3D simulations of oxygenated rocky planetary climates and observational predictions

There are now hundreds of known terrestrial exoplanets (rocky planets orbiting other stars), with ~60 considered potentially habitable worlds. In the next two decades, several state-of-the art observatories will observe these exoplanets with unprecedented sensitivity, requiring the parallel use of computational models to constrain their climates. Using Earth’s inhabited paleoclimates as templates may elucidate which exoplanets could host life. I use WACCM6, a three-dimensional (3D) Earth System Model, to simulate Earth’s oxygenated paleoclimates, as well as the climates of Earth-like terrestrial exoplanets. I use these simulations as input to the Planetary Spectrum Generator, a radiative transfer suite, to predict spectroscopic telescope transmission spectra and direct imaging spectra observations of exoplanets. Earth's atmosphere has been oxygenated for the past 2.4 billion years. I find that different amounts of O2 alters the 3D distribution of temperature, clouds, dynamics, and composition, with reduced ozone (O3) concentrations between 0.1 - 50% the present atmospheric level of O2 compared to previous 1D and 3D modelling. Considering these scenarios as Earth-analogue exoplanets, I predict their transmission and direct imaging spectra with next generation telescopes, finding that annual variability in reflected light, which depends on both clouds and composition, could be observable through state-of-the-art high-contrast imaging. I perform simulations of TRAPPIST-1e and Proxima Centauri b, two potentially tidally locked habitable zone exoplanets. Three distinct layers of atmospheric super rotation are resolved in the data. Furthermore, uncertainty in the incident ultraviolet (UV) radiation may lead to ambiguities when interpreting observations and inferring atmospheric oxygenation scenarios. This can be partially resolved with a dedicated, sensitive UV observatory. This thesis demonstrates the requirement for model development to better estimate the O2-O3 relationship across a variety of (exo)planets. Such advances are important for reconstructing Earth's paleoclimates, and are crucial for efforts to determine if any exoplanets host Earth-like biospheres.