Articles | Volume 8, issue 2
Earth Syst. Sci. Data, 8, 697–751, 2016
Earth Syst. Sci. Data, 8, 697–751, 2016
Review article
12 Dec 2016
Review article | 12 Dec 2016

The global methane budget 2000–2012

Marielle Saunois1, Philippe Bousquet1, Ben Poulter2, Anna Peregon1, Philippe Ciais1, Josep G. Canadell3, Edward J. Dlugokencky4, Giuseppe Etiope5, David Bastviken6, Sander Houweling7,8, Greet Janssens-Maenhout9, Francesco N. Tubiello10, Simona Castaldi11,12,13, Robert B. Jackson14, Mihai Alexe9, Vivek K. Arora15, David J. Beerling16, Peter Bergamaschi9, Donald R. Blake17, Gordon Brailsford18, Victor Brovkin19, Lori Bruhwiler4, Cyril Crevoisier20, Patrick Crill21, Kristofer Covey22, Charles Curry23, Christian Frankenberg24, Nicola Gedney25, Lena Höglund-Isaksson26, Misa Ishizawa27, Akihiko Ito27, Fortunat Joos28, Heon-Sook Kim27, Thomas Kleinen19, Paul Krummel29, Jean-François Lamarque30, Ray Langenfelds29, Robin Locatelli1, Toshinobu Machida27, Shamil Maksyutov27, Kyle C. McDonald31, Julia Marshall32, Joe R. Melton33, Isamu Morino25, Vaishali Naik34, Simon O'Doherty35, Frans-Jan W. Parmentier36, Prabir K. Patra37, Changhui Peng38, Shushi Peng1, Glen P. Peters39, Isabelle Pison1, Catherine Prigent40, Ronald Prinn41, Michel Ramonet1, William J. Riley42, Makoto Saito27, Monia Santini13, Ronny Schroeder31,43, Isobel J. Simpson17, Renato Spahni28, Paul Steele29, Atsushi Takizawa44, Brett F. Thornton21, Hanqin Tian45, Yasunori Tohjima27, Nicolas Viovy1, Apostolos Voulgarakis46, Michiel van Weele47, Guido R. van der Werf48, Ray Weiss49, Christine Wiedinmyer30, David J. Wilton16, Andy Wiltshire50, Doug Worthy51, Debra Wunch52, Xiyan Xu42, Yukio Yoshida27, Bowen Zhang45, Zhen Zhang2,53, and Qiuan Zhu54 Marielle Saunois et al.
  • 1Laboratoire des Sciences du Climat et de l'Environnement, LSCE-IPSL (CEA-CNRS-UVSQ), Université Paris-Saclay 91191 Gif-sur-Yvette, France
  • 2NASA Goddard Space Flight Center, Biospheric Science Laboratory, Greenbelt, MD 20771, USA
  • 3Global Carbon Project, CSIRO Oceans and Atmosphere, Canberra, ACT 2601, Australia
  • 4NOAA ESRL, 325 Broadway, Boulder, CO 80305, USA
  • 5Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma 2, via V. Murata 605 00143 Rome, Italy
  • 6Department of Thematic Studies – Environmental Change, Linköping University, 581 83 Linköping, Sweden
  • 7Netherlands Institute for Space Research (SRON), Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands
  • 8Institute for Marine and Atmospheric Research, Sorbonnelaan 2, 3584 CA, Utrecht, the Netherlands
  • 9European Commission Joint Research Centre, Ispra (Va), Italy
  • 10Statistics Division, Food and Agriculture Organization of the United Nations (FAO), Viale delle Terme di Caracalla, Rome 00153, Italy
  • 11Dipartimento di Scienze Ambientali, Biologiche e Farmaceutiche, Seconda Università di Napoli, via Vivaldi 43, 81100 Caserta, Italy
  • 12Far East Federal University (FEFU), Vladivostok, Russky Island, Russia
  • 13Euro-Mediterranean Center on Climate Change, Via Augusto Imperatore 16, 73100 Lecce, Italy
  • 14School of Earth, Energy & Environmental Sciences, Stanford University, Stanford, CA 94305-2210, USA
  • 15Canadian Centre for Climate Modelling and Analysis, Climate Research Division, Environment and Climate Change Canada, Victoria, BC, V8W 2Y2, Canada
  • 16Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
  • 17Department of Chemistry, University of California Irvine, 570 Rowland Hall, Irvine, CA 92697, USA
  • 18National Institute of Water and Atmospheric Research, 301 Evans Bay Parade, Wellington, New Zealand
  • 19Max Planck Institute for Meteorology, Bundesstraße 53, 20146 Hamburg, Germany
  • 20Laboratoire de Météorologie Dynamique, LMD-IPSL, Ecole Polytechnique, 91120 Palaiseau, France
  • 21Department of Geological Sciences and Bolin Centre for Climate Research, Svante Arrhenius väg 8, 106 91 Stockholm, Sweden
  • 22School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511, USA
  • 23School of Earth and Ocean Sciences, University of Victoria, P.O. Box 1700 STN CSC, Victoria, BC, Canada V8W 2Y2
  • 24Jet Propulsion Laboratory, M/S 183-601, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
  • 25Met Office Hadley Centre, Joint Centre for Hydrometeorological Research, Maclean Building, Wallingford OX10 8BB, UK
  • 26Air Quality and Greenhouse Gases Program (AIR), International Institute for Applied Systems Analysis (IIASA), 2361 Laxenburg, Austria
  • 27Center for Global Environmental Research, National Institute for Environmental Studies (NIES), Onogawa 16-2, Tsukuba, Ibaraki 305-8506, Japan
  • 28Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Sidlerstr. 5, 3012 Bern, Switzerland
  • 29CSIRO Oceans and Atmosphere, Aspendale, Victoria 3195, Australia
  • 30NCAR, P.O. Box 3000, Boulder, CO 80307-3000, USA
  • 31Department of Earth and Atmospheric Sciences, City University of New York, New York, NY 10031, USA
  • 32Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, 07745 Jena, Germany
  • 33Climate Research Division, Environment and Climate Change Canada, Victoria, BC, V8W 2Y2, Canada
  • 34NOAA, GFDL, 201 Forrestal Rd., Princeton, NJ 08540, USA
  • 35School of Chemistry, University of Bristol, Cantock's Close, Clifton, Bristol BS8 1TS, UK
  • 36Department of Physical Geography and Ecosystem Science, Lund University, Sölvegatan 12, 223 62, Lund, Sweden
  • 37Department of Environmental Geochemical Cycle Research, JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
  • 38Department of Biology Sciences, Institute of Environment Science, University of Quebec at Montreal, Montreal, QC H3C 3P8, Canada
  • 39Center for International Climate and Environmental Research – Oslo (CICERO), Pb. 1129 Blindern, 0318 Oslo, Norway
  • 40CNRS/LERMA, Observatoire de Paris, 61 Ave. de l'Observatoire, 75014 Paris, France
  • 41Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology (MIT), Building 54-1312, Cambridge, MA 02139, USA
  • 42Earth Sciences Division, Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, CA 94720, USA
  • 43Institute of Botany, University of Hohenheim, 70593 Stuttgart, Germany
  • 44Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan
  • 45International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, 602 Duncan Drive, Auburn, AL 36849, USA
  • 46Space & Atmospheric Physics, The Blackett Laboratory, Imperial College London, London SW7 2AZ, UK
  • 47KNMI, P.O. Box 201, 3730 AE, De Bilt, the Netherlands
  • 48Faculty of Earth and Life Sciences, Earth and Climate Cluster, VU Amsterdam, Amsterdam, the Netherlands
  • 49Scripps Institution of Oceanography (SIO), University of California San Diego, La Jolla, CA 92093, USA
  • 50Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, UK
  • 51Environnement Canada, 4905, rue Dufferin, Toronto, Canada
  • 52Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario, Canada
  • 53Swiss Federal Research Institute WSL, Birmensdorf 8059, Switzerland
  • 54State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling, Shaanxi 712100, China

