We investigate the impacts of external forcings and internal climate variability (ICV) on global-mean surface air temperature (GMST) variations (1850–2014) in observation and an ensemble of sixth Coupled Model Intercomparison Project (CMIP6) historical simulations. Using multiple regression models, we estimate that 83% of the observed GMST variance is explained by global-scale anthropogenic forcing. Most CMIP6 models underestimate this anthropogenic contribution (median explained variance is 67%), but compare better with observation when the North Atlantic regional contribution is included in the anthropogenic forcing (median 77%). The ICV contributions to the GMST variance are ∼8% for observation and ∼7% for the models (median). The models' GMST responses to the external forcings and ICV vary widely, with the two responses being oppositely related. The North Atlantic predominantly drives the free GMST variability in observations, whereas the Pacific drives this in most CMIP6 models due to stronger than observed simulated GMST-Pacific ICV relationships.

中文翻译：

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观测和 CMIP6 模式中全球平均地表温度对外部强迫和内部气候变率的不同响应

我们调查了外部强迫和内部气候变率 (ICV) 对全球平均地表气温 (GMST) 变化（1850-2014 年）的影响，以及第六次耦合模型比对项目 (CMIP6) 历史模拟的集合。使用多元回归模型，我们估计 83% 的观察到的 GMST 方差是由全球规模的人为强迫解释的。大多数 CMIP6 模型都低估了这种人为贡献（解释方差中位数为 67%），但当北大西洋区域贡献包含在人为强迫中时（中位数为 77%），与观测相比会更好。ICV 对 GMST 方差的贡献对于观察为 ~8%，对于模型（中位数）为 ~7%。模型对外部强迫和 ICV 的 GMST 响应差异很大，两个反应是相反的相关。北大西洋主要推动观测中的自由 GMST 变异性，而太平洋在大多数 CMIP6 模型中推动了这一变化，因为它比观察到的模拟 GMST-太平洋 ICV 关系更强。