Impact Triggered Runaway Greenhouse on Mars

摘要

When a planet is in radiative equilibrium, the incoming solar flux balances the outgoing long-wave flux. If something were to perturb the system slightly, say the incoming solar flux increased, the planet would respond by radiating at a higher surface temperature. Since any radiation that comes in must go out, if the incoming is increased, the outgoing must also increase, and this increase manifests itself as a warmer equilibrium temperature. The increase in solar flux would correspond to an increase in temperature, which would increase the amount of water vapor in the atmosphere due to increased evaporation. Since water vapor is a greenhouse gas, it would absorb more radiation in the atmosphere leading to a yet warmer equilibrium temperature. The planet would reach radiative equilibrium at this new temperature. There exists a point, however, past which this positive feedback leads to a 'runaway' situation. In this case, the planet does not simply evaporate a little more water and eventually come to a slightly higher equilibrium temperature.