Satellite Based Estimation of Global Biogenic Methane Emissions
Atmospheric CH4 is derived from both natural and anthropogenic sources, and the rapid increase in atmospheric CH4 levels over the past two centuries has predominantly been a result of increased anthropogenic emissions. Nonetheless, natural sources have also changed as a result of global change, and quantifying the fluxes of CH4 from these sources, and their associated climatic feedbacks, is of paramount importance. In this thesis I have developed a method to upscale the global CH4 emissions from UV irradiation of foliar pectin (chapter 2). I have quantified the magnitude and distribution of CH4 emissions from wetlands on a global scale and determined the sensitivity of wetlands to temporal changes in water volume and temperature (chapters 3 and 4). Finally I determine that tropical wetland organic matter decomposition on a global scale behaves non-linearly over seasonal timescales. This implies a substantially different seasonality in CH4 emissions from wetlands (chapter 5). I show that (i) satellites such as MODIS and GRACE can be used to improve the understanding of individual CH4 sources and sinks, and (ii) the newly available satellite observations of CH4 can be effectively used for more than constraining atmospheric chemistry and transport model inversions. Moreover, the work shown in this thesis has contributed new biogenic CH4 source estimates, but has also posed new questions which will ultimately help guide new projects in the atmospheric CH4 research area.