Livestock production is a significant contributor to global greenhouse gas (GHG) emissions, with implications for climate change and the environment. According to the Food and Agriculture Organization (FAO), the livestock sector accounts for 14.5% of global anthropogenic GHG emissions, which is more than the entire transportation sector (FAO, 2013). As the global demand for livestock products continues to grow, driven by population growth, urbanization, and rising incomes, the environmental impact of livestock production is likely to increase, posing challenges for sustainable development and climate change mitigation.
Greenhouse gases are atmospheric gases that absorb and emit radiation within the thermal infrared range, trapping heat in the Earth's atmosphere and contributing to global warming. The primary GHGs associated with livestock production are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which have different global warming potentials (GWP) and atmospheric lifetimes. CO2 has a GWP of 1 and an atmospheric lifetime of hundreds to thousands of years, while CH4 has a GWP of 28-36 and an atmospheric lifetime of 12 years, and N2O has a GWP of 265-298 and an atmospheric lifetime of 121 years (IPCC, 2014).
The livestock sector contributes to GHG emissions through various pathways, including enteric fermentation, manure management, feed production, land-use change, and energy use. Enteric fermentation, which is the digestive process in ruminant animals such as cattle, sheep, and goats, is the largest source of livestock-related GHG emissions, accounting for 39% of the sector's total emissions (FAO, 2013).
Manure management, which involves the storage, treatment, and application of animal waste, is another significant source of GHG emissions, particularly CH4 and N2O. Feed production, which includes the cultivation, processing, and transportation of animal feed, contributes to GHG emissions through land-use change, fertilizer use, and energy consumption. Land-use change, such as deforestation and grassland conversion for pasture and feed crops, releases stored carbon and reduces the capacity of ecosystems to sequester carbon.
Mitigating the environmental impact of livestock production requires a comprehensive understanding of the sources and pathways of GHG emissions, as well as the potential solutions and trade-offs. This article provides an in-depth analysis of the role of livestock in greenhouse gas emissions, drawing on the latest scientific evidence and data. It explores the different livestock production systems and their associated GHG emissions, the regional and global trends in livestock-related emissions, and the potential mitigation strategies and their co-benefits and challenges.
Livestock Production Systems and Greenhouse Gas Emissions
Livestock production systems vary widely across regions and scales, from extensive grazing systems to intensive industrial systems, with different implications for GHG emissions and environmental sustainability. Understanding the diversity and complexity of livestock production systems is essential for assessing their environmental impact and identifying appropriate mitigation strategies.
Extensive Grazing Systems
Extensive grazing systems, also known as rangelands or pasturelands, are characterized by low stocking densities, minimal inputs, and reliance on natural vegetation for animal feed. These systems are prevalent in arid and semi-arid regions, such as Africa, Central Asia, and Latin America, and support the livelihoods of millions of pastoralists and agro-pastoralists. Extensive grazing systems account for about 26% of the global land area and 27% of the global livestock population (FAO, 2018).
The GHG emissions from extensive grazing systems are primarily associated with enteric fermentation and land-use change. Enteric fermentation in ruminant animals, such as cattle, sheep, and goats, produces CH4 as a byproduct of the digestive process. The amount of CH4 emitted per animal depends on factors such as the type and quality of feed, the animal's age and productivity, and environmental conditions. In extensive grazing systems, where animals rely on low-quality natural vegetation, the CH4 emissions per unit of product (e.g., milk or meat) are generally higher than in intensive systems, due to lower feed efficiency and longer production cycles (Herrero et al., 2013).
Land-use change, such as the conversion of forests and grasslands to pastureland, is another significant source of GHG emissions in extensive grazing systems. Deforestation and grassland degradation release stored carbon and reduce the capacity of ecosystems to sequester carbon, contributing to CO2 emissions. In some regions, such as the Amazon and the Cerrado in Brazil, the expansion of pastureland for beef production has been a major driver of deforestation and biodiversity loss (zu Ermgassen et al., 2020). However, well-managed grasslands can also act as carbon sinks, sequestering carbon in the soil and vegetation, and providing ecosystem services such as water regulation and biodiversity conservation (Conant et al., 2017).
