Communication of uncertainty in the Working Group II Fourth Assessment

A set of terms to describe uncertainties in current knowledge is common to all parts of the IPCC Fourth Assessment, based on the Guidance Notes for Lead Authors of the IPCC Fourth Assessment Report on Addressing Uncertainties1, produced by the IPCC in July 2005.

Description of confidence

On the basis of a comprehensive reading of the literature and their expert judgement, authors have assigned a confidence level to the major statements in the Report on the basis of their assessment of current knowledge, as follows:

Terminology Very high confidence High confidence Medium confidence Low confidence Very low confidence

Degree of confidence in being correct

At least 9 out of 10 chance of being correct

About 8 out of 10 chance

About 5 out of 10 chance

About 2 out of 10 chance

Less than a 1 out of 10 chance

Description of likelihood

Likelihood refers to a probabilistic assessment of some well-defined outcome having occurred or occurring in the future, and may be based on quantitative analysis or an elicitation of expert views. In the Report, when authors evaluate the likelihood of certain outcomes, the associated meanings are:

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 to 99% probability 66 to 90% probability 33 to 66% probability 10 to 33% probability 1 to 10% probability <1% probability


Table I.3. Cross-chapter Case Studies: location in text.

The impact of the European 2003 heatwave


Scene-setting and overview

The European heatwave of 2003 Impacts on sectors

Ecological impacts of the European heatwave 2003

European heatwave impact on the agricultural sector

Industry, settlement and society: impacts of the 2003 heatwave in Europe

Chapter: Chapter 12

Chapter 4 Chapter 5 Chapter 7

Location in chapter: 12.6.1

Box 4.1 Box 5.1 Box 7.1

The European heatwave 2003: health impacts and adaptation

Chapter 8

Box 8.1

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