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Renewed growth of atmospheric methane
Center for Global Change Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
Center for Global Change Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia
School of Chemistry, University of Bristol, Bristol, UK
Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia
Center for Global Change Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia
Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia
Scripps Institution of Oceanography, UCSD, La Jolla, California, USA
School of Chemistry, University of Bristol, Bristol, UK
Scripps Institution of Oceanography, UCSD, La Jolla, California, USA
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
Scripps Institution of Oceanography, UCSD, La Jolla, California, USA
Scripps Institution of Oceanography, UCSD, La Jolla, California, USA
Australian Government Bureau of Meteorology, Melbourne, Victoria, Australia
Following almost a decade with little change in global atmospheric methane mole fraction, we present measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) networks that show renewed growth starting near the beginning of 2007. Remarkably, a similar growth rate is found at all monitoring locations from this time until the latest measurements. We use these data, along with an inverse method applied to a simple model of atmospheric chemistry and transport, to investigate the possible drivers of the rise. Specifically, the relative roles of an increase in emission rate or a decrease in concentration of the hydroxyl radical, the largest methane sink, are examined. We conclude that: 1) if the annual mean hydroxyl radical concentration did not change, a substantial increase in emissions was required simultaneously in both hemispheres between 2006 and 2007; 2) if a small drop in the hydroxyl radical concentration occurred, consistent with AGAGE methyl chloroform measurements, the emission increase is more strongly biased to the Northern Hemisphere.
Received 17 September 2008; accepted 16 October 2008; published 20 November 2008.
Citation: (2008), Renewed growth of atmospheric methane, Geophys. Res. Lett., 35, L22805, doi:10.1029/2008GL036037.
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