Habitable Climates

TL;DR

This paper uses energy-balance models to evaluate the spatial and temporal habitability of Earth-like planets, highlighting the importance of climate dynamics and planetary properties in habitability assessments.

Contribution

It introduces a framework for assessing planetary habitability using simple seasonal energy-balance models, considering factors like rotation rate and land-ocean distribution.

Findings

Habitability varies significantly with planetary rotation and land-ocean fractions.

Climate stability against snowball events is crucial for habitability.

Traditional habitable zone assessments may overlook key climatic conditions.

Abstract

According to the standard liquid-water definition, the Earth is only partially habitable. We reconsider planetary habitability in the framework of energy-balance models, the simplest seasonal models in physical climatology, to assess the spatial and temporal habitability of Earth-like planets. We quantify the degree of climatic habitability of our models with several metrics of fractional habitability. Previous evaluations of habitable zones may have omitted important climatic conditions by focusing on close Solar System analogies. For example, we find that model pseudo-Earths with different rotation rates or different land-ocean fractions have fractional habitabilities that differ significantly from that of the Earth itself. Furthermore, the stability of a planet's climate against albedo-feedback snowball events strongly impacts its habitability. Therefore, issues of climate dynamics may be central in assessing the habitability of discovered terrestrial exoplanets, especially if astronomical forcing conditions are different from the moderate Solar System cases.