This chapter examines the processes underlying long-term climate change on Mars, focusing on the so-called “faint young Sun paradox,” in which evidence of ancient rivers contradicts results from astronomy that the Sun's output in the first billion years of the solar system was seventy percent of its current value. The fascination with Mars stems in part from the possibility that life could have evolved there. Searching for evidence of liquid water, past and present, is therefore a major objective. Another objective is understanding Mars's climate, past and present. As on Earth, climate change is recorded in Mars's sediments and ice deposits. The chapter first provides an overview of Mars's climate before discussing the presence of carbon dioxide in the atmosphere. It also considers condensation, evaporation, greenhouse warming, atmospheric water vapor, and the process of terraforming on Mars.
Long-term trends in the atmospheric water vapor content estimated from ground-based GPS data