Revisiting the greenhouse effect of non-greenhouse gases in the atmosphere of Earth-like planets

We investigate the impact of non-greenhouse gases (e.g., N2, CO, and O2) on the surface temperatures of Earth-like planets. Non-greenhouse gases are transparent to infrared radiation and do not directly heat the planetary surface. However, as non-greenhouse gases become abundant, the total atmospheric pressure increases then the absorption lines of greenhouse gases broaden. Consequently, the atmosphere absorbs a wider range of infrared wavelengths, leading to an indirect warming effect caused by non-greenhouse gases. On the contrary, since gas molecules scatter visible light from the host star, an increase in total atmospheric pressure may increase the planetary albedo; Higher atmospheric pressure decreases energy absorbed by the surface, potentially cooling the planetary climate. Wordsworth & Pierrehumbert (2013) described both cases in which surface temperature can increase and decrease with an increase in atmospheric N2 partial pressure. While changes in surface temperature are qualitatively controlled by which of the warming or cooling effects of non-greenhouse gases is dominant, the practical indicator of these two effects remains uncertain. In this study, we employ a one-dimensional planetary climate model (Kasting et al., 1984) to assess the impact of non-greenhouse gases on surface temperatures comprehensively. We conduct parameter surveys on various levels of N2 and CO2 abundance under several host star types and relative humidity models to observe the surface temperature response. We then identify the actual conditions leading to the transition of planetary surface cooling/warming and discuss how non-greenhouse gases control the surface temperature of Earth-like planets.