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Challenge: Differences between social & natural sciences Information used Analyses

Guidance Notes for Lead Authors of the IPCC Fourth Assessment Report on Addressing Uncertainties. Challenge: Differences between social & natural sciences Information used Analyses Indicators of change. Table 1. A simple typology of uncertainties. Often underestimated by experts!.

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Challenge: Differences between social & natural sciences Information used Analyses

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  1. Guidance Notes for Lead Authors of theIPCC Fourth Assessment Report on Addressing Uncertainties • Challenge: • Differences between social & natural sciences • Information used • Analyses • Indicators of change

  2. Table 1. A simple typology of uncertainties Often underestimated by experts!

  3. Some Recommendations to IPCC Authors • Treat uncertainty • Review information available on uncertainty • Make expert judgments - but watch for “group think” • Use appropriate precision: - sign change? - trend? - order of magnitude (powers of 10) - range of values? - probability distribution?

  4. Levels of Confidence Uncertainty based on expert judgment Terminology Degree of confidence (in being correct) Very High confidence At least 9 out of 10 chance 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

  5. Likelihood Probability assessment of an outcome (past or future) Terminology Likelihood of the occurrence/ outcome Virtually certain > 99% probability of occurrence Very likely > 90% probability Likely > 66% probability About as likely as not 33 to 66% probability Unlikely < 33% probability Very unlikely < 10% probability Exceptionally unlikely < 1% probability

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