Uncertainties in modeling CH₄ emissions from northern wetlands in glacial climates: effect of hydrological model and CH₄ model structure

Methane (CH₄) fluxes from northern wetlands may have influenced atmospheric CH₄ concentrations at climate warming phases during the 800 000 years and at present global warming. Including these CH₄ fluxes in earth system models is essential to understand feedbacks between climate and atmospheric composition. <br><br> Attempts to model CH₄ fluxes from wetlands have been undertaken previously using various approaches. Here, we test a process-based wetland CH₄ flux model (PEATLAND-VU) which includes details of soil-atmosphere CH₄ transport. The model has been used to simulate CH₄ emissions from continental Europe in different glacial climates and the present climate. <br><br> This paper displays results on the sensitivity of modeling glacial terrestrial CH₄ fluxes to basic tuning parameters of the model, to different approaches in modeling of the water table, and to model structure. For testing the model structure, PEATLAND-VU has been compared to a simpler modeling approach based on wetland primary production estimated from a vegetation model (BIOME). The tuning parameters are the CH₄ production rate from labile organic carbon and its temperature sensitivity. <br><br> The modelled fluxes prove comparatively insensitive to hydrology representation, and sensitive to microbial parameters and model structure. Glacial climate emissions are also highly sensitive to assumptions on the extent of ice cover and exposed seafloors. Wetland expansion on low relief exposed seafloor areas, may have compensated for a decrease of wetland area due to continental ice cover.