The path to climate neutrality for California dairies

Abstract In recent years, dairy farms have come under scrutiny with pressure to curb their environmental impacts. Since 1950, the California dairy industry has made strides in reducing greenhouse gas (GHG) emissions per kilogram of milk produced. However, total GHG emissions have remained near constant over the past 15 years. Most on-farm dairy production emissions are in the form of methane (CH 4 ) emissions produced via enteric fermentation, where CH 4 is produced as a byproduct of feed digestion, and manure management. Methane is a powerful but short-lived GHG. Historically, GWP100 has been utilized to describe a GHG emission’s warming impact over a 100-year time span. To better characterize the impact of CH 4 on atmospheric warming, a relatively new accounting system named global warming potential star (GWP*) has been proposed to consider the production and degradation of this short-living GHG. Characterizing greenhouse gases by how they warm our atmosphere instead of the number of emissions produced is a better metric for the true impact of the emissions on atmospheric warming. The goal of this research is to use GWP* to analyze the impact of potential GHG emissions scenarios from California dairy and the impact of those scenarios on atmospheric warming. Utilizing GWP* can help discern when an industry or sector has achieved climate neutrality or no annual warming contributions from industry. This paper also investigates the necessary amount of CH 4 reduction needed and the time point at which the dairy sector can achieve climate neutrality. The scenarios are business-as-usual (BAU), 40% reduction in manure CH 4 emissions (40 MAN) by applying anaerobic digestion and its alternative technologies, and 40 MAN along with a 10.6% reduction in enteric fermentation CH 4 emissions via 1/3 of California’s cows fed the feed additive 3-nitrooxypropanol (40 MAN+EF). Under GWP100 in 2030, carbon dioxide equivalents (CO 2 e) for the 40 MAN and the 40 MAN + EF scenarios were reduced by 18 and 22%, respectively compared to the BAU. For all three scenarios, the relative warming impact of the industry decreased over time due to constant herd sizes and total annual emissions. By aggressively decreasing CH 4 emissions under the 40 MAN and 40 MAN+EF scenarios, there is the possibility for the California dairy industry to reach climate neutrality by the year 2027. These scenarios have more CH 4 naturally removed in the atmosphere than is emitted, thus lowering atmospheric contributions from the industry. These scenarios could be adopted by dairies in other states and countries to help the global dairy industry to achieve climate goals through persistent CH 4 mitigation.