A model for the mean global surface temperature of an Earth-like planet derived from the geological history of Earth

Surface temperature is a critical aspect for assessing the habitability of Earth-like planets. This temperature is determined by various factors such as albedo and greenhouse. The data collected from the JWST and upcoming space telescopes, such as the Habitable Worlds Observatory, would be crucial for constraining surface temperatures. In this study, we modeled the mean global surface temperature of Earth-like planets using for calibration the paleotemperatures of Earth in the last 750 million years. The model considers factors such as the distribution of different types of surface fractions (e.g., vegetation, ice, desert, ocean, and clouds), Bond albedo, and greenhouse effect. The model was fitted to theoretical and experimental data from paleotemperatures and satellite data using a Markov chain Monte Carlo (MCMC) analysis. Our results showed that changes in albedo due to variations in land-ocean ratios only led to a ± 2°C change from the current mean global temperature of 15°C. An Earth-like planet, with a similar stellar flux and atmospheric composition as Earth, should have a normalized greenhouse of 0.3 to 0.5 to support temperate conditions. We also defined a new planetary property, the “thermality,” which conveniently relates surface temperatures to stellar flux and other atmospheric properties. We found that the thermality of the Earth during the Phanerozoic was fairly constant, albeit the changes in albedo and greenhouse conditions. Our model can be used to constrain the mean global surface temperature of rocky planets, such as those in the TRAPPITS-1 system, based on JWST observations.