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AGU: Reviews of Geophysics

 

Keywords

  • anthropogenic
  • deforestation
  • Holocene

Index Terms

  • Paleoceanography: Anthropogenic effects
  • Paleoceanography: Astronomical forcing
  • Paleoceanography: Greenhouse gases

Abstract

REVIEWS OF GEOPHYSICS, VOL. 45, RG4001, 37 PP., 2007
doi:10.1029/2006RG000207

The early anthropogenic hypothesis: Challenges and responses

William F. Ruddiman

Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA

Ruddiman (2003) proposed that late Holocene anthropogenic intervention caused CH4 and CO2 increases that kept climate from cooling and that preindustrial pandemics caused CO2 decreases and a small cooling. Every aspect of this early anthropogenic hypothesis has been challenged: the timescale, the issue of stage 11 as a better analog, the ability of human activities to account for the gas anomalies, and the impact of the pandemics. This review finds that the late Holocene gas trends are anomalous in all ice timescales; greenhouse gases decreased during the closest stage 11 insolation analog; disproportionate biomass burning and rice irrigation can explain the methane anomaly; and pandemics explain half of the CO2 decrease since 1000 years ago. Only ∼25% of the CO2 anomaly can, however, be explained by carbon from early deforestation. The remainder must have come from climate system feedbacks, including a Holocene ocean that remained anomalously warm because of anthropogenic intervention.

Received 22 June 2006; accepted 26 March 2007; published 31 October 2007.

Citation: Ruddiman, W. F. (2007), The early anthropogenic hypothesis: Challenges and responses, Rev. Geophys., 45, RG4001, doi:10.1029/2006RG000207.

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