Variability and quasi-decadal changes in the methane budget over the period 2000-2012

• Published in: Atmospheric Chemistry and Physics
• Main 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, Bruhwiler, Lori, Crevoisier, Cyril, Crill, Patrick, Covey, Kristofer, Frankenberg, Christian, Gedney, Nicola, Hoeglund-Isaksson, Lena, Ishizawa, Misa, Ito, Aki
• Other Authors: Saunois, M (reprint author), Univ Paris Saclay, Lab Sci Climat & Environnem, LSCE IPSL, CNRS UVSQ CEA, F-91191 Gif Sur Yvette, France., Univ Paris Saclay, Lab Sci Climat & Environnem, LSCE IPSL, CNRS UVSQ CEA, F-91191 Gif Sur Yvette, France., NASA, Goddard Space Flight Ctr, Biospher Sci Lab, Greenbelt, MD 20771 USA., CSIRO, Oceans & Atmosphere, Global Carbon Project, Canberra, ACT 2601, Australia., NOAA, ESRL, 325 Broadway, Boulder, CO 80305 USA., Ist Nazl Geofis & Vulcanol, Sez Roma 2, Via V Murata 605, I-00143 Rome, Italy., Babes Bolyai Univ, Fac Environm Sci & Engn, Cluj Napoca, Romania., Linkoping Univ, Dept Themat Studies, Environm Change, S-58183 Linkoping, Sweden., Netherlands Inst Space Res SRON, Sorbonnelaan 2, NL-3584 CA Utrecht, Netherlands., Inst Marine & Atmospher Res, Sorbonnelaan 2, NL-3584 CA Utrecht, Netherlands., European Commiss Joint Res Ctr, Ispra, VA, Italy., Food & Agr Org United Nations FAO, Stat Div, Viale Terme Caracalla, I-00153 Rome, Italy., Seconda Univ Napoli, Dipartimento Sci & Tecnol Ambientali Biol & Farma, Via Vivaldi 43, I-81100 Caserta, Italy., FEFU, Vladivostok, Russia., Euro Mediterranean Ctr Climate Change, Via Augusto Imperatore 16, I-73100 Lecce, Italy., Stanford Univ, Sch Earth Energy & Environm Sci, Stanford, CA 94305 USA., Environm & Climate Change Canada, Canadian Ctr Climate Modelling & Anal, Climate Res Div, Victoria, BC V8W 2Y2, Canada., Univ Sheffield, Dept Anim & Plant Sci, Sheffield S10 2TN, S Yorkshire, England., Univ Calif Irvine, 570 Rowland Hall, Irvine, CA 92697 USA., Nat Inst Water & Atmospher Res, 301 Evans Bay Parade, Wellington, New Zealand., Univ Paris Saclay, CNRS, Ecole Polytech, Lab Meteorol Dynam,LMD IPSL, F-91120 Palaiseau, France., Dept Geol Sci, Svante Arrhenius Vag 8, S-10691 Stockholm, Sweden., Bolin Ctr Climate Res, Svante Arrhenius Vag 8, S-10691 Stockholm, Sweden., Yale Univ, Sch Forestry & Environm Studies, New Haven, CT 06511 USA., CALTECH, Geol & Planetary Sci, Pasadena, CA 91125 USA., Jet Prop Lab, MS 183-601,4800 Oak Grove Dr, Pasadena, CA 91109 USA., Joint Ctr Hydrometeorol Res, Hadley Ctr, Met Off, Maclean Bldg, Wallingford OX10 8BB, Oxon, England., IIASA, Air Qual & Greenhouse Gases Program AIR, A-2361 Laxenburg, Austria., Natl Inst Environm Studies, Ctr Global Environm Res, Onogawa 16-2, Tsukuba, Ibaraki 3058506, Japan., Univ Bern, Climate & Environm Phys, Phys Inst, Sidlerstr 5, CH-3012 Bern, Switzerland., Univ Bern, Oeschger Ctr Climate Change Res, Sidlerstr 5, CH-3012 Bern, Switzerland., Max Planck Inst Meteorol, Bundesstr 53, D-20146 Hamburg, Germany., CSIRO, Oceans & Atmosphere, Aspendale, Vic 3195, Australia., NCAR, POB 3000, Boulder, CO 80307 USA., Environm & Climate Change Canada, Climate Res Div, Victoria, BC V8W 2Y2, Canada., NOAA, GFDL, 201 Forrestal Rd, Princeton, NJ 08540 USA., Univ Bristol, Sch Chem, Cantocks Close, Bristol BS8 1TS, Avon, England., UiT Arctic Univ Norway, Dept Arctic & Marine Biol, Fac Biosci Fisheries & Econ, N-9037 Tromso, Norway., JAMSTEC, Kanagawa Ku, Dept Environm Geochem Cycle Res, 3173-25 Showa