The stability of climate on Venus

The climate of Venus is to a large degree controlled by the radiative properties of its massive atmosphere. However, volcanic outgassing and surface-atmosphere interactions may moderate the atmospheric abundances of CO₂ and other radiatively important volatiles. Recently, work on the interpretation of the impact cratering record has placed limits on the magnitude of the volcanic flux. Additionally, recent laboratory data on the equilibria and kinetics of possible surface-atmosphere reactions under Venus-like conditions provide important insights into the role that they may play in moderating Venus' climate. The surface temperature and pressure on Venus coincide approximately with the P-T equilibrium of the calcite-wollastonite mineral reaction, and atmospheric sulfur species are probably involved in rapid heterogeneous reactions with the surface. Perturbations to the atmospheric inventory of radiatively active species may have a significant impact on the climate of Venus and upon the stability of the greenhouse effect. Through the use of a Venus climate model that couples atmospheric radiative-convective equilibrium with surface processes, we show that it is likely that Venus' climate is at or near a state of unstable equilibrium. Furthermore, we show that only moderate perturbations in the abundances of radiatively active volatiles may be sufficient to precipitate changes to new climate regimes.