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Late Holocene methane rise caused by orbitally controlled increase in tropical sources


Considerable debate surrounds the source of the apparently ‘anomalous’1 increase of atmospheric methane concentrations since the mid-Holocene (5,000 years ago) compared to previous interglacial periods as recorded in polar ice core records2. Proposed mechanisms for the rise in methane concentrations relate either to methane emissions from anthropogenic early rice cultivation1,3 or an increase in natural wetland emissions from tropical4 or boreal sources5,6. Here we show that our climate and wetland simulations of the global methane cycle over the last glacial cycle (the past 130,000 years) recreate the ice core record and capture the late Holocene increase in methane concentrations. Our analyses indicate that the late Holocene increase results from natural changes in the Earth's orbital configuration, with enhanced emissions in the Southern Hemisphere tropics linked to precession-induced modification of seasonal precipitation. Critically, our simulations capture the declining trend in methane concentrations at the end of the last interglacial period (115,000–130,000 years ago) that was used to diagnose the Holocene methane rise as unique. The difference between the two time periods results from differences in the size and rate of regional insolation changes and the lack of glacial inception in the Holocene. Our findings also suggest that no early agricultural sources are required to account for the increase in methane concentrations in the 5,000 years before the industrial era.

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Figure 1: Time series of model and ice core data for the last glacial cycle.
Figure 2: A comparison of model- and data-based CH 4 concentrations from the current interglacial and the previous interglacial (Eemian) periods.
Figure 3: Temporal and spatial patterns of modelled methane emission changes for the last glacial cycle.


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J.S.S. and P.J.V. thank the BBC for commissioning the climate simulations for their TV series, The Incredible Human Journey. Thanks are also due to I. Woodward and M. Lomas for earlier SDGVM development. P.J.V. and D.J.B. acknowledge additional support through Royal Society-Wolfson Research Merit Awards and the Leverhulme Trust. J.S.S. thanks R. Bailey for comments.

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Authors and Affiliations



J.S.S. and P.J.V. performed the climate model simulations. P.J.V. performed initial analysis of methane emissions from experiment ALL. J.S.S. performed the main analysis, sensitivity experiments and led the writing of the paper with contributions from all other authors. P.F. and D.J.B. contributed expertise concerning methane emissions and the carbon cycle. D.J.B. and S.N. evolved the development of the vegetation and methane models.

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Correspondence to Joy S. Singarayer.

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The authors declare no competing financial interests.

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Singarayer, J., Valdes, P., Friedlingstein, P. et al. Late Holocene methane rise caused by orbitally controlled increase in tropical sources. Nature 470, 82–85 (2011).

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