Geological Forcing of Surface Temperatures on Venus

Introduction. Epochs of widespread plains emplacement on Venus would have significantly perturbed atmospheric inventories of water and sulfur gases. These gases are potent infrared absorbers that act preferentially to block outgoing thermal radiation within carbon dioxide spectral windows. Small changes in their abundances can significantly alter the efficiency of the Venus atmospheric greenhouse and hence globallyaveraged surface temperatures [1]. However, they are also the primary reactants in producing Venus’ global cloud cover and hence high planetary albedo. Atmospheric water and sulfur dioxide together influence Venus’ surface temperature in two competing ways -by producing clouds which reduce solar forcing, and by amplifying the Venus greenhouse effect. In addition to possible rapid changes in the concentrations of these gases due to volcanic outgassing, other planetary-scale processes involving the transport, escape and crustal sequestering of volatiles affect abundances over time, driving changes in climate.