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.
Source
Bayesian Analysis of the Glacial-Interglacial Methane Increase Constrained by Stable Isotopes and Earth System Modeling
Study at a glance
- Design
- Computational / modelling — MCMC inversion of LGM vs preindustrial CH4 and isotopes in a three-box model
- N
- Ice-core constraints and Earth-system flux priors; not an observational sample N
- Population
- Atmospheric methane budget from LGM to late preindustrial (ice-core constrained)
- Outcome
- Required source reductions and isotope shifts poorly matched by process models
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
Authors nested Hopcroft et al. Earth-system methane budgets in a three-box isotope model, added leaf-δ13C and chlorine sinks, then used MCMC to invert LGM versus preindustrial ice-core CH4, δ13C, and δD.
What they found
CH4 rose from 375 to 680 ppbv while δ13CH4 fell from −43 to −48‰. Standard LGM fluxes give 447 ppbv and almost no isotope shift. Leaf discrimination adds only ~0.6‰. Posterior wetlands must fall more than models simulate; geologic and fire sources also matter.
The limits
What it doesn't show
High-latitude peat and CH3Cl sources remain poorly represented; a 54 Tg/yr modern geologic source cannot fit the LGM reduction; Cl from extra LGM sea salt is not in the model.
Key terms
- LGM
- Last Glacial Maximum, the last peak ice-age climate.
- δ13CH4
- Carbon-13 composition of atmospheric methane.
- Three-box model
- Simple atmosphere used to mix methane sources and sinks isotopically.
- Wetland methane
- Biogenic CH4 from inundated soils, the largest natural source.
- MCMC
- Markov chain Monte Carlo sampling of posterior source strengths.
Flashcards
Research intelligence for this paper
See its role on concept claims, tensions it is part of, placement history, and related discoveries.
Quiz yourself
LGM to preindustrial CH4:
Common questions
LGM vs preindustrial CH4?
About 375 to 680 ppbv.
Needed source change?
About a 50% reduction at the LGM.
Do bottom-up models match isotopes?
No—they underpredict concentration and isotope shifts.
Leaf δ13C role?
Limited (~0.6‰ of the atmospheric signal).
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