The global methane budget 2000-2017

Marielle Saunois; Ann R. Stavert; Ben Poulter; Philippe Bousquet; Josep G. Canadell; Robert B. Jackson; Peter A. Raymond; Edward J. Dlugokencky; Sander Houweling; Prabir K. Patra; Philippe Ciais; Vivek K. Arora; David Bastviken; Peter Bergamaschi; Donald R. Blake; Gordon Brailsford; Lori Bruhwiler; Kimberly M. Carlson; Mark Carrol; Simona Castaldi; Naveen Chandra; Cyril Crevoisier; Patrick M. Crill; Kristofer Covey; Charles L. Curry; Giuseppe Etiope; Christian Frankenberg; Nicola Gedney; Michaela I. Hegglin; Lena Höglund-Isaksson; Gustaf Hugelius; Misa Ishizawa; Akihiko Ito; Greet Janssens-Maenhout; Katherine M. Jensen; Fortunat Joos; Thomas Kleinen; Paul B. Krummel; Ray L. Langenfelds; Goulven G. Laruelle; Licheng Liu; Toshinobu MacHida; Shamil Maksyutov; Kyle C. McDonald; Joe McNorton; Paul A. Miller; Joe R. Melton; Isamu Morino; Jurek Müller; Fabiola Murguia-Flores; Vaishali Naik; Yosuke Niwa; Sergio Noce; Simon O'Doherty; Robert J. Parker; Changhui Peng; Shushi Peng; Glen P. Peters; Catherine Prigent; Ronald Prinn; Michel Ramonet; Pierre Regnier; William J. Riley; Judith A. Rosentreter; Arjo Segers; Isobel J. Simpson; Hao Shi; Steven J. Smith; L. Paul Steele; Brett F. Thornton; Hanqin Tian; Yasunori Tohjima; Francesco N. Tubiello; Aki Tsuruta; Nicolas Viovy; Apostolos Voulgarakis; Thomas S. Weber; Michiel Van Weele; Guido R. Van Der Werf; Ray F. Weiss; Doug Worthy; Debra Wunch; Yi Yin; Yukio Yoshida; Wenxin Zhang; Zhen Zhang; Yuanhong Zhao; Bo Zheng; Qing Zhu; Qiuan Zhu; Qianlai Zhuang

doi:10.5194/essd-12-1561-2020

The global methane budget 2000-2017

Marielle Saunois
, Ann R. Stavert
, Ben Poulter
, Philippe Bousquet
, Josep G. Canadell
, Robert B. Jackson
, Peter A. Raymond
, Edward J. Dlugokencky
, Sander Houweling
, Prabir K. Patra
, Philippe Ciais
, Vivek K. Arora
, David Bastviken
, Peter Bergamaschi
, Donald R. Blake
, Gordon Brailsford
, Lori Bruhwiler
, Kimberly M. Carlson
, Mark Carrol
, Simona Castaldi

Naveen Chandra, Cyril Crevoisier, Patrick M. Crill, Kristofer Covey, Charles L. Curry, Giuseppe Etiope, Christian Frankenberg, Nicola Gedney, Michaela I. Hegglin, Lena Höglund-Isaksson, Gustaf Hugelius, Misa Ishizawa, Akihiko Ito, Greet Janssens-Maenhout, Katherine M. Jensen, Fortunat Joos, Thomas Kleinen, Paul B. Krummel, Ray L. Langenfelds, Goulven G. Laruelle, Licheng Liu, Toshinobu MacHida, Shamil Maksyutov, Kyle C. McDonald, Joe McNorton, Paul A. Miller, Joe R. Melton, Isamu Morino, Jurek Müller, Fabiola Murguia-Flores, Vaishali Naik, Yosuke Niwa, Sergio Noce, Simon O'Doherty, Robert J. Parker, Changhui Peng, Shushi Peng, Glen P. Peters, Catherine Prigent, Ronald Prinn, Michel Ramonet, Pierre Regnier, William J. Riley, Judith A. Rosentreter, Arjo Segers, Isobel J. Simpson, Hao Shi, Steven J. Smith, L. Paul Steele, Brett F. Thornton, Hanqin Tian, Yasunori Tohjima, Francesco N. Tubiello, Aki Tsuruta, Nicolas Viovy, Apostolos Voulgarakis, Thomas S. Weber, Michiel Van Weele, Guido R. Van Der Werf, Ray F. Weiss, Doug Worthy, Debra Wunch, Yi Yin, Yukio Yoshida, Wenxin Zhang, Zhen Zhang, Yuanhong Zhao, Bo Zheng, Qing Zhu, Qiuan Zhu, Qianlai Zhuang

