It is welcome news when methane emissions fall through improved manure management. But to assess greenhouse gases as a whole, we need to ask one more question: what happened to the other gases? Chapter 5 of Technology and Solutions for Demonstrating Carbon Reduction looks at manure greenhouse gases through the relationship between methane and nitrous oxide. The aim is to check both the pathways that have decreased and those that may have increased.
A distinction to make first as you read the book
Follow the process step by step, from the part where the technology is applied through the subsequent treatment stages. A change in storage method can also change where or when gases are produced. Simply moving treatment outside the farm does not mean emissions have disappeared. It helps to write down how much of other gases, energy use, transport, and treatment costs is included. If some items cannot be calculated precisely, it is also important to note the likely direction of their effects and what additional data are needed.
GWP is an indicator that compares the impact of a greenhouse gas with carbon dioxide over a defined time horizon. GWP100 and GWP20 use 100-year and 20-year horizons, respectively. The same mass of methane converts to a different amount of carbon dioxide equivalent depending on the indicator and time horizon used, so state both the original mass and the conversion basis. Do not add together or directly compare values calculated with different indicators as if they were results under the same conditions.
Most methane emissions from ruminants come from enteric fermentation. Understanding this process helps explain why mitigation is difficult and where intervention points may lie.
Manure methane emissions are affected by organic matter, temperature, storage duration, and management practices. Long-term anaerobic storage of liquid manure can increase methane production. However, the size of atmospheric emissions cannot be judged from whether storage is sealed alone. Also examine whether the gas produced is captured, flared, or used, as well as leakage and uncombusted emissions. IPCC methodology also distinguishes methane conversion factors by management practice from recovered methane.
The manure pathway also produces nitrous oxide (N2O), in addition to methane. On a GWP100 basis, nitrous oxide is a much more powerful greenhouse gas than methane, and it is generated during nitrogen treatment processes. There is a trade-off here. Aerobic manure treatment intended to reduce methane emissions can increase nitrous oxide emissions. Conversely, capturing methane through anaerobic digestion reduces methane, but other emissions may arise from managing the digestate.
The greenhouse gas effect of improved manure management should be assessed by looking at changes in both the relevant methane and nitrous oxide emissions. Ammonia and water-quality impacts should be considered separately as environmental performance indicators. Do not simply add all of these together in a single greenhouse gas unit; distinguish the emissions boundary and assessment method for each indicator.
Absolute emissions are total emissions within a defined period and boundary; intensity is emissions per unit of product. Even if production efficiency lowers intensity, total emissions may rise when production scales up. Show the two indicators separately, and align the comparison period and product definitions. Assess total-emissions targets and product efficiency for their respective purposes, while presenting the results together to make the relationship between scale changes and efficiency gains easier to understand.
What to look for in the field
Imagine a farm changing its storage method or treatment conditions. If the organic matter, temperature, or storage period changes, the conditions for methane production change too. At the same time, we need to look at how nitrogen moves and is treated. A concentration decline at a single point cannot explain the overall greenhouse gas effect.
The book recommends presenting absolute emissions, intensity, and production volume together when describing a farm’s emissions-reduction performance. This is a practical recommendation for distinguishing changes in totals from changes in efficiency; it is not a universal requirement across all reporting systems. The GHG Protocol Corporate Standard requires reporting absolute emissions and makes ratio indicators optional. The Scope 3 Standard also recommends that companies using intensity targets report absolute emissions for the relevant boundary alongside them. In actual reporting, first check the required items under the applicable standards, laws, and contracts.
In livestock methane, there are temptations to overstate in both directions. Technology companies have an incentive to present large reduction effects, while industry defenders have an incentive to understate emissions. Either side can produce a desired conclusion simply by adjusting indicator selection and boundary setting.
Questions to ask in an investment review
When comparing technologies, start by checking which gases and treatment stages are included. Also check whether additional energy use and management costs have been left out of the claimed improvement. If a treatment process has been moved off the farm, confirm how that stage was handled in the calculation.
3-NOP is a feed-additive approach that inhibits an enzymatic reaction in methane production. Explaining its mechanism of action is different from establishing its effects under actual feeding conditions. Results can vary with dose, feed composition, intake, and production stage, so read the trial conditions as well. Check permitted conditions of use and evidence on safety and productivity before deciding the scope of application.
The reason to refer to this process when developing a methodology of our own in Korea is not only to obtain international approval. These requirements are the minimum conditions for ensuring an emissions-reduction claim holds up.
Records for feed-additive-based mitigation should connect purchasing and delivery with feed mixing and actual feeding. They should make it possible to check which product was used for which herd and when, including any periods when use stopped. Evidence that the product was actually fed and the basis for the emissions-reduction factor are different kinds of evidence, so manage them separately. The fact that records exist does not, by itself, establish a quantified reduction for that farm.
A question to leave with before closing the book
The results of manure methane mitigation are easier to understand when the boundaries and conditions are stated together. Take it step by step: what decreased, and what else changed? Asking about the overall effect helps clarify the technology’s actual scope of application.
About the author
Bongjun Lee graduated from the Graduate School of Management of Technology (MOT) at Sogang University. He spent seven years at Infitron Co., Ltd. and 20 years at Honeywell, working for a total of 27 years in gas measurement in service engineering, technical sales, and channel management. He is now the founder of AI Safety Korea Co., Ltd., where he is researching livestock methane monitoring and measurement, reporting, and verification (MRV) systems using sensors, AI, and data analytics.