Assessing the climate impact of dairy farming: Incorporation of climate modelling and food-feed competition.

Dairy production is a major source of global greenhouse gas (GHG) emissions, especially non‑carbon dioxide (CO2) emissions. Climate impact assessments of dairy farming need to account for differences between short- and long-lived GHGs, and for the net contribution of dairy production to human food supply. Based on survey data from 48 confined dairy farms in Henan, China, we found that in the production of one kg of human-edible protein (HEP) in milk and meat, an average of 18.1 kg CO2, 1.16 kg methane (CH4) and 0.03 kg nitrous oxide (N2O) were emitted. Results from a reduced-complexity climate model showed that, under constant emission rates, the near-term warming caused by Henan dairy production was largely dominated by CH4 emissions (from 84 % in Year 1 to 55 % in Year 100), while long-term warming was mostly dominated by CO2 emissions (from 11 % in Year 1 to 56 % in Year 500). Reduction of CH4 emissions on these dairy farms is essential in the coming years given the urgency to tackle climate change, but full decarbonization of CO2 emissions along the dairy chain -including those from energy used during upstream processes such as feed production and processing -is vital to limit global warming in the long run. In addition, 1.5 kg of HEP in cattle feed was used to produce 1 kg of HEP in milk and meat. Using these 1.5 kg of HEP for human consumption directly would therefore save 0.5 kg of HEP, and prevent the emission of an additional 12.6 kg CO2, 1.15 kg CH4 and 0.02 kg N2O. Results indicate the high cost of the dairy systems in terms of both climate change and food security, and could help to guide climate actions in the Chinese dairy sector while considering food security objectives.