Liquid water on Mars: An energy balance climate model for CO2/H2O atmospheres |
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| Authors: | MI Hoffert AJ Callegari CT Hsieh W Ziegler |
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| Institution: | 1. Department of Applied Science, New York University, New York, New York 10003, USA |
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| Abstract: | Geologic evidence of the prior existence of liquid water on Mars suggests surface temperatures Ts were once considerably warmer than at present; and that such a condition may have arisen from a larger atmospheric greenhouse. Here we develop a simple climate model for a CO2/H2O Mars atmosphere including water vapor-longwave opacity feedback in the atmosphere and temperature-albedo feedback at surface icecaps, under the assumption that once the Martian surface pressure was ps ≥ 1 atm CO2. Longwave flux to space is computed as a function of Ts and ps using band-absorption models for the effect of the 15-μm fundamental, and the 10- and 15-μm hot bands, of the CO2 molecule; as well as the pure rotation bands and e continuum of H2O. The derived global radiative balance predicts a global mean surface temperature of 283°K at 1 atm CO2. When the emission model is coupled to a latitudinally resolved energy balance climate model, including the effect of poleward heat transfer by atmospheric baroclinic eddies, the solutions vary, depending on ps. We considered two cases: (1) the present Mars (ps ? 0.007 atm) with pressure-buffering by solid CO2 icecaps, and limited poleward heat flux by the atmosphere; and (2) a hypothetical “hot Mars” (ps ? 1.0 atm), whose much higher CO2 amount augmented by H2O evaporative feedback yields a theoretical Ts distribution with latitude admitting liquid water over 95% of the surface, water icecaps at the poles, and a diminished equator-to-pole temperature gradient relative to the present. |
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