Tag: methane

Examining GWP*: An Alternative Approach to Measuring Methane’s Impact

Posted on April 29, 2025 by - Insights

Cows

An overview of GWP* and the Farm Carbon Toolkit position on alternative metrics for carbon footprinting.

Methane plays a crucial role in climate change, but accurately measuring its impact has long been a challenge. The most commonly used metric for measuring its impact is GWP100, which calculates its warming effect over a 100-year period. However, GWP100 does not fully reflect the gas’s short-lived nature in the atmosphere, potentially misrepresenting its impact compared to other greenhouse gases.

As a result, an alternative approach, known as GWP*, has been developed to address the challenges of measuring methane using GWP100, while offering a more dynamic picture of the gas’s real-time warming impact. At Farm Carbon Toolkit, we recognise the growing discussion around methane reporting and the potential benefits – as well as limitations – of using GWP*. This article explores the differences between GWP100 and GWP*, their implications for farmers, and how GWP* could be responsibly integrated into emissions reporting.

What is Global Warming Potential and How is it Measured?

Global Warming Potential is a measure used to compare the impact of different greenhouse gases on atmospheric warming over a specific period, relative to carbon dioxide. Since each greenhouse gas varies in how much heat it traps and how long it remains in the atmosphere, Global Warming Potential provides a standardised way to assess their contribution to climate change.

Carbon dioxide is used as the baseline because it is the most abundant greenhouse gas. GWP100 is the most widely used version of the Global Warming Potential metric, measuring the average warming potential of a gas over 100 years. This approach is the international standard used in greenhouse gas reporting, including in the Intergovernmental Panel on Climate Change (IPCC) guidelines.

Carbon dioxide remains in the atmosphere for the longest – up to a thousand years – but has the smallest warming impact of greenhouse gases and a GWP100 score of 1. However, as it is the most abundant and long-lasting GHG, this does not diminish its warming impact. In comparison, other greenhouse gases, such as methane and nitrous oxide, have significantly higher warming effects over shorter timeframes. The GWP100 for nitrous oxide is 265, meaning that one tonne of nitrous oxide causes the same amount of warming as 265 tonnes of carbon dioxide over a 100-year period. This is calculated with consideration for nitrous oxide’s 100-150 year lifespan.

GWP100 Limitations

While GWP100 is a useful tool for measuring the impact of different greenhouse gases, it has limitations. For gases like nitrous oxide and carbon dioxide, which persist in the atmosphere for hundreds or thousands of years respectively, GWP100 works well, providing an accurate comparison of their long-term warming effects. However, for methane – a potent greenhouse gas that remains in the atmosphere for only about 12 years – GWP100 fails to capture its true impact on climate change. Methane’s potency is not fully reflected when assessed over a 100-year period. While it persists for a short time, it traps heat much more effectively than carbon dioxide, significantly contributing to warming during that period.

As the science of climate change and greenhouse gas emissions evolves, it’s clear that alternative metrics will be necessary to provide a more accurate picture of methane’s role in climate change and to guide effective mitigation strategies.

GWP*: A New – but Incomplete – Approach

One such alternative metric is GWP*, which has been developed to better reflect methane’s global warming impact. Unlike standard GWP100, which assumes that emissions remain constant over time, GWP* accounts for methane’s faster breakdown in the atmosphere. As a result, GWP* can provide a clearer picture of how changes in methane emissions affect the climate in real-time, rather than assuming the gas has the same long-term impact as carbon dioxide.

Given the limitations of GWP100 in accurately reflecting methane’s warming impact, it may seem logical to switch entirely to GWP*. However, GWP* cannot be used to create a carbon footprint on its own.

One of the main reasons for this is that GWP* is not yet an internationally recognised reporting metric. While it is gaining traction in climate science discussions, it has not been formally adopted by key regulatory bodies such as the IPCC.

A further challenge of using GWP* alone is that it can cause confusion for emissions reduction efforts, especially at the farm level. GWP* measures the relative change in methane emissions over time, rather than just the total emissions. This means that small, natural variations in factors like herd size or crop activity can cause large fluctuations in carbon footprints from one year to the next. For example, a change in management practices can result in higher methane emissions, causing a spike in the carbon footprint. Conversely, a reduction in emissions, for example, from improving the efficiency of livestock production, has a greater immediate impact on reducing a farm’s reported warming contribution. These fluctuations can make emissions appear inconsistent, even if the farm’s overall environmental impact is improving. The danger is that such variability can make it harder to track long-term progress and could undermine efforts to reduce emissions.

Because of this, GWP* is most effective when applied over longer timescales and at larger scales, such as national-level carbon accounting over several decades. At this level, GWP* helps provide a more accurate picture of methane’s true warming potential, without the misleading volatility that occurs when used for annual farm-level reporting. 

For these reasons, while GWP* offers important insights into methane’s role in climate change, it should be used alongside existing GWP100 calculations rather than replacing them entirely. Employing GWP* in a way that accounts for long-term trends, rather than short-term variability, ensures that methane’s impact is assessed more accurately while still maintaining consistency in emissions reporting.