The GHG emissions from extensive grazing systems vary widely across regions and production practices. For example, a study by Herrero et al. (2013) estimated that the global average GHG emissions from extensive grazing systems were 2.8 kg CO2-eq per kg of protein, with regional variations ranging from 1.7 kg CO2-eq per kg of protein in Latin America and the Caribbean to 6.5 kg CO2-eq per kg of protein in Sub-Saharan Africa. The study also found that improving the productivity and efficiency of extensive grazing systems, through practices such as improved grazing management, feed supplementation, and animal health care, could reduce GHG emissions by 20-50% per unit of product.
Mixed Crop-Livestock Systems
Mixed crop-livestock systems integrate crop and livestock production on the same farm or landscape, using crops for animal feed and animal manure for crop fertilization. These systems are widespread in many parts of the world, particularly in Asia, Africa, and Latin America, and account for about 48% of the global livestock population (FAO, 2018). Mixed crop-livestock systems can be classified into different types, such as rainfed or irrigated, intensive or extensive, and subsistence or commercial, depending on the agroecological conditions, the level of inputs, and the market orientation.
The GHG emissions from mixed crop-livestock systems are associated with enteric fermentation, manure management, feed production, and energy use. Enteric fermentation in ruminant animals, such as cattle, buffaloes, and small ruminants, is a major source of CH4 emissions, particularly in systems with low-quality feed and low productivity. Manure management, which involves the storage, treatment, and application of animal waste, contributes to CH4 and N2O emissions, depending on the manure management practices and the environmental conditions.
Feed production, which includes the cultivation, processing, and transportation of crops and crop residues for animal feed, contributes to CO2, CH4, and N2O emissions through land-use change, fertilizer use, and energy consumption. Energy use, such as electricity and fossil fuels for irrigation, mechanization, and transportation, also contributes to CO2 emissions.
The GHG emissions from mixed crop-livestock systems vary widely across regions and production practices. For example, a study by Gerber et al. (2013) estimated that the global average GHG emissions from mixed crop-livestock systems were 5.2 kg CO2-eq per kg of protein, with regional variations ranging from 3.1 kg CO2-eq per kg of protein in Latin America and the Caribbean to 7.5 kg CO2-eq per kg of protein in South Asia. The study also found that improving the productivity and efficiency of mixed crop-livestock systems, through practices such as improved feed quality, manure management, and energy efficiency, could reduce GHG emissions by 20-40% per unit of product.
Intensive Industrial Systems
Intensive industrial systems, also known as confined animal feeding operations (CAFOs) or factory farms, are characterized by high stocking densities, specialized breeds, and reliance on external inputs such as feed, energy, and antibiotics. These systems are prevalent in developed countries, such as the United States, Europe, and China, and are increasingly adopted in developing countries, particularly for poultry and pig production. Intensive industrial systems account for about 9% of the global livestock population but produce about 40% of the global livestock output (FAO, 2018).
The GHG emissions from intensive industrial systems are primarily associated with feed production, manure management, and energy use. Feed production, which includes the cultivation, processing, and transportation of feed crops such as soybeans, maize, and wheat, is a major source of GHG emissions, particularly CO2 and N2O. The expansion of feed crop production, particularly in tropical regions such as the Amazon and Southeast Asia, has been a significant driver of deforestation and biodiversity loss (zu Ermgassen et al., 2020).
Manure management, which involves the storage, treatment, and disposal of large quantities of animal waste, contributes to CH4 and N2O emissions, depending on the manure management practices and the environmental conditions. Energy use, such as electricity and fossil fuels for heating, cooling, ventilation, and transportation, also contributes to CO2 emissions.
The GHG emissions from intensive industrial systems vary widely across regions and production practices. For example, a study by MacLeod et al. (2013) estimated that the global average GHG emissions from intensive industrial systems were 3.3 kg CO2-eq per kg of protein, with regional variations ranging from 2.4 kg CO2-eq per kg of protein in Europe to 4.2 kg CO2-eq per kg of protein in North America.
