2:15 PM - 2:30 PM
[U11-03] Revisiting the greenhouse effects of non-greenhouse gases: Impact of water vapor feedback
Keywords:Earth-like planet, Atmosphere
The atmospheres of Earth-like planets, including early Earth, may contain large amounts of CO due to degassing from reducing mantles (e.g., Sossi et al. 2020) or photochemical instability of atmospheric CO2 (e.g., Hu et al. 2020). Although the surface environment of a planet is strongly related to its atmospheric composition, there are still many unresolved aspects of the surface environment when non-greenhouse gases such as CO are present in large amounts in the atmosphere.
In terms of planetary climate, non-greenhouse gases have effects that contribute to warming and cooling (e.g., Goldblatt et al. 2009; Wordsworth & Pierrehumbert 2013). Warming is thought to be caused by pressure broadening of the absorption linewidth of greenhouse gases in infrared wavelengths due to increased atmospheric pressure, while cooling is the result of stronger Rayleigh scattering. Theoretical calculations have shown that both warming and cooling can occur in environments with large amounts of non-greenhouse gases, and the reasons for this have been explained by the above effects (Wordsworth & Pierrehumbert 2013). However, the quantitative conditions under which warming and cooling can occur have not been clarified.
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 (an example of non-greenhouse gases) and CO2 (greenhouse gas) abundance under several relative humidity models to observe the surface temperature response.
In addition to traditional effects (pressure broadening and Rayleigh scattering), we found that water vapor feedback to cause warming is essential in determining surface temperature. A control experiment without water vapor feedback shows that warming by the impact of pressure broadening is rather limited. We examine when and how the impact of non-greenhouse gases becomes vital over a wide range of CO2 and N2 partial pressures and clarify the role of water in the determination of surface temperature. Thanks to the proximity in molecular weights, our results can readily be adapted to CO-rich atmospheres.
In terms of planetary climate, non-greenhouse gases have effects that contribute to warming and cooling (e.g., Goldblatt et al. 2009; Wordsworth & Pierrehumbert 2013). Warming is thought to be caused by pressure broadening of the absorption linewidth of greenhouse gases in infrared wavelengths due to increased atmospheric pressure, while cooling is the result of stronger Rayleigh scattering. Theoretical calculations have shown that both warming and cooling can occur in environments with large amounts of non-greenhouse gases, and the reasons for this have been explained by the above effects (Wordsworth & Pierrehumbert 2013). However, the quantitative conditions under which warming and cooling can occur have not been clarified.
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 (an example of non-greenhouse gases) and CO2 (greenhouse gas) abundance under several relative humidity models to observe the surface temperature response.
In addition to traditional effects (pressure broadening and Rayleigh scattering), we found that water vapor feedback to cause warming is essential in determining surface temperature. A control experiment without water vapor feedback shows that warming by the impact of pressure broadening is rather limited. We examine when and how the impact of non-greenhouse gases becomes vital over a wide range of CO2 and N2 partial pressures and clarify the role of water in the determination of surface temperature. Thanks to the proximity in molecular weights, our results can readily be adapted to CO-rich atmospheres.