By Lindsey Thurman, for the PLOS Ecology Community

With the recent publication of the 2014 IPCC report on Climate Change, the 2014 US National Climate Assessment, and the upcoming Paris 2015 UN Climate Conference, it’s no surprise that the scientific consensus on human-caused climate change has reached approximately 97%.

The messages we are offering, like President Obama’s opening speech at GLACIER, are incredibly powerful so why is public understanding of this consensus still so low? And how will the world respond to an international climate agreement when the majority don’t understand that we [scientists] agree on the climate? This presents a serious challenge to the most important outcome of Paris 2015 — moving forward on public policy action.

This spring, Myers et al (2015) published a paper empirically examining this disagreement over the level of agreement and offered a fairly straightforward solution to improving public understanding: KISS.

Keep It Short & Simple 😉 Some of you may be familiar with this acronym. I’m obviously embellishing the author’s message, but it’s more or less the same.

In the first part of this study, the authors conducted a survey of adults online based on known demographic characteristics to resemble the American adult population. They provided 5 statements describing scientific agreement on human-caused climate change. The first 4 statements were numeric assertions, whereas the last was non-numeric; testing the hypothesis that numeric messages will result in higher estimates of scientific agreement because they present explicit facts. These statements were as follows:

“97.5% of climate scientists agree…” “97%…” “97 out of 100…” [There’s only 100 climate scientists?!] “More than 9 out of 10…” [There’s only 10 climate scientists?!!!] “An overwhelming majority …” [So, like 7?]

Each of these messages was presented within an ad alongside either the American Association for the Advancement of Science (AAAS) logo, or a control with just a cell phone ad. This was an interesting test of public manipulation — can the message be enhanced by pairing it with a reputable source? The authors also measured each participant’s political ideology (ranging from very liberal to very conservative) to test for motivated reasoning, i.e. the influence of the politically-polarized nature of the “debate”. After being presented with these questions, the participants were asked to estimate the percent of scientific consensus on climate change on a sliding scale, as well as their confidence with respect to their answer.

As expected, the ambiguity of the non-numeric statement (“An overwhelming majority…”) did not increase participant’s estimates of scientific consensus on climate change. [According to the authors, “We found that numeric statements resulted in higher estimates of the scientific agreement.”]

Interestingly, the numeric messages had a similar effect regardless of people’s political ideologies. The authors hypothesize that this may have something to do with the use of the AAAS logo, which may be perceived as an unbiased, credible source to most. Yes, apparently even Republicans. It’s possible that had the authors used a logo from NOAA, or some other climatologically-based organization, there may have actually been a back-fire in responses from conservative participants if they perceive those organizations to be biased. Thankfully they didn’t use the EPA logo. Amiright?

A second part to this study looked further into the idea that numbers are not perceived in a vacuum. For example, in a separate study, when women were asked to estimate their risk of breast cancer, they consistently overestimated it — this is likely due to the fact that they had no information to compare their estimates.

The authors tested this comparative context by requiring participants to estimate the level of scientific consensus prior to reading information about actual levels of consensus. They predicted that this “information gap” would increase the perception of scientific agreement compared to just being presented the information and asking for their estimates (as in part 1 of the study). This method actually worked better at increasing people’s estimates of scientific consensus on climate change, as well as their confidence in those estimates, than the previous method. The authors refer to this second method as “estimation and reveal”.

While this paper provides solid evidence that a simple, clear message can increase people’s perception of the scientific consensus on climate change, it may not necessarily change how we process or respond to the issue.

Take, for instance, the videos of the chairman of the Paris 2015 conference and President Obama’s speech mentioned previously. Their messages, while accurate and extremely captivating (and often depressing) to those on board with climate change, never explicitly tell you that 97% of climate scientists overwhelmingly agree upon human-caused climate change. They just say things like “The science is stark” and “We know that we are under threat”. Well, what is the science and who is ‘we’? How many of us agree on this threat? After reading the Myer et al (2015) paper, I now realize that this is a critical message and I have to question whether or not the public is even absorbing the rest of the information, much less being motivated to take action.

van der Linden et al. (2015) take it a step further to show how important this numeric message can be as it essentially links public perception and action.

The authors present a gateway belief model wherein perceived scientific agreement on climate change is a “gateway belief” that can either support or undermine other beliefs about climate change (e.g. that it’s actually happening, human-caused, and/or worrisome), which in turn influence public action.

If you’re an ecologist like me, this is essentially the trophic cascade of communication. The authors found that public understanding of the scientific consensus is consequential as it increases the belief that climate change is happening, human-caused, and worrisome.

One of the key take home messages from this paper is that ambiguity in scientific facts causes people to use consensus among perceived experts to guide their beliefs and actions on climate change. These perceived experts may be contributing to the “misinformation surplus” described by the authors, while the scientific consensus “information deficit” persists.

In essence, the authors collectively propose a tangible strategy for shrinking the information deficit (the “estimation and reveal” method) via consensus-messaging campaigns to reduce skepticism and increase the public’s desire for action.

I am interested to see how the message is shared after the Paris 2015 conference. How universal will this climate agreement be? 100%?

Lindsay Thurman is a Ph.D. Candidate in the Department of Fisheries & Wildlife at Oregon State University and Research and a Fellow with the Department of the Interior’s Northwest Climate Science Center. Her blog is The Cascadae Project. On Twitter @ectothurm