Response: An “externally-valid” approach to consensus messaging
Friday, June 20, 2014 at 1:42PM
Dan Kahan

John Cook, science communication scholar and co-author of Quantifying the consensus on anthropogenic global warming in the scientific literature, Environmental Research Letters 8, 024024 (2013), has supplied this thoughtful response to the first of my posts on "messaging consensus." --dmk38

Over the last decade, public opinion about human-caused global warming has shown little change. Why? Dan Kahan suggests cultural cognition is the answer: 

When people are shown evidence relating to what scientists believe about a culturally disputed policy-relevant fact ... they selectively credit or dismiss that evidence depending on whether it is consistent with or inconsistent with their cultural group’s position. 

It’s certainly the case that cultural values influence attitudes towards climate. In fact, not only do cultural values play a large part in our existing beliefs, they also influence how we process new evidence about climate change. But this view is based on lab experiments. Does Kahan’s view that cultural cognition is the whole story work out in the real world? Is that view “externally valid”?

The evidence says no. A 2012 Pew surveys of the general public found that even among liberals, there is low perception of the scientific consensus on human-caused global warming. When Democrats are asked “Do scientists agree earth is getting warmer because of human activity?”, only 58% said yes. There’s a significant "consensus gap” even for those whose cultural values predispose them towards accepting the scientific consensus. A “liberal consensus gap”.

My own data, measuring climate perceptions amongst US representative samples, confirms the liberal consensus gap. The figure below shows what people said in 2013 when asked how many climate scientists agree that humans are causing global warming. The x-axis is a measure of political ideology (specifically, support for free markets). For people on the political right (e.g., more politically conservative), perception of scientific consensus decreases, just as cultural cognition predicts. However, the most relevant feature for this discussion is the perceived consensus on the left.

At the left of the political spectrum, perceived consensus is below 70%. Even those at the far left are not close to correctly perceiving the 97% consensus. Obviously cultural cognition cannot explain the liberal consensus gap. So what can? There are two prime suspects. Information deficit and/or misinformation surplus. 

Kahan suggests that misinformation casting doubt on the consensus is ineffective on liberals. I tend to agree. Data I’ve collected in randomized experiments supports this view. If this is the case, then it would seem information deficit is the driving force behind the liberal consensus gap. It further follows that providing information about the consensus is necessary to close this gap. 

So cultural values and information deficit both contribute to the consensus gap. Kahan himself suggests that science communicators should consider two channels: information content and cultural meaning. Arguing that one must choose between the information deficit model or cultural cognition is a false dichotomy. Both are factors. Ignoring one or the other neglects the full picture. 

But how can there be an information deficit about the consensus? We’ve been communicating the consensus message for years! Experimental research by Stephan Lewandowsky, a recent study by George Mason University and my own research have found that presenting consensus information has a strong effect on perceived consensus. If you bring a participant into the lab, show them the 97% consensus then have them fill out a survey asking what the scientific consensus is, then lo and behold, perception of consensus shoots up dramatically. 

How does this “internally valid” lab research gel with the real-world observation that perceived consensus hasn’t shifted much over the last decade? A clue to the answer lies with a seasoned communicator whose focus is solely on “externally valid” approaches to messaging. To put past efforts at consensus messaging into perspective, reflect on these words of wisdom from Republican strategist and messaging expert Frank Luntz on how to successfully communicate a message: 

“You say it again, and you say it again, and you say it again, and you say it again, and you say it again, and then again and again and again and again, and about the time that you're absolutely sick of saying it is about the time that your target audience has heard it for the first time. And it is so hard, but you've just got to keep repeating, because we hear so many different things -- the noises from outside, the sounds, all the things that are coming into our head, the 200 cable channels and the satellite versus cable, and what we hear from our friends.” 

When it comes to disciplined, persistent messaging, scientists aren’t in the same league as strategists like Frank Luntz. And when it comes to consensus, this is a problem. Frank Luntz is also the guy who said: 

“Voters believe that there is no consensus about global warming in the scientific community.  Should the public come to believe that the scientific issues are settled, their views about global warming will change accordingly.  Therefore, you need to continue to make the lack of scientific certainty a primary issue in the debate, and defer to scientists and other experts in the field.” 

Luntz advocated casting doubt on the consensus for one simple reason. When people understand that scientists agree that humans are causing global warming, then they’re more likely to support policies to mitigate climate change. Confuse people about consensus, and you delay climate action. 

This finding has subsequently been confirmed by studies in 2011 and 2013. But a decade before social scientists figured it out, Luntz was already putting into place strategies to drum home the “no consensus” myth, with the purpose of reducing public support for climate action. 

Reflecting on the disinformation campaign and the social science research into consensus messaging, Ed Maibach at George Mason University incorporates both the “internally valid” social science research and the “externally valid” approach of Frank Luntz:

We urge scientific organizations to patiently, yet assertively inform the public that, based on the evidence, more than 97% of climate experts are convinced that human-caused climate change is happening. Some scientific organizations may argue that they have already done this through official statements. We applaud them for their efforts to date, yet survey data clearly demonstrate that the message has not yet reached or engaged most Americans. Occasional statements and press releases about the reality of human-caused climate change are unfortunately not enough to cut through the fog—it will take a concerted, ongoing effort to inform Americans about the scientific consensus regarding the realities of climate change.

How do we achieve this? Maibach suggests climate scientists should team up with social scientists and communication professionals. What should scientists be telling the public? Maibach advises:

In media interviews, public presentations, and even neighborhood and family gatherings, climate scientists should remember that many people do not currently understand that there is an overwhelming scientific consensus about human-caused climate change. Tell them, and give them the numbers.

The book Made To Stick looks at “sticky” messages that have caught the attention in the public’s eyes. It runs through many real-world case studies (e.g., externally valid examples) to demonstrate that sticky ideas are simple, concrete, unexpected and tell a story. For a general public who think there is a 50:50 debate among climate scientists, learning that 97% of climate scientists agree that humans are causing global warming ticks many of the sticky boxes.


Article originally appeared on cultural cognition project (
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