Global nitrous oxide emissions from livestock manure during 1890-2020: An IPCC tier 2 inventory.

Nitrous oxide (NO) emissions from livestock manure contribute significantly to the growth of atmospheric NO, a powerful greenhouse gas and dominant ozone-depleting substance. Here, we estimate global NO emissions from livestock manure during 1890-2020 using the tier 2 approach of the 2019 Refinement to the 2006 IPCC Guidelines. Global NO emissions from livestock manure increased by ~350% from 451 [368-556] Gg N year in 1890 to 2042 [1677-2514] Gg N year in 2020. These emissions contributed ~30% to the global anthropogenic NO emissions in the decade 2010-2019. Cattle contributed the most (60%) to the increase, followed by poultry (19%), pigs (15%), and sheep and goats (6%). Regionally, South Asia, Africa, and Latin America dominated the growth in global emissions since the 1990s. Nationally, the largest emissions were found in India (329 Gg N year), followed by China (267 Gg N year), the United States (163 Gg N year), Brazil (129 Gg N year) and Pakistan (102 Gg N year) in the 2010s. We found a substantial impact of livestock productivity, specifically animal body weight and milk yield, on the emission trends. Furthermore, a large spread existed among different methodologies in estimates of global NO emission from livestock manure, with our results 20%-25% lower than those based on the 2006 IPCC Guidelines. This study highlights the need for robust time-variant model parameterization and continuous improvement of emissions factors to enhance the precision of emission inventories. Additionally, urgent mitigation is required, as all available inventories indicate a rapid increase in global NO emissions from livestock manure in recent decades.