抄録
We construct a one-dimensional energy balance climate model for Mars which incorporates greenhouse effect of CO2 and latitudinal heat transport so that we can express a latitudinal temperature gradient and change of an areal extent of a polar ice cap. By considering energy balance and CO2 budget among atmosphere, ice caps, and regolith, we investigate stability and evolution of the climate system of Mars. Under the present condition there are two stable steady state solutions of the system. One corresponds to a partial ice-covered solution (the present state), and the other is a warmer ice-free solution. Although this is also predicted by previous studies, these solutions are qualitatively different from them. When we assume CO2 as a dominant greenhouse gas for a warm and wet climate on the early Mars, we found that the total amount of CO2 within the whole system should have been larger than that at present and have decreased by some removal processes. We also found that a climate jump must have occurred during the evolution from the early warm climate to the present state, and ice caps on the early Mars might have extended to the mid-latitude. The atmospheric pressure may have decreased further after the climate jump.
