Browsing by Author "Michel, SE"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Global fossil methane emissions constrained by multi-isotopic atmospheric methane histories.
    (American Geophysical Union, 2025-02-28) Fujita, T; Graven, H; Zazzeri, G; Hmiel, B; Petrenko, VV; Smith, AM; Michel, SE; Morimoto, S
    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.
  • No Thumbnail Available
    Item
    Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions
    (Springer Nature, 2020-02-19) Hmiel, B; Petrenko, VV; Dyonisius, MN; Buizert, C; Smith, AM; Place, PF; Harth, CM; Beaudette, R; Hua, Q; Yang, B; Vimont, I; Michel, SE; Severinghaus, JP; Etheridge, DM; Bromley, T; Schmitt, J; Faïn, X; Weiss, RF; Dlugokencky, E
    Atmospheric methane (CH4) is a potent greenhouse gas, and its mole fraction has more than doubled since the preindustrial era1. Fossil fuel extraction and use are among the largest anthropogenic sources of CH4 emissions, but the precise magnitude of these contributions is a subject of debate2,3. Carbon-14 in CH4 (14CH4) can be used to distinguish between fossil (14C-free) CH4 emissions and contemporaneous biogenic sources; however, poorly constrained direct 14CH4 emissions from nuclear reactors have complicated this approach since the middle of the 20th century4,5. Moreover, the partitioning of total fossil CH4 emissions (presently 172 to 195 teragrams CH4 per year)2,3 between anthropogenic and natural geological sources (such as seeps and mud volcanoes) is under debate; emission inventories suggest that the latter account for about 40 to 60 teragrams CH4 per year6,7. Geological emissions were less than 15.4 teragrams CH4 per year at the end of the Pleistocene, about 11,600 years ago8, but that period is an imperfect analogue for present-day emissions owing to the large terrestrial ice sheet cover, lower sea level and extensive permafrost. Here we use preindustrial-era ice core 14CH4 measurements to show that natural geological CH4 emissions to the atmosphere were about 1.6 teragrams CH4 per year, with a maximum of 5.4 teragrams CH4 per year (95 per cent confidence limit)—an order of magnitude lower than the currently used estimates. This result indicates that anthropogenic fossil CH4 emissions are underestimated by about 38 to 58 teragrams CH4 per year, or about 25 to 40 per cent of recent estimates. Our record highlights the human impact on the atmosphere and climate, provides a firm target for inventories of the global CH4 budget, and will help to inform strategies for targeted emission reductions 9,10. © The Author(s), under exclusive licence to Springer Nature Limited 2020.
  • Thumbnail Image
    Item
    Using ice core measurements from Taylor Glacier, Antarctica to calibrate in situ cosmogenic 14C production rates by muons
    (Copernicus Publications, 2022-01-26) Dyonisius, MN; Petrenko, VV; Smith, AM; Hmiel, B; Neff, PD; Yang, B; Hua, Q; Schmitt, J; Shackleton, SA; Buizert, C; Place, PF; Menking, JA; Beaudette, R; Harth, CM; Kalk, M; Roop, H; Bereiter, B; Armanetti, C; Vimont, I; Michel, SE; Brook, EJ; Severinghaus, JP; Weiss, RF; McConnell, JR
    Cosmic rays entering the Earth’s atmosphere produce showers of secondary particles such as neutrons and muons. The interaction of these neutrons and muons with oxygen-16 (16O) in minerals such as ice and quartz can produce carbon-14 (14C). Analyses of in situ produced cosmogenic 14C in quartz are commonly used to investigate the Earth’s landscape evolution. In glacial ice, 14C is also incorporated through trapping of 14C-containing atmospheric gases (14CO2, 14CO, and 14CH4). Understanding the production rates of in situ cosmogenic 14C is important to deconvolve the in situ cosmogenic and atmospheric 14C signals in ice, both of which contain valuable paleoenvironmental information. Unfortunately, the in situ 14C production rates by muons (which are the dominant production mechanism at depths of > 6 m solid ice equivalent) are uncertain. In this study, we use measurements of in situ 14C in ancient ice (> 50 kilo-annum before present, ka BP) from the Taylor Glacier ablation site, Antarctica in combination with a 2D ice flow model to better constrain the rates of 14C production by muons. We find that the commonly used values for muogenic 14C production rates (Heisinger et al., 2002a, 2002b) in ice are too high by factors of 5.7 (3.6–13.9, 95 % confidence interval) and 3.7 (2.0–11.9 95 % confidence interval) for negative muon capture and fast muon interactions, respectively. Our constraints on muogenic 14C production rates in ice allow for future measurements of 14C in ice cores to be used for other applications and imply that muogenic 14C production rates in quartz are overestimated as well. © Author(s) 2022.