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| GEC-1994-06 : Methane from the House of Tudor and the Ming Dynasty |  |
| You can download this working paper in PDF format (146.13K). |
| By:
Subak, S. | |
| Current efforts to predict the time scale and magnitude of global warming depend upon knowledge of baseline greenhouse gas concentrations as well as the dynamics of gas exchange among natural and anthropogenic reservoirs. Implicit in the notion of the enhanced greenhouse effect is the idea that the contribution to concentrations prior to the mid-19th century reflected only natural processes. New research is revealing that pre-industrial human activity may have disrupted natural biogeochemical cycles. This paper summarises anthropogenic activities for the early modern, pre-industrial, period that may have contributed to a pre-industrial greenhouse signal, and changes in atmospheric chemistry. The research is based on the historical record and current estimates of CH4 emission factors. Methane emissions are estimated for biomass burning, enteric fermentation and irrigated agriculture. It is concluded that anthropogenic CH4 emissions were likely to have been at least 55 Tg/CH4/year in 1500 and preceding centuries, contributing to a total annual emissions flux of at least 210 Tg CH4. At least half of the anthropogenic emissions were likely to have been due to biomass burning, with the remaining from irrigated agriculture and animals. These conclusions suggest that the concentration of OH in the atmosphere - the main removal process for CH4 - may have been greater than today, given that recent deconvolution analysis indicates that a total source strength of only 170 Tg CH4 a year during the 16th century is consistent with total estimated CH4 sinks and natural sources at 20th century levels. | |
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