Estimating the power of Mars’ greenhouse effect

Extensive modeling of Mars in conjunction with in situ observations suggests that the annual average global mean surface temperature is T s ¯ ∼ 202 K . Yet its effective temperature, i.e., the temperature at which a blackbody radiates away the energy it absorbs, is Te ∼ 208 K. How can a planet with a CO2 atmosphere have a mean annual surface temperature that is actually less than its effective temperature? We use the Ames General Circulation Model explain why this is the case and point out that the correct comparison of the effective temperature is with the effective surface temperature Tse, which is the fourth root of the annual and globally averaged value of T s 4 . This may seem obvious, but the distinction is often not recognized in the literature.