Climate Sensitivity of the Flexible Global Ocean–Atmosphere–Land System Model

Projections of future climate change by climate system models depend on the sensitivities of models to specified greenhouse gases. To reveal and understand the different climate sensitivities of version 2 of the grid-point and spectral Flexible Global Ocean–Atmosphere–Land System Model, FGOALS-g2 and FGOALS-s2, respectively, which were developed by the National Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics/Institute of Atmospheric Physics (LASG/IAP), global mean surface air temperature responses to idealized CO₂ forcing are investigated by using the output of abruptly quadrupling CO₂ experiments. The globally averaged near-surface air temperature is characterized by a fast response to CO₂ forcing during the first 20 years and a slow response afterward. The climate sensitivity, defined as the equilibrium temperature under doubled CO₂ forcing, estimated by Gregory regression method, is approximately 3.7 K in FGOALS-g2 and 4.5 K in FGOALS-s2. The larger sensitivity of FGOALS-s2 is mainly attributed to a weaker negative long wave clear-sky feedback and stronger positive shortwave clear-sky feedback at the fast-response stage, as evidenced by the more rapid response of water vapor increase and sea-ice decrease in FGOALS-s2 than that in FGOALS-g2. At the slow-response stage in FGOALS-s2, larger responses of increasing total cloud fraction and condensed water path result in a stronger negative shortwave cloud feedback, which tends to reduce the sensitivity of the model.

This study was supported by the Strategic Priority Research Program—Climate Change: Carbon Budget and Related Issues of the Chinese Academy of Sciences under Grant No. XDA05110301.

Authors and Affiliations

1. LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

   Xiaolong Chen & Tianjun Zhou

2. Climate Change Research Center, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

   Zhun Guo & Tianjun Zhou

Corresponding author

Correspondence to Tianjun Zhou .

Editors and Affiliations

1. Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, People's Republic of China

   Tianjun Zhou

2. Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, People's Republic of China

   Yongqiang Yu

3. Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, People's Republic of China

   Yimin Liu

4. Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, People's Republic of China

   Bin Wang

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