Reducing Methane Emissions From Livestock: Opportunities And Issues

Generated Summary

This report, based on a workshop entitled “Methane Emissions From Ruminants” held in February 1989, examines the issues related to reducing methane (CH4) emissions from livestock-agriculture systems. It focuses on characterizing emissions, identifying and evaluating options for emission reduction, and understanding the implications for global climate change. The study uses the Atmospheric Stabilization Framework (ASF) developed by the EPA to assess the impact of different scenarios on global warming. The research approach involves analyzing the global sources and sinks of CH4, with a specific focus on ruminant animals, to identify and evaluate strategies for mitigation. The methodology includes an assessment of methane yields, animal populations, and the impact of different management practices and technologies. The goal is to understand the contribution of livestock to atmospheric methane and develop effective strategies to reduce these emissions, considering factors such as animal productivity, waste management, and economic implications.

Key Findings & Statistics

• The atmospheric abundance of methane is increasing at a rate of approximately 1.0 percent per year.
• The atmospheric concentration of CH4 has approximately doubled in the past 200 to 300 years.
• The primary cause of increasing CH4 concentrations is increasing emissions of CH4.
• Anthropogenic sources account for about 60 percent of current CH4 emissions.
• Ruminant animals produce significant quantities of CH4 as part of their digestive processes, accounting for nearly one-fourth of the total anthropogenic emissions, or about 15 percent of total emissions.
• A 10 to 20 percent reduction in anthropogenic CH4 emissions is required to stabilize atmospheric concentrations at their current levels.
• A 50 percent reduction in CH4 emissions from ruminants will contribute about 50 to 75 percent of the emissions reductions needed to stabilize atmospheric CH4 concentrations.
• Reductions in livestock-related CH4 emissions could reduce anticipated equilibrium warming increases on the order of one to six percent by 2100.
• The global population of managed ruminants has been increasing globally for over 30 years.
• According to FAO statistics, the numbers of managed ruminants in 1987 included: 1.3 billion cattle; 1.2 billion sheep; 0.5 billion goats; 0.1 billion buffalo; and 19 million camels.
• The atmospheric lifetime of CH4 is on the order of 10 years.
• The range of destruction and accumulation rates presented in WMO (1986) implies a range of lifetimes of about 7.4 years to 15.1 years, with a middle value of about 10 years.
• The recent rates of increase are on the order of about 0.017 ppmv per year, or about one percent of the current average global level of abundance of about 1.7 ppmv.
• Current estimates indicate that these sources account for about 60 percent of current CH4 emissions, with ruminant animals accounting for nearly one fourth of this, or about 15 percent of the total.
• In the U.S., the number of dairy cows has stabilized or declined.
• The total population of cattle, buffalo, goats, and sheep are combined into “Livestock Units” using the following population multipliers: cattle – 0.8; buffalo – 1.0; sheep – 0.1, goats – 0.1.
• The data indicate that the abundance of atmospheric CH4 has increased primarily in the last 300 years, with relatively stable levels prior to that time at about one-half the current levels.
• The population of managed ruminants has been increasing globally for over 30 years.
• The study by Crutzen et al. is the most comprehensive description of CH4 emissions to date.
• Bovines, including all cattle used for beef production, milk production, and draft animals, are the largest source, accounting for 70 percent of the total estimate and about 75 percent of the CH4 emissions from managed ruminants.
• The total of these estimated emissions is about 71 Tg/yr, over 75 percent of which is associated with cattle.
• Crutzen et al. estimate an additional 2.9 Tg/yr of CH4 emissions associated with the digestive systems of pigs, horses, mules, and humans.
• Approximately 2 to 6 Tg/yr of emissions is estimated for wild ruminants throughout the world, and emissions from large non-ruminants are expected to be small. The overall total for these sources of CH4 is on the order of about 80 Tg/yr.
• In the developing world, both feed intake and quality may have declined.
• The scenarios labeled “with reduction” show a range of 25 percent to 75 percent reduction from the baseline rate of emissions from ruminant animals starting in 1990.
• The mean annual increase in CH4 emission from domestic animals and humans over the past 20 years has been 0.6 Tg, or 0.75% per year.
• The US cattle population is made up of 10% dairy cows, 12.5% beef cattle on feed and 77.5% cattle on range.
• The average annual CH4 production by cattle in the US is 58 kg per animal per year.

