3D climate simulations of the Archean find that methane has a strong cooling effect at high concentrations

TL;DR

This study uses 3D climate modeling to show that methane's role in Archean climate was complex, with high concentrations causing cooling rather than warming, influenced by atmospheric circulation and radiative effects.

Contribution

The paper demonstrates the importance of 3D models in accurately assessing methane's climatic effects during the Archean, revealing a cooling effect at high concentrations.

Findings

Maximum surface warming of 7 K at specific methane levels.

Increased equator-to-pole temperature differences at high methane concentrations.

Circulation changes significantly influence methane's radiative impact.

Abstract

Methane is thought to have been an important greenhouse gas during the Archean, although its potential warming has been found to be limited at high concentrations due to its high shortwave absorption. We use the Met Office Unified Model, a general circulation model, to further explore the climatic effect of different Archean methane concentrations. Surface warming peaks at a pressure ratio CH$_4$:CO$_2$ of approximately 0.1, reaching a maximum of up to 7 K before significant cooling above this ratio. Equator-to-pole temperature differences also tend to increase up to pCH$_4$ $\leq$300 Pa, which is driven by a difference in radiative forcing at the equator and poles by methane and a reduction in the latitudinal extend of the Hadley circulation. 3D models are important to fully capture the cooling effect of methane, due to these impacts of the circulation.