Université Versailles-Saint Quentin
Commonwealth Scientific and Industrial Research Organization
NASA Goddard Space Flight Center
Stanford University
Yale University
National Oceanic and Atmospheric Administration
SRON - Netherlands Institute for Space Research
Vrije Universiteit Amsterdam
JAMSTEC
Chiba University
Meteorological Research Branch
Linköping University
European Commission Joint Research Centre
Long Beach VA and University of California
NIWA
New York University
University of Hawaii
University of Campania L. Vanvitelli
RUDN University
Euro Mediterranean Center on Climage Change
Stockholm University
Skidmore College
University of Victoria
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Universitatea Babes-Bolyai — Facultatea de Fizica
California Institute of Technology
Science Division
Now at Met Office Hadley Centre
University of Reading
International Institute for Applied Systems Analysis (IIASA)
National Institute for Environmental Studies of Japan
The City College of New York
University of Bern
Max Planck Institute for Meteorology
Université Libre de Bruxelles
Purdue University
European Centre for Medium-Range Weather Forecasts
Lund University
University of Bristol
JMA Meteorological Research Institute
University of Leicester
Universite du Quebec A Montreal
Tsinghua University
Center for International Climate Research (CICERO)
Sorbonne Univ.
Massachusetts Institute of Technology
Ernest Orlando Lawrence Berkeley National Laboratory
Southern Cross University
Netherlands Organisation for Applied Scientific Research (TNO)
Auburn University
Pacific Northwest National Laboratory
University of Maryland
Food and Agriculture Organization of the United Nations
Finnish Meteorological Institute
Imperial College London
Technical University of Crete
University of Rochester
Royal Netherlands Meteorological I.
Scripps Institution of Oceanography
University of Toronto
University of Maryland, College Park
Hohai University

Résultats de recherche: Contribution à un journal › Article › Revue par des pairs

2280 Citations (Scopus)

Résumé

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 <a hrefCombining double low line"https://doi.org/10.18160/GCP-CH4-2019">https://doi.org/10.18160/GCP-CH4-2019</a> (Saunois et al., 2020) and from the Global Carbon Project.

langue originale	Anglais
Pages (de - à)	1561-1623
Nombre de pages	63
journal	Earth System Science Data
Volume	12
Numéro de publication	3
Les DOIs	https://doi.org/10.5194/essd-12-1561-2020
état	Publié - 15 juil. 2020

SDG des Nations Unies

Ce résultat contribue à ou aux Objectifs de développement durable suivants

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SDG 15 Vie sur terre

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10.5194/essd-12-1561-2020

Contient cette citation

Saunois, M., R. Stavert, A., Poulter, B., Bousquet, P., G. Canadell, J., B. Jackson, R., A. Raymond, P., J. Dlugokencky, E., Houweling, S., K. Patra, P., Ciais, P., K. Arora, V., Bastviken, D., Bergamaschi, P., R. Blake, D., Brailsford, G., Bruhwiler, L., M. Carlson, K., Carrol, M., ... Zhuang, Q. (2020). The global methane budget 2000-2017. Earth System Science Data, 12(3), 1561-1623. https://doi.org/10.5194/essd-12-1561-2020

@article{1ee2adcc167c4c84b3dae14de8fa10f7,

title = "The global methane budget 2000-2017",

abstract = "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 https://doi.org/10.18160/GCP-CH4-2019 (Saunois et al., 2020) and from the Global Carbon Project.",

