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Rising atmospheric methane: 2007–2014 growth and isotopic shift

Research output: Contribution to journalArticle

  • E. G. Nisbet
  • E. J. Dlugokencky
  • M. R. Manning
  • D. Lowry
  • R. E. Fisher
  • J. L. France
  • S. E. Michel
  • J. B. Miller
  • J. W C White
  • B. Vaughn
  • P. Bousquet
  • J. A. Pyle
  • N. J. Warwick
  • M. Cain
  • R. Brownlow
  • G. Zazzeri
  • M. Lanoisellé
  • A. C. Manning
  • E. Gloor
  • D. E J Worthy
  • E. G. Brunke
  • C. Labuschagne
  • E. W. Wolff
  • A. L. Ganesanhttp://orcid.org/0000-0001-5715-8923
Original languageEnglish
Pages (from-to)1356-1370
Number of pages15
JournalGlobal Biogeochemical Cycles
Volume30
Issue number9
Early online date27 Sep 2016
DOIs
DateAccepted/In press - 2 Sep 2016
DateE-pub ahead of print - 27 Sep 2016
DatePublished (current) - 12 Oct 2016

Abstract

From 2007 to 2013, the globally averaged mole fraction of methane in the atmosphere increased by 5.7 ± 1.2 ppb yr−1. Simultaneously, δ13CCH4 (a measure of the 13C/12C isotope ratio in methane) has shifted to significantly more negative values since 2007. Growth was extreme in 2014, at 12.5 ± 0.4 ppb, with a further shift to more negative values being observed at most latitudes. The isotopic evidence presented here suggests that the methane rise was dominated by significant increases in biogenic methane emissions, particularly in the tropics, for example, from expansion of tropical wetlands in years with strongly positive rainfall anomalies or emissions from increased agricultural sources such as ruminants and rice paddies. Changes in the removal rate of methane by the OH radical have not been seen in other tracers of atmospheric chemistry and do not appear to explain short-term variations in methane. Fossil fuel emissions may also have grown, but the sustained shift to more 13C-depleted values and its significant interannual variability, and the tropical and Southern Hemisphere loci of post-2007 growth, both indicate that fossil fuel emissions have not been the dominant factor driving the increase. A major cause of increased tropical wetland and tropical agricultural methane emissions, the likely major contributors to growth, may be their responses to meteorological change.

    Research areas

  • atmospheric methane, isotopic measurement, growth

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    Rights statement: This is the final published version of the article (version of record). It first appeared online via Wiley at http://doi.org/10.1002/2016GB005406. Please refer to any applicable terms of use of the publisher.

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