The global methane budget 2000-2017

Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations).

For the 2008-2017 decade, global methane emissions are estimated by atmospheric inversions (a top-down approach) to be 576 Tg CH4 yr-1 (range 550-594, corresponding to the minimum and maximum estimates of the model ensemble). Of this total, 359 Tg CH4 yr-1 or ĝ1/4 60 % is attributed to anthropogenic sources, that is emissions caused by direct human activity (i.e. anthropogenic emissions; range 336-376 Tg CH4 yr-1 or 50 %-65 %). The mean annual total emission for the new decade (2008-2017) is 29 Tg CH4 yr-1 larger than our estimate for the previous decade (2000-2009), and 24 Tg CH4 yr-1 larger than the one reported in the previous budget for 2003-2012 (Saunois et al., 2016). Since 2012, global CH4 emissions have been tracking the warmest scenarios assessed by the Intergovernmental Panel on Climate Change. Bottom-up methods suggest almost 30 % larger global emissions (737 Tg CH4 yr-1, range 594-881) than top-down inversion methods. Indeed, bottom-up estimates for natural sources such as natural wetlands, other inland water systems, and geological sources are higher than top-down estimates. The atmospheric constraints on the top-down budget suggest that at least some of these bottom-up emissions are overestimated. The latitudinal distribution of atmospheric observation-based emissions indicates a predominance of tropical emissions (ĝ1/4 65 % of the global budget, < 30ĝ  N) compared to mid-latitudes (ĝ1/4 30 %, 30-60ĝ  N) and high northern latitudes (ĝ1/4 4 %, 60-90ĝ  N). The most important source of uncertainty in the methane budget is attributable to natural emissions, especially those from wetlands and other inland waters.

Some of our global source estimates are smaller than those in previously published budgets (Saunois et al., 2016; Kirschke et al., 2013). In particular wetland emissions are about 35 Tg CH4 yr-1 lower due to improved partition wetlands and other inland waters. Emissions from geological sources and wild animals are also found to be smaller by 7 Tg CH4 yr-1 by 8 Tg CH4 yr-1, respectively. However, the overall discrepancy between bottom-up and top-down estimates has been reduced by only 5 % compared to Saunois et al. (2016), due to a higher estimate of emissions from inland waters, highlighting the need for more detailed research on emissions factors. Priorities for improving the methane budget include (i) a global, high-resolution map of water-saturated soils and inundated areas emitting methane based on a robust classification of different types of emitting habitats; (ii) further development of process-based models for inland-water emissions; (iii) intensification of methane observations at local scales (e.g., FLUXNET-CH4 measurements) and urban-scale monitoring to constrain bottom-up land surface models, and at regional scales (surface networks and satellites) to constrain atmospheric inversions; (iv) improvements of transport models and the representation of photochemical sinks in top-down inversions; and (v) development of a 3D variational inversion system using isotopic and/or co-emitted species such as ethane to improve source partitioning.

The data presented here can be downloaded from (Saunois et al., 2020) and from the Global Carbon Project. © 2020 Copernicus GmbH. All rights reserved.

