In Negative Feeback, we increased our simulation's incoming solar power from 200 W/m2 to 400 W/m2 and saw the surface warm by only a 5°C. It turned out that the increasing solar power was almost entirely compensated for by an increase in cloud thickness, so that the power penetrating to the surface remained almost constant. We now ask ourselves, what will happen if we drop the solar power all the way down to 100 W/m2? Will our Radiating Clouds be able to stop the world from cooling?
We started our Circulating Cells program (CC11) in its equilibrium state for 350 W/m2 solar power (RC_14000hr), and reduced the solar power to 100 W/m2. The following graph shows surface air temperature and atmospheric cloud depth for the first five hundred hours.
In the first ten hours, the surface temperature drops by a few degrees. This is what we might expect during one of Earth's nights. After three hundred hours, the surface temperature has dropped to −5°C and there are hardly any clouds left in the sky. The following graph shows the world cooling down to a new, clear-sky equilibrium of −50°C. The graph also shows the solar power penetrating to the surface. Once the sky clears, the penetration is exactly equal to 100 W/m2. We saved the final state of the atmosphere in RC_100W.
We conclude that 100 W/m2 is insufficient solar power to warm the Earth above the freezing point of water, and therefore insufficient solar power to generate the cycle of evaporation and precipitation that stabilizes our climate.