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 Summary for Policymakers, when authors

evaluate the likelihood of certain outcomes, the associated meanings are:

Terminology

Likelihood of the occurrence/ outcome

Virtually certain

>99% probability of occurrence

Very likely

90 to 99% probability

Likely

66 to 90% probability

About as likely as not

33 to 66% probability

Unlikely

10 to 33% probability

Very unlikely

1 to 10% probability

Exceptionally unlikely

<1% probability

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