Saunois M.1 , R. Stavert A. , Poulter B.3 , Bousquet P.1 , G. Canadell J. , B. Jackson R. , A. Raymond P. , J. Dlugokencky E. , Houweling S.7, 8 , K. Patra P. , Ciais P.1 , K. Arora V. , Bastviken D.12 , Bergamaschi P.13 , R. Blake D. , Brailsford G.15 , Bruhwiler L.6 , M. Carlson K. , Carrol M.70 , Castaldi S. 18, 19, 20 , Chandra N.9 , Crevoisier C.21 , M. Crill P. , Covey K.23 , L. Curry C. , Etiope G.25, 26 , Frankenberg C.27, 28 , Gedney N.29 , I. Hegglin M. , Höglund-Isaksson L.31 , Hugelius G.32 , Ishizawa M.33 , Ito A.33 , Janssens-Maenhout G.13 , M. Jensen K. , Joos F.35 , Kleinen T.36 , B. Krummel P. , L. Langenfelds R. , G. Laruelle G. , Liu L. 39 , MacHida T.33 , Maksyutov S.33 , C. McDonald K. , McNorton J.40 , A. Miller P. , R. Melton J. , Morino I.33 , Müller J.35 , Murguia-Flores F.43 , Naik V.44 , Niwa Y.33, 45 , Noce S.20 , O'Doherty S.46 , J. Parker R. , Peng C.48 , Peng S.49 , P. Peters G. , Prigent C.51 , Prinn R.52 , Ramonet M.1 , Regnier P.38 , J. Riley W. , A. Rosentreter J. , Segers A.55 , J. Simpson I. , Shi H.56 , J. Smith S. , Paul Steele L. , F. Thornton B. , Tian H.56 , Tohjima Y.72 , N. Tubiello F. , Tsuruta A.60 , Viovy N.1 , Voulgarakis A.61, 62 , S. Weber T. , Van Weele M. , R. Van Der Werf G. , F. Weiss R. , Worthy D.66 , Wunch D.67 , Yin Y.1, 27 , Yoshida Y.33 , Zhang W.41 , Zhang Z.68 , Zhao Y.1 , Zheng B.1 , Zhu Q.53, 69 , Zhu Q.53, 69 , Zhuang Q.39
Copernicus GmbH
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  • 1 Laboratoire des Sciences du Climat et de l'Environnement, LSCE-IPSL (CEA-CNRS-UVSQ), Université Paris-Saclay, Gif-sur-Yvette, 91191, France
  • 2 Global Carbon Project, Csiro Oceans and Atmosphere, Aspendale, VIC 3195, Australia
  • 3 Nasa Goddard Space Flight Center, Biospheric Science Laboratory, Greenbelt, MD 20771, United States
  • 4 Department of Earth System Science, Woods Institute for the Environment, and Precourt Institute for Energy, Stanford University, Stanford, CA 94305-2210, United States
  • 5 Yale School of the Environment, Yale University, New Haven, CT 06511, United States
  • 6 Noaa Global Monitoring Laboratory, 325 Broadway, Boulder, CO 80305, United States
  • 7 Sron Netherlands Institute for Space Research, Sorbonnelaan 2, Utrecht, 3584, Netherlands
  • 8 Vrije Universiteit Amsterdam, Department of Earth Sciences, Earth and Climate Cluster Vu Amsterdam, Amsterdam, Netherlands
  • 9 Research Institute for Global Change, Jamstec, 3173-25 Showa-machi, Kanazawa, Yokohama, 236-0001, Japan
  • 10 Center for Environmental Remote Sensing, Chiba University, Chiba, Japan
  • 11 Canadian Centre for Climate Modelling and Analysis, Climate Research Division, Environment and Climate Change Canada, Victoria, BC V8W 2Y2, Canada
  • 12 Department of Thematic Studies-Environmental Change, Linköping University, Linköping, 581 83, Sweden
  • 13 European Commission Joint Research Centre, Via E. Fermi 2749, Ispra (Va), 21027, Italy
  • 14 Department of Chemistry, University of California Irvine, 570 Rowland Hall, Irvine, CA 92697, United States
  • 15 National Institute of Water and Atmospheric Research, 301 Evans Bay Parade, Wellington, New Zealand
  • 16 Department of Environmental Studies, New York University, New York, NY 10003, United States
  • 17 Department of Natural Resources and Environmental Management, University of Hawai'I, Honolulu, HI 96822, United States
  • 18 Dipartimento di Scienze Ambientali, Biologiche e Farmaceutiche, Università Degli Studi della Campania Luigi Vanvitelli, via Vivaldi 43, Caserta, 81100, Italy
  • 19 Department of Landscape Design and Sustainable Ecosystems, Rudn University, Moscow, Russian Federation
  • 20 Impacts on Agriculture, Forests, and Ecosystem Services Division, Centro Euro-Mediterraneo sui Cambiamenti Climatici, Via Augusto Imperatore 16, Lecce, 73100, Italy
  • 21 Laboratoire de Météorologie Dynamique, LMD-IPSL, Ecole Polytechnique, Palaiseau, 91120, France
  • 22 Department of Geological Sciences and Bolin Centre for Climate Research, Stockholm University, Svante Arrhenius väg 8, Stockholm, 106 91, Sweden
  • 23 Environmental Studies and Sciences Program, Skidmore College, Saratoga Springs, NY 12866, United States
  • 24 Pacific Climate Impacts Consortium, University of Victoria, University House 1, P.O. Box 1700 STN CSC, Victoria, BC V8W 2Y2, Canada
  • 25 Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma 2, via V. Murata 605, Rome, 00143, Italy
  • 26 Faculty of Environmental Science and Engineering, Babes Bolyai University, Cluj-Napoca, Romania
  • 27 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, United States
  • 28 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91125, United States
