Methane is the second most dominant type of greenhouse gas (GHG) after carbon dioxide, accounting for 17.3 percent of the GHGs emitted globally. Methane breaks down much faster than carbon dioxide but is up to 80 times more powerful at warming the planet over the short term. Reducing methane emissions is a highly impactful climate mitigation strategy with the power to deliver immediate benefits over the short term—when emissions reduction matters most. In the context of a rapidly closing window of time to avert the most catastrophic impacts of global climate change, methane reduction is essential for limiting global temperature rise.
Agriculture is the single largest source of methane in the world, and the bulk of agricultural methane emissions come from livestock farming, particularly cattle. One cow can produce 250 to 500 liters of methane a day through digestion, a process in ruminant cattle known as enteric fermentation.[1] Enteric fermentation by cows and other ruminants, including sheep and goats, accounts for around one third of global methane emissions.[2] This large share of methane emissions makes animal agriculture our most important tool for methane mitigation.
Under current climate policies and plans, and without changes in consumer dietary preferences, methane emissions from cattle are expected to continue increasing through 2030 due to the rising demand for meat from a growing and increasingly wealthy global population.[3] Research now shows that without changes to production and consumption, methane from the world’s 1.5 billion beef and dairy cattle will be the main driver of a further 0.7 degrees Celsius of average global temperature rise by the end of this century, beyond the 1 degree of average climate warming that has already occurred.[4]
In response to the need to reduce the climate impact of cattle farming, the largest industrial meat producers have proposed adjusting farmed animals’ diets with feed additives to reduce methane production without scaling back animal farming. Building on research showing the potential for certain varieties of seaweed to reduce methane produced during enteric fermentation, meat companies and food retailers, including Fonterra and UK supermarket chain Morrisons, are working with researchers and seaweed start-ups to begin large-scale feedlot trials. Meat producers and policymakers find the idea of feed additives attractive because it avoids the politically unpopular avenues of proposing that consumers reduce meat consumption and that farmers raise fewer animals.
Small-scale trials of seaweed’s methane-cutting potential have shown some early promise. However, closely examining the feasibility of achieving large-scale methane reduction through feed additives and the challenges inherent in delivering seaweed additives to more than a billion cows without exacerbating the negative animal welfare and environmental impacts of livestock farming reveals that seaweed feed additives are not the easy carbon solution portrayed by meat producers.
Evidence for Methane Reduction via Seaweed Feed Additives
Seaweeds can reduce the amount of methane cows produce by altering the microbial composition in their rumen (the largest of their four stomachs) or inhibiting an enzyme in their digestive system that contributes to methane production. Some types of seaweed are more effective than others, based on variable content of bromoform, the organic chemical compound responsible for suppressing methane production.
For instance, a 2019 study by the University of California, Davis, found that feed containing 1% of Asparagopsis armata reduced methane production by 12 Holstein dairy cows by 67%.[5] Similarly, a more recent study by the same researchers showed that using Asparagopsis taxiformis as a feed additive reduced enteric methane production by 82% in beef cattle, using a sample of 21 Angus-Hereford steers.[6] These two small-scale studies have garnered significant media attention and have spurred wide interest in continued study of the methane reduction potential of seaweeds.
Similarly, a study from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), supported by Meat and Livestock Australia, found that 0.10% and 0.20% of red seaweed added to the feed of 20 beef cattle on a high grain diet decreased methane emissions up to 40% and 98%, respectively.[7]
Seaweed feed additives can only be effectively and consistently administered on feedlots, but the majority of methane is produced before cows arrive on a feedlot.
Researchers at the University of Queensland also examined the potential for seaweed farming to reduce terrestrial agricultural expansion and the greenhouse gas emissions caused by land use change.[8] They found that supplementing 0.05% of feed for ruminant livestock with red seaweed farmed in the ocean could also spare 50 million hectares of agricultural land by 2050 by reducing the need for terrestrial feed crops, while they[9] and others[10] have also highlighted caveats of feasibility and social-ecological impact.
