a. Will the "runaway state" also be realized in 3D system?
In the following sections, the results of parameter studies with the various values of the solar constant will be presented. The time evolutions of surface temperature and outgoing longwave radiation (OLR) for each experiment will be presented first.
Figure 1 shows the time evolution of the global mean values for surface temperature and OLR in four cases: experiments S1200, S1380. S1570, and S1800. In the case of S ≤ 1570 W/m2, the OLR value becomes nearly equal to the global mean value of the incident solar radiation flux at around Day 500. In contrast, OLR decreases with time in the case of S1800, and falls to 320 W/m2 at Day 1000. In this case, the atmosphere can only emit energy flux smaller than the global mean incident solar radiation flux of 450 W/m2.
The global mean surface temperature (red line in Fig. 1) changes along with the change in the OLR, and in the case of S S ≤ 1570 W/m2, eventually reach certain equilibrium values. However, for S1800, the surface temperature continues to rise with time and an equilibrium state could not be reached, thereby resulting in a thermally runaway state. This state corresponds to the runaway greenhouse state discussed in Nakajima et al. (1992). (The reason for this will be discussed in the section entitled "What Determines a Runaway Limit?")
Figure 1: The time evolution of global mean values of the surface temperature (K, red line) and OLR (W/m2, green line) for four cases.