Sea ice in Earth system models

Sea ice is a crucial component of any large-scale Earth System Model (ESM). In this chapter, we describe how sea ice is represented in ESMs and how the models can be used to understand and predict the evolution of sea ice. We outline in particular the simplifications that are necessary to represent sea ice in ESMs, discuss the importance of tuning, and analyse the impact of internal variability on the evolution of ice–climate interactions. We also discuss how the usefulness of an ESM to answer a specific question can be established. We survey examples of learning from ESMs with regard to feedbacks, differences in sea-ice change in the two hemispheres, and future sea-ice evolution. Finally, we discuss new research directions to enhance the realism of sea-ice processes in future sea-ice components of ESMs.