How Could GWP* be Applied to Farms?

In theory, GWP* could be used alongside GWP100 to provide a more accurate representation of a farm’s long-term methane emissions. However, applying GWP* in a practical and reliable way would require specific data and methodologies that are still under development.

To integrate GWP* into farm-level carbon footprinting, methane emissions would first need to be separated from other greenhouse gases in the emissions inventory and treated differently. Unlike GWP100, which applies a single factor to all emissions, GWP* relies on understanding the historical emissions data of methane — typically covering at least 20 years. This historical data is essential because GWP* calculates methane’s impact based on its rate of change over time, rather than treating all emissions as having an equal long-term effect. 

For an annual carbon report, the current year’s methane emissions would be adjusted based on the historical trend in emissions and a GWP* constant that scales the calculation to methane’s lifespan. However, this GWP* constant is still under development, with debates over the extent to which methane should be scaled, and, as such, has not yet been universally accepted. Once adjusted, the GWP* methane value would then be multiplied by the GWP100 emissions factor to integrate it into the overall farm footprint.

Essentially, this approach modifies a farm’s yearly methane emissions based on historical trends, scaling them to better reflect methane’s atmospheric lifespan before incorporating them into a GWP100-based report. While this suggests that GWP* could theoretically be applied in annual farm reports, it requires two critical components: comprehensive legacy data on methane emissions and an agreed-upon GWP calculation constant – both of which are still being refined by climate scientists.

The use of GWP* will show the most dramatic impact on the carbon footprint of extensive ruminant livestock farmers, where a high proportion of their emissions come from enteric methane emissions. Currently, for these types of systems, under the current footprint methodology, there remain limited management options for mitigation of emissions other than reducing stock numbers.

Until these foundational elements are fully developed and standardised, GWP* cannot yet be seamlessly implemented into farm carbon footprinting. However, as research continues and reporting frameworks evolve, there may be future opportunities for farms to integrate GWP* into their emissions assessments in a way that balances accuracy with practical usability.

Distinguishing Between Methane Sources

While GWP* offers a more nuanced way to assess the impact of short-lived greenhouse gases like methane, it is equally important to differentiate between biogenic and anthropogenic methane sources when applying this metric.

Biogenic methane – produced naturally through biological processes such as enteric fermentation in livestock, wetlands, and peatlands – should be adjusted using GWP*. This is because biogenic methane is broken down in the atmosphere at roughly the same rate that it is produced, meaning that when emissions remain stable, there is no net increase in atmospheric methane levels. This natural balance is an essential factor in ensuring that methane’s impact is not overstated when using GWP100.

Anthropogenic methane, on the other hand, originates from human activities such as fossil fuel extraction, waste management, and slurry management. Unlike stable biogenic methane sources, anthropogenic sources add to the atmospheric methane stockpile, meaning these emissions accumulate over time rather than cycling naturally. Because of this, applying a GWP* adjustment to anthropogenic methane could underestimate its long-term climate impact, as it does not break down at the same rate that it is emitted. 

Another key consideration is that as anthropogenic methane breaks down, it eventually converts into carbon dioxide, contributing to the long-term stockpile in the atmosphere. Since carbon dioxide persists for thousands of years, this means that anthropogenic methane has a dual impact – it plays a role in short-term warming as methane and then adds to long-term warming through its carbon dioxide byproduct.

These distinctions raise important questions about how GWP* should be applied. Should emissions from degraded peat bogs or residue burning be classified as natural or human-driven? Should increasing herd sizes in agriculture be considered an anthropogenic influence? The way these questions are answered will determine which methane emissions qualify for GWP* adjustments and which should be assessed using traditional GWP100 methods.

To ensure accurate and fair carbon footprint assessments, clear guidelines on how to apply GWP* in different contexts are essential. As the science behind methane accounting evolves, so too must the frameworks that determine when and how GWP* is used in emissions reporting.

Looking Ahead: The Role of GWP* in Farm Carbon Reporting

The debate around GWP* reflects its potential to improve how we account for methane emissions, particularly for livestock systems that feel misrepresented by GWP100. While it offers a more realistic view of methane’s short-term climate impact, its sensitivity to year-on-year changes can create volatility in farm-level reporting and complicate efforts to track progress reliably.

There is also a risk that GWP* could be misused, allowing businesses to claim emissions reductions without making genuine changes, or pressuring farmers into quick fixes like reducing herd sizes. To avoid these outcomes, any use of GWP* must be transparent, grounded in science, and applied fairly across all sectors. Done well, it could become a valuable tool – alongside GWP100 – for building a more accurate and trusted approach to agricultural carbon footprinting.

At Farm Carbon Toolkit, we remain committed to exploring how GWP* can be integrated responsibly into emissions reporting, ensuring that any changes reflect both scientific accuracy and practical fairness for farmers. We are exploring how GWP* can be appropriately implemented alongside the current GWP100 reports as part of a dual reporting system. With this in mind, we recommend continuing to produce reports using GWP100 now, as these will provide a valuable baseline to support dual reporting in the future. Given the significant impact of timespan on GWP* data, we are considering solutions based on multi-year reporting to improve accuracy and consistency. 

