Rising atmospheric methane: 2007–2014 growth and isotopic shift

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, δ 13 C CH4 (a measure of the 13 C/ 12 C 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…

• SR
  Sight Research UK

  Awards: NE/I013342/1, ncas10009, NE/I02934X/1, NE/N016548/1, NE/F006160/1, NE/L010992/1, NE/I014683/1, NE/I010750/1, NE/K006045/1, NE/N015657/1, NE/I028874/1, NE/N016211/1, NE/F020937/1, NE/M005836/1, NE/I029161/1, NE/N016238/1
• MO
  Met Office
• NO
  National Oceanic and Atmospheric Administration
• NE
  Natural Environment Research Council

  Awards: NE/I02934X/1, NE/N016211/1, ncas10009, NE/I028874/1, NE/F020937/1, NE/M005836/1, NE/N016238/1, NE/N015657/1, NE/I029161/1, NE/I014683/1, NE/M005836/1, NE/F006160/1, NE/I013342/1, NE/I028874/1, NE/N016211/1, NE/N016548/1, NE/I010750/1, NE/K006045/1, NE/K006045/1, NE/L010992/1
• RH
  Royal Holloway, University of London

  Award: NE/N016211/1