Climate uncertainties caused by unknown land distribution on habitable M-Earths

Abstract

A planet’s surface conditions can significantly impact its climate and habitability. In this study, we use the 3D general circulation model ExoPlaSim to systematically vary dayside land cover on a synchronously rotating, temperate rocky planet under two extreme and opposite continent configurations, in which either all of the land or all of the ocean is centred at the substellar point. We identify water vapour and sea ice as competing drivers of climate, and we isolate land-dependent regimes under which one or the other dominates. We find that the amount and configuration of land can change the planet’s globally averaged surface temperature by up to ∼20 K, and its atmospheric water vapour content by several orders of magnitude. The most discrepant models have partial dayside land cover with opposite continent configurations. Since transit spectroscopy may permit observations of M-dwarf planets’ atmospheres, but their surfaces will be difficult to observe, these land-related climate differences likely represent a limiting uncertainty in a given planet’s climate, even if its atmospheric composition is known. Our results are robust to variations in atmospheric CO2 concentration, stellar temperature, and instellation.

Predictions for Observable Atmospheres of Trappist-1 Planets from a Fully Coupled Atmosphere–Interior Evolution Model

“…runaway greenhouse (ranging from 0 to 0.2) and temperate states (ranging from 0 to 0.5) with a smooth transition between the two (Pluriel et al 2019). This constant albedo assumption neglects feedbacks between bulk atmospheric composition and planetary reflectivity, but it is adequate for sampling the broad range of climate states attributable to varying aerosol properties and surface coverage (Shields et al 2013;Kopparapu et al 2017;Rushby et al 2020;Macdonald et al 2022).…”

“…Temperature-dependence of continental weathering, T efold 5-30 K Plausible Earth-like range (Krissansen- 0.0-0.5 (Kopparapu et al 2017;Macdonald et al 2022;Rushby et al 2020;Shields et al 2013).…”

The Role of Water Vapor in the Response of the Extratropical Circulation of Earth‐Like Planets to Obliquity Changes

“…Also, depending on planetary and stellar properties, many of these planets could be susceptible to runaway warming or cooling, potentially leading to a snowball scenario (Shaw & Graham, 2020), resulting in planetary properties far beyond the range of climates considered here. The presence of continents could also significantly complicate these results, changing patterns of surface albedo, heat capacity, and water availability, as has been shown to be relevant for the climate of tidally locked exoplanets (Lewis et al., 2018; Macdonald et al., 2022). Clouds could also play a large role, altering regional optical depth and albedo.…”

Tropical Cyclones on Tidally Locked Rocky Planets: Dependence on Rotation Period

“…Notably, we do not include a dynamic ocean with motions forced by wind stress from the overlying atmosphere, which has been shown to result in a characteristic eastward offset in the SST maximum (known as a lobster planet, Hu & Yang 2014). We also assume an aquaplanet and thus do not include any continents in our simulations, which have been shown to potentially have a large effect on moisture availability and surface enthalpy fluxes (Lewis et al 2018;Salazar et al 2020;Macdonald et al 2022). We anticipate that including a dynamic ocean and/or continents may shift the region of tropical cyclone favorability toward the regions near the equator with the warmest SSTs.…”