Comparative Planetary Climatology

In the last three decades we have experienced the first close-up exploration of the planets of the solar system. American, Russian, and (increasingly) European planetary space missions have now explored the atmospheres and environments of many different worlds, returning data with which we can begin to understand the Earth in its wider context as never before. The new discipline of Comparative Planetary Climatology deals with the climate on Earth-like planets and addresses the physical processes that determine environmental conditions, the stability in each case against climate change, and the development of new experiments to further investigate these. By comparing the processes at work on Mars, Venus and Titan to those on our own planet we may gain a deeper understanding of global change on the Earth, the origin and evolution over the long term of this habitable world, and the processes behind threats such as greenhouse warming. Model temperature profiles which give a description of the state of the climate for all four of the terrestrial planet atmospheres in terms of simple physics, can be employed to study, and eventually to answer, questions of climate stability and change, such as: What do the climate systems on all four planets have in common? How stable are their current climates? What controls their stability? What change has taken place and why? What is the chronology of past changes? Can we make plausible predictions of future change? What are the appropriate measurement objectives for future space missions that seek to address these and other climate-related questions further?