The Global Methane Budget: 2000–2012
Authors: Saunois Marielle , Bousquet Philippe , Poulter Ben , Peregon Anna , Ciais Philippe , Canadell Josep G. , Dlugokencky Edward J. , Etiope Giuseppe , Bastviken David , Houweling Sander , Janssens-Maenhout Greet , Tubiello Francesco N. , Castaldi Simona , Jackson Robert B. , Alexe Mihai , Arora Vivek K. , Beerling David J. , Bergamaschi Peter , Blake Donald R. , Brailsford Gordon , Brovkin Victor , Bruhwiler Lori , Crevoisier Cyril , Crill Patrick , Curry Charles , Frankenberg Christian , Gedney Nicola , Höglund-Isaksson Lena , Ishizawa Misa , Ito Akihiko , Joos Fortunat , Kim Heon-Sook , Kleinen Thomas , Krummel Paul , Lamarque Jean-François , Langenfelds Ray , Locatelli Robin , Machida Toshinobu , Maksyutov Shamil , McDonald Kyle C. , Marshall Julia , Melton Joe R. , Morino Isamu , O'Doherty Simon , Parmentier Frans-Jan W. , Patra Prabir K. , Peng Changhui , Peng Shushi , Peters Glen P. , Pison Isabelle , Prigent Catherine , Prinn Ronald , Ramonet Michel , Riley William J. , Saito Makoto , Schroeder Ronny , Simpson Isobel J. , Spahni Renato , Steele Paul , Takizawa Atsushi , Thornton Brett F. , Tian Hanqin , Tohjima Yasunori , Viovy Nicolas , Voulgarakis Apostolos , van Weele Michiel , van der Werf Guido , Weiss Ray , Wiedinmyer Christine , Wilton David J. , Wiltshire Andy , Worthy Doug , Wunch Debra B. , Xu Xiyan , Yoshida Yukio , Zhang Bowen , Zhang Zhen , Zhu Qiuan 
Published: June 2016

Abstract. The global methane (CH4) budget is becoming an increasingly important component for managing realistic pathways to mitigate climate change. This relevance, due to a shorter atmospheric lifetime and a stronger warming potential than carbon dioxide, is challenged by the still unexplained changes of atmospheric CH4 over the past decade. Emissions and concentrations of CH4 are continuing to increase making CH4 the second most important human-induced greenhouse gas after carbon dioxide. Two major difficulties in reducing uncertainties come from the large variety of diffusive CH4 sources that overlap geographically, and from the destruction of CH4 by the very short-lived hydroxyl radical (OH). To address these difficulties, we have established a consortium of multi-disciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate research on the methane cycle, and producing regular (~biennial) updates of the global methane budget. This consortium includes atmospheric physicists and chemists, biogeochemists of surface and marine emissions, and socio-economists who study anthropogenic emissions. Following Kirschke et al. (2013), we propose here the first version of a living review paper that integrates results of top-down studies (T-D, exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models, inventories, and data-driven approaches (B-U, including process-based models for estimating land surface emissions and atmospheric chemistry, and inventories for anthropogenic emissions, data-driven extrapolations). For the 2003–2012 decade, global methane emissions are estimated by T-D inversions at 558 Tg CH4 yr−1 (range [540–568]). About 60 % of global emissions are anthropogenic (range [50–65 %]). B-U approaches suggest larger global emissions (736 Tg CH4 yr−1 [596–884]) mostly because of larger natural emissions from individual sources such as inland waters, natural wetlands and geological sources. Considering the atmospheric constraints on the T-D budget, it is likely that some of the individual emissions reported by the B-U approaches are overestimated, leading to too large global emissions. Latitudinal data from T-D emissions indicate a predominance of tropical emissions (~64 % of the global budget,