Abstract
It has been suggested that late-Holocene human activities caused the increase in atmospheric methane (CH4) concentration that otherwise would have been a naturally decreasing trend. As one of the places where rice farming originated, China has been considered to play a significant role in pre-industrial changes in atmospheric CH4 concentrations. To establish the climatic context since the first rice cultivation and to evaluate the relative roles of monsoon climate and rice cultivation on late Holocene CH4 rise, we synthesized climate data from China to examine the Holocene trends in monsoon precipitation. The results show high monsoon rainfall from 10,000 to 7000 years ago, and declining precipitation in the late Holocene as shown by most reconstructions. The decreasing trend in monsoon precipitation is consistent with that in other north tropical monsoon regions, and is opposite to the trend in CH4 concentrations. After ruling out several other natural factors and estimating CH4 emissions from early rice farming, we conclude that the late-Holocene methane increase has been significantly influenced by the expansion of early rice paddy fields during the period of declining monsoon precipitation.
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