Negative verbal probabilities undermine communication of climate science

Abstract

The Intergovernmental Panel on Climate Change (IPCC) recommends describing low-probability outcomes using negative verbal probability terms such as unlikely, rather than positive terms such as a small probability. However, we propose that this choice of probability terms might undermine public perception and understanding of climate science. Across eight preregistered experiments (N = 4,150), we find that participants perceive outcomes described with negative low probability terms as reflecting lower scientific consensus than probabilistically equivalent but positively framed terms. The effect persists after controlling for beliefs in climate change, familiarity with the IPCC and political orientation, although it weakens when the projected values exceeded participants’ personal expectations. Participants also associate negative low-probability terms more strongly with extreme outcomes and judge them as less evidence-based than their positive counterparts. We recommend using positive verbal probabilities to communicate comparable levels of uncertainty without undermining perceptions of scientific consensus and evidence.