Role of OH variability in the stalling of the global atmospheric CH[subscript 4] growth rate from 1999 to 2006
Author(s)McNorton, Joe; Chipperfield, Martyn P.; Gloor, Manuel; Wilson, Chris; Feng, Wuhu; Hayman, Garry D.; Rigby, Matt; Krummel, Paul B.; Weiss, Ray F.; Young, Dickon; Dlugokencky, Ed; Montzka, Steve A.; O'Doherty, Simon; Prinn, Ronald G; ... Show more Show less
Role of OH variability in the stalling of the global atmospheric CH4 growth rate from 1999 to 2006
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The growth in atmospheric methane (CH[subscript 4]) concentrations over the past 2 decades has shown large variability on a timescale of several years. Prior to 1999 the globally averaged CH[subscript 4] concentration was increasing at a rate of 6.0 ppb yr[superscript −1], but during a stagnation period from 1999 to 2006 this growth rate slowed to 0.6 ppb yr[superscript −1]. From 2007 to 2009 the growth rate again increased to 4.9 ppb yr[superscript −1]. These changes in growth rate are usually ascribed to variations in CH[subscript 4] emissions. We have used a 3-D global chemical transport model, driven by meteorological reanalyses and variations in global mean hydroxyl (OH) concentrations derived from CH[subscript 3]CCl[subscript 3] observations from two independent networks, to investigate these CH[subscript 4] growth variations. The model shows that between 1999 and 2006 changes in the CH[subscript 4] atmospheric loss contributed significantly to the suppression in global CH[subscript 4] concentrations relative to the pre-1999 trend. The largest factor in this is relatively small variations in global mean OH on a timescale of a few years, with minor contributions of atmospheric transport of CH[subscript 4] to its sink region and of atmospheric temperature. Although changes in emissions may be important during the stagnation period, these results imply a smaller variation is required to explain the observed CH[subscript 4] trends. The contribution of OH variations to the renewed CH[subscript 4] growth after 2007 cannot be determined with data currently available.
DepartmentMassachusetts Institute of Technology. Center for Global Change Science
Atmospheric Chemistry and Physics
McNorton, Joe et al. “Role of OH Variability in the Stalling of the Global Atmospheric CH[subscript 4] Growth Rate from 1999 to 2006.” Atmospheric Chemistry and Physics 16.12 (2016): 7943–7956.
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