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The interpretation of IPCC probabilistic statements around the world


The Intergovernmental Panel on Climate Change (IPCC) uses verbal descriptions of uncertainty (for example, Unlikely) to convey imprecision in its forecasts and conclusions. Previous studies showed that the American public misinterprets these probabilistic statements. We report results from a multi-national study involving 25 samples in 24 countries and 17 languages. As predicted, laypeople interpret IPCC statements as conveying probabilities closer to 50% than intended by the IPCC authors. We show that an alternative presentation format supplementing the verbal terms with numerical ranges increases the correspondence between the public’s interpretations and the IPCC guidelines, and the terms are better differentiated. These qualitative patterns are remarkably stable across all samples and languages. In fact, interpretations of the terms in various languages are more similar under the new presentation format. These results suggest changing the way the IPCC communicates uncertainty.

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Figure 1: Distribution of the best probability estimates of the 4 terms by condition across 25 samples.
Figure 2: Cumulative distributions of rates of consistency with IPCC guidelines under the two conditions, across all 25 samples.
Figure 3: Consistency rates with IPCC guidelines in the two conditions, by sample.
Figure 4: The two-dimensional representation of the 4 target terms in the 25 samples in the Translation condition (stress = 0.009; left panel) and the VN condition (stress = 0.006; right panel).

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The work was supported by Grant no. 1125879 from the US National Science Foundation. The authors thank the local collaborators who translated and back translated the surveys and helped in local adjustments: W. Au (China and Hong Kong), M. Balassiano (Brazil), I. Barbopoulos (Sweden), J. Fuller (Korea), C. G. Vallejo (Chile), L. Hadar (Israel), A. Hansla (Sweden), E. Hölzl (Germany), Z. Hichy (Italy), M. Juanchich (France), A. Maydeu-Olivares (Spain), K. Nakamura (Japan), D. Őnkal (Turkey), M. Sirota (Slovakia), P. Śleboda (Poland), J. Sokolowska (Poland), G. Villejoubert (UK), C. Witteman (The Netherlands) and A. MacLean, for assistance in coordination of data collection.

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D.V.B.: initiated project, design, data analysis, and lead writer of the paper. H-H.P.: Coordinated data collection, design, data analysis, and writing. S.B.B.: Design, data analysis, and writing. M.S.: Data analysis and writing.

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Correspondence to David V. Budescu.

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Budescu, D., Por, HH., Broomell, S. et al. The interpretation of IPCC probabilistic statements around the world. Nature Clim Change 4, 508–512 (2014).

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