Communicating scientific uncertainties: Effects of message and audience characteristics in the context of microplastic health risks

Communicating uncertainties is central to science communication, yet evidence on its effects is inconclusive. In an online experiment with a quasi-representative sample in Austria (<i>N</i> = 1126), we investigated the effects of <i>message</i> (uncertainty type) and <i>audience</i> characteristics (science-specific attitudes/beliefs) as potential moderating factors on risk perception and policy support in the context of microplastic health effects. Uncertainty communication, specifically communicated lack of scientific consensus (<i>consensus uncertainty</i>), triggered lower risk perception (small effect), and indirectly decreased policy support through message credibility and risk perception. These negative effects were lower (and not statistically significant) when communicating the remaining knowledge gaps (<i>deficient uncertainty</i>). Beliefs about science as a debate were positively associated with risk perception, trust in scientists with policy support and preference for information about uncertain science with both. However, these audience characteristics did not moderate the effects of uncertainty communication. The results highlight the importance of considering uncertainty types in environmental and health risk communication.