IPCC Terminology

The Intergovernmental Panel on Climate Change (IPCC) has developed the following agreed to language to characterize uncertainly and provide a comprehensive account of all aspects of assessment of the risks associated with climate change.

The IPCC uses the following terms to indicate the assessed likelihood of an outcome or a result:

• Virtually certain > 99% probability of occurrence
• Very likely, 99% to 90%
• Likely, 90% to 66%
• About as likely as not, 66% to 33%
• Unlikely, 33% to 10%
• Very unlikely, 1% to 10%
• Exceptionally unlikely, less than 1%

The following terms are used to express confidence in a statement:

• Very high confidence, at least a 9 out of 10 chance of being correct
• High confidence, about an 8 out of 10 chance
• Medium confidence, about a 5 out of 10 chance
• Low confidence, about a 2 out of 10 chance
• Very low confidence, less than a 1 out of 10 chance