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TABLE D.1 Language Adopted by the IPCC to Describe Confidence About Facts or the Likelihood of an Outcome

Terminology for Describing Confidence About Facts

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

Terminology for Describing Likelihood of an Outcome

Virtually certain

More than 99 chances out of 100

Extremely likely

More than 95 chances out of 100

Very likely

More than 90 chances out of 100


More than 65 chances out of 100

More likely than not

More than 50 chances out of 100

About as likely as not

Between 33 and 66 chances out of 100


Less than 33 chances out of 100

Very unlikely

Less than 10 chances out of 100

Extremely unlikely

Less than 5 chances out of 100

Exceptionally unlikely

Less than 1 chance out of 100

SOURCE: IPCC (2007a).

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