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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L12809, doi:10.1029/2006GL026199, 2006

Impact of meteorology and emissions on methane trends, 1990–2004

Arlene M. Fiore

Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey, USA


Larry W. Horowitz

Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey, USA


Edward J. Dlugokencky

Earth System Research Laboratory, NOAA, Boulder, Colorado, USA


J. Jason West

Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, New Jersey, USA


Abstract

Over the past century, atmospheric methane (CH4) rose dramatically before leveling off in the late 1990s. The processes controlling this trend are poorly understood, limiting confidence in projections of future CH4. The MOZART-2 global tropospheric chemistry model qualitatively captures the observed CH4 trend (increasing in the early 1990s and then leveling off) with constant emissions. From 1991–1995 to 2000–2004, the CH4 lifetime versus tropospheric OH decreases by 1.6%, reflecting increases in OH and temperature. The rise in OH stems from an increase in lightning NOx as parameterized in the model. A simulation including annually varying anthropogenic and wetland CH4 emissions, as well as the changes in meteorology, best reproduces the observed CH4 distribution, trend, and seasonal cycles. Projections of future CH4 abundances should consider climate-driven changes in CH4 sources and sinks.

Received 2 March 2006; accepted 16 May 2006; published 24 June 2006.

Index Terms: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions (0426, 1610); 0330 Atmospheric Composition and Structure: Geochemical cycles (1030); 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0414 Biogeosciences: Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912).

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Citation: Fiore, A. M., L. W. Horowitz, E. J. Dlugokencky, and J. J. West (2006), Impact of meteorology and emissions on methane trends, 1990–2004, Geophys. Res. Lett., 33, L12809, doi:10.1029/2006GL026199.