Cloud Feedback on Earth's Long-term Climate Simulated by a Near-global Cloud-permitting Model

TL;DR

This study uses a near-global cloud-permitting model to investigate long-term cloud feedback mechanisms that may help resolve the Faint Young Sun Problem by stabilizing Earth's climate through cloud-induced albedo changes.

Contribution

It demonstrates the existence and magnitude of a stabilizing shortwave cloud feedback using an explicit cloud-resolving model, advancing understanding beyond previous models with parameterized convection.

Findings

A stabilizing shortwave cloud feedback of about 6 W/m² was confirmed.

Low-level clouds increase with higher insolation and lower CO₂, stabilizing climate.

Cloud feedback accounts for roughly 14-16% of the energy needed to offset a 20-30% fainter Sun.

Abstract

The Sun becomes brighter with time, but Earth's climate is roughly temperate for life during its long-term history; for early Earth, this is known as the Faint Young Sun Problem (FYSP). Besides the carbonate-silicate feedback, recent researches suggest that a long-term cloud feedback may partially solve the FYSP. However, the general circulation models they used cannot resolve convection and clouds explicitly. This study re-investigates the clouds using a near-global cloud-permitting model without cumulus convection parameterization. Our results confirm that a stabilizing shortwave cloud feedback does exist, and its magnitude is $\approx$6 W m$^{-2}$ or 14% of the energy required to offset a 20% fainter Sun than today, or $\approx$10 W m$^{-2}$ or 16% for a 30% fainter Sun. When insolation increases and meanwhile CO$_2$ concentration decreases, low-level clouds increase, acting to stabilize the climate by raising planetary albedo, and vice versa.