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No inter-hemispheric δ13CH4 trend observed

Nature volume 486, pages E3E4 (28 June 2012) | Download Citation

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Abstract

Arising from Kai, F. M., Tyler, S. C., Randerson, J. T. & Blake, D. R. Nature 476, 194–197 (2011)10.1038/nature10259

To understand the reasons for global CH4 changes since the 1990s, Kai et al.1 evaluated a combined record of observed tropospheric CH4 mole fractions as well as δ13C-CH4 and δD-CH4 measurements from mid latitudes of both hemispheres. Their data set shows a strongly decreasing inter-hemispheric difference (IHD) in δ13C-CH4 from −0.24 ± 0.11‰ during 1989–1993 to −0.10 ± 0.04‰ during 2001–2005, which they largely attribute to decreasing rice emissions during the last two decades. Here we show that the experimental data used by Kai et al.1 are probably biased because the authors used only one continental mountain station (Niwot Ridge, Colorado, USA) as representative of the entire Northern Hemisphere, thereby incorrectly determining the IHD of δ13C-CH4. Our more comprehensive data set—representing background air in both hemispheres—shows that the IHD of δ13C-CH4 has changed by less than 0.05‰ since 1990; the conclusion drawn by Kai et al.1 of a significant reduction of NH microbial sources is, thus, not constrained by our data.

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Author information

Affiliations

  1. *Institut für Umweltphysik, Heidelberg University, 69120 Heidelberg, Germany

    • I. Levin
    • , C. Veidt
    • , R. Heinz
    •  & C. Poß
  2. †Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309-0450, USA

    • B. H. Vaughn
    •  & J. W. C. White
  3. ‡National Institute of Water and Atmospheric Research Ltd., Wellington 6021, New Zealand

    • G. Brailsford
    •  & T. Bromley
  4. §Antarctic Research Centre, Victoria University of Wellington, Wellington 6140, New Zealand

    • D. Lowe
  5. NOAA/ESRL, Boulder, Colorado 80305-3337, USA

    • J. B. Miller
  6. ¶Cooperative Institute for Research in Environmental Science, University of Colorado, Boulder, Colorado 80309-0216, USA

    • J. B. Miller

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Competing interests

Competing financial interests: declared none.

Corresponding author

Correspondence to I. Levin.

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DOI

https://doi.org/10.1038/nature11175

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