The study also found that improving the productivity and efficiency of intensive industrial systems, through practices such as precision feeding, manure treatment, and energy efficiency, could reduce GHG emissions by 10-30% per unit of product.
Regional and Global Trends in Livestock-Related Greenhouse Gas Emissions
The contribution of livestock to global GHG emissions varies across regions and production systems, reflecting differences in agroecological conditions, production practices, and socio-economic factors. Understanding the regional and global trends in livestock-related GHG emissions is essential for prioritizing mitigation efforts and designing context-specific policies and interventions.
Regional Trends
The regional distribution of livestock-related GHG emissions reflects the diversity and intensity of livestock production systems across the world.
According to the FAO (2013), the regions with the highest livestock-related GHG emissions are:
- Latin America and the Caribbean (25% of global livestock-related GHG emissions) - are dominated by extensive grazing systems for beef production, particularly in Brazil and Argentina.
- East and Southeast Asia (24%) - characterized by rapid growth in intensive industrial systems for poultry and pig production, particularly in China and Vietnam.
- South Asia (14%) - is dominated by mixed crop-livestock systems for dairy production, particularly in India and Pakistan.
- Sub-Saharan Africa (12%) - characterized by extensive grazing systems for pastoral and agro-pastoral production, particularly in the Sahel and the Horn of Africa.
- Europe (10%) - characterized by intensive industrial systems for poultry, pig, and dairy production, with increasing trends towards sustainable intensification and agroecological practices.
- North America (7%) - dominated by intensive industrial systems for beef, poultry, and pig production, with increasing trends towards consolidation and vertical integration.
The regional trends in livestock-related GHG emissions are influenced by various drivers and pressures, such as population growth, urbanization, income growth, dietary changes, and trade policies. For example, the rapid growth in livestock production and consumption in East and Southeast Asia, particularly for poultry and pork, has been driven by rising incomes, urbanization, and changing dietary preferences, as well as government policies and investments in the livestock sector (Thornton, 2010). In contrast, the extensive grazing systems in Latin America and Sub-Saharan Africa have been influenced by factors such as land availability, climate variability, and cultural traditions, as well as market access and trade policies (Herrero et al., 2013).
Global Trends
The global trends in livestock-related GHG emissions reflect the increasing demand for livestock products, particularly in developing countries, as well as the intensification and specialization of livestock production systems. According to the FAO (2013), global livestock-related GHG emissions increased by 51% between 1961 and 2010, from 1.4 to 2.1 gigatonnes CO2-eq per year, driven by population growth, income growth, and dietary changes. The largest increases in livestock-related GHG emissions occurred in developing countries, particularly in Asia and Latin America, while the emissions in developed countries remained relatively stable or decreased.
The global trends in livestock-related GHG emissions also reflect the changing composition and efficiency of livestock production systems. For example, the share of monogastric animals (poultry and pigs) in global livestock production increased from 37% in 1961 to 69% in 2010, while the share of ruminant animals (cattle, buffaloes, sheep, and goats) decreased from 63% to 31% (FAO, 2013). This shift towards monogastric production, which is more efficient in terms of feed conversion and GHG emissions per unit of product, has contributed to the decoupling of livestock production and GHG emissions in some regions, such as Europe and North America (Gerber et al., 2013).
However, the global trends in livestock-related GHG emissions also highlight the challenges and trade-offs associated with livestock production and sustainability. For example, the expansion of livestock production, particularly in tropical regions, has been a significant driver of deforestation, biodiversity loss, and soil degradation, with implications for carbon sequestration, water regulation, and ecosystem services (zu Ermgassen et al., 2020). The intensification of livestock production, particularly in industrial systems, has also raised concerns about animal welfare, public health, and social equity, as well as the externalization of environmental and social costs (Steinfeld et al., 2006).
