Inversion of the global methane cycle using chance constrained programming: Methodology and results

This paper presents a new methodology for constraining. sources and sinks in mass balances and applies it to a global model of methane. Sources and sinks are treated as random variables that are constrained by isotopic mass balance and ice-core data. A chance constrained programming formulation is used to perform inverse calculations and determine constrained bounds on sources of methane. Budgets consistent with atmospheric concentrations, flux measurements, and priors on model variables and parameters are derived. It is observed that global budgets of methane presented in the literature have greater uncertainty ranges than allowed by the constraints on its global cycle. The analysis shows that emissions from rice paddies and wetlands may be lower than presented in previous budgets, a result that is in agreement with recent estimates based on flux measurements. Ranges for other anthropogenic sources such as biomass burning, and fossil and landfill emissions are also obtained. Sensitivity analysis is used to determine the key uncertain parameters in the global methane budget.