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

TL;DR

This study uses a 3D climate model to explore how unknown land distribution on habitable M-Earths can cause significant climate uncertainties, affecting temperature and water vapor levels.

Contribution

It systematically analyzes the impact of land configuration on climate variability, highlighting the importance of land distribution in habitability assessments.

Findings

Land configuration can alter global temperature by up to 20K.

Water vapor and sea ice are key climate drivers.

Surface land distribution introduces significant climate uncertainty.

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 20K, 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 not their surfaces, 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.