Articles | Volume 17, issue 3
Atmos. Chem. Phys., 17, 2255–2277, 2017

Special issue: Twenty-five years of operations of the Network for the Detection...

Atmos. Chem. Phys., 17, 2255–2277, 2017

Research article 14 Feb 2017

Research article | 14 Feb 2017

The recent increase of atmospheric methane from 10 years of ground-based NDACC FTIR observations since 2005

Whitney Bader1,2, Benoît Bovy1, Stephanie Conway2, Kimberly Strong2, Dan Smale3, Alexander J. Turner4, Thomas Blumenstock5, Chris Boone6, Martine Collaud Coen7, Ancelin Coulon8, Omaira Garcia9, David W. T. Griffith10, Frank Hase5, Petra Hausmann11, Nicholas Jones10, Paul Krummel12, Isao Murata13, Isamu Morino14, Hideaki Nakajima14, Simon O'Doherty15, Clare Paton-Walsh10, John Robinson3, Rodrigue Sandrin2, Matthias Schneider5, Christian Servais1, Ralf Sussmann11, and Emmanuel Mahieu1 Whitney Bader et al.
  • 1Institute of Astrophysics and Geophysics, University of Liège, Liège, Belgium
  • 2Department of Physics, University of Toronto, Toronto, ON, M5S 1A7, Canada
  • 3National Institute of Water and Atmospheric Research, NIWA, Lauder, New Zealand
  • 4School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
  • 5Karlsruhe Institute of Technology (KIT), Institute of Meteorology and Climate Research (IMK-ASF), Karlsruhe, Germany
  • 6Department of Chemistry, University of Waterloo, Waterloo, ON, N2L 3G1, Canada
  • 7Federal Office of Meteorology and Climatology, MeteoSwiss, 1530 Payerne, Switzerland
  • 8Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
  • 9Izana Atmospheric Research Centre (IARC), Agencia Estatal de Meteorologia (AEMET), Izaña, Spain
  • 10School of Chemistry, University of Wollongong, Wollongong, Australia
  • 11Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen, Germany
  • 12CSIRO Oceans & Atmosphere, Aspendale, Victoria, Australia
  • 13Graduate School of Environment Studies, Tohoku University, Sendai 980-8578, Japan
  • 14National Institute for Environmental Studies (NIES), Tsukuba, Ibaraki 305-8506, Japan
  • 15Atmospheric Chemistry Research Group (ACRG), School of Chemistry, University of Bristol, Bristol, UK

Abstract. Changes of atmospheric methane total columns (CH4) since 2005 have been evaluated using Fourier transform infrared (FTIR) solar observations carried out at 10 ground-based sites, affiliated to the Network for Detection of Atmospheric Composition Change (NDACC). From this, we find an increase of atmospheric methane total columns of 0.31 ± 0.03 % year−1 (2σ level of uncertainty) for the 2005–2014 period. Comparisons with in situ methane measurements at both local and global scales show good agreement. We used the GEOS-Chem chemical transport model tagged simulation, which accounts for the contribution of each emission source and one sink in the total methane, simulated over 2005–2012. After regridding according to NDACC vertical layering using a conservative regridding scheme and smoothing by convolving with respective FTIR seasonal averaging kernels, the GEOS-Chem simulation shows an increase of atmospheric methane total columns of 0.35 ± 0.03 % year−1 between 2005 and 2012, which is in agreement with NDACC measurements over the same time period (0.30 ± 0.04 % year−1, averaged over 10 stations). Analysis of the GEOS-Chem-tagged simulation allows us to quantify the contribution of each tracer to the global methane change since 2005. We find that natural sources such as wetlands and biomass burning contribute to the interannual variability of methane. However, anthropogenic emissions, such as coal mining, and gas and oil transport and exploration, which are mainly emitted in the Northern Hemisphere and act as secondary contributors to the global budget of methane, have played a major role in the increase of atmospheric methane observed since 2005. Based on the GEOS-Chem-tagged simulation, we discuss possible cause(s) for the increase of methane since 2005, which is still unexplained.

Short summary
An increase of 0.31 ± 0.03 % year−1 of atmospheric methane is reported using 10 years of solar observations performed at 10 ground-based stations since 2005. These trend agree with a GEOS-Chem-tagged simulation that accounts for the contribution of each emission source and one sink in the total methane. The GEOS-Chem simulation shows that anthropogenic emissions from coal mining and gas and oil transport and exploration have played a major role in the increase methane since 2005.
Final-revised paper