When we talk about reducing methane, the first things that come to mind are often a promising additive or a piece of equipment. But I suggest that we first look together at where the methane we want to reduce comes from. Chapter 5 of Technology and Solutions for Demonstrating Carbon Reduction also starts with emissions pathways within the livestock system. We can explain the effects of livestock methane mitigation only when the target and indicators are clear.
A distinction to make first as you read the book
It may help to start by drawing the emissions pathways. Separate methane produced in the rumen from methane produced while manure is stored, and mark where the technology acts. Then connect each pathway to the data that can explain the change. Measuring in the same barn does not mean that every pathway can be explained at once. To avoid reading an effect on one source as a change across the whole farm, it helps to document the scope and what is left out.
Methane remains in the atmosphere for about 12 years, a shorter period than carbon dioxide, whose effects last for hundreds of years or more. At the same time, methane’s radiative forcing per unit of mass is much greater. This combination makes methane a distinctive target for reduction.
Methane reduction is an important means of limiting near-term warming. However, the fact that emissions from one sector have fallen does not, by itself, let us conclude that the global atmospheric methane concentration will decline within a given period. The concentration pathway depends on total emissions and removal processes in the atmosphere, while the temperature impact also depends on the scale and duration of the reduction. That is why rapid and sustained methane reductions matter.
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.
Methane from enteric fermentation is released mainly through the mouth and nose, so breath-collection equipment measures gases around the animal’s head. GreenFeed attracts animals with feed and captures gas from those that visit. However, if observations are concentrated at particular times, such as just after feeding, they may not represent daily emissions. Check the distribution of visit and measurement times and the quality of gas capture. For chambers and tracer-gas methods, apply each method’s principles for time integration and sample design.
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.
What to look for in the field
Think about methane from the cow’s digestive process and methane produced while manure is stored. Even on the same farm, the conditions that affect them and the data needed to assess them are different. If the effect of a technology addressing one pathway is described as a reduction across the whole farm, emissions sources may have been left out. That is why the measurement boundary should be written down from the start.
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.
If feed efficiency improves so that the same output is achieved with fewer inputs, there may be potential to reduce emissions. However, results vary with the methane conversion rate, emissions from feed production, and changes in output, so we cannot conclude that both total methane and emissions intensity will necessarily decline. Changes in raising period, fertility rate, mortality, and feed formulation should also be assessed against production outcomes and the emissions boundary.
Questions to ask in an investment review
As an investor, it is also useful to check which emissions source the proposed solution addresses. Ask whether the technology actually intervenes in that pathway and what data were used to compare its effects. Keep in mind that the broad label “methane reduction” covers technologies with different approaches and cost structures.
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.
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
When the starting point is specific, the next questions become easier too. Follow the sequence: where did the emissions arise, what action was taken, and what changed? The book’s discussion of methane science provides a foundation for understanding those connections.
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.