Machi, Yokohama, Kanagawa 2360001, Japan., JAMSTEC, Kanagawa Ku, Inst Arctic Climate & Environm Res, 3173-25 Showa Machi, Yokohama, Kanagawa 2360001, Japan., Univ Quebec, Inst Environm Sci, Dept Biol Sci, Montreal, PQ H3C 3P8, Canada., Northwest A&F Univ, State Key Lab Soil Eros & Dryland Farming Loess P, Yangling 712100, Shaanxi, Peoples R China., Peking Univ, Coll Urban & Environm Sci, Sino French Inst Earth Syst Sci, Beijing 100871, Peoples R China., CICERO Ctr Int Climate Res, Pb 1129 Blindern, N-0318 Oslo, Norway., MIT, Bldg 54-1312, Cambridge, MA 02139 USA., Lawrence Berkeley Natl Lab, Climate & Ecosystem Sci Div, 1 Cyclotron Rd, Berkeley, CA 94720 USA., Univ New Hampshire, Dept Civil & Environm Engn, Durham, NH 03824 USA., Japan Meteorol Agcy, Chiyoda Ku, 1-3-4 Otemachi, Tokyo 1008122, Japan., Auburn Univ, Sch Forestry & Wildlife Sci, lnt Ctr Climate & Global Change Res, 602 Duncan Dr, Auburn, AL 36849 USA., Imperial Coll London, Blackett Lab, Space & Atmospher Phys, London SW7 2AZ, England.
• Format: Journal/Newspaper
• Language: English
• Published: ATMOSPHERIC CHEMISTRY AND PHYSICS 2017
• Subjects: GLOBAL ATMOSPHERIC ETHANE; NATURAL-GAS PRODUCTION; PROCESS-BASED MODEL; CH4 EMISSIONS; FOSSIL-FUEL; GROWTH-RATE; INTERANNUAL VARIABILITY; TERRESTRIAL ECOSYSTEMS; BIOGEOCHEMISTRY MODEL; SURFACE MEASUREMENTS; Antarctic; Canada; Norway; Antarc*; Australian Antarctic Division
• Online Access: https://hdl.handle.net/20.500.11897/470796; https://doi.org/10.5194/acp-17-11135-2017

Following the recent Global Carbon Project (GCP) synthesis of the decadal methane (CH4) budget over 2000-2012 (Saunois et al., 2016), we analyse here the same dataset with a focus on quasi-decadal and inter-annual variability in CH4 emissions. The GCP dataset integrates results from top-down studies (exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models (including process-based models for estimating land surface emissions and atmospheric chemistry), inventories of anthropogenic emissions, and data-driven approaches. The annual global methane emissions from top-down studies, which by construction match the observed methane growth rate within their uncertainties, all show an increase in total methane emissions over the period 2000-2012, but this increase is not linear over the 13 years. Despite differences between individual studies, the mean emission anomaly of the top-down ensemble shows no significant trend in total methane emissions over the period 2000-2006, during the plateau of atmospheric methane mole fractions, and also over the period 2008-2012, during the renewed atmospheric methane increase. However, the top-down ensemble mean produces an emission shift between 2006 and 2008, leading to 22 [16-32] Tg CH4 yr(-1) higher methane emissions over the period 2008-2012 compared to 2002-2006. This emission increase mostly originated from the tropics, with a smaller contribution from mid-latitudes and no significant change from boreal regions. The regional contributions remain uncertain in top-down studies. Tropical South America and South and East Asia seem to contribute the most to the emission increase in the tropics. However, these two regions have only limited atmospheric measurements and remain therefore poorly constrained. The sectorial partitioning of this emission increase between the periods 2002-2006 and 2008-2012 differs from one atmospheric inversion study to another. However, all