I admire skepticism. Being cool-headed about empirical situations helps you make informed conclusions, and hence decisions, even as you might labour under the pressure of those situations.
Science constitutes formalized skepticism: strictly so in its theoretical, dehumanized sense; more approximately so in the way that scientists as a whole practice their craft. But science’s skepticism is self-correcting: an individual’s work within a scientific framework becomes, on the larger scale and through transparent reporting, peer review and what these days is called the wisdom of crowds, part of a huge, robust (if never truly watertight) skeptical project. There might be skeptical celebrities like James Randi, but scientists are the front-line troops of skepticism, working in the occasionally soul-destroying trenches. (Yes, I did do a science PhD: why did you ask?)
The IPCC and its members have produced some of the most consistently skeptical (and intellectually honest) research on climate change in the world. Every report it produces has to be agreed by consensus among its members, so their 2007 publication might be the most skeptical document yet in the annals of climate change: skeptics from 194 countries all have to agree on the content of each report. We see in this process that, as with the pursuit of science more generally, skepticism is additive: when two skeptics consider evidence and then agree, the agreement is stronger, skeptically speaking, than one from either skeptic alone.
In the real world this empirical strength can also be a political weakness: the IPCC accepted that honest skeptics could not just report the most extreme conclusions, yet we’ve discovered since that people have barely paid attention to even the least dramatic ones they reported. As we’re only just discovering, the IPCC’s skepticism was so strong as to approach, in the wider political context, intellectual conservatism.
Taking scientists as the biggest body of trained, knowledgeable climate skeptics we have, the majority skeptical position of the whole body of climate change research might be summarized from the IPCC report as:
Skeptics: climate change is happening; it’s almost certainly man-made; it would only recover on a long timescale, whatever we did to fix it”
As the IPCC were not vigorous or hyperbolic in their conclusions, let’s call this the best-case scenario, because there’s a clear relationship between the rate of climate change and its impact on human society. What other positions are there, then? Well, worse-case scenarios, basically. So what room for argument is there within a skeptical framework? The answer is: not much. Keep looking at the meta-analyses and look for any research that might contradict the skeptically-established conclusions above.
What place has “denialism” in the context of skepticism? In contrast with skeptics, a denialist does not refrain from commenting until the evidence has spoken for itself. A denialist denies the skeptics’ position: whether through lay ignorance, political motiviation or another askeptical reason. Let me make it clear that lay ignorance is itself understandable—if not entirely reasonable, in a country with daily papers, a network of libraries and science taught in schools—but it’s when it’s mistaken for anything more than ignorance that it becomes denialism. This isn’t a case of “us and them”, of excluding non-scientists, but rather about requiring healthy respect for empiricism and its tried and tested tools before anyone can enter into the debate, about increasing the generation of light rather than heat.
Skepticism, as we have seen, is additive. The combined work of many skeptics is itself very skeptical indeed. But skepticism is not multiplicative. You can’t, for example, excuse homeopathy in any intelligent manner by trying to discredit double-blind trials as the best indicator we currently have for clinical efficacy. (You might be able to discuss such higher matters as e.g. the philosophical validity of scientific induction, but you’d better have at least read about Carnap first so as not to prove yourself a dickhead.) To be skeptical of the efficacy of skeptical reasoning in the context of standard empirical study is therefore to deny the primacy of the empirical world (interpreted through standard data analysis) over one’s preferred theories about it; that philosophy is, ultimately, denialism.
To say that the term “denialism” is divisive might be factually correct but is rhetorically fatuous. “Denialism” divides intellectual reasoning into skeptical and non-skeptical, which is essential for meta-analysing any set of conclusions form a number of sources. Within an intellectual framework you cannot reconcile on the one hand viewpoints which are incorrectly held (as determined by that framework’s value system), with on the other hand those which are correctly held (ditto), and hope ever to arrive at a correctly held conclusion. For example, if one man does not believe the sky is blue, but claims it to be bright purple, then even if we apply some mealy-mouthed relativism and ultimately agree to start by calling the sky faintly indigo, we not merely begin at a factually incorrect standpoint, but we also begin at a point that neither the bluesky denialist (“bright purple, not backsliding indigo!”) nor the skeptic (“it’s not really indigo at all, but blue, well, a mixture of wavelengths”) is happy with! The division might even be described in terms of employment: no scientist, engineer or philosopher worth his salt would want a denialist working in his research group. They pollute the skeptic’s water supply, at source.
To fail to use “denialism” and “denialist”—whether in the context of flat-earthers, perpetual-motion enthusiasts or most recently geocaust denialism—and to kindly assume that such people must be “skeptics” instead is to insult the intellectual rigour of every skeptic whoever lived. Skepticism is hard, and it does it a disservice to confuse it with lazy—in the sense of unresearched, or unsupported—dismissiveness. Denialist viewpoints are factually incorrect and at odds with skeptical empiricism, and empiricism has a duty to itself to make that clear.