Evolution of the Climate System of Mars: Effects of Obliquity Change

Introduction: Greenhouse effect of CO2 may have been the most important factor for the Martian surface environment throughout the history of Mars. Polar ice caps and surface regolith are considered to be large CO2 reservoirs to exchange CO2 with the atmosphere on the Mars (atmosphere-ice caps-regolith (AIR) system). In this respect, Mars has an essentially different climate system from that of the Earth. It is well known that abrupt climate changes (“climate jump”) can occur due to changes in the solar radiation [1] and/or in the atmospheric CO2 pressure [2] during the Earth's history. In the case of Mars, stability and evolution of the Martian climate system has been also discussed for a long time [e.g., 3, 4]. For example, it is suggested that the climate jump due to decrease in the total amount of CO2 in the AIR system must have occurred during the Martian history [4]. However, all the previous studies are under the condition of annual mean solar radiation. In reality, its seasonal variation may have significant effects on the energy balance in the Martian climate system. It is, therefore, necessary to evaluate effects of the seasonal change of the solar incident flux due to the inclined rotation axis. It is known that obliquity of Mars (inclination of the Martian rotation axis) could have changed between 0° and 60° [e.g., 5]. Obliquity variation could have profound effects on the climate system of Mars. In this study, we investigate behaviors of a one-dimensional energy balance climate model under the condition of seasonal change of the solar incident flux and variations in the obliquity. Model: We introduce a one-dimensional energy balance climate model (EBM) with seasonal changes of solar incident flux developed by James and North [6]. The EBM is represented mathematically as follows: