Multidecadal preindustrial methane variability can be explained by noise in the source-sink imbalance

Area of Science:

• Paleoclimatology
• Atmospheric Chemistry
• Climate Modeling

Background:

• Ice core data reveal preindustrial atmospheric methane (CH4) variability of ~30 ppb (~5%) on multidecadal to centennial timescales.
• Previous research linked this variability to climate events (e.g., Little Ice Age) or human activities affecting CH4 sources and sinks.

Purpose of the Study:

• To investigate source and sink dynamics that could explain observed preindustrial methane variability in ice core records.
• To determine if random fluctuations, rather than large-scale climate forcing, can account for CH4 excursions.

Main Methods:

• Development of a simple model incorporating methane lifetime and firn processes.
• Simulation of synthetic ice core records using unforced random perturbations to model source-sink imbalance.
• Analysis of model output to match spectral features of observed ice core data.

Main Results:

• The model demonstrates that white noise fluctuations in the methane source-sink imbalance can replicate observed ice core variability.
• Fast-varying sources/sinks (e.g., weather-driven, interannual wetland emissions) can significantly impact atmospheric methane levels.
• Source-sink imbalance timescales shorter than a century are consistent with ice core records, with shorter timescales requiring larger fluctuation amplitudes.

Conclusions:

• Preindustrial atmospheric methane variability can arise from intrinsic, rapid fluctuations in its sources and sinks.
• Rapid preindustrial source-sink variability may explain modern methane growth rate variability.
• Constraining methane dynamics using preindustrial ice core data can improve models for evaluating current methane trends.