined compass for recognizing members of each group. As far as I can tell there are three central premises of the science of climate change, stated in my opinion in increasing order of uncertainty:

1. The climate is warming.

2. This warming is unprecedented and is almost certainly because of human influence.

3. This unprecedented warming is going to do some very bad (or at least unpredictable) things.

To me it appears that almost nobody except the most rabid fundamentalist denier would have a problem with the first point. Personally I would also call someone who disagrees with the second point as at least leaning toward being a denier; to me there's really no other good explanation for the warming that we have seen except human activity.

The third point is where it gets more interesting. There are people who agree that humans are warming the planet, but then wonder about the exact details of the effects: How much will it exactly warm? Will it warm equally everywhere? And most importantly - and this is something Bjorn Lomborg has often asked - would the favorable effects of the warming outweigh the unfavorable ones? Many of these questions involve prediction and they ask if the science and art of climate change is predictive enough. I have to say that in most cases I place people who ask these kinds of questions in the "skeptic" camp, although there are sometimes exceptions. It's also not escaped my notice that the difference between denial and skepticism sometimes simply comes down to whether someone is just throwing around opinions or actually sweating the details.

But that's enough of what I think. What do readers think? Who in your opinion is a "skeptic" and who is a "denier"? And let's also involve the other side, the one which thinks that the whole thing is a giant communist scam or misguided science or whatever. What kinds of terms do you have for the moderate and extreme varieties in your sworn enemies and how do you define them?

Friendly housekeeping note: More than for other posts I am going to have the comments on this post on a tight leash since I don't want the comments section to morph into a mudfest. Strong disagreement and criticism are fine, strenuous arguments are ok, interpretive dance videos are especially welcome; unhinged rants are not. What we are looking for is a spectrum of opinion on definitions. Maybe something approaching a consensus will emerge from the comments or maybe opinion will be as diverse as species of beetles. In either case with enough commenters it should be interesting.