3D Modeling of the Early Martian Climate

The early Martian climate is an enigma: evidence for flowing liquid water on the surface 3-4 Ga is conclusive, but Mars’ orbital distance and the faintness of the young Sun mean that long term warm, wet surface conditions require a massive greenhouse effect. Various solutions have been proposed over the years, but most previous modeling of early Mars warming mechanisms has been limited to simplistic 1D climate models. Here I present recent 3D climate simulations that have shed new light on this problem. We have built a model that includes self-consistent representations of the cycles of both CO2 and H2O for the first time, including a flexible correlated-k scheme for the radiative transfer. Results show that a pure CO2-H2O greenhouse alone is incapable of warming early Mars above global mean temperatures of about 240 K, even when the climate effects of clouds are taken into account. Nonetheless, for atmospheric pressures greater than a fraction of a bar, adiabatic cooling causes transport of snow and ice to the valley network regions under a wide range of conditions. Here I show that in combination with episodic warming events, this robust transport mechanism may be able to account for much of the fluvial geology without the need to invoke a long-term warm, wet early Mars. Implications for Gale crater and the probability of Martian life are also discussed.