Seaweed is not the only feed additive being tested on beef and dairy cattle. An organic compound that inhibits cows’ methane production called 3-NOP[11] received approval to be marketed in the European Union in 2022. Essential oils[12] and legumes[13] are also being trialed.
Is methane reduction via seaweed feed additives feasible?
Although these early research results seem promising, they have very important limitations. Writing in Wired in 2021, Jan Dutkiewicz, a policy fellow at Harvard Law School, and Matthew Hayek, Assistant Professor in Environmental Studies at New York University, pointed out that seaweed trials thus far have been very small-scale, and it isn’t clear how additives could be scaled up to work for a global cattle population of 1.5 billion cows–100 million of which reside in the US alone, most of them beef cattle.
Dutkiewicz and Hayek reveal a basic timing mismatch hampering the proposed administration of feed additives. Industrially raised beef cattle typically spend the first 9 to 15 months of their lives grazing on open pasture, during which time they emit most of their enteric methane. After this time, they are sent to feedlots where they can gain weight eating grain-based feed.[14] Most cattle—even many cattle whose meat is sold as “pasture-raised”—are ‘finished’ on grain in this way during the last few months of their lives.
Dutkiewicz and Hayek note that feedlots are the only practical place where cattle could be fed seaweed additives since it is in this setting where their intake is controlled, and the seaweed could be easily diluted in feed grain. Cows are unlikely to eat red seaweed otherwise or while grazing because they don’t like its taste. Thus, seaweed feed additives can only be effectively and consistently administered on feedlots, while the majority of methane is produced before cows arrive on a feedlot. Even if cows could be induced to eat seaweed while grazing, the less controlled environment of grazing land would also introduce other variables that could impact seaweed’s efficacy in unknown ways.
Converting the world’s 1.5 billion cattle from pasture to feedlots in order to administer seaweed effectively for methane reduction would create secondary environmental and health impacts that would likely undermine any potential emissions savings.
Deep ethical and environmental complications soon become evident. While cattle naturally graze on grass, and grazing allows cattle to live healthier lives and express natural behaviors that lead to higher welfare, methane production is lower on feedlots because cattle digest grain more quickly, reducing the time for methane to form during enteric fermentation. Cows raised entirely on feedlots also reach ideal slaughter weight at a younger age, further reducing methane production by shortening the lifetime of the animals. On this basis, the meat industry and others using a productive mindset that prioritizes maximizing profits from animal farming have even proposed intensifying cattle farming worldwide as a way to reduce overall GHG emissions from beef production. However, such a strategy ignores both the incalculable impact such a step would have on cattle and the potential environmental and human health impacts of such a scenario.
Methane Reduction via Seaweed Feed Additives Would be Undesirable
In truth, converting 1.5 billion cattle worldwide from pasture to feedlots in order to administer seaweed effectively for methane reduction would create secondary environmental and health impacts that would likely undermine any potential emissions savings.
Around 40 percent of arable land globally is already used to grow feed for livestock.[15] In the European Union, the proportion of cropland used for feed production reaches 63 percent.[16] Growing feed for livestock produces significant nitrous oxide emissions, mainly due to the use of artificial fertilizers. While enteric fermentation from ruminant livestock (mostly cattle) produces 1.6 to 2.7 billion tons of GHGs—primarily methane—each year, producing livestock feed generates a further 1.3 to 2 billion tons of nitrous oxide, another potent greenhouse gas. The global warming potential of nitrous oxide is nearly 300 times higher than that of carbon dioxide, and there is already 20% more of it in the atmosphere compared to pre-industrial times, mostly due to farming.[17]
Liberal use of pesticides to produce livestock feed crops is also associated with serious environmental and human health consequences. The US used 235 million pounds of pesticides on soy and corn crops in 2018 alone, polluting air and waterways. People living near industrial animal farms can suffer from noxious odors and air pollution that cause respiratory problems, eye irritation, and headaches. Particulate matter in the air can also contribute to asthma, bronchitis, and cardiac arrest.[18]
Cattle also generate a significant amount of manure. In intensive farming systems, some manure is spread on land as fertilizer, becoming an additional source of nitrous oxide emissions as well as a significant source of nitrogen pollution. Nitrogen pollution has reached a crisis point in several countries, most notably the Netherlands, where the government is now trying to tackle nitrogen pollution in ecologically sensitive areas through a 30 percent reduction in livestock numbers by buying out livestock farms and transitioning others to raise animals less intensively.
