AUTHORS: Shijie Shu, Atul K. Jain – University of Illinois at Urbana-Champaign
ABSTRACT: Methane is the second most important Earth’s greenhouse gas with a global warming potential (GWP) 28 - 36 times higher than carbon dioxide. Although recent quantification of land-atmosphere methane fluxes received higher attention, calculated global natural methane sources/sinks based on most state-of-the-art models remain highly uncertain. One of the important reasons is that most approaches or models focus on estimating methane fluxes from the natural wetland by ignoring the sink through soil methane oxidation in non-wetland soil and the methane emission from the wet soil with high water table. In this study, we incorporate soil gas diffusion and methane dynamics into a land surface model, Integrated Science and Assessment Model (ISAM), to evaluate the importance by including the soil oxidation and wet soil methane fluxes on estimating the global natural methane sources/sinks for the recent past decade (2001–2009). We develop a general bottom-up framework by coupling a gas diffusion module with the vertically resolved soil hydrology and methane dynamics to estimate the relative contributions of both soil methane oxidation and net emission. Evaluation of the historical simulation using ISAM shows a general match of the wetland methane emission pattern comparing to WetCHARTs global wetland methane emission product. In addition, the new estimation from ISAM shows a higher natural methane emission after considering the contribution from seasonal inundation and wet soil. Results from the model simulation under RCP4.5 and RCP8.5 climate scenarios show an important role of soil oxidation affecting the estimated natural methane source by purging over 30% of the produced gross methane. Under the RCP8.5 case, we find the wetter and warmer climate can largely change the pattern of dry soil methane sink and wet soil methane emission and overall can contribute an extra amount of global methane emission.
