The choice of words being used in the global warming debate indicates something about the people choosing those words.
For a long time now, many defenders of global warming science (e.g., Phil Plait) have been using the phrase “global warming denier” to intentionally put certain people in the same intellectual and moral sorting bucket as holocaust deniers. More recently, some have attempted to equate global warming skepticism with creationism. This Science Insider article, for example, asks the question “Is climate change education the new evolution?” and complains about “an ideological drive from pressure groups to ‘teach the controversy’ where no scientific controversy exists.”
There are certainly many closed-minded ideologues in the global warming debate who have earned such scorn. But neither those who use the “denier” pejorative, nor those who attempt to put global warming skepticism on par with creationism, have precisely defined who they are talking about when dishing out that kind of scorn, and consequently they are unfairly painting many legitimate skeptics as crackpots.
As I discussed here, there exists an entire spectrum of beliefs about global warming. Some believe global warming isn’t happening; some believe it is happening but is caused by natural factors; some believe it is caused by both human and natural contributions, but are uncertain about which dominates; some believe it is dominated by human contributions; and some believe it is caused virtually entirely by human activity.
Exactly which of these people are being referred to by those who cry “deniers”?
Exactly which of these people are among those who are calling to “teach the controversy” where, it is claimed, “no scientific controversy exists”?
Some of the controversy that exists is legitimate; thus it is important, if we wish to be fair-minded, to make a distinction between “deniers” and legitimate skeptics.
It is not controversial that the globe has been warming. The temperature record is quite clear, and anybody who claims that global warming isn’t happening is either misinformed or in denial of the evidence. So one could fairly call those people “deniers” (but it would be nice to explicitly define that this is what you mean).
It is also beyond legitimate controversy that CO2 is a greenhouse gas, and adding it to the atmosphere, all other things being equal, will raise the global average temperature over time.1
It should also be noncontroversial that there is, or at least there has been in modern times, a natural component to modern global warming (without yet claiming whether it’s the predominant factor). The Little Ice Age ended around or not long after 1849, at which point the earth began naturally warming. Given the kinds of time scales usually discussed in the context of global warming cycles, it is not unreasonable to think the warming continuing to date since then might include at least a component of natural warming related to this emergence from a cold period.
There is quite a bit of legitimate controversy surrounding the use of current climate models, which simplify or neglect many phenomena and rely not just on CO2 but on questionable positive feedback mechanisms to account for as much as 70%-80% of the predicted warming (in the more catastrophic predictions).
So it is entirely legitimate to question the degree to which scientists have pinned down the exact balance of human vs. natural contributions, and to be skeptical of the more catastrophic predictions being made.
But because of the ambiguity of the phrase “global warming denier” and claims that “no controversy exists”, one is left with the impression that all these types of skeptics are being referred to. Lumping the legitimate skeptics in with the true deniers is misleading and unfair. It is at best an unintended over-generalization, and at worst a deplorable and intellectually dishonest attempt to discredit legitimate skeptics and quash their concerns with the ongoing climate science by associating them with crackpots.
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1 Note, though, that this is a diminishing effect; the more CO2 you add, the less the temperature rises. If, for example, adding 200 parts per million (ppm) of CO2 to the atmosphere raises the temperature by 1C, then to raise the temperature by another 1C you need to add 400 parts per million; to raise it by yet another 1C, you need to add 800 ppm; and so on.