Consistent Treatment of Uncertainties in the IPCC

Guidance Notes for Lead Authors

Within the scope of the IPCC work program, a paper has been elaborated that provides guidance to the Lead Authors of the IPCC Assessment Reports on key aspects of their work. In particular, the guidance notes are intended to assist Lead Authors of the Fifth Assessment Report (AR5) in a more consistent treatment of uncertainties across all three Working Groups. They also address key elements of the recommendations made by the 2010 independent review of the IPCC by the InterAcademy Council.

Teaser: Consistent Treatment of Uncertainties in the IPCC

The AR5 will rely on two metrics for communicating the degree of certainty in key findings:

  • Confidence in the validity of a finding, based on the type, amount, quality, and consistency of evidence (e.g., mechanistic understanding, theory, data, models, expert judgment) and the degree of agreement. Confidence is expressed qualitatively.
  • Quantified measures of uncertainty in a finding expressed probabilistically (based on statistical analysis of observations or model results, or expert judgment).

In June 2010, ProClim- organized a workshop with Swiss experts representing multiple disciplines and with journalists, focusing on the communication of uncertainties in the IPCC Summary for Policymakers (SPMs). The workshop results served as an input with regard to the guidance notes for Lead Authors of the IPCC.


  • Forecast
  • Scenario
  • Uncertainty