top-down studies suggest smaller changes in fossil fuel emissions (from oil, gas, and coal industries) compared to the mean of the bottom-up inventories included in this study. This difference is partly driven by a smaller emission change in China from the top-down studies compared to the estimate in the Emission Database for Global Atmospheric Research (EDGARv4.2) inventory, which should be revised to smaller values in a near future. We apply isotopic signatures to the emission changes estimated for individual studies based on five emission sectors and find that for six individual top-down studies (out of eight) the average isotopic signature of the emission changes is not consistent with the observed change in atmospheric (CH4)-C-13. However, the partitioning in emission change derived from the ensemble mean is consistent with this isotopic constraint. At the global scale, the top-down ensemble mean suggests that the dominant contribution to the resumed atmospheric CH4 growth after 2006 comes from microbial sources (more from agriculture and waste sectors than from natural wetlands), with an uncertain but smaller contribution from fossil CH4 emissions. In addition, a decrease in biomass burning emissions (in agreement with the biomass burning emission databases) makes the balance of sources consistent with atmospheric (CH4)-C-13 observations. In most of the top-down studies included here, OH concentrations are considered constant over the years (seasonal variations but without any inter-annual variability). As a result, the methane loss (in particular through OH oxidation) varies mainly through the change in methane concentrations and not its oxidants. For these reasons, changes in the methane loss could not be properly investigated in this study, although it may play a significant role in the recent atmospheric methane changes as briefly discussed at the end of the paper. EU FP7 GEOCARBON project; National Environmental Science Program - Earth Systems and Climate Change Hub; NASA [NNX07AK10G]; Swiss National Science Foundation; National Science and Engineering Research Council of Canada (NSERC) discovery grant; China's QianRen Program; Research Council of Norway project [209701]; Swedish Research Council VR; ERC [725546]; Environment Research and Technology Development Fund of the Ministry of the Environment, Japan [A2-1502]; Office of Science, Office of Biological and Environmental Research of the US Department of Energy as part of the RGCM BGC-Climate Feedbacks SFA [DE-AC02-05CH11231]; European Commission Seventh Framework Programme (FP7) project MACCII [283576]; European Commission Horizon Programme project MACC-III [633080]; ESA Climate Change Initiative Greenhouse Gases Phase 2 project; NASA Carbon Monitoring Program [NNX12AP84G, NNX14AO73G]; Joint DECC/Defra Met Office Hadley Centre Climate Programme [GA01101]; ERC Advanced grant (CDREG) [322998]; NERC [NE/J00748X/1]; CSIRO Australia; Australian Bureau of Meteorology; Australian Institute of Marine Science; Australian Antarctic Division; NOAA USA; Meteorological Service of Canada; National Aeronautic and Space Administration (NASA) [NAG5-12669, NNX07AE89G, NNX11AF17G, NNX07AE87G, NNX07AF09G, NNX11AF15G, NNX11AF16G]; Department of Energy and Climate Change (DECC, UK) [GA01081]; Commonwealth Scientific and Industrial Research Organisation (CSIRO Australia); Bureau of Meteorology (Australia) SCI(E) ARTICLE 18 11135-11161 17