Sulfur in the early martian atmosphere revisited: Experiments with a 3-D Global Climate Model

Volcanic SO₂ in the martian atmosphere has been invoked as a way to create a sustained or transient greenhouse during early martian history. Many modeling studies have been performed to test the feasibility of this hypothesis, resulting in a range of conclusions, from highly feasible to highly improbable. In this study we perform a wide range of simulations using the 3-D Laboratoire de Météorologie Dynamique Generic Global Climate Model (GCM) in order to place earlier results into context and to explore the sensitivity of model outcomes to parameters such as SO₂ mixing ratio, atmospheric H₂O content, background atmospheric pressure, and aerosol size, abundance, and composition. We conclude that SO₂ is incapable of creating a sustained greenhouse on early Mars, and that even in the absence of aerosols, local and daily temperatures rise above 273 K for only for limited periods with favorable background CO₂ pressures. In the presence of even small amounts of aerosols, the surface is dramatically cooled for realistic aerosol sizes. Brief, mildly warm conditions require the co-occurrence of many improbable factors, while cooling is achieved for a wide range of model parameters. Instead of causing warming, sulfur in the martian atmosphere may have caused substantial cooling, leading to the end of clement climate conditions on early Mars.