Mitigation Strategies and Their Potential
Mitigating the GHG emissions from livestock production requires a combination of technological, management, and policy interventions, tailored to the specific contexts and challenges of different production systems and regions. The mitigation strategies can be classified into three broad categories: (1) reducing the emissions intensity of livestock production, (2) sequestering carbon in soils and biomass, and (3) reducing the demand for livestock products.
Reducing Emissions Intensity
Reducing the emissions intensity of livestock production involves improving the efficiency and productivity of livestock systems so that more output (e.g., milk, meat, eggs) can be produced with fewer inputs (e.g., feed, water, energy) and lower emissions per unit of product.
Some of the key strategies for reducing emissions intensity include:
- Improving animal genetics and breeding: Selecting and breeding animals with higher productivity, feed efficiency, and disease resistance can reduce the emissions intensity of livestock production, by increasing the output per animal and reducing the number of animals required to meet the demand (Hristov et al., 2013). For example, improving the milk yield of dairy cows through genetic selection and breeding can reduce the CH4 emissions per unit of milk by 10-30%, depending on the production system and the level of improvement (Gerber et al., 2013).
- Optimizing animal nutrition and feeding: Providing animals with balanced and digestible diets, matched to their nutritional requirements and production stage, can reduce the emissions intensity of livestock production, by improving the feed conversion efficiency and reducing the CH4 emissions from enteric fermentation (Hristov et al., 2013). For example, supplementing the diets of ruminant animals with high-quality forages, grains, or feed additives (e.g., oils, tannins, saponins) can reduce the CH4 emissions per unit of product by 5-20%, depending on the type and level of supplementation (Beauchemin et al., 2020).
- Improving animal health and welfare: Preventing and treating animal diseases, injuries, and stress can reduce the emissions intensity of livestock production, by improving the productivity, fertility, and longevity of animals, and reducing the mortality and morbidity rates (Hristov et al., 2013). For example, vaccinating animals against common diseases, such as mastitis, pneumonia, and parasites, can reduce the emissions intensity of livestock production by 5-10%, depending on the disease prevalence and the effectiveness of the vaccine (Gerber et al., 2013).
- Improving manure management and utilization: Collecting, storing, treating, and utilizing animal manure efficiently and sustainably can reduce the emissions intensity of livestock production, by reducing the CH4 and N2O emissions from manure decomposition, and recycling the nutrients and organic matter back to the soil (Herrero et al., 2013). For example, covering manure storage facilities, composting or anaerobically digesting manure, and applying manure to crops or pastures based on nutrient requirements can reduce the CH4 and N2O emissions from manure management by 30-80%, depending on the technology and the management practices (Gerber et al., 2013).
Sequestering Carbon
Sequestering carbon in soils and biomass involves increasing the uptake and storage of atmospheric CO2 in agricultural and natural ecosystems, through practices that enhance the photosynthesis and biomass production of plants, and the accumulation and stabilization of soil organic matter.
Some of the key strategies for sequestering carbon include:
- Improving grassland and rangeland management: Adopting sustainable grazing practices, such as rotational grazing, adaptive multi-paddock grazing, and silvopastoralism, can increase the carbon sequestration in grasslands and rangelands, by enhancing the productivity and diversity of vegetation, reducing soil erosion and degradation, and promoting the formation and stabilization of soil organic matter (Conant et al., 2017). For example, a meta-analysis by Conant et al. (2017) found that improved grazing management practices increased soil carbon sequestration by an average of 0.28 Mg C ha−1 yr−1, with a range of 0.03 to 1.3 Mg C ha−1 yr−1, depending on the climate, soil type, and management intensity.
- Integrating trees and shrubs in livestock systems: Incorporating trees and shrubs in livestock systems, through practices such as agroforestry, silvopastoralism, and fodder banks, can increase the carbon sequestration in biomass and soils, by increasing the photosynthesis and biomass production of plants, providing shade and shelter for animals, and reducing the pressure on natural forests (Rao et al., 2015). For example, a study by Rao et al. (2015) estimated that silvopastoral systems in Latin America could sequester an average of 1.7 Mg C ha−1 yr−1, with a range of 0.5 to 3.6 Mg C ha−1 yr−1, depending on the tree species, density, and management practices.
