The area, volume, and behavior of Arctic and Antarctic sea ice is one of the factors being examined in the latest generation of climate models. In CMIP6 (Coupled Model Intercomparison Project Phase 6), new model runs are being compared with earlier results from CMIP5 and with observations over recent years [for example see Shu et al 2020].
In SIMIP Community , the authors compute several metrics using Arctic sea-ice area from the multi-model ensemble mean, as well as the individual models’ ensemble members to consider internal variability. Reassuringly, they find that satellite observations of sea-ice area are within the spread of these new simulations. They also find that the sensitivity of Arctic sea ice to changes in anthropogenic forcing is better captured by these latest models. However, it is still unclear why most of the models fail to simultaneously simulate both a plausible evolution of sea-ice area and of global mean surface temperature. The figure above highlights the year of the first ice-free summer in the Arctic and also shows the correspondence to CO2 emissions and global mean surface temperature.
A surprising result from these new simulations is that the first ice-free summer does not really depend on the emission scenario. As the sea-ice area has already shrunk, internal variability is more important than the forced change needed to lose the remaining summer sea-ice area.
Citation: Community, SIMIP . Arctic sea ice in CMIP6. Geophysical Research Letters, 47, e2019GL086749. https://doi.org/10.1029/2019GL086749
—Gudrun Magnusdottir, Editor, Geophysical Research Letters