Use systematic reviews to inform IPCC uncertainty assessments

Acknowledging that effective communication of uncertainty is a critical element of scientific assessment, the IPCC has adopted a standardized uncertainty assessment framework to enhance transparency and dependability in its findings. Despite these efforts, author teams frequently encounter difficulties in the assessment process, leading to unclear assessment justifications and confusion among readers of the report.

Our study displays how to use rigorous and transparent evidence synthesis methods, typically found in systematic reviews and meta-analyses, to enhance the assessment of uncertainties. Focusing on empirical ex-post evidence, we show how IPCC authors can use the information provided by gold standard systematic reviews to evaluate all dimensions that are relevant for the assessment of uncertainty – type, amount, quantity, quality, consistency and agreement – while providing a clear and traceable rationale for their assessment decision.

To better guide and structure the assessment, we advocate for the adoption of assessment summary tables, inspired by the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) evidence-to-decision framework. These tables streamline the assessment process and significantly boost transparency.

Our approach demonstrates a practical and effective method for authors to adhere to the IPCC’s standards for uncertainty assessment, thereby contributing to more reliable and credible scientific assessments in the field of climate action.