CoachThe runaway greenhouse limit is the largest flux of infrared radiation that a planet with an ocean can send to space. A runaway greenhouse is the state of a planet that absorbs more sunlight than that limit: it cannot balance its budget until the whole ocean has evaporated and the surface has heated far beyond it. A moist greenhouse is the state of a planet, short of the runaway, whose surface is warm enough for its stratosphere to hold a large mixing ratio of water vapour, which ultraviolet light splits and whose hydrogen escapes.