author = "Marielle Saunois and \{R. Stavert\}, Ann and Ben Poulter and Philippe Bousquet and \{G. Canadell\}, Josep and \{B. Jackson\}, Robert and \{A. Raymond\}, Peter and \{J. Dlugokencky\}, Edward and Sander Houweling and \{K. Patra\}, Prabir and Philippe Ciais and \{K. Arora\}, Vivek and David Bastviken and Peter Bergamaschi and \{R. Blake\}, Donald and Gordon Brailsford and Lori Bruhwiler and \{M. Carlson\}, Kimberly and Mark Carrol and Simona Castaldi and Naveen Chandra and Cyril Crevoisier and \{M. Crill\}, Patrick and Kristofer Covey and \{L. Curry\}, Charles and Giuseppe Etiope and Christian Frankenberg and Nicola Gedney and \{I. Hegglin\}, Michaela and Lena H{\"o}glund-Isaksson and Gustaf Hugelius and Misa Ishizawa and Akihiko Ito and Greet Janssens-Maenhout and \{M. Jensen\}, Katherine and Fortunat Joos and Thomas Kleinen and \{B. Krummel\}, Paul and \{L. Langenfelds\}, Ray and \{G. Laruelle\}, Goulven and Licheng Liu and Toshinobu MacHida and Shamil Maksyutov and \{C. McDonald\}, Kyle and Joe McNorton and \{A. Miller\}, Paul and \{R. Melton\}, Joe and Isamu Morino and Jurek M{\"u}ller and Fabiola Murguia-Flores and Vaishali Naik and Yosuke Niwa and Sergio Noce and Simon O'Doherty and \{J. Parker\}, Robert and Changhui Peng and Shushi Peng and \{P. Peters\}, Glen and Catherine Prigent and Ronald Prinn and Michel Ramonet and Pierre Regnier and \{J. Riley\}, William and \{A. Rosentreter\}, Judith and Arjo Segers and \{J. Simpson\}, Isobel and Hao Shi and \{J. Smith\}, Steven and \{Paul Steele\}, L. and \{F. Thornton\}, Brett and Hanqin Tian and Yasunori Tohjima and \{N. Tubiello\}, Francesco and Aki Tsuruta and Nicolas Viovy and Apostolos Voulgarakis and \{S. Weber\}, Thomas and \{Van Weele\}, Michiel and \{R. Van Der Werf\}, Guido and \{F. Weiss\}, Ray and Doug Worthy and Debra Wunch and Yi Yin and Yukio Yoshida and Wenxin Zhang and Zhen Zhang and Yuanhong Zhao and Bo Zheng and Qing Zhu and Qiuan Zhu and Qianlai Zhuang",

year = "2020",

month = jul,

day = "15",

doi = "10.5194/essd-12-1561-2020",

language = "English",

volume = "12",

pages = "1561--1623",

journal = "Earth System Science Data",

issn = "1866-3508",

publisher = "Copernicus Publications",

number = "3",

}

Saunois, M, R. Stavert, A, Poulter, B, Bousquet, P, G. Canadell, J, B. Jackson, R, A. Raymond, P, J. Dlugokencky, E, Houweling, S, K. Patra, P, Ciais, P, K. Arora, V, Bastviken, D, Bergamaschi, P, R. Blake, D, Brailsford, G, Bruhwiler, L, M. Carlson, K, Carrol, M, Castaldi, S, Chandra, N, Crevoisier, C, M. Crill, P, Covey, K, L. Curry, C, Etiope, G, Frankenberg, C, Gedney, N, I. Hegglin, M, Höglund-Isaksson, L, Hugelius, G, Ishizawa, M, Ito, A, Janssens-Maenhout, G, M. Jensen, K, Joos, F, Kleinen, T, B. Krummel, P, L. Langenfelds, R, G. Laruelle, G, Liu, L, MacHida, T, Maksyutov, S, C. McDonald, K, McNorton, J, A. Miller, P, R. Melton, J, Morino, I, Müller, J, Murguia-Flores, F, Naik, V, Niwa, Y, Noce, S, O'Doherty, S, J. Parker, R, Peng, C, Peng, S, P. Peters, G, Prigent, C, Prinn, R, Ramonet, M, Regnier, P, J. Riley, W, A. Rosentreter, J, Segers, A, J. Simpson, I, Shi, H, J. Smith, S, Paul Steele, L, F. Thornton, B, Tian, H, Tohjima, Y, N. Tubiello, F, Tsuruta, A, Viovy, N, Voulgarakis, A, S. Weber, T, Van Weele, M, R. Van Der Werf, G, F. Weiss, R, Worthy, D, Wunch, D, Yin, Y, Yoshida, Y, Zhang, W, Zhang, Z, Zhao, Y, Zheng, B, Zhu, Q, Zhu, Q & Zhuang, Q 2020, 'The global methane budget 2000-2017', Earth System Science Data, VOL. 12, Numéro 3, p. 1561-1623. https://doi.org/10.5194/essd-12-1561-2020

