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

Global Methane Emissions Through an Isotopic Lens

Alice Drinkwater1,2, Tim Arnold1,2, and Paul Palmer1
Alice Drinkwater et al.
  • 1University of Edinburgh School of GeoSciences, Edinburgh, United Kingdom
  • 2National Physical Laboratory, Teddington, United Kingdom

Changes in atmospheric methane (CH4) are mainly driven by natural, anthropogenic and pyrogenic emissions and oxidation by OH.

There is no consensus about the underlying explanations about hemispheric-scale changes in atmospheric methane (CH4). This is partly due to sparse data that do not exclusively identify individual changes in surface emissions and surface and atmospheric losses of CH4. This challenge represents a major scientific weakness in our understanding of this potent greenhouse gas, with implications for meeting global climate policy obligations.  A confounding challenge is that the regional importance of individual emission sources change with time due to, for example, innovations in agricultural practices, climate-sensitive wetlands, and political decisions associated with climate friendlier transitional fuels.  

Here we use bulk isotope ratios δ13C and δD of CH4 that have been previously shown to provide effective constraints on source apportionment: different CH4 sources have characteristic isotope ratios. One of the key challenges associated with using these data is that region-specific isotope ratios change with time due to varying source prevalance, in addition to source signatures having inherent uncertainties. We use the GEOS-Chem global 3-D chemical transport model to describe the spatial and temporal isotopic behaviour of atmospheric CH4. We develop a Maximum A-Posteriori inverse method to simultaneously infer time dependent CH4 emissions and isotope ratios from in situ data. 

We will report the magnitude, distribution and source attribution of CH4 emissions from 2004 to 2017, inferred from in situ measurements of total atmospheric CH4 mole fraction and the corresponding measurements of δ13C and δD. We will compare our results with previous studies.

How to cite: Drinkwater, A., Arnold, T., and Palmer, P.: Global Methane Emissions Through an Isotopic Lens, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-745,, 2019


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