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The early anthropogenic hypothesis: Challenges and responses
Author(s) -
Ruddiman William F.
Publication year - 2007
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/2006rg000207
Subject(s) - holocene , deforestation (computer science) , greenhouse gas , climate change , environmental science , biomass burning , climatology , insolation , anomaly (physics) , global warming , oceanography , atmospheric sciences , geology , geography , meteorology , aerosol , physics , condensed matter physics , computer science , programming language
Ruddiman (2003) proposed that late Holocene anthropogenic intervention caused CH 4 and CO 2 increases that kept climate from cooling and that preindustrial pandemics caused CO 2 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 CO 2 decrease since 1000 years ago. Only ∼25% of the CO 2 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.