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Investigation of the Global Methane Budget Based on Improved Measurement Datasets and Prior Emission Information

X. Lan1,2, S. Schwietzke1,2, S. Basu1,2, L. Bruhwiler2, E. Dlugokencky2, S.E. Michel3, O.A. Sherwood3, G. Etiope4, Q. Zhuang5, L. Liu5, Y. Oh5, J.B. Miller2, G. Petron1,2, B.H. Vaughn3 and P.P. Tans2

1Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309; 303-497-3615, E-mail: xin.lan@noaa.gov
2NOAA Earth System Research Laboratory, Global Monitoring Division (GMD), Boulder, CO 80305
3Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, CO 80309
4Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome 605 00143, Italy
5Purdue University, West Lafayette, IN 47907

The global atmospheric CH4 abundance was stable during 1999 to 2007, but has significantly increased ever since. The reasons behind the post-2007 increase in global CH4 remain uncertain. Current debates include changes in major sources and sinks. Another uncertainty in the CH4 budget concerns the quantification of emission magnitudes from individual CH4 source categories. The emission magnitudes are not well understood considering that bottom-up estimates of all CH4 sources surpass top-down estimates by more than 30%. These uncertainties are partially caused by the sparsity of global atmospheric measurements and the difficulty in accurately quantifying CH4 sources at policy-relevant spatial scales. Analyses using spatially representative isotopic (δ13CH4) source signatures to partition source contributions are still limited.

Understanding emission magnitudes from individual sources and their contributions to temporal changes in CH4 abundance is important to predict the response of CH4 sources to future climate and design mitigation policies. This study attempts to improve our understanding of the CH4 budget by using forward and inverse modeling with the following features: (a) an extensive atmospheric CH4 and δ13C-CH4 measurement dataset with contributions from 32 laboratories worldwide complemented by remote sensing products, (b) newly developed gridded CH4 and δ13C-CH4 maps of geologic seeps and (c) improved spatially resolved δ13CH4 signatures from wetland emissions. In addition to illustrating these features, this presentation will highlight our new model results to evaluate different source and sink scenarios by comparing observed and simulated long-term trends and spatial gradients of CH4 and δ13CH4.

Figure 1

Figure 1. Overview of combined NOAA/INSTAAR (blue/cyan) and external (red/yellow) atmospheric CH4 and δ13C-CH4 dataset compiled for this study. Only “fixed” sites are shown, and additional data include measurements from container ships and aircraft routes.