Methane emission from mud volcanoes - Towards a global estimate

Natural emission of methane from geologic sources has been recently recognised as an important component of the atmospheric methane budget. While some authors have focused their attention only on submarine gas seepage and gas hydrates, recent studies have suggested that also mud volcanoes (MVs) on land and microseepage in hydrocarbon-prone areas are significant methane sources. A new global estimate of methane flux from MVs has recently been made on the basis of new experimental flux data (including diffuse microseepage around craters and vents), and a new data-set on MV sizes. The emission results conservatively to be between 6 and 9 Mt/y, that is, the same level as the ocean and hydrates sources. The global geological methane flux, including MVs, submarine seepage, microseepage in petroliferous basins and geothermal flux, would conservatively amount to 35-45 Mt/y, that is, comparable to other sources or sinks considered in the IPCC tables.