Greenhouse gas emissions from global production and use of nitrogen synthetic fertilisers in agriculture

The global agri-food system relies on synthetic nitrogen (N) fertilisation to increase crop yields, yet the use of synthetic N fertiliser is unsustainable. In this study we estimate global greenhouse (GHG) emissions due to synthetic N fertiliser manufacture, transportation, and field use in agricultural systems. By developing the largest field-level dataset available on N 2 O soil emissions we estimate national, regional and global N 2 O direct emission factors (EFs), while we retrieve from the literature the EFs for indirect N 2 O soil emissions, and for N fertiliser manufacturing and transportation. We find that the synthetic N fertiliser supply chain was responsible for estimated emissions of 1.25 GtCO 2 e in 2018, representing 21.5% of agriculture direct emissions and 2.4% of global GHG emissions. Synthetic N fertiliser production accounted for 35.2% of total synthetic N fertiliser-associated emissions, while field emissions accounted for 62.4% and transportation accounted for the remaining 2.4%.The top four emitters together, China, India, USA and EU28 accounted for 63% of the total. Historical trends reveal the great disparity in total and per capita N use and efficiency in regional food production. Reducing overall production and use of synthetic N fertilisers offers large mitigation potential and in many cases realisable potential to reduce emissions.