Climate Uncertainties Caused By Unknown Land Distribution On Habitable M-Earths

Dayside orthographic projections of sample RandCont models with 40-60% dayside land cover (row labels). Left to right: landmap, net precipitation (defined as precipitation minus evaporation), cloud fraction, and surface temperature. Clouds and precipitation are always concentrated near the substellar point, but their exact distribution depends on the shape of the land. Evaporation takes place over ocean elsewhere on the dayside. Surface temperatures are highest on dry land.

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.

Evelyn Macdonald, Adiv Paradise, Kristen Menou, Christopher Lee

Comments: 13 pages, 10 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2110.04310 [astro-ph.EP] (or arXiv:2110.04310v1 [astro-ph.EP] for this version)
Submission history
From: Evelyn Macdonald
[v1] Fri, 8 Oct 2021 18:00:03 UTC (2,002 KB)

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