Warming the early Earth - CO2 reconsidered

TL;DR

This study revises the estimated CO2 levels needed to prevent early Earth from freezing, showing that lower concentrations than previously thought could suffice, aligning better with geological evidence.

Contribution

The paper introduces an updated radiative-convective model with new absorption data, reducing the estimated CO2 requirements for early Earth and resolving previous discrepancies with sediment data.

Findings

CO2 partial pressures of about 2.9 mb are sufficient to keep early Earth warm.

Updated model reduces CO2 estimates by up to an order of magnitude.

Results are robust across variations in model parameters.

Abstract

Despite a fainter Sun, the surface of the early Earth was mostly ice-free. Proposed solutions to this so-called "faint young Sun problem" have usually involved higher amounts of greenhouse gases than present in the modern-day atmosphere. However, geological evidence seemed to indicate that the atmospheric CO2 concentrations during the Archaean and Proterozoic were far too low to keep the surface from freezing. With a radiative-convective model including new, updated thermal absorption coefficients, we found that the amount of CO2 necessary to obtain 273 K at the surface is reduced up to an order of magnitude compared to previous studies. For the late Archaean and early Proterozoic period of the Earth, we calculate that CO2 partial pressures of only about 2.9 mb are required to keep its surface from freezing which is compatible with the amount inferred from sediment studies. This conclusion was not significantly changed when we varied model parameters such as relative humidity or surface albedo, obtaining CO2 partial pressures for the late Archaean between 1.5 and 5.5 mb. Thus, the contradiction between sediment data and model results disappears for the late Archaean and early Proterozoic.