A large spread in model estimates of the equilibrium climate sensitivity (ECS), defined as the global mean near-surface air-temperature increase following a doubling of atmospheric CO₂ concentration, leaves us greatly disadvantaged in guiding policy-making for climate change adaptation and mitigation. In this study, we show that the projected ECS in the latest generation of climate models is highly related to seasonal variations of extratropical low-cloud fraction (LCF) in historical simulations. Marked reduction of extratropical LCF from winter to summer is found in models with ECS > 4.75 K, in accordance with the significant reduction of extratropical LCF under a warming climate in these models. In contrast, a pronounced seasonal cycle of extratropical LCF, as supported by satellite observations, is largely absent in models with ECS < 3.3 K. The distinct seasonality in extratropical LCF in climate models is ascribed to their different prevailing cloud regimes governing the extratropical LCF variability.

_{平衡气候敏感性（ECS）（定义为大气 CO 2}浓度加倍后全球平均近地表气温升高）的模型估计值存在很大差异，使我们在指导气候变化适应和政策制定方面处于极大的不利地位。减轻。在这项研究中，我们表明，最新一代气候模型中预测的 ECS 与历史模拟中温带低云部分 (LCF) 的季节变化高度相关。在 ECS > 4.75 K 的模型中发现从冬季到夏季温带 LCF 显着减少，这与这些模型中气候变暖时温带 LCF 的显着减少一致。相比之下，在 ECS < 3.3 K 的模型中，卫星观测所支持的温带 LCF 明显的季节性周期基本上不存在。气候模型中温带 LCF 的明显季节性归因于它们控制温带 LCF 变化的不同盛行云态。 。