Arctic and Antarctic sea ice has undergone significant and rapid change with the changing climate. Here, we present preindustrial and historical results from the newly released Community Earth System Model Version 2 (CESM2) to assess the Arctic and Antarctic sea ice. Two configurations of the CESM2 are available that differ only in their atmospheric model top and the inclusion of comprehensive atmospheric chemistry, including prognostic aerosols. The CESM2 configuration with comprehensive atmospheric chemistry has significantly thicker Arctic sea ice year‐round and better captures decreasing trends in sea ice extent and volume over the satellite period. In the Antarctic, both CESM configurations have similar mean state ice extent and volume, but the ice extent trends are opposite to satellite observations. We find that differences in the Arctic sea ice between CESM2 configurations are the result of differences in liquid clouds. Over the Arctic, the CESM2 configuration without prognostic aerosol formation has fewer aerosols to form cloud condensation nuclei, leading to thinner liquid clouds. As a result, the sea ice receives much more shortwave radiation early in the melt season, driving a stronger ice albedo feedback and leading to additional sea ice loss and significantly thinner ice year‐round. The aerosols necessary for the Arctic liquid cloud formation are produced from different precursor emissions and transported to the Arctic. Thus, the main reason sea ice differs in the Arctic is the transport of cloud‐impacting aerosols into the region, while the Antarctic remains relatively pristine from extrapolar aerosol transport.

中文翻译：

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社区地球系统模型版本2中的北极和南极海冰平均状态及其对大气化学的影响

随着气候的变化，北极和南极海冰发生了重大而迅速的变化。在这里，我们介绍了最新发布的社区地球系统模型版本2（CESM2）的工业化和历史结果，以评估北极和南极海冰。CESM2的两种配置可供选择，它们的区别仅在于其大气模型顶部和包括全面的大气化学（包括预后的气溶胶）在内。具有全面大气化学成分的CESM2配置全年四季北极海冰明显更厚，并更好地捕获了卫星期间海冰范围和体积的下降趋势。在南极，两种CESM构造的平均状态冰范围和体积均相似，但冰范围趋势与卫星观测结果相反。我们发现，CESM2配置之间北极海冰的差异是液态云差异的结果。在北极地区，没有预后气溶胶形成的CESM2配置具有较少的气溶胶来形成云凝结核，从而导致液云变薄。结果，海冰在融化季节的早期受到了更多的短波辐射，从而驱动了更强的冰反照率反馈，并导致了更多的海冰流失和全年明显变薄的冰。形成北极液态云所必需的气溶胶是由不同的前体排放产生的，并被输送到北极。因此，北极海冰不同的主要原因是影响云的气溶胶向该区域的迁移，而南极洲相对极地气溶胶的迁移仍然相对原始。