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 (exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models, inventories and data-driven approaches (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 top-down inversions at 558 Tg CH4 yr−1, range 540–568. About 60 % of global emissions are anthropogenic (range 50–65 %). Since 2010, the bottom-up global emission inventories have been closer to methane emissions in the most carbon-intensive Representative Concentrations Pathway (RCP8.5) and higher than all other RCP scenarios. Bottom-up approaches suggest larger global emissions (736 Tg CH4 yr−1, range 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 top-down budget, it is likely that some of the individual emissions reported by the bottom-up approaches are overestimated, leading to too large global emissions. Latitudinal data from top-down emissions indicate a predominance of tropical emissions (∼ 64 % of the global budget, < 30° N) as compared to mid (∼ 32 %, 30–60° N) and high northern latitudes (∼ 4 %, 60–90° N). Top-down inversions consistently infer lower emissions in China (∼ 58 Tg CH4 yr−1, range 51–72, −14 %) and higher emissions in Africa (86 Tg CH4 yr−1, range 73–108, +19 %) than bottom-up values used as prior estimates. Overall, uncertainties for anthropogenic emissions appear smaller than those from natural sources, and the uncertainties on source categories appear larger for top-down inversions than for bottom-up inventories and models.

The most important source of uncertainty on the methane budget is attributable to emissions from wetland and other inland waters. We show that the wetland extent could contribute 30–40 % on the estimated range for wetland emissions. Other priorities for improving the methane budget include the following: (i) the development of process-based models for inland-water emissions, (ii) the intensification of methane observations at local scale (flux measurements) to constrain bottom-up land surface models, and at regional scale (surface networks and satellites) to constrain top-down inversions, (iii) improvements in the estimation of atmospheric loss by OH, and (iv) improvements of the transport models integrated in top-down inversions. The data presented here can be downloaded from the Carbon Dioxide Information Analysis Center ( and the Global Carbon Project.

Short summary
An accurate assessment of the methane budget is important to understand the atmospheric methane concentrations and trends and to provide realistic pathways for climate change mitigation. The various and diffuse sources of methane as well and its oxidation by a very short lifetime radical challenge this assessment. We quantify the methane sources and sinks as well as their uncertainties based on both bottom-up and top-down approaches provided by a broad international scientific community.