The upper end of the equilibrium climate sensitivity (ECS) has increased substantially in the latest Coupled Model Intercomparison Projects phase 6 with eight models (as of this writing) reporting an ECS > 5°C. The Community Earth System Model version 2 (CESM2) is one such high‐ECS model. Here we perform paleoclimate simulations of the Last Glacial Maximum (LGM) using CESM2 to examine whether its high ECS is realistic. We find that the simulated LGM global mean temperature decrease exceeds 11°C, greater than both the cooling estimated from proxies and simulated by an earlier model version (CESM1). The large LGM cooling in CESM2 is attributed to a strong shortwave cloud feedback in the newest atmosphere model. Our results indicate that the high ECS of CESM2 is incompatible with LGM constraints and that the projected future warming in CESM2, and models with a similarly high ECS, is thus likely too large.

中文翻译：

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通过最后一次冰河最大值的模拟评估社区地球系统模型版本2的平衡气候敏感性

在最新的耦合模型比对项目第6阶段中，平衡气候敏感性（ECS）的上限已经大大增加，报告的ECS> 5°C的模型有8个（截至撰写本文时）。社区地球系统模型版本2（CESM2）就是这样一种高ECS模型。在这里，我们使用CESM2对“最后冰川期”（LGM）进行古气候模拟，以检查其高ECS是否现实。我们发现，模拟的LGM全球平均温度下降超过11°C，大于从代理估算和由较早模型版本（CESM1）进行模拟的冷却。CESM2中的大型LGM冷却归因于最新大气模型中强大的短波云反馈。我们的结果表明，CESM2的高ECS与LGM约束不兼容，并且预计CESM2的未来变暖，