Other Important Findings

• The main anthropogenic sources of CH4 include ruminant animals, animal wastes, rice paddies, biomass burning, and termites.
• The destruction of atmospheric CH4 is driven primarily by its oxidation in the troposphere and stratosphere by the hydroxyl radical, OH.
• The main anthropogenic sources of CH4 include: ruminant animals (primarily cattle, buffalo, and sheep); rice paddies; biomass burning; animal wastes; and termites from disturbed forests.
• Animals, and in particular ruminants, are an important source of CH4 emissions on a global scale.
• Emissions from animals in developing countries remain uncertain.
• Reductions in CH4 emissions from animals will assist in reducing the rate of CH4 increases, and may be one important component in attempts to stabilize atmospheric CH4 concentrations.
• Although potential options for reducing emissions may be promising, they must be demonstrated and evaluated.
• The scientific infrastructure exists to greatly increase levels of research to find solutions to limiting CH4 emissions from livestock.
• The levels of methane production from ruminant animals can be described in terms of a “methane yield,” which is defined as the amount of CH4 produced as a percentage of the gross food energy intake of the animal.
• The level and type of diet a ruminant consumes has a strong influence on an animal’s CH4 yield and on the amount of CH4 produced by the animal.
• The manner in which an animal population is managed will influence the overall level of CH4 emissions.
• The productivity of dairy cows is primarily measured by the amount of milk produced per cow per year.
• The amount of CH4 generated and emitted from manure depends on the manner in which the manure is handled.
• Most ruminants in the world are in developing countries where levels of intake and feed characteristics are very different from the diet of U.S. dairy cows.
• Declining animal numbers in the U.S., Europe, and other developed nations, while milk and meat production continue to increase.
• The technical feasibility and cost of achieving emissions reductions of this magnitude from livestock remain to be quantified.
• The report identifies improved emissions characterization, evaluation of impacts, and assessment of methods of implementation as key areas for analysis.
• The range of emissions reductions is shown for illustrative purposes.

Limitations Noted in the Document

• The study acknowledges uncertainties in emissions estimates, particularly in developing countries.
• The scenarios used for analysis are based on assumptions that may not fully reflect real-world conditions.
• The study focuses only on the global warming benefits of reducing methane emissions, and it does not cover all benefits.
• The analysis does not fully account for the complexity of factors influencing methane emissions, particularly in regard to waste management.
• The study acknowledges the difficulty in counting animals, especially in developing countries.
• The results presented in Exhibit 2-1. One would not expect to find animals consuming highly digestible feed (e.g., 70 percent or higher) at levels near maintenance. Similarly, one would not expect to find animals consuming low digestible feed (e.g., 50 to 60 percent) at 3.0 times maintenance.
• Estimates of current emission rates by source show the relatively large uncertainties that remain regarding the allocation of total emissions among source categories.
• The study highlights that coordination is required among domestic and international institutions of many types.
• The study does not include potential CH, emissions associated with wastes.
• The range is driven by uncertainties in the atmospheric lifetime of CH4.

Conclusion

The report emphasizes the critical need to address and reduce methane emissions from ruminant animals to mitigate climate change. The research highlights the significant contribution of livestock to global methane production, estimating that it accounts for approximately 15% of total anthropogenic emissions. The analysis reveals that reducing methane emissions from ruminants could yield substantial benefits, potentially reducing global warming by 0.1°C to 0.4°C by 2100. This benefit is amplified by the reduction in tropospheric ozone, which is also a greenhouse gas. The study identifies several key areas for improvement, including better characterization of emissions rates, particularly in developing countries, and the development and evaluation of various mitigation options such as alternative feeding practices, increased productivity, and waste management strategies. The findings suggest that reductions in methane emissions from livestock are not only feasible but also comparable to other measures contemplated for mitigating climate change, such as promoting natural gas and implementing emission controls. The study acknowledges the complexities in estimating methane emissions and highlights the need for comprehensive data collection and analysis, especially in areas with less-developed animal management practices. Furthermore, the study promotes the implementation of practical solutions to enhance productivity and reduce methane release. By addressing the challenges in animal agriculture and providing incentives, the study suggests that it may be possible to reduce methane emissions from livestock without increasing the cost of production. The analysis indicates that the scenarios of methane emissions from ruminant animals in the two scenarios in the EPA Report seem plausible. While the exact impact on global warming is uncertain, the study concludes that reducing emissions from ruminant animals is a promising strategy. This can be achieved through innovative feeding techniques and through an increased efficiency in production. The research underscores the potential for a two-pronged approach: enhancing animal productivity and reducing environmental impact. It supports the idea that reducing methane emissions from livestock is a key step towards mitigating climate change, and it stresses that understanding and implementing these measures should be a priority as part of an overall strategy for reducing future global warming and its impacts.