Climate change risk – what is it and how should it be expressed?

This paper provides new knowledge on how to understand and describe climate change risk. This type of risk is of the utmost importance for us all, but current approaches for conceptualizing and characterizing it, as for example used by the Intergovernmental Panel on Climate Change (IPCC), suffer from severe weaknesses, resulting in poor communication and misguidance. Two main problems are that the risk concept is too strongly associated with statistically expected values, and that the risk characterizations fail to integrate probabilities and judgments of the strength of the knowledge supporting these. The present paper points to and discusses these weaknesses. It shows how a solid risk science foundation can be formed, which clarifies the meaning of key climate change risk concepts and supports and improves the evidence-informed communication and decision-making. Specifically, the paper provides insights on the nexus between climate change risk, uncertainties and knowledge, including the potential for surprises, as well as the links between risk and vulnerability (resilience). Recommendations are provided on how to assess uncertainties in relation to risk, using precise and imprecise probabilities, combining these with strength of knowledge judgement, and establishing scientific processes to scrutinize the underlying knowledges basis with respect to potential surprises.