1. Livestock are raised in 208 countries around the world for human consumption. This sector provides meat-based protein, milk and supply raw material for other industrial products. It is estimated that globally between 600 million (Thornton et al., 2002; Thornton et al., 2009) and 1.3 billion (The World Bank, 2020; van de Steeg et al., 2009) people are dependent on livestock for their livelihood. Livestock contributes only 1.5 percent to the global economy.
2. Livestock production occupies up to 75 percent of global agricultural land (Foley et al., 2011) and up to 45 percent of the land surface of the planet (Ritchie and Roser, 2013). Livestock farming consumes 30 percent of agricultural freshwater (Mekonnen and Hoekstra, 2012; Ran et al., 2017), 58 percent of the economically appropriated plant biomass and farmed animals have come to dominate the biosphere with 60 percent of all mammals on the planet being domesticated.
3. From a nutritional and economic perspective, livestock products play a surprisingly small role in our diets and economy. Livestock products provide only 17 percent of average global calorie intake and 30 percent of average global protein intake (Mottet et al., 2017), and livestock now consume more human edible protein than they produce (Steinfeld et al., 2006a).
4. Total number of livestock estimated to be raised in 2018 are 28.6 billion. It includes 1.4 billion cattle, 206 million buffaloes, 1.2 billion sheep, a little over 1 billion goats, 978 million pigs, and 24 billion poultry.
5. Total greenhouse gas (GHG) emissions from the production of six types of livestock (cattle, buffaloes, sheep, goats, pigs and poultry) are estimated to be in the range of 10.7 – 16.9 gigatonnes (Gt) of CO2 equivalents (CO2e) assuming a global warming potential (GWP) for methane of 34 and 86 respectively.
6. This includes enteric fermentation (CH4) between 3.4 – 8.8 Gt CO2e, manure management (CH4) between 343 – 890 Mt CO2e, manure management (N2O) at 119 Mt CO2e, manure grazing (N2O) at 870 Mt CO2e, animal feed (CO2) at 143 Mt CO2e, fertiliser (N2O) at 253 Mt CO2e, fertiliser (CO2) at 291 Mt CO2e, crop residue (N2O) at 77 Mt CO2e, foregone soil carbon sequestration (CO2) at 1.4 Gt CO2e, LUC for pasture expansion (CO2) at 1.8 Gt CO2e, LUC for cropland expansion (CO2) at 141 Mt CO2e, degraded grazing land (CO2) at 244 Mt CO2e, animal respiration (CO2) at 1.86 Gt.
7. Our results show that, total livestock related emissions are in the range of 19.2 – 30.3 percent of the total anthropogenic global emissions from all economic sectors (55.6 Gt in 2018).
8. Our results include estimates for foregone soil carbon sequestration from the land that is used to grow animal feed, land use change (LUC) due to pasture and cropland expansion, degraded grazing land and includes animal respiration, However, we did not include transport, energy and processing related emissions due to lack of publicly available granular data at local to global scale. We assume that our estimates would significantly improve if we include energy, transport and processing related emissions.
9. We also estimated carbon sequestration potential from afforestation of cropland that is currently used to grow animal feed. It ranged from 38 Gt CO2 assuming low biomass estimates to 225 Gt CO2 assuming the highest estimates of biomass accumulation.
10. Further research can help to refine these estimates by using granular data about each stage of livestock value chain
11. While we estimate total GHG emissions attributable to global livestock sector, there are several other environmental, social and health impacts that need further attention by future research, practice and policy.