It's journal club time (episode 391)! Lewandowsky et al. on scientific consensus - Cultural Cognition of Health

Thanks to the many friends who sent me emails, made late night phone calls, or showed up at my front door (during the time when the storm had knocked out internet & phone service) to make sure I saw Lewandowsky, Gignac, & Vaughan’s The pivotal role of perceived scientific consensus in acceptance of science in Nature Climate Change . It’s a really cool paper!

LGV present observational and experimental evidence relating to public perceptions of scientific consensus on climate change and other issues. CCP did a study on scientific consensus a couple yrs ago,  — Kahan, D.M., Jenkins-Smith, H. & Braman, D. Cultural Cognition of Scientific Consensus. J. Risk Res. 14, 147-174 (2011)–which is one of the reasons my friends wanted to be sure I saw this one.

The paper presents two basic findings. I’ll say something about each one.

Finding 1: Perceptions of scientific consensus determine public beliefs about climate change–and in essentially the same way that they determine it on other risk issues .

In the observational study, the respondents (200 individuals who were solicted to participate in person in downtown Perth, Australia) indicated their beliefs about (a) the link between human CO 2 emissions and climate change (anthropogenic global warming or “AGW”), (b) the link between the HIV virus and AIDS, and (c) the link between smoking and lung cancer.  The respondents also estimated the degree to which scientists believed in such links. LGV then fit a structural equation model to the data and found that a single “latent” factor — perception of scientific consensus with respect to the link in question — explained the respondents’ beliefs, and “fit” the data better than models that posited independent relationships between respondents’ beliefs and their perceptions of scientific consensus on these matters. So basically, people believe what they think experts believe about all these risks.

Surprised? “Of course not. That’s obvious!”

Shame on you, if that is how you reacted. It would have been just as “obvious!” I think, if they had found that perceptions of scientific consensus didn’t explain variance in perceptions of beliefs in AGW, or that such perceptions bear a relationship to AGW distinct from the ones on other risks. That’s because lots of people believe that skepticism about climate change is associated with unwillingness to trust or believe scientists. If that were true, then then the difference between skeptics and believers wouldn’t be explained by what they think scientific consensus is; it would be explained by their willing to defer to that consensus.

Most social science consists in deciding between competing plausible conjectures. In the case of climate change conflict, two plausible conjectures are (1) that people are divided on the authority of science and (2) that people agree on the authority of science but disagree about what science is saying on climate change. LGV furnish more evidence more supportive of (2) than (1). (BTW, if you are curious about how divided Australians are on climate change, check this out.)

In that regard, moreover, their finding is exactly in line with the CCP one. Using a large ( N = 1500) nationally representative sample of US adults, we measured perceptions of scientific consensus on climate change, nuclear power risks, and gun control. These are highly contentious issues, on which American citizens are culturally divided. Nevertheless, we found that no cultural group perceives that the view that is predominant among its own members is contrary to scientific consensus. (We also found that all the groups were as likely to be mistaken as correct about scientific consensus across the run of issues, at least if we treated the “expert national consensus reports” of the National Academy of Sciences as the the authority on what that consensus is.)

So next time you hear someone saying “climate skeptics are anti-science,” “the climate change controversy reflects the diminishing authority of/trust in scientists” etc., say “oh, really? What’s your evidence for that? And how does it relate to the LGV and CCP studies?”

Finding no. 2: When advised that there is overwhelming scientific consensus in favor of AGW, people are more likely to believe in AGW — and this goes for “individualists,” just like everyone else.

The experiment subjects (100 individuals also solicited to participate in person in Perth, Australia) indicated their AGW beliefs after being randomly assigned to one of two conditions: a “consensus information” group, which was advised by the experimenters that there is overwhelming scientific consensus (97%) on AGW; and a “no information” group, which was not supplied any information on the state of scientific opinion.

LGV found, first, that subjects in the consensus-information group were more likely to express belief in AGW. This result adds even more weight to the surmise that popular division over climate change rests not on a division over the authority or credibility of scientists but on a division over perceptions of scientific consensus.

Second, LGV found that the impact of consensus-information exposure had a stronger effect on subjects as their scores on a “free-market individualism” worldview measure increased. In other words, relative to their counterparts in the no-information condition, subjects who scored high in “individualism” were particularly likely to form a stronger belief in AGW when exposed to scientific-consensus information.

Although also perfectly plausible, this finding should definitely raise informed eyebrows.

Public opinion on climate change in Australia , as in the US, is culturally divided.  Consistent with other studies, LGV found that individualism generally predicted skepticism about AGW.

We know (in the sense of “believe provisionally, based on the best available evidence and subject to any valid contrary evidence that might in the future be adduced”; that’s all one can ever mean by “know” if one actually gets the logic of scientific discovery) that individualist skepticism toward AGW is not based on skepticism toward the authority of science. Both the observational component of the LGV study and the earlier CCP study support the view that individualists are skeptical because they aren’t convinced that there is a scientific consensus on AGW.

Well, why? What explains cultural division over perceptions of scientific consensus?

One conjecture — let’s call it “cultural information skew” or the CIS — would be that individualists and communitarians (i.e., non-individualists) are exposed to different sources of information, and the information the former receives represents scientific consensus to be lower than does the information the latter receives.

But another conjecture — call it “culturally biased assimilation” or CBA — would be that individualists and communitarians are culturally predisposed to credit evidence of scientific consensus selectively in patterns that fit their predisposition to form and maintain beliefs consistent with the ones that prevail within their cultural groups. CBA doesn’t imply that individualists and communitarians are necessarily getting the same information. But it would predict disagreement on what consensus is even when people with those predispositoins are supplied with the same evidence.