Climate science: How a believer becomes a skeptic

In recent research published in the journal PLOS ONE, USC and Australian researchers explored the powerful effect of repetition on people's beliefs.

In two rounds studies, they found that even the strongest believers in climate science -- those categorized as "alarmed" believers -- felt that the skeptical and pro-climate beliefs seemed more true when they encountered them a second time.

"It could take as little as a single repetition to make someone feel as though a claim were true," said Norbert Schwarz, a study co-author and provost professor of psychology at USC Dornsife College of Letters, Arts and Sciences and USC Marshall School of Business. "It's certainly concerning, especially when you consider how many people are exposed to both truthful and false claims and either spread them or are persuaded by them to make decisions that might affect the planet.."

Truthiness

According to psychology research, people are more likely to feel statements are true if those statements reflect their own beliefs.

However, their perceptions can be changed if they encounter repeated statements. The more they are exposed to those statements, the more valid the statements seem. Psychologists refer to this as "truthiness" -- or, more formally -- the "illusory truth effect."

The team of researchers wondered how people who said they firmly believe in climate science would respond when they encountered climate-skeptical statements.

The researchers worked with 52 participants in the first round of study and 120 in the second. Almost all of the participants -- except for 10% -- believed in and endorsed climate science -- evidence that humans are mainly responsible for climate change.

In both studies, the participants were asked to rate the truth of a series of statements that were climate-skeptical, supportive of climate-science, or weather-related filler statements. Fifteen minutes later, they reviewed another round of claims -- half of which turned out to repeat the earlier statements. The participants then rated these claims on a six-point scale ranging from "definitely true" to "definitely false."

In the second round, the participants also were asked to determine if the claim seemed scientific or climate-skeptic.

Most of the participants (90%) supported climate science. They ranged from "concerned" people, who believe climate change is a problem, but take little action, to "alarmed" people who report the highest level of concern about climate change. Less than 10% assumed that climate change is not an important problem.

Independent of the strength of their convictions, the climate science believers considered all of the claims, including those that opposed their own beliefs in climate science, more valid when they were repeated. This was true even among the so-called "alarmed" participants, who were strongest climate science believers.

"People find claims of climate skeptics more credible when they have been repeated just once," said the study's lead author, Mary Jiang, of The Australian National University. "Surprisingly, this increase in belief as a result of repetition occurs even when people identify as a strong endorser of climate science."

Schwarz noted that the study indicates that there is a benefit to amplifying messages if they are truthful and reinforce action such as healthy behaviors. But repetition can also be harmful if the messages repeat falsehoods.

"In short, this study emphasizes what we have learned over the years, and that is: We should not repeat false information. Instead, we must repeat what is true so that it becomes familiar and more likely to be believed," Schwarz said.