Manure that is not spread on land as fertilizer requires storage, most commonly in manure lagoons. Nutrient runoff and pollution generated by manure lagoons contaminate water, requiring large amounts of clean water to dilute residues to safe levels. These lagoons also emit additional methane and nitrous oxide as the manure decomposes.
Growing seaweed at large scales can also have potentially negative ecological impacts, even if successful. Growing enough seaweed to supplement 0.5% of ruminant diets could require less than a million hectares of ocean area, making seaweed feed additives more space-efficient than hypothetical production of seaweed for large-scale human food or biofuels.[19] However, researchers note that some species of seaweed could become invasive, writing that large-scale farming in new areas means “the potential for escape and ecological degradation.”
Additionally, there are diminishing returns to the sustainability benefits of seaweed as a feed additive because the optimal amount of seaweed in cows’ diets is less than 2%. After that maximum is reached, growing or administering more will not further improve emissions savings or the amount of land spared. Another caveat is that the estimated gains in methane reduction rests on certain assumptions that, in reality, may or may not be met. One assumption is that the seaweed improves cows’ feed conversion efficiency, while a second assumption holds that “all ruminant livestock will respond uniformly to supplementation,” although variation in effectiveness is a far more likely result, equating to lower emissions savings.
Joseph McFadden, Associate Professor of dairy cattle biology at Cornell University, has warned against expecting too much from feed additives. “Studies of feed additive supplementation in cattle that span months—even years—are needed to confirm the persistency of methane reduction and animal safety,” he wrote in Time Magazine. “Diet, environment, management, animal genetics, and their microbiome are expected to uniquely influence the degree of methane reduction for feed additives. However, we have a limited understanding of how these factors impact the short and long-term efficacy of feed additives to inhibit methane production by cows.”
Using seaweed as a methane-reducing feed additive would increase the animal agriculture industry’s strain on natural resources and cause untold additional harm to farmed animals.
Despite these limitations, media coverage of and government support for seaweed feed additives is often optimistic, potentially allowing meat companies to use it to greenwash their business model by downplaying its climate impact and positioning themselves as part of the solution. Meat producers commonly promote meat as good for human health and the environment while undermining the idea of meat reduction as a reasonable way to cut GHG emissions. Similar tactics are also used by one of the most well-known scientists representing animal farming in a favorable light, Frank Mitloehner, and the CLEAR Center at UC Davis, which he runs. The CLEAR Center purports to be a research center but has been described by critics as more of a promotional communications project which gears its meat-friendly messaging toward a consumer public trying to understand the connection between food choices and climate change.
For consumers weighing information about consumption impacts, favorable messaging and uptake of seaweed feed additives could also have an insidious negative effect if additives become publicly regarded as a viable climate solution, reducing negative consumer perceptions of industrial meat production and meat consumption. A potential increase in global consumption of industrial meat and dairy products due to rising consumer demand would greatly exacerbate the many negative impacts of meat consumption on water use, the wider environment, and human health.
Outlook for the Seaweed Industry
Though seaweed as a feed additive is still in the trial phase, the seaweed industry is already growing significantly. Production more than tripled from 2000 to 2018, reaching 32.4 million tons. By 2019, global seaweed trade was worth $5.6 billion. The industry is expected to continue growing to meet the demand for more sustainable sources of food.
Currently, animal feed is not the main market for seaweed products. Rather, human food was the source of greatest demand for seaweed in 2021. The largest seaweed-producing countries are China, Indonesia, and the Philippines, which cultivate the greatest number of seaweed varieties and produce seaweed mainly as human food. Other main uses for seaweed are the extraction of carrageenan and agar as food additives.[20] In the U.S., seaweed farming is the fastest-growing aquaculture sector, cultivating mainly brown seaweeds like sugar kelp—a variety not particularly effective as a methane inhibitor in cattle feed.
