Modeling Global Extent of Wetlands Under Changing Climate Conditions
Global wetlands are believed to be climate sensitive and are the largest natural emitters of methane (CH4), a potent greenhouse gas. However, the emission size and change with climate is poorly constrained. Earth system models are developing the capability to simulate these wetlands and their methane production. The Wetland and Wetland CH4 Intercomparison of Models Project is evaluating the ability of models to simulate large-scale wetland characteristics and their methane emissions, which are essential for evaluating key uncertainties in methane emission mechanisms and parameters. Ten modeling groups, including U.S. Department of Energy researchers at Lawrence Berkeley National Laboratory, ran eight global and two regional models with a common experimental protocol using the same climate and atmospheric carbon dioxide (CO2) forcing datasets. The models demonstrate extensive disagreement in their simulations of wetland areal extent and CH4 emissions in both space and time. All models show a strong positive response to increased atmospheric CO2 concentrations in both CH4 emissions and wetland area. In response to increasing global temperatures, on average, the models decreased wetland area and CH4 fluxes, primarily in the tropics, but the magnitude and sign of the response varied greatly. Models were least sensitive to increased global precipitation, with a consistent small positive response in CH4 fluxes and wetland area. We presently do not have sufficient wetland methane observation datasets to evaluate model fluxes, severely restricting our ability to model global wetland CH4 emissions with confidence. The large range in predicted CH4 emission rates leads to the conclusion that there is both substantial parameter and structural uncertainty in large-scale CH4 emission models, even after accounting for uncertainties in wetland areas. Clearly, significant research is needed both in modeling and measuring wetland sources of methane and their responses to climate.
Wania, R., et al. 2013. Present State of Global Wetland Extent and Wetland Methane Modelling: Methodology of a Model Intercomparison Project (WETCHIMP),” Geoscientific Model Development 6, 617–41, DOI: 10.5194/gmd-6-617-2013.
Melton, J. R., et al. 2013. “Present State of Global Wetland Extent and Wetland Methane Modelling: Conclusions from a Model Intercomparison Project (WETCHIMP),” Biogeosciences, 10, 753–88. DOI: 10.5194/bg-10-753-2013