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assessment reports. In particular, quantitative probabilities (subjective or objective) should be assigned only to well-defined outcomes and only when there is adequate evidence in the literature and when authors have sufficient confidence in the results. Assigning probabilities to an outcome makes little sense unless researchers are confident in the underlying evidence (Risbey and Kandlikar, 2007), so use of the current likelihood scale should suffice. Recommendation ►Quantitative probabilities (as in the likelihood scale) should be used to describe the probability of well-defined outcomes only when there is sufficient evidence. Authors should indicate the basis for assigning a probability to an outcome or event (e.g., based on measurement, expert judgment, and/or model runs). The Working Group II Summary for Policymakers in the Fourth Assessment Report contains many vague statements of ‘high confidence’ that are not supported sufficiently in the literature, not put into perspective, or are difficult to refute. The Committee believes that it is not appropriate to assign probabilities to such statements. There is, moreover, a danger that the confidence scale may be misinterpreted as indicating a statistical level of confidence in an outcome. Subjective probabilities may be assigned legitimately to well-defined outcomes using the likelihood scale. The presentation of results in the Fifth Assessment Report would be strengthened by assigning subjective probabilities only to well-defined conclusions. Recommendation ►The confidence scale should not be used to assign subjective probabilities to ill-defined outcomes. Studies have found that individuals interpret the words in the likelihood scale very differently (Morgan et al., 2009; Patt and Schrag, 2003), even when given the terminology and probability scale in Table 3.3 (Budescu et al., 2009). An individual is more likely to understand the authors’ intent if results are stated using both probability ranges and words (Budescu et al., 2009). 40 Climate change assessments | Review of the processes and procedures of the IPCC
Recommendation ►The likelihood scale should be stated in terms of probabilities (numbers) in addition to words to improve understanding of uncertainty. Studies suggest that informal elicitation measures, especially those designed to reach consensus, lead to different assessments of probabilities than formal measures. (Protocols for conducting structured expert elicitations are described in Cooke and Goossens [2000].) Informal procedures often result in probability distributions that place less weight in the tails of the distribution than formal elicitation methods, possibly understating the uncertainty associated with a given outcome (Morgan et al., 2006; Zickfeld et al., 2007). Recommendation ► Where practical, formal expert elicitation procedures should be used to obtain subjective probabilities for key results. Climate change assessments | Review of the processes and procedures of the IPCC 41
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October 2010 Climate change assessm
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Climate change assessments
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Foreword In March 2010, the InterAc
Page 7 and 8: Contents Foreword iii Committee to
Page 9 and 10: Preface Since its founding more tha
Page 11 and 12: IAC report review This report was e
Page 13 and 14: Acknowledgements Community input wa
Page 15 and 16: management structure comprises the
Page 17 and 18: amount of evidence available and th
Page 19 and 20: 1. Introduction The Intergovernment
Page 21 and 22: assessment, they must carry out the
Page 23 and 24: Number of authors 1500 1200 900 600
Page 25 and 26: BOX 1.2 Roles of participants in IP
Page 27 and 28: The IPCC assessment process in brie
Page 29 and 30: Preparation of the Synthesis Report
Page 31 and 32: 2. Evaluation of IPCC’s assessmen
Page 33 and 34: authors are chosen and others are n
Page 35 and 36: efore incorporating them (Appendix
Page 37 and 38: ange of viewpoints offered and pote
Page 39 and 40: for rejected comments. In the case
Page 41 and 42: Summary for Policymakers A Summary
Page 43 and 44: in each of the three Working Group
Page 45 and 46: 3. IPCC’s evaluation of evidence
Page 47 and 48: Table 3.3 Likelihood scale used by
Page 49 and 50: models, conditional on the SRES sce
Page 51 and 52: 4. The likelihood scale used by Wor
Page 53 and 54: change. The area suitable for agric
Page 55 and 56: Fourth Assessment Report by present
Page 57: not consistently followed in the fo
Page 61 and 62: 4. Governance and management The IP
Page 63 and 64: The IPCC makes all of its major dec
Page 65 and 66: The IPCC Bureau The IPCC Bureau com
Page 67 and 68: Ismail A.R. El Gizouli (Sudan - Act
Page 69 and 70: ex officio member of the Executive
Page 71 and 72: were interviewed by the Committee o
Page 73 and 74: Working Groups and Technical Suppor
Page 75 and 76: Recommendation ►The IPCC should c
Page 77 and 78: 5. Conclusions IPCC’S processes a
Page 79 and 80: Editors could help them provide the
Page 81 and 82: Increasing transparency. Transparen
Page 83 and 84: making the assessment reports short
Page 85 and 86: esponded to the Committee’s quest
Page 87 and 88: dents have suggested testing the co
Page 89 and 90: References Agrawala, S., 1998a, Con
Page 91 and 92: Kahan, D., 2010, Fixing the communi
Page 93 and 94: Appendix A Letters of request to th
Page 95 and 96: Climate change assessments | Review
Page 97 and 98: Climate change assessments | Review
Page 99 and 100: Appendix B Questionnaire on IPCC pr
Page 101 and 102: F. Crooks, CSIR/SABS, South Africa
Page 103 and 104: Girma Orssengo, University of Weste
Page 105 and 106: Appendix D Excerpts of IPCC procedu
Page 107 and 108: IPCC review process (IPCC, 1999, Se
Page 109 and 110:
4.2.4.2 Second review (by governmen
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Plan to treat issues of uncertainty
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C. An order of magnitude can be giv
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14. Likelihood, as defined in Table
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Appendix E Committee biographies Ha
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to 2001, he worked at the Frontier
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Appendix F Acronyms and abbreviatio
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IAC Secretariat Het Trippenhuis Klo
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