In my last blog, I described five types of climate change denier. Not all of them are equally serious, and “denier” needs to be construed broadly. But all of them feed into the phenomenon of denying human-caused climate change. Here’s a recap:

• The Deceiver knows that he or she is distorting the science and does so willfully.
• The Deceived is victim of the deception and hence just has false beliefs about climate change and the science around it.
• The Self-Deceived actively seeks out evidence (or “evidence”) that supports the denialist position, often because denial is part of his or her cultural identity.
• The Skeptic is a sophisticate who claims the evidence doesn’t show one way or another whether human-caused climate change is occurring—but is often biased against the validity of the scientific evidence for climate change.
• The Truly Ignorant does not know or claim to know about climate change; this could be because of lack of interest or due to being bewildered by all the conflicting information in the popular media.

The types have lots of overlap, but they are in principle (and often in practice) distinct.

In this blog, I want to apply this taxonomy to a prominent controversy in the psychological literature about climate change denial and go some of the way to resolving it. The key idea is that elements of two different types can and often do co-exist in the same person.

On the one hand, Dan Kahan argues that increasing people’s knowledge of science—and even climate science in particular—does not increase acceptance of human-caused climate change (where that means agreeing on a survey that there is “solid evidence” of human-caused global warming; see the graphs below). This is surprising, because one would think that knowing the science would aid in accepting it. Kahan’s experimental strategy is to measure people’s scientific literacy and check whether it has a meaningful relationship to their climate change acceptance. His short answer is that it doesn’t: higher levels of scientific literacy don’t correlate with greater acceptance of climate change. The average scientific literacy of deniers is no lower than the average scientific literacy of acceptors.

If it’s not scientific literacy, what does Kahan think is going on?

His answer is the Cultural Cognition Thesis. People embrace positions on climate change that support their social identities: liberal, conservative, communitarian, individualist, etc. People often know what scientists say about climate change. But that doesn’t mean that they’ll express agreement with it. An oil executive, for example, might know some of the science but commit to denying climate change out of allegiance to the in-group of people in the oil industry.

Kahan’s finer-grained picture is this. Among liberals (and scientists themselves, of course), increased scientific knowledge is associated with greater climate change acceptance. But among conservatives, it’s the opposite: knowing more about science is associated with decreased climate change acceptance. That, of course, is depressing. Knowing more science gives conservatives additional tools for denying climate change in a sophisticated-sounding way. Here are two of his key graphs. Notice that in the right-hand graph the trends go in opposite directions for liberals and conservatives.

If Kahan is right, reason and persuasion (at least on this topic) keep little company together.

On the other hand, Michael Ranney’s research seems to demonstrate the opposite of Kahan’s. Ranney and colleagues have designed interventions that teach people the mechanisms of how global warming works. And in their experiments, they show that teaching those mechanisms strengthens acceptance (they probed acceptance by using various measures of belief that human-caused climate change was occurring). For them, mechanistic knowledge is key.

What exactly is this mechanistic knowledge? It’s knowledge about the moving parts and causal structure of a system. It turns out that even most people who accept global warming don’t know the following basic information: greenhouse gasses, like CO₂ and methane, increase the atmosphere’s ability to absorb infrared rays; absorbing infrared rays warms the atmosphere; so more greenhouse gasses lead to higher temperatures as light reflects as infrared rays off the earth’s surface. (See also Ranney’s website with videos: HowGlobalWarmingWorks.org.) Ranney’s position is that when people learn those mechanisms they increase their acceptance.

If Ranney is right, reason and persuasion are allies.

How shall we resolve this controversy?

To start, Kahan’s and Ranney’s data aren’t strictly contradictory. Kahan, though he measured various aspects of climate change knowledge, didn’t assess the specific mechanistic knowledge found in Ranney’s interventions, as Ranney points out. So it could be that mechanistic learning has special properties that produce acceptance. But the deeper question is why that would be the case.

I think the answer is that humans have both the ability to be persuaded by reason and to engage in “identity protective cognition” (as Kahan calls it). For any given topic that’s neutral with respect to identity, learning through reason is the default. To pick a random topic, say you just wanted to learn about prairie animals in Kansas; you’d probably look articles up, think them through, and come to rational conclusions that constitute better knowledge about those animals. No identity protective cognition. But when a topic is a litmus test for cultural identity, mechanisms of identity protective cognition kick in.

Still, even when a topic is covered in identity politics, the human ability to think about it rationally has not disappeared; it’s just become suppressed. So what’s needed is a tactic for jogging people out of their identity protective mode and into their rational learning mode.

This is what Ranney’s experiments do. By presenting information about how global warming works that is clear and novel to most people, Ranney’s interventions spark curiosity and get them to let their identity protective guard down. The mechanistic knowledge isn’t something they’ve heard before in the ongoing culture war, so it seems less like an assault and more like straightforward information.

In other words, The Self-Deceiver and The Truly Ignorant often co-exist in the same person. The Self-Deceiver is the type that Kahan reveals; The Truly Ignorant is the type that Ranney shows is ready to absorb new information: the one who says, “Huh, I didn’t know that.”

Ranney, for the time being, seems to have found a way to get behind people’s identity-protective shields. That’s great. But if his methods become widespread, as I hope they do, you can be sure that The Deceivers and The Self-Deceivers will find new shields against them. So my resolution to the controversy is this: Kahan studies the identity-protective shields; Ranney looks for the cracks between them. Both, in my view, are doing the right thing by studying what they study. Saving the planet depends not just on cutting emissions; it depends also on changing the minds of people who are in denial, which depends in turn on understanding the psychology.