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Continuing decline in the growth rate of the atmospheric methane burden

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Abstract

The global atmospheric methane burden has more than doubled since pre-industrial times1,2, and this increase is responsible for about 20% of the estimated change in direct radiative forcing due to anthropogenic greenhouse-gas emissions. Research into future climate change and the development of remedial environmental policies therefore require a reliable assessment of the long-term growth rate in the atmospheric methane load. Measurements have revealed that although the global atmospheric methane burden continues to increase2 with significant interannual variability3,4, the overall rate of increase has slowed2,5. Here we present an analysis of methane measurements from a global air sampling network that suggests that, assuming constant OH concentration, global annual methane emissions have remained nearly constant during the period 1984–96, and that the decreasing growth rate in atmospheric methane reflects the approach to a steady state on a timescale comparable to methane's atmospheric lifetime. If the global methane sources and OH concentration continue to remain constant, we expect average methane mixing ratios to increase slowly from today's 1,730 nmol mol−1 to ∼1,800 nmol mol−1, with little change in the contribution of methane to the greenhouse effect.

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Figure 1: Result of spatial and temporal smoothing of CH4 measurements from CMDL air sampling network sites.
Figure 2: Results of calculations of CH4 source and sink from mass-balance equation and intersemihemispheric difference are plotted as a function of time.

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Acknowledgements

We thank all agencies that have assisted us with the cooperative air sampling network, and Blue Star Line for their continued support of our sampling efforts. We are grateful for the efforts of all network observers, and thank T. Conway and R. Cicerone for comments. This work was supported in part by the Atmospheric Chemistry Proejct of the NOAA Climate and Global Change Program and the US Environmental Protection Agency.

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Authors and Affiliations

  1. NOAA Climate Monitoring and Diagnostics Laboratory, 325 Broadway, Boulder, 80303, Colorado, USA

    E. J. Dlugokencky, K. A. Masarie, P. M. Lang & P. P. Tans

  2. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, 80309, Colorado, USA

    K. A. Masarie

Authors
  1. E. J. Dlugokencky
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  2. K. A. Masarie
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  3. P. M. Lang
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  4. P. P. Tans
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Correspondence to E. J. Dlugokencky.

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Dlugokencky, E., Masarie, K., Lang, P. et al. Continuing decline in the growth rate of the atmospheric methane burden. Nature 393, 447–450 (1998). https://doi.org/10.1038/30934

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