Geological emissions of C-bearing gases: CO2 vs CH4 in the global atmospheric budget. Giuseppe Etiope Istituto Nazionale di Geofisica e Vulcanologia Roma

Título: Geological emissions of C-bearing gases: CO₂ vs CH₄ in the global atmospheric budget

Ponente: Giuseppe Etiope, Istituto Nazionale di Geofisica e Vulcanologia, Roma.

Resumen:

One of the fundamental questions in the terrestrial carbon budget is the impact on climate and environment of the natural geological sources of greenhouse gases, i.e. the lithosphere and mantle degassing, compared to the biological sources. Research carried out in the last 15 years provided the first estimates of global emissions into the atmosphere of endogenous CO₂ and CH₄, which are the main greenhouse and C-bearing gases produced in the Earth interior. The amount of carbon dioxide released into the atmosphere from volcanic and non-volcanic areas was conservatively estimated to be at least ~800 Tg/y. This value is two and three orders of magnitude lower than the global CO₂ amounts emitted from anthropogenic and natural biologic activity, respectively. Accordingly, global geological CO₂ emissions are not particularly relevant for the atmospheric CO₂ budget; but they can be important on local scale, especially in geothermal or tectonically active areas, where geogas may mix with biological gas (e.g., soil respiration) thus confounding ecosystem C budgets. Geological methane emissions are instead relevant for the global methane budget. Recent estimates of geo-methane emissions (from natural gas seepage in sedimentary basins and geothermal manifestations) are about 60 Tg/y, which is only 6 times lower than anthropogenic sources and about 10% of total methane sources. Geological sources of methane, although neglected in the past, represent the second largest natural emission of this gas to the troposphere, after wetlands. They are now considered as a new class of greenhouse-gas source for the European (EEA/EMEP) and US (EPA) emission inventories, and are endorsed in the latest (2013) IPCC assessment report.