A new study, published in PLOS One, highlights a disturbing phenomenon: when people are repeatedly exposed to claims, they tend to believe them more, even if the claims are false or counter to their beliefs. This research focused specifically on climate change, examining whether repetition could make even climate-skeptical claims seem more truthful to those who support climate science. The results show that repetition increases the perception of truth not only for claims aligned with climate science but also for those that contradict it.
The study, led by Yangxueqing (Mary) Jiang, a PhD student in psychology at the Australian National University, aimed to explore a pressing issue in today’s information landscape: the spread of misinformation, particularly around climate change. While it is well-established that repeating a claim can make it seem more believable—an effect known as the “illusory truth effect”—most previous research has focused on general knowledge or trivia. Jiang and her team wanted to push this understanding further by examining whether the same effect would hold when it comes to strongly held beliefs, such as attitudes about climate change.
“Even though some 97+ percent of climate scientists agree that climate change is to a large extent human-made, media reports have long pursued ‘balance’ by allowing climate skeptics to add a (scientifically questionable) comment,” said study author Norbert Schwarz, a provost professor at the University of Southern California and co-director of the USC Dornsife Mind & Society Center.
“This increases the public’s exposure to climate-skeptical claims. Psychological research has long shown that repeated exposure to a claim increases its acceptance as true. What was less clear is whether a repetition would even do so for people who hold opposing beliefs, that is, people who are well informed about climate science and convinced that it is caused by human activity.”
To investigate whether repetition influences the perceived truth of climate-related claims, the researchers conducted two experiments involving participants who generally supported climate science. These participants were recruited through Amazon’s Mechanical Turk platform. In both experiments, the researchers exposed participants to a mix of climate-related claims—some aligned with climate science, and others consistent with climate skepticism.
The experiments followed a similar design, utilizing a well-established method to measure the “illusory truth effect.” Participants were first shown a series of climate-related statements, half of which supported climate science and half of which aligned with climate skepticism. After a brief delay, participants were shown another set of statements, which included both previously seen (repeated) and new claims. They were then asked to rate how true they believed each statement to be on a scale.
The first experiment involved 52 participants, and the second expanded the sample size to 120 participants. Both experiments followed a similar structure: participants were presented with claims, completed a delay task, and then rated the truth of both repeated and non-repeated claims. In the second experiment, the researchers added an additional measure to gauge participants’ attitudes toward climate change in more detail, using a well-validated survey to categorize their beliefs and concern about climate change.
Climate science endorsers consistently rated climate-science-aligned claims as more truthful than climate-skeptic claims. However, when claims were repeated, participants rated them as more believable, even when the claims contradicted their prior beliefs about climate change. This “illusory truth effect” was evident for both pro-attitudinal claims (those that aligned with participants’ support for climate science) and counter-attitudinal claims (those that aligned with climate skepticism).
In both experiments, participants showed an increased belief in repeated claims compared to non-repeated ones. Importantly, this effect was observed even for the strongest supporters of climate science. Those who were most alarmed by climate change, as categorized in the second experiment, were still more likely to believe repeated climate-skeptical claims than non-repeated ones, though they remained more inclined to support climate science overall. The findings suggest that repetition has a powerful influence on perceived truth, even in the face of strong, pre-existing beliefs.
“We expected that repetition increases perceived truth, as has been found many times,” Schwarz told PsyPost. “But we were surprised that people’s prior beliefs did not attenuate this effect. Our participants’ prior attitudes made no difference — repetition had the same influence on those who endorsed climate science only weakly and those who endorsed it most strongly.”
The study also revealed that the illusory truth effect applied to all types of claims, not just climate-related ones. Participants were also exposed to neutral weather-related claims, and the repetition of these claims led to an increased perception of truth, just as with the climate claims. This pattern underscores the idea that repetition impacts belief across a wide range of topics, regardless of whether the claims are aligned with existing beliefs or not.
“Do not repeat false information! And do not provide a platform to those who want to spread it,” Schwarz said. “Repetition increases the perceived credibility of information — even when we recognize it as problematic. Only repeat what’s true.”
While this study sheds important light on the power of repetition, it has some limitations. For one, the participants were largely supporters of climate science, which means the findings may not fully apply to climate skeptics. Understanding how repeated climate-science claims affect skeptics would be a valuable area for future research. Similarly, the study only looked at the effects of a single repetition of a claim. It remains unclear how many repetitions are needed to produce more long-lasting changes in belief, or whether additional exposure to contradictory information could reverse the effect.
“This work is part of a research program into intuitions of truth: What makes an idea ‘feel right?’ And how can it feel ‘right’ even when we know better?” Schwarz noted.
The study, “Repetition increases belief in climate-skeptical claims, even for climate science endorsers,” was authored by Yangxueqing Jiang, Norbert Schwarz, Katherine J. Reynolds, and Eryn J. Newman.
