Fig. 3. ECS and climate feedback parameters in the Eocene simulations.

(A) The ECS (in °C) in the PI (black circle) and Eocene 1×, 3×, and 6× simulations (red filled circles) as a function of the atmospheric CO₂ concentration. For comparison, ECSs in previous Eocene simulations (3) and in CAM4 slab ocean simulations are shown as gray open markers and blue filled circles, respectively. ECS for Eocene 6× is shown as a smaller marker than the other Eocene simulations, as it is estimated from the 6× and 9× experiments instead of using slab ocean simulations (Materials and Methods). (B) Climate feedback parameters (in W m⁻² K⁻¹) diagnosed from the two-way PRP method as a function of the atmospheric CO₂ concentration in the Eocene simulations. Surface albedo (ALB), cloud (CLD), lapse rate (LPR), Planck (PLK), and water vapor (WVP) feedback parameters are shown. The cloud feedback parameter is further decomposed into shortwave and longwave components. For reference, feedback parameters in the PI simulation are denoted as open markers. Detailed numbers and uncertainty are shown in table S3. (C) Contributions to the shortwave cloud feedback parameter from cloud fraction, scattering, and absorption properties calculated from the approximated PRP method using the Eocene 1× and 9× simulations.