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  • Yokohata, T., S. Emori, T. Nozawa, T. Ogura, M. Kawamiya, Y. Tsushima, T. Suzuki, S. Yukimoto, A. Abe-Ouchi, H. Hasumi, A. Sumi, and M. Kimoto, 2008: Comparison of equilibrium and transient responses to CO2 increase in eight state-of-the-art climate models. Tellus A. In press.

We compared the climate response of doubled CO2 equilibrium experiments (2XCO2) by atmosphere-slab ocean coupled general circulation models (ASGCMs) and that of 1\% per year CO2 increase experiments (1%CO2) by atmosphere-ocean coupled general circulation models (AOGCMs) using eight state-of-the-art climate models. Climate feedback processes in 2XCO2 are different from those in 1%CO2, and the equilibrium climate sensitivity (T_2x) in 2XCO2 is different from the effective climate sensitivity (T_2x,eff) in 1%CO2. The difference between T_2x and T_2x,eff is from -1.3 K to 1.6 K, a large part of which can be explained by the difference in the ice-albedo and cloud feedback. The largest contribution is cloud SW feedback, and the difference in cloud SW feedback for 2XCO2 and 1%CO2 could be determined by the distribution of the SAT anomaly which causes differences in the atmospheric thermal structure. An important factor which determines the difference in ice-albedo feedback is the initial sea ice distribution at the Southern Ocean, which is generally overestimated in 2XCO2 as compared to 1%CO2 and observation. Through the comparison of climate feedback processes in 2XCO2 and 1%CO2, the possible behaviour of the time evolution of T_2x,eff is discussed.

Last Updated: 2008-05-27

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