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The global methane budget 2000-2012

Research output: Contribution to journalArticle

  • Marielle Saunois
  • Philippe Bousquet
  • Ben Poulter
  • Anna Peregon
  • Philippe Ciais
  • Josep G. Canadell
  • Edward J. Dlugokencky
  • Giuseppe Etiope
  • David Bastviken
  • Sander Houweling
  • Greet Janssens-Maenhout
  • Francesco N. Tubiello
  • Simona Castaldi
  • Robert B. Jackson
  • Mihai Alexe
  • Vivek K. Arora
  • David J. Beerling
  • Peter Bergamaschi
  • Donald R. Blake
  • Gordon Brailsford
  • Victor Brovkin
  • Lori Bruhwiler
  • Cyril Crevoisier
  • Patrick Crill
  • Kristofer Covey
  • Charles Curry
  • Christian Frankenberg
  • Nicola Gedney
  • Lena Höglund-Isaksson
  • Misa Ishizawa
  • Akihiko Ito
  • Fortunat Joos
  • Heon Sook Kim
  • Thomas Kleinen
  • Paul Krummel
  • Jean François Lamarque
  • Ray Langenfelds
  • Robin Locatelli
  • Toshinobu Machida
  • Shamil Maksyutov
  • Kyle C. McDonald
  • Julia Marshall
  • Joe R. Melton
  • Isamu Morino
  • Vaishali Naik
  • Simon O'Dohertyhttp://orcid.org/0000-0002-4051-6760
  • Frans Jan W Parmentier
  • Prabir K. Patra
  • Changhui Peng
  • Shushi Peng
  • Glen P. Peters
  • Isabelle Pison
  • Catherine Prigent
  • Ronald Prinn
  • Michel Ramonet
  • William J. Riley
  • Makoto Saito
  • Monia Santini
  • Ronny Schroeder
  • Isobel J. Simpson
  • Renato Spahni
  • Paul Steele
  • Atsushi Takizawa
  • Brett F. Thornton
  • Hanqin Tian
  • Yasunori Tohjima
  • Nicolas Viovy
  • Apostolos Voulgarakis
  • Michiel Van Weele
  • Guido R. Van Der Werf
  • Ray Weiss
  • Christine Wiedinmyer
  • David J. Wilton
  • Andy Wiltshire
  • Doug Worthy
  • Debra Wunch
  • Xiyan Xu
  • Yukio Yoshida
  • Bowen Zhang
  • Zhen Zhang
  • Qiuan Zhu
Original languageEnglish
Pages (from-to)697-751
Number of pages55
JournalEarth System Science Data
Volume8
Issue number2
Early online date12 Dec 2016
DOIs
DateAccepted/In press - 30 Sep 2016
DateE-pub ahead of print - 12 Dec 2016
DatePublished (current) - Dec 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 (g1/4 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 558g Tgg CH4g yrg'1, range 540-568. About 60g % of global emissions are anthropogenic (range 50-65g %). 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 (736g Tgg CH4g yrg'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 (g1/4 64g % of the global budget, &lt;g 30°g N) as compared to mid (g1/4g 32g %, 30-60°g N) and high northern latitudes (g1/4 4g %, 60-90°g N). Top-down inversions consistently infer lower emissions in China (g1/4 58g Tgg CH4g yrg'1, range 51-72, g'14g %) and higher emissions in Africa (86g Tgg CH4g yrg'1, range 73-108, +19g %) 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 30-40g % 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 (<a hrefCombining double low line"http://doi.org/10.3334/CDIAC/GLOBAL-METHANE-BUDGET-2016-V1.1" targetCombining double low line"-blank">http://doi.org/10.3334/CDIAC/GLOBAL-METHANE-BUDGET-2016-V1.1</a>) and the Global Carbon Project.

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    Rights statement: This is the final published version of the article (version of record). It first appeared online via Earth System Science Data at https://doi.org/10.5194/essd-8-697-2016 . Please refer to any applicable terms of use of the publisher.

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