Enteric methane emissions: why we should care, where we currently stand, and mitigation strategies

Authors: Beck, Matthew; PROCTOR, JARRET - Texas A&M University; LONG, NATHAN - Texas A&M University; GOUVÊA, VINICIUS - Texas A&M Agrilife; THOMPSON, LOGAN - Kansas State University

Submitted to: Proceeding of Plains Nutrition Council Symposium
Publication Type: Proceedings
Publication Acceptance Date: 3/23/2023
Publication Date: 9/12/2023
Citation: Beck, M.R., Proctor, J.A., Long, N.S., Gouvêa, V.N., Thompson, L.R. 2023. Enteric methane emissions: why we should care, where we currently stand, and mitigation strategies. In: Proceedings of the Plains Nutrition Council Spring Conference, April 5-7, 2023, San Antonio, Texas. p. 38-49.

Interpretive Summary: Enteric methane emissions are the largest source of methane emissions in the U.S., with the beef industry being responsible for the majority of this methane source. The current method adopted as international convention, relates methane emissions to a carbon dioxide equivalent basis by multiplying the methane emissions by its global warming potential on a 100-year basis (the U.S. Environmental Protection Agency uses 25). This method is termed global warming potential-100 (GWP100). When employing the GWP100 method, enteric methane emissions from the beef industry account for 2.1% of the total U.S. greenhouse gas emissions. Further separating this emissions, the cow-calf sector accounts for 1.5%, the stocker sector for 0.3%, and the feedlot sector for 0.27% of the total U.S. greenhouse gas emissions. However, since GWP100 was adopted as convention in the early 1990s, its appropriateness for methane and other greenhouse gases with short atmospheric lifespans has been highly debated. Methane has an atmospheric lifespan of 12-years. This means that in years where emission rates are decreasing, there will be less absolute methane concentrations in the atmosphere. To account for the short-lifespan of gases like methane, a new metric termed GWP-star (GWP*) has been proposed. The GWP* method has been shown to more appropriately relate gases like methane to their actual contributions to climate warming when using climate models. When employing GWP* to the beef industry, the values obtained, which relate to implied contributions to climate warming, are 92% lower than those obtained by the GWP100 method. Further, if methane emission rates are reduced to a great enough degree, then the GWP* method yields negative values, indicating that those changing emission rates are carbon offsets. This may suggest that carbon credits could be sold, which may provide actual economic incentives to mitigate enteric methane. This proceedings paper was written for an invited presentation, where current and future research plans from the Livestock Nutrient Management Research Unit in collaboration with Texas A&M AgriLife Research and Kansas State University will be presented.

Technical Abstract: Enteric methane (CH4) emissions are now the largest source of CH4 emissions in the U.S. (27%) – surpassing natural gas systems for the lead source in the U.S. Environmental Protection Agency’s (EPA) latest report. Furthermore, the beef industry is the largest source of enteric CH4 emissions in the U.S. at around 71.5% of total U.S. enteric CH4 emissions. Total U.S. enteric CH4 accounts for 2.9% and the enteric CH4 from the beef industry accounts for 2.1% of U.S. total greenhouse gas emissions (GHG). When separating these emissions by production sector, the cow-calf sector is responsible for 73% of the beef industry’s total enteric CH4 emissions, with the remainder arising from the stocker (14.1%) and feedlot (12.9%) sectors. This means that 1.5%, 0.3%, and 0.27% of the U.S. GHG emissions are from the cow-calf, stocker, and feedlot sectors, respectively. These contributions to U.S. GHG emissions are derived by relating CH4 emissions to a carbon dioxide (CO2) equivalent basis (CO2-e) by multiplying the CH4 emissions by its global warming potential (EPA uses 25 for CH4 on a 100-year time horizon; GWP100). The GWP100 became convention following the Kyoto Protocol in 1997. Since then, the appropriateness for short-lived climate forcers (SLCF; e.g., CH4 has a 12-year atmospheric lifespan) has been greatly debated. Recently, an alternative method has been proposed that accounts for SLCF, which is termed GWP-star (GWP*). Employing the GWP* method to enteric CH4 emissions reduces the obtained value (i.e., implied climate warming) by 92% compared to the GWP100 method. When using the GWP* method, mitigating enteric CH4 to a great enough degree will provide estimates that suggest actual climate cooling effects. This provides the potential for enteric CH4 mitigation to provide carbon sinks, which may provide economic incentives to adopt mitigation strategies if a carbon credit market can be created. In this proceeding paper we go in-depth into these concepts described above, mitigation strategies our team have explored, future strategies worthy of investigation, the most promising mitigation strategies to date, and, lastly, potential GHG offsets if these strategies are adopted.