Increases of population and expansion of rice agriculture in Asia, and anthropogenic methane emissions since 5000 BP

CO2 and CH4 composition of the atmosphere increased rapidly following the industrial revolution. Recently Ruddiman has suggested that increases in the anthropogenic contribution to atmospheric greenhouse gases had actually begun thousands of years earlier. Research on climates indicates that a cooling and drying trend developed from about 5000 BP across the Asian monsoonal region. Archaeological and biological data reveal that from about the same time there was an important transition point corresponding to the rapid growth of population and expansion of cultivated rice areas. Extensive deforestation also occurred from this time. The expansion of rice agriculture and extended wetland areas provided more sources of methane emissions, and thus contributed to greenhouse gas budgets. The climate impacts of increased anthropogenic methane emissions were possibly counterbalanced in part by any natural decrease from orbital forcing. The methane contribution from rice paddy areas is estimated to be smaller than 250 ppb for the middle-late Neolithic. The 1000-ppb methane rise after industrial era coincides closely with the rapid growth of global human populations, and anthropogenic driven sources.