Faint young Sun paradox remains

TL;DR

The paper investigates the faint young Sun paradox, demonstrating that reducing cloud and surface reflectivity alone cannot explain the warm early Earth climate, implying a stronger greenhouse effect was necessary.

Contribution

It provides a quantitative analysis showing that cloud and surface albedo reductions are insufficient to resolve the paradox, emphasizing the need for higher greenhouse gases.

Findings

Albedo reduction falls short by a factor of two to resolve the paradox

A stronger greenhouse effect is required for a temperate Archean climate

Low CO2 levels are incompatible with warm early Earth conditions

Abstract

The Sun was fainter when the Earth was young, but the climate was generally at least as warm as today; this is known as the `faint young Sun paradox'. Rosing et al. [1] claim that the paradox can be resolved by making the early Earth's clouds and surface less reflective. We show that, even with the strongest plausible assumptions, reducing cloud and surface albedos falls short by a factor of two of resolving the paradox. A temperate Archean climate cannot be reconciled with the low level of CO2 suggested by Rosing et al. [1]; a stronger greenhouse effect is needed.