Emission characteristics of methane and nitrous oxide from livestock in Inner Mongolia during the past 21 years

To achieve regional greenhouse gas (GHG) emission reduction in Inner Mongolia, estimation of methane (CH₄) and nitrous oxide (N₂O) emissions from livestock is indispensable. The emission factors and calculation methods stated in The 2006 IPCC Guidelines for National Greenhouse Gas Inventories and The Guidelines for Provincial Greenhouse Gas Inventories (Trial) were used to estimate CH₄ and N₂O emissions from livestock in Inner Mongolia over 21 years, based on the livestock inventory from 2000 to 2020 in the China Veterinary Yearbook of Animal Husbandry. The results showed that, from 2000 to 2020, the average annual stock of livestock was 66,120,500 heads, the average annual emissions of intestinal CH₄, fecal CH₄, and fecal N₂O from livestock were 808.60 Gg, 55.06 Gg, and 13.63 Gg, respectively. The intestinal CH₄ emission peaked in 2015 at 920.95 Gg, while the fecal CH₄ and fecal N₂O emissions peaked in 2006 at 65.63 Gg and 15.45 Gg, respectively. The average total GHG emissions of livestock were 877.29 Gg from 2000 to 2020, of which the intestinal CH₄ emissions accounted for 92.5% of the total GHG emissions of livestock. The CH₄ emissions from the intestine occupied 92.17% of the total livestock GHG emissions, the fecal CH₄ emissions accounted for 6.28% of the total livestock GHG emissions, while the fecal N₂O emissions occupied 1.55% of the total livestock GHG emissions. Ruminant livestock intestinal CH₄ emissions accounted for 83.7%～91.1% of total livestock GHG emissions, with an overall increasing trend, including a faster increase in 2000－2004 and 2016－2017, a steadily increasing trend in 2005－2016, and a leveling off in 2017－2020. CH₄ and N₂O emissions from the domestic livestock manure in Inner Mongolia showed an overall trend of increasing and then decreasing, while livestock intestinal CH₄ emissions showed an overall trend of increasing and then leveling off during the 21 years. The total GHG emissions from livestock were mainly influenced by intestinal CH₄ emissions from ruminant livestock rather than by CH₄ and N₂O emissions from manure. We believe that this study provides data references and theoretical support for reducing greenhouse gas emissions from livestock in future carbon reduction explorations and efforts in Inner Mongolia.