  • 29 Met Office Hadley Centre, Joint Centre for Hydrometeorological Research, Maclean Building, Wallingford, OX10 8BB, United Kingdom
  • 30 Department of Meteorology, University of Reading, Earley Gate, Reading, RG6 6BB, United Kingdom
  • 31 Air Quality and Greenhouse Gases Program (AIR), International Institute for Applied Systems Analysis (IIASA), Laxenburg, 2361, Austria
  • 32 Department of Physical Geography and Bolin Centre for Climate Research, Stockholm University, Stockholm, 106 91, Sweden
  • 33 Center for Global Environmental Research, National Institute for Environmental Studies (NIES), Onogawa 16-2, Tsukuba, Ibaraki, 305-8506, Japan
  • 34 Department of Earth and Atmospheric Sciences, City College of New York, City University of New York, New York, NY 10031, United States
  • 35 Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Sidlerstr. 5, Bern, 3012, Switzerland
  • 36 Max Planck Institute for Meteorology, Bundesstr. 53, Hamburg, 20146, Germany
  • 37 Climate Science Centre, Csiro Oceans and Atmosphere, Aspendale, VIC 3195, Australia
  • 38 Department Geoscience, Environment and Society, Université Libre de Bruxelles, Brussels, 1050, Belgium
  • 39 Department of Earth, Atmospheric, Planetary Sciences, Department of Agronomy, Purdue University, West Lafayette, IN 47907, United States
  • 40 Research Department, European Centre for Medium-Range Weather Forecasts, Reading, United Kingdom
  • 41 Department of Physical Geography and Ecosystem Science, Lund University, Sölvegatan 12, Lund, 223 62, Sweden
  • 42 Climate Research Division, Environment and Climate Change Canada, Victoria, BC V8W 2Y2, Canada
  • 43 School of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, United Kingdom
  • 44 NOAA/Geophysical Fluid Dynamics Laboratory (GFDL), 201 Forrestal Rd, Princeton, NJ 08540, United States
  • 45 Meteorological Research Institute (MRI), Nagamine 1-1, Tsukuba, Ibaraki, 305-0052, Japan
  • 46 School of Chemistry, University of Bristol, Cantock's Close, Clifton, Bristol, BS8 1TS, United Kingdom
  • 47 National Centre for Earth Observation, University of Leicester, Leicester, LE1 7RH, United Kingdom
  • 48 Department of Biology Sciences, Institute of Environment Science, University of Quebec at Montreal, Montreal, QC H3C 3P8, Canada
  • 49 Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing, 100871, China
  • 50 Cicero Center for International Climate Research, Pb. 1129 Blindern, Oslo, 0318, Norway
  • 51 Observatoire de Paris, Université Psl, Sorbonne Université, CNRS, Lerma, Paris, France
  • 52 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology (MIT), Building 54-1312, Cambridge, MA 02139, United States
  • 53 Climate and Ecosystem Sciences Division, Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, CA 94720, United States
  • 54 Centre for Coastal Biogeochemistry, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia
  • 55 Tno, Dep. of Climate Air and Sustainability, P.O. Box 80015, Utrecht, NL-3508-TA, Netherlands
  • 56 International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, 602 Duncan Drive, Auburn, AL 36849, United States
  • 57 Joint Global Change Research Institute, Pacific Northwest National Lab, College Park, MD 20740, United States
  • 58 Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 20740, United States
  • 59 Statistics Division, Food and Agriculture Organization of the United Nations (FAO), Viale Delle Terme di Caracalla, Rome, 00153, Italy
  • 60 Finnish Meteorological Institute, P.O. Box 503, Helsinki, 00101, Finland
  • 61 Department of Physics, Imperial College London, London, SW7 2AZ, United Kingdom
  • 62 School of Environmental Engineering, Technical University of Crete, Chania, Greece
  • 63 Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, United States
  • 64 Knmi, P.O. Box 201, 3730 AE, De Bilt, Netherlands
  • 65 Scripps Institution of Oceanography (SIO), University of California San Diego, San diego, CA 92093, United States
  • 66 Environment and Climate Change Canada, 4905, rue Dufferin, Toronto, Canada
  • 67 Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON, Canada
  • 68 Department of Geographical Sciences, University of Maryland, College Park, MD 20740, United States
  • 69 College of Hydrology and Water Resources, Hohai University, Nanjing, 210098, China
  • 70 Nasa Goddard Space Flight Center, Computational and Information Science and Technology Office, Greenbelt, MD 20771, United States
  • 71 School of Earth and Ocean Sciences, University of Victoria, P.O. Box 1700 STN CSC, Victoria, V8W 2Y2 BC, Canada
  • 72 Center for Environmental Measurement and Analysis, National Institute for Environmental Studies (NIES), Onogawa16-2, Tsukuba, Ibaraki, 305-8506, Japan
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