Model Analysis of the Factors Regulating Trends and Variability of Methane, Carbon Monoxide and OH

Methane (CH4) is the second most important anthropogenic greenhouse gas (GHG). Its 100-year global warming potential (GWP) is 25 times larger than that for carbon dioxide. Oxidation of CH4 by OH is the main loss process, thus affecting the oxidizing capacity of the atmosphere and contributing to the global ozone background. The 100-yr integrated GWP of CH4 is sensitive to changes in OH levels and feedbacks of CH4 emission itself. In this study we implement a computationally efficient CH4-CO-OH parameterization into the NASA GEOS5-AGCM to simulate CO, OH and CH4 over the last three decades. We use this efficient interactive parameterization to investigate the CH4, CO and OH trends and variability and will compare the results to a CH4-only (with fixed CO and OH fields) as well as to a full chemistry model setup, constrained with CH4 fluxes, to see how differences in simulated OH may impact methane. We will investigate the key chemical processes that may affect the global OH budgets and thus the CH4 lifetime and trends. In this context, we will investigate the global OH-recycling as well as the impact of important OH sources. The results will be validated with a suite of ground based and satellite measurements. The results are expected to improve our understanding of OH and CH4 global budget and trends.