Models of enteric methane emission and nitrogen excretion by sheep and cattle: Recommendations for the UK national greenhouse gas inventory

There is a global effort to reduce anthropogenic sources of greenhouse gas (GHG) emissions to the atmosphere. In 2019, the overall contribution of agricultural GHG emissions to the UK total was 11%. Agriculture was responsible for approximately 50% of total UK methane production and 70% of total nitrous oxide production. Nitrogen excretion from livestock is a significant environmental concern, leading to nitrate leaching, ammonia volatilisation, and nitrous oxide emissions. To meet the requirements of the Climate Change Act and track changes in emissions attributable to agricultural activity, the UK needs to adopt more sophisticated methods of measuring, reporting and verifying GHG emissions for inventory purposes. Development of country- and region-specific emission factors allows the use of Tier 2/3 reporting methods, increasing the precision of GHG inventory calculations and helping to reduce the uncertainty of current default emission factors. Currently, the UK inventory does not use regression equations to calculate nitrogen excretion from ruminants.