While there are clear limitations to and likely negative impacts associated with cultivating seaweed as a cattle feed additive, seaweed farming can be beneficial in certain contexts and at smaller scales. Coastal communities in the Global South see ways to benefit economically from the growing market for seaweed.[21] Seaweed production may also contribute to carbon sequestration goals; producing 500 million tons of seaweed would absorb 135 million tons of atmospheric carbon.[22]
Conclusion
Despite the buzz around seaweed’s methane-reduction potential, there are serious feasibility limitations and persistent knowledge gaps that make seaweed’s methane reductions hypothetical at best. Additionally, seaweed feed additives carry a high likelihood of unintended negative consequences for animals and for the planet, indicating that a widespread shift to plant-based food consumption remains the best and most feasible option for cutting the climate and environmental impacts of agriculture.
In the name of uncertain methane reduction benefits, using seaweed as a methane-reducing feed additive would increase the animal agriculture industry’s strain on natural resources and cause untold additional harm to farmed animals. By comparison, reducing the number of ruminant animals farmed by the industrial food system is both the more environmentally sound and the more ethical option.
Meanwhile, a growing number of studies show that most plant-based foods generate lower production emissions while using less water and land than the farming of animal products. With a shift to plant-based food systems, the amount of land needed to produce food would shrink by up to 75 percent, freeing up land to be rewilded and sequester carbon in the process.
As the most recent report from the Intergovernmental Panel on Climate Change has made clear, drastic action is urgently needed to limit global temperature rise as much as possible over the near term.[23] With or without seaweed feed additives, production and consumption change de-emphasizing cattle farming remains the ethical choice and the single most powerful tool for quickly making the necessary GHG emissions cuts to ensure the global food system’s future.
[1] K. A. Johnson and D. E. Johnson, “Methane Emissions from Cattle,” Journal of Animal Science 73, no. 8 (August 1995): 2483–92, https://doi.org/10.2527/1995.7382483x.
[2] United Nations Environment Programme and Climate & Clean Air Coalition, “Global Methane Assessment: Benefits and Costs of Mitigating Methane Emissions” (Nairobi, Kenya: United Nations Environment Programme, May 6, 2021), https://www.unep.org/resources/report/global-methane-assessment-benefits-and-costs-mitigating-methane-emissions.
[3] United Nations Environment Programme and Climate & Clean Air Coalition, “Global Methane Assessment: Benefits and Costs of Mitigating Methane Emissions” (Nairobi, Kenya: United Nations Environment Programme, May 6, 2021), https://www.unep.org/resources/report/global-methane-assessment-benefits-and-costs-mitigating-methane-emissions.
[4] Catherine C. Ivanovich et al., “Future Warming from Global Food Consumption,” Nature Climate Change 13, no. 3 (March 2023): 297–302, https://doi.org/10.1038/s41558-023-01605-8.
[5] Breanna M. Roque et al., “Inclusion of Asparagopsis Armata in Lactating Dairy Cows’ Diet Reduces Enteric Methane Emission by over 50 Percent,” Journal of Cleaner Production 234 (October 10, 2019): 132–38, https://doi.org/10.1016/j.jclepro.2019.06.193.
[6] Breanna M. Roque et al., “Red Seaweed (Asparagopsis Taxiformis) Supplementation Reduces Enteric Methane by over 80 Percent in Beef Steers,” Plos One 16, no. 3 (2021): e0247820, https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0247820.
[7] Robert D. Kinley et al., “Mitigating the Carbon Footprint and Improving Productivity of Ruminant Livestock Agriculture Using a Red Seaweed,” Journal of Cleaner Production 259 (June 20, 2020): 120836, https://doi.org/10.1016/j.jclepro.2020.120836.
[8] Scott Spillias et al., “Reducing Global Land-Use Pressures with Seaweed Farming,” Nature Sustainability 6, no. 4 (April 2023): 380–90, https://doi.org/10.1038/s41893-022-01043-y.
