Trends and variability in Arctic sea ice and sea ice export into the North Atlantic from an historical ensemble from the UK CMIP6 Earth System Model

We compare a 16 member, historical (1850-2014) ensemble of the UKESM1 climate model with observations and reanalysis data. UKESM1 is the UK Earth System model used for the Coupled Model Intercomparison Project Phase 6. In spite of a strong overestimation of ice thickness in the Central Arctic, simulated winter ice extent and Fram Strait ice export are realistic. This signifies that ice thickness bias in the Central Arctic is mainly caused by local thermodynamic processes, rather than by ocean/ice transport between the Arctic and Atlantic. The realistic Fram Strait export allows us to derive meaningful conclusions from analysing trends and variability in the UKESM1 ensemble. We present an early analysis of the interactions between sea ice changes, sea surface temperature, and ocean heat content anomalies in the North Atlantic, and infer the extent to which changes in these quantities are part of decadal variability or a sign of a permanent climate change.