Climate change assessments Review of the processes and ...

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11. Three forms of language are given in Tables 2, 3 and 4 to describe different aspects of confidence and uncertainty and to provide consistency across the AR4. 12. Table 2 considers both the amount of evidence available in support of findings and the degree of consensus among experts on its interpretation. The terms defined here are intended to be used in a relative sense to summarize judgments of the scientific understanding relevant to an issue, or to express uncertainty in a finding where there is no basis for making more quantitative statements. A finer scale for describing either the amount of evidence (columns) or degree of consensus (rows) may be introduced where appropriate, however, if a mid-range category is used authors should avoid over-using that as a ‘safe’ option that communicates little information to the reader. Where the level of confidence is ‘high agreement much evidence’, or where otherwise appropriate, describe uncertainties using Table 3 or 4. Table 2. Qualitatively defined levels of understanding Level of agreement or consensus High agreement limited evidence ... High agreement much evidence ... ... ... Low agreement limited evidence ... Low agreement much evidence Amount of evidence (theory, observations, models) 13. A level of confidence, as defined in Table 3, can be used to characterize uncertainty that is based on expert judgment as to the correctness of a model, an analysis or a statement. The last two terms in this scale should be reserved for areas of major concern that need to be considered from a risk or opportunity perspective, and the reason for their use should be carefully explained. Table 3. Quantitatively calibrated levels of confidence Terminology Degree of confidence in being correct Very high confidence At least 9 out of 10 chance of being correct High confidence About 8 out of 10 chance Medium confidence About 5 out of 10 chance Low confidence About 2 out of 10 chance Very low confidence Less than 1 out of 10 chance 96 Climate change assessments | Review of the processes and procedures of the IPCC
14. Likelihood, as defined in Table 4, refers to a probabilistic assessment of some well defined outcome having occurred or occurring in the future. The categories defined in this table should be considered as having ‘fuzzy’ boundaries. Use other probability ranges where more appropriate but do not then use the terminology in table 4. Likelihood may be based on quantitative analysis or an elicitation of expert views. The central range of this scale should not be used to express a lack of knowledge – see paragraph 12 and Table 2 for that situation. There is evidence that readers may adjust their interpretation of this likelihood language according to the magnitude of perceived potential consequences [8]. Table 4. Likelihood scale Terminology Virtually certain Very likely Likely About as likely as not Unlikely Very unlikely Exceptionally unlikely Likelihood of the occurrence/outcome > 99% probability of occurrence > 90% probability > 66% probability 33 to 66% probability < 33% probability < 10% probability < 1% probability 15. Consider the use of tabular, diagrammatic or graphical approaches to show the primary sources of uncertainties in key findings, the range of outcomes, and the factors and relationships determining levels of confidence. References 1. Moss, R., and S. Schneider. 2000. Uncertainties, in Guidance Papers on the Cross Cutting Issues of the Third Assessment Report of the IPCC, edited by R. Pachauri, T. Taniguchi, and K. Tanaka, Intergovernmental Panel on Climate Change (IPCC), Geneva. 2. Manning, M.R., M. Petit, D. Easterling, J. Murphy, A. Patwardhan, H-H. Rogner, R. Swart, and G. Yohe (Eds). 2004. IPCC Workshop on Describing Scientific Uncertainties in Climate Change to Support Analysis of Risk and of Options: Workshop report. Intergovernmental Panel on Climate Change (IPCC), Geneva. 3. Morgan, M.G., and M. Henrion. 1990. Uncertainty: A Guide to Dealing with Uncertainty in Quantitative Risk and Policy Analysis., Cambridge University Press, Cambridge, UK. (See particularly chapter 6 ‘Human judgment about and with uncertainty’.) 4. Lempert, R. J., S.W. Popper, and S.C. Bankes. 2003. Shaping the Next One Hundred Years: New Methods for Quantitative Long-Term Policy Climate change assessments | Review of the processes and procedures of the IPCC 97
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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
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Contents Foreword iii Committee to
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Preface Since its founding more tha
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IAC report review This report was e
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Acknowledgements Community input wa
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management structure comprises the
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amount of evidence available and th
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1. Introduction The Intergovernment
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assessment, they must carry out the
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Number of authors 1500 1200 900 600
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BOX 1.2 Roles of participants in IP
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The IPCC assessment process in brie
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Preparation of the Synthesis Report
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2. Evaluation of IPCC’s assessmen
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authors are chosen and others are n
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efore incorporating them (Appendix
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ange of viewpoints offered and pote
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for rejected comments. In the case
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Summary for Policymakers A Summary
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in each of the three Working Group
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3. IPCC’s evaluation of evidence
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Table 3.3 Likelihood scale used by
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models, conditional on the SRES sce
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4. The likelihood scale used by Wor
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change. The area suitable for agric
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Fourth Assessment Report by present
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not consistently followed in the fo
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Recommendation ►The likelihood sc
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4. Governance and management The IP
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Page 65 and 66: The IPCC Bureau The IPCC Bureau com
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Page 71 and 72: were interviewed by the Committee o
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Page 77 and 78: 5. Conclusions IPCC’S processes a
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Page 85 and 86: esponded to the Committee’s quest
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Page 89 and 90: References Agrawala, S., 1998a, Con
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Page 105 and 106: Appendix D Excerpts of IPCC procedu
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