Runaway greenhouse

A runaway greenhouse is a loss of thermal balance when absorbed stellar power exceeds the maximum outgoing thermal radiation available to a water-rich atmosphere in the relevant climate state. Surface warming increases atmospheric water vapour and hence infrared opacity. The layers emitting to space need not warm as rapidly as the surface, allowing outgoing power to approach a limit rather than increasing indefinitely with surface temperature.

If absorbed power remains above that limit, the climate cannot settle into the same ocean-bearing equilibrium and continued warming drives evaporation. The criterion concerns the whole atmospheric radiative transfer problem; a large ordinary greenhouse effect alone does not establish a runaway. Bond albedo, clouds, stellar spectrum and atmospheric inventory affect its threshold and the resulting circumstellar habitable zone.