Guidance Note for Lead Authors of the IPCC Fifth Assessment Report on Consistent Treatment of Uncertainties

These guidance notes are intended to assist Lead Authors of the Fifth Assessment Report (AR5) in the consistent treatment of uncertainties across all three Working Groups. These notes define a common approach and calibrated language that can be used broadly for developing expert judgments and for evaluating and communicating the degree of certainty in findings of the assessment process. These notes refine background material provided to support the Third and Fourth Assessment Reports [1] and [2]; they represent the results of discussions at a Cross-Working Group Meeting on Consistent Treatment of Uncertainties convened in July of 2010 [3]. They also address key elements of the recommendations made by the 2010 independent review of the IPCC by the InterAcademy Council [4]. Review Editors play an important role in ensuring consistent use of this calibrated language within each Working Group report. Each Working Group will supplement these notes with more specific guidance on particular issues consistent with the common approach given here.