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D.H. Grinspoon (LASP, University of Colorado)
The surface temperature of Venus is a sensitive function of the abundances of greenhouse gases and also of cloud structure. Outgassing of CO2, H2O and SO2 has most likely played a major role in establishing both the planetary albedo, through cloud formation, and high surface temperatures through the greenhouse effect. It follows that changes in the global volcanic flux lead to changes in surface temperature. Surface temperature, in turn, influences the degree of partial melting at depth and the rheology of the crust. It is becoming increasingly clear that the unique geological features of the Venusian surface must be understood in the context of its climate history. I will discuss recent climate models of Venus and summarize post-Magellan views of Venusian geological history, with an emphasis on those aspects of the surface record with implications for climate history. The surface record indicates that the rate and style of volcanism have gone through dramatic changes during the past billion years, with at least one epoch of resurfacing at rates much greater than those at present. I will present results of an evolutionary climate model that calculates surface temperature evolution in response to outgassing of volatiles, heterogeneous reactions of atmospheric gases with surface minerals, and the exospheric escape of hydrogen. Several mysteries of Venusian geology may possibly be explained by past climate change.