11:15 〜 11:30
[ACG35-08] Verifying global fugitive fossil fuel CH4 emission trends using atmospheric CH4 and δ13C-CH4 observations
キーワード：Methane, Stable carbon isotope ratio of CH4 , Fugitive fossil fuel CH4 emission , ACTM
Reducing methane (CH4) emissions is now a top priority for climate action because of its short lifetime and high global warming potential. Emissions from fossil fuel exploitation sectors (oil-gas extraction, coal mining, geological), accounting for 33% of global anthropogenic CH4 emissions, are the most attractive and cost-effective mitigation option. However, the estimated CH4emissions and trends of the fossil-fuel sector are largely uncertain across the existing inventories (e.g., EDGAR, GAINSv4, FAO estimates, etc.) and source/sink inversions of atmospheric CH4. The atmospheric CH4 data alone do not provide source-type information and hence cannot constrain magnitudes of specific sectors. Stable carbon isotope ratio of CH4 (δ13C-CH4) in the atmosphere is controlled by relative contributions from different source types with distinctive isotope signatures, and could help to probe sectoral emissions with the help of the atmospheric chemistry-transport model (ACTM).
We have simulated the global history (1985-2020) of CH4 and δ13C-CH4 using MIROC4-ACTM and compared with the measurement results at networks of monitoring stations (e.g., INSTAAR, TU/NIPR, MPI, etc.). The base simulations (based on anthropogenic CH4 emissions from the EDGARv6 database) could not reproduce the observed atmospheric CH4 and δ13C-CH4(Fig. 1). The discrepancy between the observed and modelled CH4 and δ13C-CH4 suggest incomplete knowledge of emissions used for baseline simulations. Different sensitivity experiments are performed by revising fugitive fossil fuel emissions (from different inventories and literature) and spatially resolved distributions of δ13C-CH4 source signatures to reproduce the measurements. The emission scenario (sONG-Coal_geol19) is then prepared by using GAINSv4 inventory for Oil and Gas, coal mining and scaled natural geological sectors, which reproduces the trend and meridional gradients in the observed CH4 and δ13C-CH4 (Fig. 1), but does not compare well with the absolute δ13C-CH4 values. Spatially resolved δ13C-CH4 source signatures in place of globally invariant source signature helps to reduce the mismatch between observed and simulated δ13C-CH4 from ~1 ‰ to less than 0.1 ‰ (magenta line lower panel of Fig. 1). The most likely emission scenario, which can reconstruct the latitudinal gradient and trends in atmospheric CH4 and δ13C-CH4 simultaneously suggests a decreasing-to-constant emissions from fossil fuel exploitations 1985-2020, contrary to an increasing trend in EDGARv6 inventory. This study suggests that the increase in atmospheric CH4 after 2006 is primarily due to microbial sources, mainly the agricultural and waste management sector. The detail will be presented in the meeting.
Figure 1. Comparison of modelled CH4 and δ13C-CH4 with observations (black circle) made by Tohoku University (TU) and National Institute of Polar Research (NIPR) at two northern and southern surface baseline stations, Ny-Alesund, Svalbard and Syowa, Antarctica.
We have simulated the global history (1985-2020) of CH4 and δ13C-CH4 using MIROC4-ACTM and compared with the measurement results at networks of monitoring stations (e.g., INSTAAR, TU/NIPR, MPI, etc.). The base simulations (based on anthropogenic CH4 emissions from the EDGARv6 database) could not reproduce the observed atmospheric CH4 and δ13C-CH4(Fig. 1). The discrepancy between the observed and modelled CH4 and δ13C-CH4 suggest incomplete knowledge of emissions used for baseline simulations. Different sensitivity experiments are performed by revising fugitive fossil fuel emissions (from different inventories and literature) and spatially resolved distributions of δ13C-CH4 source signatures to reproduce the measurements. The emission scenario (sONG-Coal_geol19) is then prepared by using GAINSv4 inventory for Oil and Gas, coal mining and scaled natural geological sectors, which reproduces the trend and meridional gradients in the observed CH4 and δ13C-CH4 (Fig. 1), but does not compare well with the absolute δ13C-CH4 values. Spatially resolved δ13C-CH4 source signatures in place of globally invariant source signature helps to reduce the mismatch between observed and simulated δ13C-CH4 from ~1 ‰ to less than 0.1 ‰ (magenta line lower panel of Fig. 1). The most likely emission scenario, which can reconstruct the latitudinal gradient and trends in atmospheric CH4 and δ13C-CH4 simultaneously suggests a decreasing-to-constant emissions from fossil fuel exploitations 1985-2020, contrary to an increasing trend in EDGARv6 inventory. This study suggests that the increase in atmospheric CH4 after 2006 is primarily due to microbial sources, mainly the agricultural and waste management sector. The detail will be presented in the meeting.
Figure 1. Comparison of modelled CH4 and δ13C-CH4 with observations (black circle) made by Tohoku University (TU) and National Institute of Polar Research (NIPR) at two northern and southern surface baseline stations, Ny-Alesund, Svalbard and Syowa, Antarctica.