- Restoring degraded lands and soils: Restoring degraded lands and soils, through practices such as revegetation, afforestation, and soil conservation, can increase the carbon sequestration in biomass and soils, by enhancing the productivity and resilience of ecosystems, reducing soil erosion and degradation, and increasing the input and stabilization of organic matter (FAO, 2019). For example, a study by FAO (2019) estimated that restoring degraded grazing lands could sequester an average of 0.5 Mg C ha−1 yr−1, with a range of 0.2 to 1.0 Mg C ha−1 yr−1, depending on the restoration methods, the initial state of degradation, and the climatic conditions.
Reducing Demand
Reducing the demand for livestock products involves shifting the consumption patterns and behaviors of individuals and societies, towards more sustainable and healthy diets, with lower environmental impacts and higher nutritional value.
Some of the key strategies for reducing demand include:
- Promoting plant-based diets: Encouraging the consumption of more plant-based foods, such as fruits, vegetables, legumes, and whole grains, and reducing the consumption of animal-based foods, particularly red and processed meats, can reduce the GHG emissions associated with livestock production, as well as improve human health and reduce the risk of chronic diseases (Willett et al., 2019). For example, a study by Springmann et al. (2018) estimated that a global shift towards more plant-based diets, in line with the dietary guidelines, could reduce the GHG emissions from food production by 29-70%, depending on the scenario and the level of adoption.
- Reducing food loss and waste: Reducing the loss and waste of food along the supply chain, from production to consumption, can reduce the GHG emissions associated with livestock production, by reducing the demand for livestock products and the resources required to produce them (FAO, 2013). For example, a study by FAO (2013) estimated that reducing food loss and waste by 50% could reduce the GHG emissions from the food system by 10-15%, depending on the region and the type of food.
- Internalizing environmental costs: Incorporating the environmental and social costs of livestock production, such as GHG emissions, biodiversity loss, and public health impacts, into the prices of livestock products, through policies such as carbon taxes, environmental regulations, and labeling schemes, can provide incentives for producers and consumers to shift towards more sustainable and low-emission practices and products (Springmann et al., 2017). For example, a study by Springmann et al. (2017) estimated that a global carbon tax on food products, based on their GHG emissions, could reduce the GHG emissions from food production by 9-19%, depending on the tax level and the response of producers and consumers.
Challenges and Opportunities for Mitigation
Mitigating the GHG emissions from livestock production is a complex and multifaceted challenge, that requires addressing the trade-offs and synergies between the environmental, economic, and social dimensions of sustainability, as well as the diversity and specificity of livestock systems and regions. Some of the key challenges and opportunities for mitigation include:
Policy and Institutional Challenges
- Lack of political will and leadership to prioritize and invest in livestock mitigation, due to competing policy agendas, vested interests, and short-term thinking.
- Inadequate or inconsistent policies and regulations to support and incentivize mitigation practices and technologies, such as carbon pricing, environmental standards, and research and development.
- Limited coordination and collaboration among the different stakeholders and sectors involved in livestock production and mitigation, such as farmers, companies, governments, and civil society organizations.
Economic and Financial Challenges
- High costs and risks associated with the adoption and scaling-up of mitigation practices and technologies, particularly for small-scale and resource-poor farmers.
- Limited access to credit, insurance, and other financial services to support the investment and transition towards low-emission livestock production.
- Inadequate or perverse subsidies and incentives that promote unsustainable and high-emission livestock production, such as feed subsidies, trade barriers, and tax exemptions.
Social and Cultural Challenges
- Limited awareness and understanding of the impacts and opportunities of livestock mitigation, among producers, consumers, and policymakers.
- Resistance to change and attachment to traditional practices and preferences, particularly in pastoral and smallholder systems.
- Unequal power relations and gender roles that limit the participation and benefits of women and marginalized groups in livestock mitigation.
