Reconciling the changes in atmospheric-methane sources and sinks between the Last Glacial Maximum and the pre-industrial era
We know from the ice record that the concentration of
atmospheric methane, [CH4], at the Last Glacial Maximum
(LGM) was roughly half that in the pre-industrial era (PI), buthow much of the difference was source-driven, and how
much was sink-driven, remains uncertain. Recent developments
include: a higher estimate of the LGM-PI change in
methane emissions from wetlands―the dominant, natural
methane source; and the possible recycling of OH consumed
in isoprene oxidation―the principal methane sink.
Here, in view of these developments, we use an atmospheric
chemistry-transport model to re-examine the main factors
affecting OH during this period: changes in air temperature
and emissions of non-methane volatile organic compounds
from vegetation. We find that their net effect was negligible(with and without an OH recycling mechanism), implyingthe change in [CH4] was almost entirely source driven―a conclusion that, though subject to significant uncertainties,can be reconciled with recent methane source estimates.