Climate diversity in the solar-like habitable zone due to varying background gas pressure

A large number of studies have responded to the growing body of confirmed terrestrial habitable zone exoplanets by presenting models of various possible climates. However, the impact of the partial pressure of background gases such as N2 has not yet been well-explored, despite the abundance of N2 in Earth’s atmosphere and the lack of constraints on its typical abundance in terrestrial planet atmospheres. We use PlaSim, a fast 3D climate model, to simulate many hundreds of climates around Sun-like stars with varying N2 partial pressures, instellations, and surface characteristics to identify the impact of the background gas partial pressure on the climate. We find that the climate’s response is nonlinear and highly sensitive to the background gas partial pressure. We identify pressure broadening of greenhouse gas (such as CO2 and H2O) absorption lines, amplification of warming or cooling by the water vapor greenhouse positive feedback, heat transport efficiency, and cooling through Rayleigh scattering as the dominant competing mechanisms that determine the equilibrium climate for a given N2 partial pressure. Finally, we show that different amounts of N2 should have a significant effect on broadband reflected light observations of terrestrial exoplanets around Sun-like stars.