Natural and anthropogenic variations in methane sources over the last 2 millennia

By drs. C.J. Sapart

1. C.J. Sapart, 1. M. Prokopiou, 1. G. Monteil, 1. C. van der Veen, 1. S. Houweling, 1. R.S.W. van de Wal, 1. M.C. Krol, 2. P. Sperlich, 2. T. Blunier, 2. D. Dahl-Jensen, 3. T. Sowers, 4. J. Chappellaz, 4. P. Martinierie, 5. K.M. Krumhardt, 5. J.O. Kaplan and 1. T. Röckmann.

1Institute for Marine and Atmospheric research Utrecht, Utrecht University, Princetonplein 5, 3584CC Utrecht, THE NETHERLANDS. 2Center for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, DENMARK. 3Earth and Environmental Systems Institute, Geoscience, 237 Deike Building, Penn State University, University Park, PA 16802, USA. 4Laboratoire de Glaciologie et Géophysique de l’Environnement (LGGE), 4 rue Molière, 38402 Saint-Martin d’Hères, FRANCE. 5Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 2, 1015 Lausanne, SWITZERLAND.

Methane (CH4) is an important greenhouse gas that is emitted from a multitude of natural and anthropogenic sources. Atmospheric levels of CH4 have varied on various timescales in the past, but in many cases the causes of these variations are not known. Isotope analysis can help unravel the underlying processes, because different source categories produce CH4 with different isotopic composition. Here we show from air trapped in Greenland ice cores that the δ13C of CH4 underwent pronounced centennial-scale variations between 200 BCE and 1500 CE without corresponding changes in mixing ratios. The long-term CH4 increase observed over this period is accompanied by a small overall δ13C decrease. Two-box model calculations suggest that the long-term CH4 increase can only be explained by an increase in emissions from biogenic sources. The centennial-scale variations in isotope ratios would most likely be due to changes in biomass burning, which may be correlated with both natural climate variations including the Medieval Climate Anomaly, and with changes in human population, land-use and important events in history.

Correspondence to Célia J. Sapart :

Willem Barentsz Poolinstituut

Bundeling van kennis, onderzoek en onderwijs over de Noord- en de Zuidpool






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