Natural wetland methane emissions simulated by ICON-XPP

Abstract. Methane emissions from natural wetlands account for about 1/3 of global methane emissions, and thus have a significant climatic impact due to methane’s high global warming potential. Among the sources of methane, those from natural wetlands have the highest uncertainty, and it is thus of key importance to understand and reduce the uncertainties in the estimates of the wetland emissions to be able to close the global methane budget. Using a coupled land and atmosphere setup, a new implementation of interactive wetlands and wetland methane emissions into the ICON-XPP Earth System Model was used to test the sensitivity of the wetland methane emissions to a number of hydrological and biogeochemical model assumptions of which some are mimicing anthropogenic influences on the Earth System. Averaged over the historical period (1855–2014) the simulated emissions are 166.2 (156.3–181.2) Tg(CH₄) yr^-1. For the 2000–2012 period the equivalent numbers 182.3 (154.3–205.1) Tg(CH₄) yr^-1 are in good agreement with estimates from other studies. Wetland methane emissions rise by about 12 % during the historical period, mainly since 1980, an increase which is due to an enhanced carbon cycle caused by the CO₂ fertilization associated with rising atmospheric CO₂ concentrations. The modeled emissions are very sensitive to changes and assumptions in the model hydrology, some dependencies only revealed through the interaction with the atmosphere (changes in the moisture recycling patterns). Therefore offline land models are only of limited value to test the influence of changes in model hydrology, which is also influenced by changes in terrestrial vegetation.