Arctic Sea Ice in CMIP6

We examine CMIP6 simulations of Arctic sea-ice area and volume. We find that CMIP6 models produce a wide spread of mean Arctic sea-ice area, capturing the observational estimate within the multimodel ensemble spread. The CMIP6 multimodel ensemble mean provides a more realistic estimate of the sensitivity of September Arctic sea-ice area to a given amount of anthropogenic CO₂ emissions and to a given amount of global warming, compared with earlier CMIP experiments. Still, most CMIP6 models fail to simulate at the same time a plausible evolution of sea-ice area and of global mean surface temperature. In the vast majority of the available CMIP6 simulations, the Arctic Ocean becomes practically sea-ice free (sea-ice area <1 × 10⁶ km²) in September for the first time before the Year 2050 in each of the four emission scenarios SSP1-1.9, SSP1-2.6, SSP2-4.5, and SSP5-8.5 examined here.