EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Impact of atmospheric radiocarbon and stable isotope measurements on understanding the global CH4 budget over 1850–2015

Ryo Fujita1,2 and Heather Graven1
Ryo Fujita and Heather Graven
  • 1Department of Physics, Imperial College London, London, United Kingdom
  • 2Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University, Sendai, Japan

Measurements of stable isotope ratios of atmospheric CH4 (δ13C-CH4, δD-CH4) have been utilized to evaluate contributions of individual CH4 sources and sinks to global atmospheric CH4 budget. However, given the uncertainty of both the source isotope signatures and kinetic isotope effects, recent estimates of the global atmospheric CH4 budget using stable isotope observations are still inconclusiveRadiocarbon measurements (Δ14C-CH4) could provide stronger additional constraint on the fossil-fuel CH4 sources (i.e.,14C-free), but the uncertainty of 14CH4 emissions from nuclear power facilities and a lack of data have limited such utilization. Here we describe new approach to estimate plausible global CHemissions and sinks scenarios over 1850–2015 using observations and one-box model simulations of atmospheric CH4, δ13C-CH4, δD-CH4, and Δ14C-CH4. As inputs to the model, we prepare a priori bottom-up CH4 emission inventories, total atmospheric CH4 lifetime, source and sink isotope signatures, nuclear power facility database, and atmospheric δ13C-CO2 and Δ14C-CO2 observations and their uncertainties. We then run a Monte Carlo simulation of atmospheric CH4, δ13C-CH4, δD-CH4, and Δ14C-CH4 over the period using the inputs with the uncertainties. By using the observational CH4 and three isotope constraints, we derive the best combinations of biogenic, anthropogenic fossil-fuel, natural geologic, biomass-burning, and nuclear power facility emissions and total CHlifetime. We find that reconciling CH4, δ13C-CH4, δD-CH4, and Δ14C-CH4 observations indicates that (1) natural geologic emissions are likely smaller than the recent bottom-up estimate 43–50 Tg CH4 yr-1 reported by Etiope et al. (2019), (2) biomass burning and anthropogenic fossil emissions are larger than current bottom-up estimates, and (3) biogenic emissions are somewhat smaller than current bottom-up estimates. Our finding suggests multiple isotope measurements, including Δ14C-CH4, have a strong potential to evaluate the current and future bottom-up global CH4 emission inventories.

How to cite: Fujita, R. and Graven, H.: Impact of atmospheric radiocarbon and stable isotope measurements on understanding the global CH4 budget over 1850–2015, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9635,, 2020