Anchoring climate change communications

Verbal probability expressions (VPEs) are frequently used to communicate risk and uncertainty. The Intergovernmental Panel on Climate Change attempts to standardise the use and interpretation of these expressions through a translation scale of numerical ranges to VPEs. A common issue in interpreting VPEs is the tendency for individuals to interpret VPEs around the midpoint of the scale (i.e. around 50%). Previous research has shown that compliance with the IPCC's standards can be improved if the numerical translation is presented simultaneously with the VPE, reducing the regressiveness of interpretations. We show that an explicit statement of the lower or upper bound implied by the expression (e.g. 0-33%; 66-100%) leads to better differentiated estimates of the probability implied by 'likely' and 'unlikely' than when the bound is not explicitly identified (e.g. less than 33%; greater than 66%).