When understanding animal agriculture and the role it plays in climate change, it is essential to understand the various sources of greenhouse gas emissions (GHG) and their respective impacts. Methane (CH4), a potent greenhouse gas, plays a role in changing climate by trapping heat in the atmosphere. In animal agriculture, enteric methane (naturally produced by cattle in the digestive system) and methane in manure capture systems are the primary sources contributors to CH4 in the atmosphere.
Traditionally, scientists utilize the 100 year Global Warming Potential (GWP100) metric to compare the impact of various greenhouse gases. This is done by converting emissions into carbon dioxide equivalents to compare the warming impact of a greenhouse gas to carbon dioxide’s warming impact over 100 years; however, this method is most accurate for long-lived gases, leaving data dedicated towards short-lived gases skewed. CH4 is one of the GHG’s with a relatively short atmospheric lifespan of just 12 years, making the rate of change in emissions crucial for assessing its climate impact.
To ensure CH4 emissions can be better linked to their warming impacts given the short-lived nature of the gas, the new method GWP* was developed by climate and atmospheric science researchers to compare emission rates to data surrounding emissions collected 20 years ago (Allen, et al. 2018). This method allows for more accurate linking of global temperature changes that occur in response to CH4 emissions. It is valuable to address the short-lived nature of CH4 to reduce its emissions from all sources.
Research has found that if done properly, CH4 mitigation practices could lower global temperatures by 0.25°C by 2050 and 0.5°C by the end of the century. If this is done in relation to the livestock industry, global temperatures could potentially be reduced by 0.09°C (Ocko et al., 2021).
Over the past 30 years, methane emissions in the animal agriculture industry have been steadily rising in the United States. Dairy and swine operations are key contributors to increasing methane emissions as the manure produced in larger confined animal operations undergoes anaerobic fermentation. This fermentation typically occurs in retention ponds and lagoons, especially on larger farms that tend to manage manure in wet, anaerobic conditions. This shift to liquid management has been shown to correspond with heightened levels of CH4 production. In relation, the enteric fermentation process found in ruminant animals in beef operations has also contributed to the rising CH4 levels found in the atmosphere.

When looking at CO2 equivalents calculated using the GWP100 and GWP* methods, data has revealed that manure methane emissions have contributed more to warming over the past decade than enteric emissions. This is primarily due to the rapid increase in large operations which contribute to a greater amount of manure, compared to the relatively stable levels of enteric emissions.
Methane emissions, whether from enteric sources or manure, have a collective impact on our environment. To tackle this issue effectively, we must recognize that methane is a short-lived gas, and is the same from all sources, but its consequences and our ability to manage it depend on a range of factors. It is important to consider the practices that take place and how they are driven by other systemic operations. So, while animal agriculture is still searching for ways to mitigate CH4 emissions, other industries that contribute significantly to greenhouse gases emissions in the atmosphere need to adapt in a comparable manner.
In conclusion, while the beef and dairy industries are contributors to methane emissions in the United States, it is crucial to recognize that mitigation strategies are being developed to better understand CH4 produced by animals and its behavior in the atmosphere. Shifting our focus to GWP* methods and prioritizing CH4 mitigation efforts can play a vital role in addressing climate change in the short term. As we strive to meet climate targets, understanding the impact of different greenhouse gases and adopting appropriate strategies is essential for a sustainable future.
References:
Allen, M.R., Shine, K.P., Fuglestvedt, J.S. et al (2018). A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation. npj Clim Atmos Sci 1, 16. https://doi.org/10.1038/s41612-018-0026-8
Beck MR, Thompson LR, Rowntree JE, Thompson TN, Koziel JA, Place SE and Stackhouse-Lawson KR (2023). “U.S. manure methane emissions represent a greater contributor to implied climate warming than enteric methane emissions using the global warming potential∗ methodology.” Front. Sustain. Food Syst. 7:1209541. doi: 10.3389/fsufs.2023.1209541
Ilissa B Ocko et al (2021). “Acting rapidly to deploy readily available methane mitigation measures by sector can immediately slow global warming.” Environ. Res. Lett. 16 054042. doi: 10.1088/1748-9326/abf9c8

Julia Giesenhagen
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