| Popis: |
The global atmospheric CH4 growth rate stagnated between 2000 and 2007, and has continued to grow since 2007. This renewed CH4 rise has been analysed with respect to a 2007 onward decline in δ13C(CH4), indicating changes in the relative contribution of CH4 sources. However, this is still subject to debate and a variety of hypotheses have been put forward. In our work, we present numerical sensitivity simulations that investigate the impact of different inventories of methane emission fluxes on the globally averaged δ13C(CH4) signature. We apply the state-of-the-art global chemistry-climate model EMAC and use a simplified approach to simulate methane loss. We include methane isotopologues and take the kinetic isotope effects in physical and chemical processes into account. We further consider regional differences in the isotopic signatures of individual emission source categories, such as, for example, the differences between signatures of tropical and boreal wetlands emissions. Based on recent emission inventories and isotopic source signatures from the literature, our chemistry climate model reproduces the actual atmospheric methane and δ13C(CH4) distribution adequately. We show that our setup is suitable to constrain the individual influence of different CH4 sources on the global average δ13C(CH4). We further present an approach to optimize the global methane level with respect to station measurements probing for a strategy to include the isotopic information into such an optimization process. |
