Abstract
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 two versions of LASG/IAP climate system model FGOALS-g2 and FGOALS-s2, we investigate the global mean surface air temperature responses to idealized CO2 forcing by using the output of abruptly quadrupling CO2 experiments. The Gregory-style regression method is used to estimate the “radiative forcing” of quadrupled CO2 and equilibrium sensitivity. The model response is separated into a fast-response stage associated with the CO2 forcing during the first 20 years, and a slow-response stage post the first 20 years. The results show that the radiative forcing of CO2 is overestimated due to the positive water-vapor feedback and underestimated due to the fast cloud processes. The rapid response of water vapor in FGOALS-s2 is responsible for the stronger radiative forcing of CO2. The climate sensitivity, defined as the equilibrium temperature change under doubled CO2 forcing, is about 3.7 K in FGOALS-g2 and 4.5 K in FGOALS-s2. The larger sensitivity of FGOALS-s2 is due mainly to the weaker negative longwave clear-sky feedback and stronger positive shortwave clear-sky feedback at the fast-response stage, because of the more rapid response of water vapor increase and sea-ice decrease in FGOALS-s2 than in FGOALS-g2. At the slow-response stage, similar to the fast-response stage, net negative clear-sky feedback is weaker in FGOALS-s2. Nevertheless, the total negative feedback is larger in FGOALS-s2 due to a larger negative shortwave cloud feedback that involves a larger response of total cloud fraction and condensed water path increase. The uncertainties of estimated forcing and net feedback mainly come from the shortwave cloud processes.
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References
Andrews T, Gregory J M, Webb M J, et al. 2012. Forcing, feedbacks and climate sensitivity in CMIP5 coupled atmosphere-ocean climate models. Geophys Res Lett, 38: L09712, doi: 10.1029/2012GL051607
Bao Q, Lin P, Zhou T, et al. 2013. The Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2: FGOALS-s2. Adv Atmos Sci, 30: 561–576
Boer G J, Yu B. 2003. Climate sensitivity and climate state. Clim Dyn, 21: 167–176
Briegleb B P. 1992. Delta-Eddington approximation for solar radiation in the NCAR Community Climate Model. J Geophys Res, 97: 7603–7612
Bryan K, Komro F G, Manabe S, et al. 1982. Transient climate response to increasing atmospheric carbon dioxide. Science, 215: 56–58
Collins W D, Rasch P J, Boville B A, et al. 2004. Description of the NCAR Community Atmosphere Model (CAM3). Tech Rep NCAR/TN-464+STR, National Center for Atmospheric Research, Boulder, CO Colman R. 2003. A comparison of climate feedbacks in general circulation models. Clim Dyn, 20: 865–873
Danabasoglu G, Gent P R. 2009. Equilibrium climate sensitivity: Is it accurate to use a slab ocean model? J Clim, 22: 2494–2499
Edwards J M, Slingo A. 1996. Studies with a flexible new radiation code. I: Choosing a configuration for a large-scale model. Q J R Meteorol Soc, 122: 689–719
Forster P M D, Taylor K E. 2006. Climate forcings and climate sensitivities diagnosed from coupled climate model integrations. J Clim, 19: 6181–6194
Gregory J M, Ingram W J, Palmer M A, et al. 2004. A new method for diagnosing radiative forcing and climate sensitivity. Geophys Res Lett, 31: L03205
Gregory J, Webb M. 2008. Tropospheric adjustment induces a cloud component in CO2 forcing. J Clim, 21: 58–71
Hansen J, Johnson D, Lacis A, et al. 1981. Climate impacts of increasing carbon dioxide. Science, 213: 957–966
Hansen J, Sato M, Ruedy R, et al. 2005. Efficacy of climate forcings. J Geophys Res, 110: D18104
Held I M, Soden B J. 2000. Water vapor feedback and global warming. Annu Rev Energy Environ, 25: 441–475
Li L J, Lin P, Yu Y, et al. 2013. The Flexible Global Ocean-Atmosphere-Land System model: Grid-point Version 2: FGOALS-g2. Adv Atmos Sci, 30: 543–560
Li C, von Storch J S, Marotzke J. 2012. Deep-ocean heat uptake and equilibrium climate response. Clim Dyn, 40: 1071–1086
Liu H, Wu G X. 1997. Impacts of land surface on climate of July and onset of summer monsoon: A study with an AGCM plus SSiB. Adv Atmos Sci, 14: 289–308
Manabe S, Bryan K. 1985. CO2-induced change in a coupled ocean-atmosphere model and its paleoclimatic implications. J Geophys Res, 90: 11689–11707
Meehl G A, Stocker T F, Collins W D, et al. 2007. Global climate projections. In: Solomon S, et al., eds. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Changes. Cambridge University Press. 747–845
Myhre G, Highwood E J, Shine K P, et al. 1998. New estimates of radiative forcing due to well mixed greenhouse gases. Geophys Res Lett, 25: 2715–2718
Ramanathan V, Cess R D, Harrison E F, et al. 1989. Cloud-radiative forcing and climate: Results from the Earth Radiation Budget Experiment. Science, 243: 57–63
Ramanathan V, Downey P. 1986. A nonisothermal emissivity and absorptivity formulation for water vapor. J Geophys Res, 91: 8649–8666
Randall D A, Wood R A, Bony S, et al. 2007. Climate models and their evaluation. In: Solomon S, et al., eds. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Changes. Cambridge University Press. 589–662
Roeckner E, Schlese U, Biercamp J, et al. 1987. Cloud optical depth feedbacks and climate modeling. Nature, 329: 139–140
Slingo J M. 1987. The development and verification of a cloud prediction scheme for the ECMWF model. Q J R Meteorol Soc, 113: 899–927
Somerville R C J, Remer L A. 1984. Cloud optical thickness feedbacks in the CO2 climate problem. J Geophys Res, 89: 9668–9672
Sun Z A, Rikus L. 1999a. Improved application of exponential sum fitting transmissions to inhomogeneous atmosphere. J Geophys Res, 104: 6291–6303
Sun Z A, Rikus L. 1999b. Parametrization of effective sizes of cirrus-cloud particles and its verification against observations. Q J R Meteorol Soc, 125: 3037–3055
Taylor K E, Ghan S J. 1992. An analysis of cloud liquid water feedback and global climate sensitivity in a general circulation model. J Clim, 5: 907–919
Taylor K E, Stouffer R J, Meehl G A. 2012. An overview of CMIP5 and the experiment design. Bull Am Meteorol Soc, 93: 485–498
Wetherald R T, Manabe S. 1988. Cloud feedback processes in general circulation models. J Atmos Sci, 45: 1397–1415
Winton M. 2006. Surface albedo feedback estimates for the AR4 climate models. J Clim, 19: 359–365
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Chen, X., Zhou, T. & Guo, Z. Climate sensitivities of two versions of FGOALS model to idealized radiative forcing. Sci. China Earth Sci. 57, 1363–1373 (2014). https://doi.org/10.1007/s11430-013-4692-4
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DOI: https://doi.org/10.1007/s11430-013-4692-4