3D Climate Simulations of the Archean Find That Methane has a Strong Cooling Effect at High Concentrations. Issue 6 (11th March 2023)

• Record Type: Journal Article
• Authors: Eager‐Nash, J. K.; Mayne, N. J.; Nicholson, A. E.; Prins, J. E.; Young, O. C. F.; Daines, S. J.; Sergeev, D. E.; Lambert, F. H.; Manners, J.; Boutle, I. A.; Wolf, E. T.; Kamp, I. E. E.; Kohary, K.; Lenton, T. M.
• Is Part Of: Journal of geophysical research. Volume 128:Issue 6(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-03-11
• Subjects: Archean -- methane -- climate; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2022JD037544
• Languages: English
• ISSNs: 2169-897X

Abstract

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 pCH4 :pCO2 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 pCH4 ≤ 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. Plain Language Summary: The Archean is a period in Earth history spanning approximately 4 to 2.5 billion years ago. During this period oxygen concentrations were much lower than today, which in turn allowed methane concentrations to be much higher during the Archean. Methane would have been produced by microbes, and depending on the exact nature of the ecosystem could have led to a wide range of atmospheric concentrations. Using a three‐dimensional climate model and with various methane concentrations in the atmosphere we show that the warming effect of methane first increases and then, at high concentrations, decreases. This decrease is stronger than those found in previous studies using one‐dimensional (single column) atmosphere models. We find that methane can only warm the Archean by up to 7 K. Key Points: Methane warming peaks at a pCH4 :pCO2 ratio of 0.1, with global‐mean surface warming <7 K Uneven meridional methane radiative forcing and changes to atmospheric circulation determine the equator‐to‐pole temperature difference 3D modeling is important to fully capture methane's cooling effect for pCH4 :pCO2 ratios greater than 0.1