Modeling the soil consumption of atmospheric methane at the global scale

Abstract

A simple scheme for the soil consumption of atmospheric methane, based on an exact solution of the one‐dimensional diffusion‐reaction equation in the near‐surface soil layer, is described. The model includes a parameterization of biological oxidation that is sensitive to soil temperature, moisture content, and land cultivation fraction. The scheme was incorporated in the Canadian Land Surface Scheme (CLASS), with forcing provided by a 21‐a, global land meteorological data set, and was calibrated using multiyear field measurements. Application of the scheme on the global scale gives an annual mean sink strength of 28 Tg CH 4 a −1 , with an estimated uncertainty range of 9–47 Tg CH 4 a −1 . A strong seasonality is present at Northern Hemisphere high latitudes, with enhanced uptake during the summer months. Under the specified surface forcings, the oxidation parameterization is more sensitive to soil moisture than to temperature. Compared to the previous work of Ridgwell et al. (1999), our empirically based water stress parameterization reduces uptake more rapidly with decreasing soil moisture, resulting in a decrease of ∼50% in the potential global sink strength. Analysis of the geographical distribution of methane consumption shows that subtropical and dry tropical ecosystems account for over half of the global uptake.