Repetition increases belief in climate-skeptical claims, even for climate science endorsers

source information [21, 48] the combined effect of counter-attitudinal claims from low credi- bility sources, especially under conditions of political polarization, has not been tested. Implications for climate science communication From the perspective of climate science communication, our results highlight the downside of repeating scientifically unsupported claims of climate skeptics: a single repetition is enough to nudge recipients towards acceptance of the repeated claim, even when their attitudes are aligned with climate science and they can correctly identify the claim as being counter-attitudi- nal. People may encounter claims in environments where veracity can be carefully inspected— hearing from a climate scientist in a lecture. However, social media and other online news out- lets are a significant source of information, where people may encounter falsehoods decoupled from evidence and where claims may be shared repeatedly and rapidly, regardless of veracity. With the proliferation of climate science misinformation on social media [61] and the repeti- tion of skeptic claims in the interest of allegedly “balanced” reporting [62], skeptic claims can affect not only recipients who may be predisposed to climate skepticism, but also recipients who are strong climate science supporters. While longitudinal analyses indicate that scientifi- cally accurate media reporting has increased in recent years [63], there remains considerable variance across countries [64] and news outlets, with more conservative news sources provid-

ing less accurate coverage of the scientific consensus across a number of scientific topics [63]. Unfortunately, the large psychological literature on illusory truth effects shows that the power of repetition is robust over longer delays [65] and difficult to undermine—neither warning people that some of the claims they hear are false [19], nor individual differences in depth of thought or critical thinking fully eliminate the effect of repetition on assessments of truth [18, 51, 52], although such variables can (sometimes) attenuate the effect size. Fortu- nately, however, the power of repetition is not limited to skeptic-aligning information—it also extends to the repetition of scientifically correct information. Our participants rated claims that were aligned with climate scientists as truer when they were repeated than when they were not, even though most of our climate science-endorsing participants were already familiar with what they read. Moreover, the influence of repetition was independent of how strongly participants endorsed climate science. This implies that it is beneficial to repeat scientist-align- ing information, even when recipients are already in agreement with it. Finally, further research is warranted to better understand whether repeating counter-atti- tudinal information has similar effects on other samples, such as climate skeptics who were underrepresented in our samples, as well as for other topics where people hold divided beliefs and attitudes, such as immigration, education, and healthcare policies. It is also important to

understand whether the effects hold over time, or with more repetitions. While ITE research demonstrates that one repetition of a trivia statement can lead to an increase in perceived truth a month after an initial exposure [65], with repeated exposures increasing perceived truth even up to 16 exposures later [66, 67], we do not know whether such persistent effects also emerge when the initial content is counter-attitudinal. For instance, under a motivated reasoning framework, people may seek out more evidence that is congruent with their beliefs [68] and regard such evidence as stronger than incongruent evidence [69], which over time may lead to more elaboration, higher accessibility, and more fluent processing of attitudinally congruent content. In sum, the present results converge with insights from other content domains [8, 47] in supporting a straightforward communication recommendation: Do not repeat false informa- tion. Instead, repeat what is true and enhance its familiarity. PLOS ONE Illusory truth effect for climate-skeptical claims PLOS ONE | https://doi.org/10.1371/journal.pone.0307294 August 7, 2024 15 / 19