Confidence levels and likelihood terms in IPCC reports: a survey of experts from different scientific disciplines

Research output: Journal contributionsJournal articlesResearchpeer-review


  • Astrid Kause
  • W. Bruine de Bruin
  • Johannes Persson
  • H. Thorén
  • L. Olsson
  • A. Wallin
  • S. Dessai
  • N. Vareman

Scientific assessments, such as those by the Intergovernmental Panel on Climate Change (IPCC), inform policymakers and the public about the state of scientific evidence and related uncertainties. We studied how experts from different scientific disciplines who were authors of IPCC reports, interpret the uncertainty language recommended in the Guidance Note for Lead Authors of the IPCC Fifth Assessment Report on Consistent Treatment of Uncertainties. This IPCC guidance note discusses how to use confidence levels to describe the quality of evidence and scientific agreement, as well likelihood terms to describe the probability intervals associated with climate variables. We find that (1) physical science experts were more familiar with the IPCC guidance note than other experts, and they followed it more often; (2) experts’ confidence levels increased more with perceptions of evidence than with agreement; (3) experts’ estimated probability intervals for climate variables were wider when likelihood terms were presented with “medium confidence” rather than with “high confidence” and when seen in context of IPCC sentences rather than out of context, and were only partly in agreement with the IPCC guidance note. Our findings inform recommendations for communications about scientific evidence, assessments, and related uncertainties.

Original languageEnglish
Article number2
JournalClimatic Change
Issue number1-2
Number of pages18
Publication statusPublished - 01.07.2022

Bibliographical note

Open Access funding enabled and organized by Projekt DEAL. The research was funded by the Swedish Research Council Formas Linnaeus grant LUCID, Lund University Centre of Excellence for Integration of Social and Natural Dimensions of Sustainability (259–2008-1718; to AK, JP, HT, LO, and NV); the Swedish Foundation for Humanities and Social Sciences’ VBE program, Science and Proven Experience (M14-0138:1; to WBdB, JP, NV, and AW); the Center for Climate and Energy Decision Making (CEDM) through a cooperative agreement between the National Science Foundation and Carnegie Mellon University (SES–0949710 and SES–1463492; to WBdB).

Publisher Copyright: © 2022, The Author(s).

    Research areas

  • Communication, Confidence, Expert judgment, IPCC, Probability, Scientific assessment, Uncertainty
  • Psychology