IPCC_Managing Risks of Extreme Events.pdf - Climate Access

Summary for PolicymakersBox SPM.2 | Treatment of UncertaintyBased on the Guidance Note for Lead Authors of the IPCC Fifth Assessment Report on Consistent Treatment of Uncertainties, 6 thisSummary for Policymakers relies on two metrics for communicating the degree of certainty in key findings, which is based on authorteams’ evaluations of underlying scientific understanding:• Confidence in the validity of a finding, based on the type, amount, quality, and consistency of evidence (e.g., mechanisticunderstanding, theory, data, models, expert judgment) and the degree of agreement. Confidence is expressed qualitatively.• Quantified measures of uncertainty in a finding expressed probabilistically (based on statistical analysis of observations or modelresults, or expert judgment).This Guidance Note refines the guidance provided to support the IPCC Third and Fourth Assessment Reports. Direct comparisons betweenassessment of uncertainties in findings in this report and those in the IPCC Fourth Assessment Report are difficult if not impossible,because of the application of the revised guidance note on uncertainties, as well as the availability of new information, improvedscientific understanding, continued analyses of data and models, and specific differences in methodologies applied in the assessedstudies. For some extremes, different aspects have been assessed and therefore a direct comparison would be inappropriate.Each key finding is based on an author team’s evaluation of associated evidence and agreement. The confidence metric provides aqualitative synthesis of an author team’s judgment about the validity of a finding, as determined through evaluation of evidence andagreement. If uncertainties can be quantified probabilistically, an author team can characterize a finding using the calibrated likelihoodlanguage or a more precise presentation of probability. Unless otherwise indicated, high or very high confidence is associated withfindings for which an author team has assigned a likelihood term.The following summary terms are used to describe the available evidence: limited, medium, or robust; and for the degree ofagreement: low, medium, or high. A level of confidence is expressed using five qualifiers: very low, low, medium, high, and very high. Theaccompanying figure depicts summary statements for evidence and agreement and their relationship to confidence. There is flexibility inthis relationship; for a given evidence and agreement statement, different confidence levels can be assigned, but increasing levels ofevidence and degrees of agreement are correlated with increasing confidence.The following terms indicate the assessed likelihood:AgreementHigh agreementLimited evidenceMedium agreementLimited evidenceLow agreementLimited evidenceHigh agreementMedium evidenceMedium agreementMedium evidenceLow agreementMedium evidenceEvidence (type, amount, quality, consistency)High agreementRobust evidenceMedium agreementRobust evidenceLow agreementRobust evidenceConfidenceScaleTerm*Virtually certainVery likelyLikelyAbout as likely as notUnlikelyVery unlikelyExceptionally unlikelyLikelihood of the Outcome99–100% probability90–100% probability66–100% probability33–66% probability0–33% probability0–10% probability0–1% probabilityA depiction of evidence and agreement statements and their relationship toconfidence. Confidence increases toward the top-right corner as suggested by theincreasing strength of shading. Generally, evidence is most robust when there aremultiple, consistent independent lines of high-quality evidence.* Additional terms that were used in limited circumstances in the FourthAssessment Report (extremely likely: 95–100% probability, more likely thannot: >50–100% probability, and extremely unlikely: 0–5% probability) mayalso be used when appropriate.____________6 Mastrandrea, M.D., C.B. Field, T.F. Stocker, O. Edenhofer, K.L. Ebi, D.J. Frame, H. Held, E. Kriegler, K.J. Mach, P.R. Matschoss, G.-K. Plattner, G.W. Yohe, and F.W. Zwiers,2010: Guidance Note for Lead Authors of the IPCC Fifth Assessment Report on Consistent Treatment of Uncertainties. Intergovernmental Panel on Climate Change(IPCC), Geneva, Switzerland, www.ipcc.ch.21