Technological and Knowledge Challenges
- Limited availability and accessibility of appropriate and affordable mitigation technologies and practices, particularly in developing countries and remote areas.
- Inadequate research and innovation to develop and adapt mitigation options to the specific contexts and needs of different livestock systems and regions.
- Limited capacity and skills of farmers, extension agents, and other stakeholders to adopt and implement mitigation practices and technologies.
Despite these challenges, there are also significant opportunities for livestock mitigation, that can provide multiple benefits for the environment, the economy, and society. Some of the key opportunities include:
Climate Change Mitigation and Adaptation
- Reducing the GHG emissions from livestock production can contribute significantly to the global efforts to mitigate climate change, in line with the Paris Agreement and the Sustainable Development Goals.
- Adapting livestock systems to the impacts of climate change, through practices such as climate-smart agriculture, agroforestry, and sustainable land management, can increase the resilience and productivity of livestock production, while also providing mitigation co-benefits.
Food Security and Nutrition
- Improving the efficiency and sustainability of livestock production can increase the availability and affordability of animal-source foods, particularly in developing countries and for vulnerable groups, such as women, children, and the poor.
- Diversifying the sources and types of animal-source foods, such as poultry, fish, and insects, can provide more nutritious and sustainable options for meeting the growing demand for protein and essential nutrients.
Livelihoods and Rural Development
- Supporting the adoption and scaling-up of low-emission livestock practices and technologies can create new jobs and income opportunities, particularly in rural areas and for small-scale farmers and pastoralists.
- Investing in the capacity building and empowerment of livestock producers and their organizations can enhance their voice, agency, and benefits in the value chain, and promote more inclusive and equitable development.
Ecosystem Services and Biodiversity
- Integrating livestock production with the conservation and sustainable use of natural resources, such as grasslands, forests, and wetlands, can provide multiple ecosystem services, such as carbon sequestration, water regulation, and habitat provision.
- Promoting the sustainable management and use of animal genetic resources, particularly local breeds and species, can contribute to the conservation of biodiversity and the resilience of livestock systems to environmental and market shocks.
Conclusion
Livestock production is a significant contributor to global GHG emissions, with important implications for climate change, food security, and sustainable development. Understanding the sources, trends, and mitigation options of livestock-related GHG emissions is essential for designing and implementing effective and equitable policies and practices, that can balance the trade-offs and synergies between the environmental, economic, and social dimensions of sustainability.
The mitigation of livestock-related GHG emissions requires a combination of technological, management, and policy interventions, tailored to the specific contexts and challenges of different production systems and regions. Some of the key strategies include reducing the emissions intensity of livestock production, sequestering carbon in soils and biomass, and reducing the demand for livestock products, through practices such as improving animal genetics and nutrition, integrating trees and shrubs in livestock systems, restoring degraded lands, promoting plant-based diets, and reducing food loss and waste.
However, the adoption and scaling-up of these mitigation strategies face several challenges, related to the policy and institutional frameworks, the economic and financial incentives, the social and cultural factors, and the technological and knowledge gaps. Overcoming these challenges requires a concerted and collaborative effort from all stakeholders, including farmers, companies, governments, and civil society organizations, to create an enabling environment for low-emission livestock production, and to promote a more sustainable and equitable food system.
At the same time, the mitigation of livestock-related GHG emissions also presents significant opportunities for achieving multiple sustainable development goals, related to climate change, food security, livelihoods, and ecosystems. By investing in low-emission livestock practices and technologies, and by promoting more sustainable and healthy consumption patterns, we can contribute to a more resilient, inclusive, and low-carbon future, that leaves no one behind.
In conclusion, the mitigation of livestock-related GHG emissions is a complex and urgent challenge, that requires a systemic and integrated approach, based on sound science, inclusive dialogue, and bold action. By working together and learning from each other, we can unlock the potential of livestock to be a part of the solution, rather than the problem, in the global fight against climate change and poverty. The journey ahead is long and difficult, but the rewards are worth it, for the sake of our planet, our people, and our future.