[9] Scott Spillias et al., “The Empirical Evidence for the Social-Ecological Impacts of Seaweed Farming,” PLOS Sustainability and Transformation 2, no. 2 (2023): e0000042, https://journals.plos.org/sustainabilitytransformation/article?id=10.1371/journal.pstr.0000042.
[10] Mónica Costa et al., “Current Knowledge and Future Perspectives of the Use of Seaweeds for Livestock Production and Meat Quality: A Systematic Review,” Journal of Animal Physiology and Animal Nutrition 105, no. 6 (2021): 1075–1102, https://doi.org/10.1111/jpn.13509.
[11] A. Melgar et al., “Dose-Response Effect of 3-Nitrooxypropanol on Enteric Methane Emissions in Dairy Cows,” Journal of Dairy Science 103, no. 7 (July 1, 2020): 6145–56, https://doi.org/10.3168/jds.2019-17840.
[12] Kenton J. Hart et al., “An Essential Oil Blend Decreases Methane Emissions and Increases Milk Yield in Dairy Cows,” Open Journal of Animal Sciences 9, no. 3 (May 8, 2019): 259–67, https://doi.org/10.4236/ojas.2019.93022.
[13] S L Woodward, G C Waghorn, and P G Laboyrie, “Condensed Tannins in Birdsfoot Trefoil (Lotus Corniculatus) Reduce Methane Emissions from Dairy Cows,” Proceedings of the New Zealand Society of Animal Production 64 (2004), https://www.nzsap.org/system/files/proceedings/ab04039.pdf.
[14] Renee Cheung and Paul McMahon, “Back to Grass: The Market Potential for U.S. Grassfed Beef,” April 2017, https://www.stonebarnscenter.org/wp-content/uploads/2017/10/Grassfed_Full_v2.pdf.
[15] Anne Mottet et al., “Livestock: On Our Plates or Eating at Our Table? A New Analysis of the Feed/Food Debate,” Global Food Security, Food Security Governance in Latin America, 14 (September 1, 2017): 1–8, https://doi.org/10.1016/j.gfs.2017.01.001.
[16] “Feeding the Problem: The Dangerous Intensification of Animal Farming in Europe” (Greenpeace, February 2019), https://www.greenpeace.org/static/planet4-eu-unit-stateless/2019/02/83254ee1-190212-feeding-the-problem-dangerous-intensification-of-animal-farming-in-europe.pdf.
[17] Hanqin Tian et al., “A Comprehensive Quantification of Global Nitrous Oxide Sources and Sinks,” Nature 586, no. 7828 (October 2020): 248–56, https://doi.org/10.1038/s41586-020-2780-0.
[18] Carrie Hribar and Mark Schultz, “Understanding Concentrated Animal Feeding Operations and Their Impact on Communities” (National Association of Local Boards of Health, 2010).
[19] Scott Spillias et al., “Reducing Global Land-Use Pressures with Seaweed Farming,” Nature Sustainability 6, no. 4 (April 2023): 380–90, https://doi.org/10.1038/s41893-022-01043-y.
[20] Alejandro H. Buschmann et al., “Seaweed Production: Overview of the Global State of Exploitation, Farming and Emerging Research Activity,” European Journal of Phycology 52, no. 4 (October 2, 2017): 391–406, https://doi.org/10.1080/09670262.2017.1365175.
[21] Flower E. Msuya et al., “Seaweed Farming in Africa: Current Status and Future Potential,” Journal of Applied Phycology 34, no. 2 (April 1, 2022): 985–1005, https://doi.org/10.1007/s10811-021-02676-w.
[22] World Bank Group, Seaweed Aquaculture for Food Security, Income Generation and Environmental Health in Tropical Developing Countries (World Bank, Washington, DC, 2016), https://doi.org/10.1596/24919.
[23] IPCC, “Climate Change 2023: Synthesis Report.,” A Report of the Intergovernmental Panel on Climate Change. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. (Geneva, Switzerland: Intergovernmental Panel on Climate Change, 2023), https://www.ipcc.ch/report/ar6/syr/downloads/report/IPCC_AR6_SYR_LongerReport.pdf.
