Arctic sea ice in two configurations of the CESM2 during the 20th and 21st centuries

The CESM2 is the version of the CESM contributed to the sixth phase of the Coupled Model Intercomparison Project (CMIP6). We analyze changes in Arctic sea ice cover in two CESM2 configurations with differing atmospheric components: the CESM2(CAM6) and the CESM2(WACCM6).

Over the historical period, the CESM2(CAM6) winter ice thickness distribution is biased thin, which leads to lower summer ice area compared to CESM2(WACCM6) and observations. In both CESM2 configurations, the timing of first ice-free conditions is insensitive to the choice of CMIP6 future emissions scenario. In fact, the probability of an ice-free Arctic summer remains low only if global warming stays below 1.5 degrees C, which none of the CMIP6 scenarios achieve.