Negations in uncertainty lexicon affect attention, decision-making and trust

The Intergovernmental Panel on Climate Change (IPCC) currently communicates uncertainty using a lexicon that features four negative verbal probabilities to convey extremely low to medium probabilities (e.g., unlikely). We compare a positive probability lexicon with the IPCC lexicon in a series of psychology experiments. We find that although the positive and negative lexicons convey a similar level of probability, the positive lexicon directs more attention towards the outcome occurrence, and encourages more cautious decisions: in our role-playing experiment it reduced the number of Type 2 errors, i.e. failures to make needed precautionary interventions. Whilst participants considered the negative lexicon more useful in making a decision, they trusted the positive lexicon more and blamed information providers less after making an incorrect decision. Our results suggest that the negative verbal framing of probabilities used by the IPCC is not neutral and has implications for how climate information is interpreted by decision-makers.