Natural and anthropogenic variations in methane sources during the past two millennia
Abstract
Methane (CH4) is an important greenhouse gas that is emitted from multiple natural and anthropogenic sources. Atmospheric levels of CH4 have varied on various timescales in the past, but in many cases the causes of these variations are not understood. Analysis of the isotopic composition of CH4 provides evidence for the environmental drivers of variations in CH4 atmospheric abundance, because different sources and sinks affect the isotopic composition of CH4 specifically. Our data from air trapped in the NEEM and EUROCORE Greenland ice cores show that the carbon isotopic composition (δ13C) of CH4 underwent pronounced centennial-scale variations between 100 BC and 1600 AD. Two-box model calculations suggest that the centennial-scale variations in isotope ratios are due to changes in both pyrogenic and biogenic sources. These changes are correlated with both natural climate variability including the Medieval Climate Anomaly and the Little Ice Age and with changes in human population, land-use and with the decline of both the Roman Empire and the Han dynasty and the Medieval period. Our findings suggest that between 100 BC and 1600 AD human activities may have been responsible for about 20-30 per cent of the total pyrogenic methane emissions and that they have therefore contributed to variations in methane emissions long before the onset of the industrial revolution.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.C54B..06S
- Keywords:
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- 0315 ATMOSPHERIC COMPOSITION AND STRUCTURE / Biosphere/atmosphere interactions;
- 0428 BIOGEOSCIENCES / Carbon cycling;
- 0490 BIOGEOSCIENCES / Trace gases;
- 0724 CRYOSPHERE / Ice cores