TY - JOUR

T1 - The global methane budget 2000-2017

AU - Saunois, Marielle

AU - R. Stavert, Ann

AU - Poulter, Ben

AU - Bousquet, Philippe

AU - G. Canadell, Josep

AU - B. Jackson, Robert

AU - A. Raymond, Peter

AU - J. Dlugokencky, Edward

AU - Houweling, Sander

AU - K. Patra, Prabir

AU - Ciais, Philippe

AU - K. Arora, Vivek

AU - Bastviken, David

AU - Bergamaschi, Peter

AU - R. Blake, Donald

AU - Brailsford, Gordon

AU - Bruhwiler, Lori

AU - M. Carlson, Kimberly

AU - Carrol, Mark

AU - Castaldi, Simona

AU - Chandra, Naveen

AU - Crevoisier, Cyril

AU - M. Crill, Patrick

AU - Covey, Kristofer

AU - L. Curry, Charles

AU - Etiope, Giuseppe

AU - Frankenberg, Christian

AU - Gedney, Nicola

AU - I. Hegglin, Michaela

AU - Höglund-Isaksson, Lena

AU - Hugelius, Gustaf

AU - Ishizawa, Misa

AU - Ito, Akihiko

AU - Janssens-Maenhout, Greet

AU - M. Jensen, Katherine

AU - Joos, Fortunat

AU - Kleinen, Thomas

AU - B. Krummel, Paul

AU - L. Langenfelds, Ray

AU - G. Laruelle, Goulven

AU - Liu, Licheng

AU - MacHida, Toshinobu

AU - Maksyutov, Shamil

AU - C. McDonald, Kyle

AU - McNorton, Joe

AU - A. Miller, Paul

AU - R. Melton, Joe

AU - Morino, Isamu

AU - Müller, Jurek

AU - Murguia-Flores, Fabiola

AU - Naik, Vaishali

AU - Niwa, Yosuke

AU - Noce, Sergio

AU - O'Doherty, Simon

AU - J. Parker, Robert

AU - Peng, Changhui

AU - Peng, Shushi

AU - P. Peters, Glen

AU - Prigent, Catherine

AU - Prinn, Ronald

AU - Ramonet, Michel

AU - Regnier, Pierre

AU - J. Riley, William

AU - A. Rosentreter, Judith

AU - Segers, Arjo

AU - J. Simpson, Isobel

AU - Shi, Hao

AU - J. Smith, Steven

AU - Paul Steele, L.

AU - F. Thornton, Brett

AU - Tian, Hanqin

AU - Tohjima, Yasunori

AU - N. Tubiello, Francesco

AU - Tsuruta, Aki

AU - Viovy, Nicolas

AU - Voulgarakis, Apostolos

AU - S. Weber, Thomas

AU - Van Weele, Michiel

AU - R. Van Der Werf, Guido

AU - F. Weiss, Ray

AU - Worthy, Doug

AU - Wunch, Debra

AU - Yin, Yi

AU - Yoshida, Yukio

AU - Zhang, Wenxin

AU - Zhang, Zhen

AU - Zhao, Yuanhong

AU - Zheng, Bo

AU - Zhu, Qing

AU - Zhu, Qiuan

AU - Zhuang, Qianlai

PY - 2020/7/15

Y1 - 2020/7/15

N2 - 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 https://doi.org/10.18160/GCP-CH4-2019 (Saunois et al., 2020) and from the Global Carbon Project.

AB - 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 https://doi.org/10.18160/GCP-CH4-2019 (Saunois et al., 2020) and from the Global Carbon Project.

U2 - 10.5194/essd-12-1561-2020

DO - 10.5194/essd-12-1561-2020

M3 - Article

AN - SCOPUS:85090281061

SN - 1866-3508

VL - 12

SP - 1561

EP - 1623

JO - Earth System Science Data

JF - Earth System Science Data

IS - 3

ER -

The global methane budget 2000-2017

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