Global fossil methane emissions constrained by multi-isotopic atmospheric methane histories.
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Date
2025-02-28
Journal Title
Journal ISSN
Volume Title
Publisher
American Geophysical Union
Abstract
The global CH4 budget of sources and sinks is highly uncertain, particularly the emissions from specific sources such as fossil fuels (FF) or agriculture. Here, we estimate plausible global CH4 source and sink scenarios using historical observations and simulations of atmospheric CH4 mole fraction and its stable isotopic (δ13C-CH4, δD-CH4) and radiocarbon (Δ14C-CH4) composition, combining constraints from all these tracers for the first time. We employ a one-box model along with a Monte Carlo particle filter technique, explicitly exploring the impact of each isotopic constraints and uncertainties in prior CH4 source and sink parameters on posterior sectorial source fractions. We find our posterior anthropogenic FF emissions at the global scale are 30% lower than previous isotope-based studies. Our analysis suggests previous δ13C-CH4-based studies are potentially biased because the current database-derived estimate of the global mean biogenic δ13C-CH4 source signature is too low and/or current sink-weighted total carbon kinetic isotope effect is underestimated. We find modern atmospheric Δ14C-CH4 data constrains lower global FF emissions after 1980s, which is contrary to the most recent finding that utilized atmospheric Δ14C-CH4 data, but supported by an independent estimate of global nuclear 14CH4 emissions. Our multi-isotopic constraints align with CH4-only inversion results, while reducing their uncertainties with greater robustness against different prior emission scenarios. We find strong constraints not only on FF emissions but also other key sources and sinks, showing that long-term multi-isotopic observations are critical for refining the global CH4 budget and developing effective CH4 emission mitigation strategies. © 2025. The Author(s). This is an open access article under the terms of the Creative Commons
Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Description
Keywords
Global analysis, Fossil fuels, Atmospheres, Agriculture, Methane, Stable isotopes, Data, Climatic change, Carbon 14, Carbon sinks, Greenhouse effect, Emission
Citation
Fujita, R., Graven, H., Zazzeri, G., Hmiel, B., Petrenko, V. V., Smith, A. M., Michel, S. E., & Morimoto, S. (2025). Global fossil methane emissions constrained by multi-isotopic atmospheric methane histories. Journal of Geophysical Research: Atmospheres, 130(5), (1-25), e2024JD041266. Doi:10.1029/2024JD041266