Atmospheric methane is a potent greenhouse gas, accounting for 18% of total greenhouse gas radiative forcing.  Atmospheric methane is 22 times more effective on a per unit mass basis than carbon dioxide in absorbing long-wave radiation on a 100-year time horizon, and it plays an important role in atmospheric ozone chemistry.  Wetlands are a large source of atmospheric methane.  However, the quantification of methane emissions from wetlands still has large uncertainties.  In this presentation, I first identify some causes for the uncertainty; illustrate the challenges to reduce the uncertainty; and then highlight opportunities for research from the global perspective.  I will present how we construct the process-based biogeochemistry models in modeling global soil methane production, oxidation, and transport.   A specific example of our modeling methane cycle activities is on our effort of quantifying net methane emissions from the Arctic wetlands and lakes. In the study, we use a process-based biogeochemistry model called TEM (the Terrestrial Ecosystem Model) to quantify these emissions with three different datasets for wetland and lake distributions. The effects of spring thaw and winter freezing on methane emissions are also incorporated into the TEM simulations.

Results/Conclusions We find that the current land and lake methane emissions range from 65 to 150 Tg per year in northern high latitudes (North 45^oN).  Seasonal changes of emissions of land and lakes due to spring thaw and winter freezing, together with fire emissions, play a significant role in determining the seasonal atmospheric methane concentration profiles simulated with a 3-D atmospheric chemistry transport model (GEOS-Chem).  Further, comparison between multiple GEOS-Chem simulations driven with different seasonal dynamics of land, lake, and wildfire emissions and satellite retrievals of methane concentrations, suggests that accurately simulating the timing of these emissions as affected by spring thaw and winter freezing and wildfires, is critical for GEOS-Chem to capture the atmospheric concentration profiles over the region.