Forcings, Feedbacks, and Climate Sensitivity in HadGEM3-GC3.1 and UKESM1
Forcings, Feedbacks, and Climate Sensitivity in HadGEM3-GC3.1 and UKESM1
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DOI：
10.1029/2019ms001866
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发表时间：
2019-12-17
影响因子：
6.8
通讯作者：
Tang, Yongming
中科院分区：
文献类型：
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作者：
Andrews, Timothy;Andrews, Martin B.;Tang, Yongming
在低（-LL）和中（-MM）分辨率的英国物理气候模式HadGEM3-GC3.1和英国地球系统模式UKESM1中评估了气候强迫、敏感性和反馈指标。HadGEM3.1-GC3.1-LL对CO2加倍的有效气候敏感性（EffCS）为5.5 K， UKESM1为5.4 K。瞬态气候响应分别为2.5 K和2.8 K。虽然EffCS比上一代模式中看到的更大，但没有发现模式的强迫或反馈过程是非典型的模式，尽管云反馈处于高端。相对较大的EffCS是典型CO2强迫与相对较小的反馈参数的不寻常组合的结果。与之前的英国气候模式HadGEM3-GC2.0相比，由于CO2强迫、地表反照率反馈和中纬度云反馈的增加，EffCS从3.2 K增加到5.5 K。所有的变化都很好理解，并且由于模型的物理改进。在更高的大气和海洋分辨率（HadGEM3-GC3.1-MM）下，海洋层积云反馈增加和南极海冰反馈减少之间存在补偿。在UKESM1中，CO2施肥效应引起地表植被变化和反照率辐射效应。HadGEM3-GC3.1-LL的历史气溶胶强迫为-1.1 W m（-2）。在HadGEM3-GC3.1-LL历史模拟中，发现云反馈比突变4 × co(2)的正反馈要小，这与观测到的历史海面温度和海冰变化强迫进行的仅大气实验一致。然而，耦合模式历史海冰趋势的变率阻碍了对模式总历史反馈的准确诊断。
Climate forcing, sensitivity, and feedback metrics are evaluated in both the United Kingdom's physical climate model HadGEM3-GC3.1 at low (-LL) and medium (-MM) resolution and the United Kingdom's Earth System Model UKESM1. The effective climate sensitivity (EffCS) to a doubling of CO2 is 5.5 K for HadGEM3.1-GC3.1-LL and 5.4 K for UKESM1. The transient climate response is 2.5 and 2.8 K, respectively. While the EffCS is larger than that seen in the previous generation of models, none of the model's forcing or feedback processes are found to be atypical of models, though the cloud feedback is at the high end. The relatively large EffCS results from an unusual combination of a typical CO2 forcing with a relatively small feedback parameter. Compared to the previous U.K. climate model, HadGEM3-GC2.0, the EffCS has increased from 3.2 to 5.5 K due to an increase in CO2 forcing, surface albedo feedback, and midlatitude cloud feedback. All changes are well understood and due to physical improvements in the model. At higher atmospheric and ocean resolution (HadGEM3-GC3.1-MM), there is a compensation between increased marine stratocumulus cloud feedback and reduced Antarctic sea-ice feedback. In UKESM1, a CO2 fertilization effect induces a land surface vegetation change and albedo radiative effect. Historical aerosol forcing in HadGEM3-GC3.1-LL is -1.1 W m(-2). In HadGEM3-GC3.1-LL historical simulations, cloud feedback is found to be less positive than in abrupt-4xCO(2), in agreement with atmosphere-only experiments forced with observed historical sea surface temperature and sea-ice variations. However, variability in the coupled model's historical sea-ice trends hampers accurate diagnosis of the model's total historical feedback.