Large-Scale Controls of Methanogenesis Inferred from Methane and Gravity Spaceborne Data

Wetlands are the largest individual source of methane (CH_4), but the magnitude and distribution of this source are poorly understood on continental scales. We isolated the wetland and rice paddy contributions to spaceborne CH_4 measurements over 2003–2005 using satellite observations of gravity anomalies, a proxy for water-table depth Γ, and surface temperature analyses T_S. We find that tropical and higher-latitude CH_4 variations are largely described by Γ and T_S variations, respectively. Our work suggests that tropical wetlands contribute 52 to 58% of global emissions, with the remainder coming from the extra-tropics, 2% of which is from Arctic latitudes. We estimate a 7% rise in wetland CH_4 emissions over 2003–2007, due to warming of mid-latitude and Arctic wetland regions, which we find is consistent with recent changes in atmospheric CH_4