Atmospheric Methane Attributes from a Decade-Long, Global, High-Resolution GEOS Simulation: Trends in Inter- and Intra-Annual Variability

Methane (CH₄) is a potent greenhouse gas and precursor for tropospheric ozone formation. Quantifying CH₄ emissions is critical for projecting future climate and air quality changes and essential for developing strategies to mitigate emissions. CH₄ is emitted into the atmosphere from a variety of biogenic, thermogenic, and pyrogenic sources and is removed from the atmosphere predominately by reaction with hydroxyl radicals. In this study, we will present results from a high-resolution simulation of atmospheric methane using NASA’s GEOS model – a highly complex yet flexible modeling system that simulates the emission and transport of a number of trace gases, including CO₂, CO and now CH₄. These simulations have been run from 2007-2018 and provide an in-depth look at the processes, source types, and fluxes responsible for natural and anthropogenic methane emissions and subsequent atmospheric trends. The robustness of the simulations is being evaluated by comparing against NOAA’s in-situ surface measurement network, JAXA and ESA greenhouse gas satellites, GOSAT and TROPOMI, and new multi-agency airborne observations over the Arctic, Amazonian and African wetlands. These comparisons demonstrate that adequately representing small-scale processes that affect measured concentrations, such as planetary boundary layer mixing and diurnal growth, convection, and complex effects of local topography are necessary to capture the spatiotemporal heterogeneity of methane as observed by atmospheric data. Finally, we will highlight specific regions, time periods and underlying processes (for e.g., Arctic-Boreal wetlands, Southwest US hotspots) that seem to dominate the inter- and intra-annual variability of atmospheric CH₄.