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Early anthropogenic CH 4 emissions and the variation of CH 4 and 13 CH 4 over the last millennium
Author(s) -
Houweling S.,
van der Werf G. R.,
Klein Goldewijk K.,
Röckmann T.,
Aben I.
Publication year - 2008
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2007gb002961
Subject(s) - environmental science , methane , biomass burning , atmospheric sciences , biomass (ecology) , fossil fuel , vegetation (pathology) , industrialisation , climate change , methane emissions , physical geography , climatology , ecology , meteorology , geology , geography , medicine , aerosol , pathology , economics , market economy , biology
This study presents a new hypothesis to explain the observed variation of CH 4 and δ 13 C‐CH 4 over the last millennium. It was originally proposed that the observed minimum of δ 13 C‐CH 4 prior to the start of industrialization is caused by a large shift in biomass burning emissions between 1400 and 1700 A.D. According to our new hypothesis, however, the δ 13 C‐CH 4 minimum is the first sign of the global rise of anthropogenic CH 4 emissions. The main idea is that emissions of isotopically depleted CH 4 , from, for example, rice cultivation, domestic ruminants, and waste treatment started increasing earlier than the isotopically enriched emissions from fossil fuel, which started with the start of industrialization. However, because the observed increase of atmospheric methane only started around 1750 A.D., these preindustrial anthropogenic emissions must have been accompanied by a net reduction of natural CH 4 sources during the Little Ice Age (LIA) compensating for the increase of anthropogenic emissions during that period. Results of transient box model simulations for the last millennium show that under the new hypothesis a close agreement can be obtained between model and measurements. Prior to 1400 A.D., low emissions from anthropogenic biomass burning require a sizable contribution of methane emissions from vegetation to explain the observed high level of δ 13 C‐CH 4 . During the Little Ice Age, a larger than expected reduction of natural sources is needed, which calls for further verification using a more sophisticated modeling approach and additional constraints from ice core measurements.