Northward shift of historical methane emission hotspots from the livestock sector in China and assessment of potential mitigation options

China contributes approximately 10% of the total global methane (CH4) emissions from its livestock sector. However, existing inventories of CH4 emissions from the livestock sector involve significant uncertainty, and the reduction potentials and spatially varying efficiencies of different technical options (adding lipid to diets, acidification, composting, anaerobic digestion, and the combination of composting and anaerobic digestion) have not been systematically assessed at the provincial level. Here, we used a bottom-up approach to compile an up-to-date high-resolution CH4 emission inventory for the livestock sector in China using provincial condition specific emission factors by considering the gross energy intake and the ambient temperature at the provincial level. A 1-km x 1-km gridded map was produced for 2014, and the temporal trends of the CH4 emissions from 1978 to 2013 were re-visited. The effects of the technical mitigation options that could have been used on CH4 emissions were further evaluated in five different scenarios. Livestock sector CH4 emissions decreased by 1.2 Tg CH4 per year from the period of 1999-2006 to the period of 2007-2014, and this rate was approximately 17-28% lower than previous estimates. During the period of 1978-2014, spatial-temporal emission trends indicated a possible relationship between the Chinese government policies and emissions to some extent and a northward shift of emission hotspots induced by economic and policy incentives. Hotspots with high mitigation potential and efficiency (the achieved reduction under a specific mitigation scenario divided by the baseline emissions from the species affected by the respective technical option) were also identified. The combination of composting and anaerobic digestion is a recommended policy, which can simultaneously address slurry and solid manure and significantly mitigated of CH4 emissions. Overall, this study provides insights into the region-dependent implementation of technical options used to reduce CH4 emissions from the livestock sector in China.