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Science 9 September 2005:
Vol. 309. no. 5741, pp. 1714 - 1717
DOI: 10.1126/science.1115193
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Reports

Unexpected Changes to the Global Methane Budget over the Past 2000 Years

D. F. Ferretti,1,2* J. B. Miller,3 J. W. C. White,1 D. M. Etheridge,4 K. R. Lassey,2 D. C. Lowe,2 C. M. MacFarling Meure,4 M. F. Dreier,1 C. M. Trudinger,4 T. D. van Ommen,5 R. L. Langenfelds4

We report a 2000-year Antarctic ice-core record of stable carbon isotope measurements in atmospheric methane ({delta}13CH4). Large {delta}13CH4 variations indicate that the methane budget varied unexpectedly during the late preindustrial Holocene (circa 0 to 1700 A.D.). During the first thousand years (0 to 1000 A.D.), {delta}13CH4 was at least 2 per mil enriched compared to expected values, and during the following 700 years, an about 2 per mil depletion occurred. Our modeled methane source partitioning implies that biomass burning emissions were high from 0 to 1000 A.D. but reduced by almost ~40% over the next 700 years. We suggest that both human activities and natural climate change influenced preindustrial biomass burning emissions and that these emissions have been previously understated in late preindustrial Holocene methane budget research.

1 Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309, USA.
2 National Institute of Water and Atmospheric Research Limited (NIWA), Post Office Box 14901, Wellington, New Zealand.
3 National Oceanic and Atmospheric Administration (NOAA), R/CMDL1, 325 Broadway, Boulder, CO 80305, USA.
4 Commonwealth Scientific and Industrial Research Organisation (CSIRO), Marine and Atmospheric Research, Private Bag 1, Aspendale, Victoria 3195, Australia.
5 Department of the Environment and Heritage, Australian Antarctic Division, and Antarctic Climate and Ecosystems CRC, Private Bag 80, Hobart, Tasmania 7001, Australia.

* To whom correspondence should be addressed. E-mail: d.ferretti{at}niwa.co.nz

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