Lettie Roach Junior Research Group Leader, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Germany.

Title: Persistent Antarctic sea ice biases in CMIP6 models in spite of the recent decade-long sharp decline

Abstract: Antarctic sea ice expanded for the first 35 years of the satellite record, but in the past 10 years has dropped to record lows. Recent studies argue that the recent decline brings climate models into better agreement with observed Antarctic sea ice trends. Here, we assess this claim by considering Antarctic sea ice area and concentration across a large number of CMIP6 simulations, and we reach a different conclusion. Even with many models that sample a large range of internal variability, we find that very few capture the observed multi-decadal expansion or the large decline after 2014. Further analysis reveals that models with trends similar to observations typically have poor simulation of climatological sea ice, its variability, and its regional patterns. The continued inability of CMIP-class models to simulate Antarctic sea ice and its observed trends severely limits our ability to understand past changes and to confidently project its evolution in the coming decades.