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AGU: Geophysical Research Letters

 

Index Terms

  • Atmospheric Composition and Structure: Evolution of the atmosphere
  • Atmospheric Composition and Structure: Troposphere—composition and chemistry
  • Global Change: Atmosphere

Abstract

GEOPHYSICAL RESEARCH LETTERS, VOL. 29, 1479, 4 PP., 2002
doi:10.1029/2001GL014521

Implications of the recent fluctuations in the growth rate of tropospheric methane

Isobel J. Simpson

Department of Chemistry, University of California, Irvine, CA, USA

Tai-Yih Chen

Institute of Earth Sciences, Academia Sinica, Nankang, Taipei, Taiwan

Donald R. Blake

Department of Chemistry, University of California, Irvine, CA, USA

F. Sherwood Rowland

Department of Chemistry, University of California, Irvine, CA, USA

Global measurements show that the mixing ratio of tropospheric methane (CH4) increased by 1.1% (19.5 ± 1.7 ppbv) over the five-year period 1996–2000, with striking fluctuations in its annual growth rate. Whereas the global CH4 growth rate reached 15.9 ± 0.7 ppbv yr−1 in 1998, the growth rate was −2.1 ± 0.8 ppbv yr−1 in 2000. This is the first time in our 23-year global monitoring program that we have measured a negative annual CH4 growth rate. The CH4 growth rate fluctuates in an unpredictable fashion, and we reemphasize that global CH4 concentrations cannot be extrapolated into the future based on past trends. As a result, we suggest that the slowing of the CH4 growth rate during much of the 1980s and 1990s cannot be used to imply that CH4 will no longer be of concern in greenhouse gas studies during this century.

Published 30 May 2002.

Citation: Simpson, I. J., T.-Y. Chen, D. R. Blake, and F. S. Rowland (2002), Implications of the recent fluctuations in the growth rate of tropospheric methane, Geophys. Res. Lett., 29(10), 1479, doi:10.1029/2001GL014521.

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