The concentration of methane in Earth’s atmosphere is increasing rapidly, which concerns atmospheric chemists because methane is a powerful contributor to global warming. Moreover, there is an acceleration in the rate of increase of methane in the atmosphere. Normally when we see such global changes, it is natural to expect a direct human cause of the problem. For methane, this has proven difficult.
Methane might be expected to increase in the atmosphere from the leakage of natural gas wells, pipelines and appliances (like gas stoves). Natural gas is nearly 100% methane, and the two names are interchangeable in modern usage. Satellite pictures show hot spots of the leakage of methane from gas wells and pipelines. Hand-held instruments show the leakage of gas from home appliances and the local pipelines that distribute natural gas in cities. These are all potential sources of the increase in methane in the atmosphere, but the rate of increase in the atmosphere can increase only if the leakage from these sources has increased in recent years.
A subtle characteristic of methane suggests this is not the case. The methane molecule consists of a carbon atom that is bound to four hydrogen atoms and thus given the formula CH4. The carbon atom comes in two forms—one with 6 protons and 6 neutrons in its nucleus, hence 12C, and the other with an extra neutron, hence 13C. Methane from natural gas is slightly richer in the latter form, so it is said to have higher value for 13C. Methane from other large sources, especially decomposition in wetlands, is slightly depleted in 13C, so it has a more negative value relative to an internationally accepted standard.
The rise in methane in Earth’s atmosphere shows an increasingly negative signature, indicating that it is unlikely that the leakage of natural gas from fossil fuels is causing the increase in the atmosphere. Rather, the increase seems likely to be associated with increasing emissions from wetlands and agriculture. A recent paper has documented an increasing emission from wetlands worldwide, albeit only a small percent increase in the large annual flux of methane from wetlands globally. Wetlands might be expected to emit more methane in warmer conditions, suggesting that the increasing flux of methane from wetlands is an indirect effect of human activities that affect our climate. Conversely, the destruction of methane by wetland microbes is apparently unchanged in warmer conditions.
All this makes it difficult to devise appropriate policy measures that might stem the growth of methane in the atmosphere. Sure, we can patch the network of pipelines that distribute natural gas to homes and industrial facilities. Some municipalities have prohibited the installation of new gas stoves. Reducing the emissions from these sources might reduce the increase of methane in the atmosphere, but they will not address the apparent new and increasing sources of methane in the atmosphere—most likely from wetlands. An increasing flux of methane from wetlands in response to global warming is an indirect effect stemming from human activities, that will be difficult to contain.
References
Jackson, R.B. 2024. Into the Clear Blue Sky, Scribner, New York
Kort, E.A., C. Frankenberg, K.R. et al. 2014. Four corners: The largest U.S. methane anomaly viewed from space. Geophysical Research Letters 41: 6898-6903
Megonigal, J.P. and W.H. Schlesinger. 2002. Methane-limited methanotrophy in tidal freshwater swamps. Global Biogeochemical Cycles 16: DOI.10.1029/2001GB001594.
Michel, S.E., X. Lan, J. Miller and J. Li. 2024. Rapid shift in methane carbon isotopes suggests microbial emissions drove record high atmospheric methane growth in 2020-2022. Proceedings of the National Academy of Sciences 121: doi.org/10.1073/pnas 2411212121
Plant, G., E.A. Kort, et al. 2019. Large fugitive methane emissions from urban centers along the U.S. East Coast. Geophysical Research Letters 46: 8500-8507
Zhang, Zhen et al. 2025. Ensemble estimates of global wetland methane emissions over 2000-2020. Biogeosciencs 22: 305-321.
