Revisiting the scattering greenhouse effect of CO2 ice clouds

TL;DR

This study reevaluates the warming effect of CO2 ice clouds on cold planets using advanced radiative transfer models, finding that previous estimates of their greenhouse impact were significantly overestimated, which affects planetary climate models.

Contribution

It introduces a more accurate radiative transfer approach to assess CO2 ice cloud effects, challenging prior simplified models and providing revised estimates of their climatic influence.

Findings

Previous models overestimated the greenhouse effect of CO2 ice clouds.

Revised models show a weaker warming impact of CO2 clouds.

Implications for early Mars, Earth, and habitable zone boundaries.

Abstract

Carbon dioxide ice clouds are thought to play an important role for cold terrestrial planets with thick CO2 dominated atmospheres. Various previous studies showed that a scattering greenhouse effect by carbon dioxide ice clouds could result in a massive warming of the planetary surface. However, all of these studies only employed simplified two-stream radiative transfer schemes to describe the anisotropic scattering. Using accurate radiative transfer models with a general discrete ordinate method, this study revisits this important effect and shows that the positive climatic impact of carbon dioxide clouds was strongly overestimated in the past. The revised scattering greenhouse effect can have important implications for the early Mars, but also for planets like the early Earth or the position of the outer boundary of the habitable zone.