How Different Is the Arctic Sea-Ice Condition Revealed by CMIP6 Models?

Rapid decline of Arctic sea-ice cover in the past two decades is one of the significant global warming signals. In this study we are trying to answer the question we asked a decade ago "how soon will we see an ice-free summer Arctic" by investigating the projections from selected CMIP6 models. Although most models from CMIP3 and CMIP5 underestimated the linear decline trend of Arctic sea-ice extent, a dozen of them do simulate the climatology of sea-ice extent (monthly mean and magnitude of seasonal cycle) in good agreement with observations. We have seen noticeable improvements from CMIP3 to CMIP5 models, and we are expecting further improvement in the CMIP6 models. Model uncertainties relative to internal variability will also be investigated in this study, and the results will be compared with previous conclusions obtained from CMIP3 and CMIP6 models.