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Why LGM methane needs a bigger wetland collapse
Ice-core CH4 and isotopes imply about a 50% source drop at the LGM; process models underpredict both concentration and isotopic shifts.
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How much did ice-core CH4 rise from LGM to late preindustrial?
From 375 to 680 ppbv.
Source: Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling · DOI · quote verified
What happened to δ13CH4 over that interval?
It depleted from −43 ± 0.3‰ to −48 ± 0.3‰.
Source: Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling · DOI · quote verified
What LGM CH4 does the standard-fire process budget produce?
447 ppbv, underestimating the observed drop and isotope shift.
Source: Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling · DOI · quote verified
What source reduction is needed for LGM CH4?
About 50%; bottom-up emissions fail to match it.
Source: Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling · DOI · quote verified
How large is the leaf-δ13C effect on atmospheric δ13CH4?
Relatively limited at 0.6‰.
Source: Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling · DOI · quote verified
What inversion method infers sources?
Metropolis-Hastings MCMC conditioned on ice-core CH4 and isotopes.
Source: Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling · DOI · quote verified
What geologic source issue is highlighted?
A ~54 TgCH4/year modern geologic source cannot be reconciled with the required LGM source drop.
Source: Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling · DOI · quote verified
What chlorine-sink change is estimated?
Boundary-layer Cl contributed only 0.12‰ to LGM δ13CH4.
Source: Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling · DOI · quote verified
Which Earth-system methane study supplies the priors?
Hopcroft et al. (H17) late-preindustrial and LGM simulations.
Source: Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling · DOI · quote verified
What extra fire scenario improves LGM CH4 at the expense of isotopes?
Low fire: LGM fires set to 10% of preindustrial.
Source: Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling · DOI · quote verified
Why might δ13CH4 still track CO2 even if leaf discrimination is small?
Covariance among CO2, sea level, and climate, plus geologic/fire sources.
Source: Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling · DOI · quote verified