Methane budget of East Asia, 1990-2015: A bottom-up evaluation

The regional budget of methane (CH₄) emissions for East Asia, a crucial region in the global greenhouse gas budget, was quantified for 1990-2015 with a bottom-up method based on inventories and emission model simulations. Anthropogenic emissions associated with fossil fuel extraction, industrial activities, waste management, and agricultural activities were derived from the Emission Database for Global Atmospheric Research version 4.3.2 and compared with other inventories. Emissions from natural wetlands and CH₄ uptake by upland soil oxidation were estimated using the Vegetation Integrative SImulator for Trace gases (VISIT), a biogeochemical model that considers historical land use and climatic conditions. Emissions from biomass burning and termites were calculated using satellite and land-use data combined with empirical emission factors. The resulting average annual estimated CH₄ budget for 2000-2012 indicated that East Asia was a net source of 67.3 Tg CH₄ yr^-1, of which 88.8% was associated with anthropogenic emissions. The uncertainty (±standard deviation) of this estimate, ±14 Tg CH₄ yr^-1, stemmed from data and model inconsistencies. The increase of the net flux from 60.2 Tg CH₄ yr^-1 in 1990 to 78.0 Tg CH₄ yr^-1 in 2012 was due mainly to increased emissions by the fossil fuel extraction and livestock sectors. Our results showed that CH₄ was a crucial component of the regional greenhouse gas budget. A spatial analysis using 0.25° × 0.25° grid cells revealed emission hotspots in urban areas, agricultural areas, and wetlands. These hotspots were surrounded by weak sinks in upland areas. The estimated natural and anthropogenic emissions fell within the range of independent estimates, including top-down estimates from atmospheric inversion models. Such a regional accounting is an effective way to elucidate climatic forcings and to develop mitigation policies. Further studies, however, are required to reduce the uncertainties in the budget.