Here we evaluate the sea ice, surface air temperature, and sea level pressure from 34 of the models used in phase 6 of the Coupled Model Intercomparison Project (CMIP6) for their biases, trends, and variability, and compare them to the CMIP5 ensemble and ERA5 for the period 1979 to 2004. The principal purpose of this assessment is to provide an overview of the ability of the CMIP6 ensemble to represent the Arctic climate, and to see how this has changed since the last phase of CMIP. Overall, we find a distinct improvement in the representation of the sea ice volume and extent, the latter mostly linked to improvements in the seasonal cycle in the Barents Sea. However, numerous model biases have persisted into CMIP6 including too-cold conditions in the winter (4-K cold bias) and a negative trend in the day-to-day variability over ice in winter. We find that under the low-emission scenario, SSP126, the Arctic climate is projected to stabilize by 2060 with an annual mean sea ice extent of around 2.5 million km2 and an annual mean temperature 4.7 K warmer than the early-twentieth-century average, compared to 1.7 K of warming globally.
