The role of geological sources in the atmospheric methane budget:aa rreap eapprais praisaall

摘要

Recent studies have demonstrated that geological emissions of methane (GEM),although not considered in the inventories of the Intergovernmental Panel on ClimateChange (IPCC),are an important greenhouse gas source.Nowadays it is recognised thatsignificant amounts of methane,produced within the Earth crust,are released naturally into theatmosphere through faults and fractured rocks.Major GEM are related to hydrocarbonproduction in sedimentary basins (biogenic and thermogenic methane),through continuousexhalation and eruptions from more than 1200 onshore and offshore mud volcanoes,throughdiffuse soil microseepage,and shallow marine seeps.The global estimates of GEM range from40 to 60 Tg y-1.This contributes to balance the isotopic budget of atmospheric methane,beingmore than enough to account for the suspected missing source of fossil methane.GEM representthe second most important natural methane source; it is more than 8% of the total emission,and20% and 27% of the total natural sources considered by top-down (IPPC-2001) and bottom-up(IPCC-1996) models,respectively.GEM,strictly controlled by geophysical and endogenous processes,are not a minor source,asgenerally assumed in the past,but have a primary role in the atmospheric GHG budget,and cannotbe disregarded anymore in the next IPCC assessment reports.