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Bayesian Analysis of the Glacial‐Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling
Author(s) -
Hopcroft Peter O.,
Valdes Paul J.,
Kaplan Jed O.
Publication year - 2018
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2018gl077382
Subject(s) - ice core , last glacial maximum , interglacial , atmospheric methane , climatology , atmospheric sciences , glacial period , stable isotope ratio , environmental science , methane , geology , physical geography , greenhouse gas , chemistry , oceanography , geography , geomorphology , physics , quantum mechanics , organic chemistry
The observed rise in atmospheric methane (CH 4 ) from 375 ppbv during the Last Glacial Maximum (LGM: 21,000 years ago) to 680 ppbv during the late preindustrial era is not well understood. Atmospheric chemistry considerations implicate an increase in CH 4 sources, but process‐based estimates fail to reproduce the required amplitude. CH 4 stable isotopes provide complementary information that can help constrain the underlying causes of the increase. We combine Earth System model simulations of the late preindustrial and LGM CH 4 cycles, including process‐based estimates of the isotopic discrimination of vegetation, in a box model of atmospheric CH 4 and its isotopes. Using a Bayesian approach, we show how model‐based constraints and ice core observations may be combined in a consistent probabilistic framework. The resultant posterior distributions point to a strong reduction in wetland and other biogenic CH 4 emissions during the LGM, with a modest increase in the geological source, or potentially natural or anthropogenic fires, accounting for the observed enrichment of δ 13 CH 4 .