As research progresses and reporting frameworks evolve, clear guidance and safeguards will be essential in ensuring GWP* supports effective, fair and transparent carbon reporting across the farming sector.

Craig Blyth-Moore is a sustainability communications professional with over a decade of experience turning complex environmental issues into clear, compelling narratives. He has written extensively on energy efficiency, renewable energy, the energy transition and sustainable logistics, helping organisations communicate their sustainability strategies with credibility and impact. 

Craig holds an MSc in Environmental Sustainability and brings both subject matter expertise and strategic insight to his work. His writing has appeared on leading global platforms including Economist Impact and the World Economic Forum, helping to inform and inspire meaningful climate action.

Methane Inhibitors in Ruminant Diets and their impact on Greenhouse Gas Emissions

Posted on January 28, 2025 by - Insights

Written by Tim Dart / Project Manager, Farm Carbon Toolkit

This article reviews the mechanisms and inputs to ruminant diets which are known to impact greenhouse gas (GHG) emissions. It explores how these can be used by ruminant livestock farmers, alongside their limitations and the need for more research into more systems-based approaches to reduce methane emissions from ruminants.

Download this article as a PDF

Background

Methane (CH4) is an important greenhouse gas in livestock-based agriculture as it is particularly potent. Over a 20-year period, methane is approximately 80 times more powerful at heating the earth than carbon dioxide (CO2), though it dissipates much more quickly (7-12 years) compared to CO2.  Because methane is such a potent greenhouse gas, anything that can be done to reduce those emissions cost-effectively and without negative impacts on animal health, welfare and productivity is beneficial. 

Ruminant animals have diverse microbial populations in their stomachs and these form a natural ecosystem in their own right. Anaerobic fermentation is a key process in the digestion of natural forage-based diets. Methane is released by anaerobic microbial activity through a process called methanogenesis and is consequentially released into the atmosphere as a by-product of digestion. Methane production also results in a loss of gross ingested energy and reduces animal growth and development, so minimising methane production can in theory lead to an increase in animal growth and productivity. 

All ruminants (cattle, but also sheep and goats) together, contribute 30% of global methane released into the earth’s atmosphere. While this briefing focuses on methane inhibitors in ruminant diets, there are also opportunities to reduce methane emissions post-digestion, such as through manure and slurry management, biodigesters and activity to increase dung beetle activity. This will be the focus of a forthcoming briefing. Strategies to reduce enteric methane production are a major focus of research, due to the significance of methane. Initiatives like the Global Methane Hub are leading work on increasing our understanding of the mechanisms for reducing methane production safely in ruminants. Feasible approaches include improved animal and feed management, such as diet formulation, which has shown potential for meaningful emissions reductions. This is an active area of interest for organisations such as the Farm Carbon Toolkit (FCT) alongside our work on strategies to reduce enteric methane production post leaving the digestive system.

The commercial backdrop

FCT is aware of the significant ongoing efforts to develop products aimed at reducing methane emissions. Much of this work has focused on supplements that can be added to the animal’s diets, as these offer clear commercial opportunities for manufacturers. However, generating robust scientific data to support solutions based on practice changes, rather than commercially sold products, has been more challenging. As a result, these approaches and beneficial practices are underrepresented in discussions about methane reduction, due to the current lack of robust evidence demonstrating their effectiveness. 

Adding supplements to ruminant diets becomes difficult to achieve when those animals are consuming a forage-based diet, grazing in the wider environment and consuming a variable and diverse range of plant species. In these situations, research into the makeup of these forages which can reduce emissions is taking place, but with no patentable product to promote, the investment in research and development is understandably less intense. As such, FCT as a farmer-led community interest company, may have a legitimate role in seeking to facilitate and advance the science in this area of research and development.

Feed supplements are now becoming commercially available in the UK. The most common supplement currently is 3-NOP (Bovaer®) which has drawn the attention of the media in recent weeks. There are thought to be other products in advanced development that are now close to market. There are other strategies and approaches where scientific data has established methane inhibitory activity which we discuss below.

Current understanding of Methane Inhibitors and their mode of action

Bovaer®

Bovaer is a synthetically manufactured enzyme inhibitor with an active ingredient called 3-Nitrooxypropanol (hence 3-NOP Bovaer). It is scientifically referred to as a Methyl co-enzyme or M reductase Inhibitor, meaning it blocks the activity of a combination of enzymes that breaks down organic compounds (under anaerobic conditions found in the rumen) and therefore prevents the final biochemical stage of methane release. It is called a reductase process (a reduction process) that would normally result in the breakdown of a glucose chain (a sugar) into CH4 (a methane compound). 3-NOP inhibits that activity.

The Food Standards Agency Website states:

Bovaer has undergone rigorous safety checks by the Food Standards Agency as part of its market authorisation process and is approved for use, and is considered safe for the consumers of milk and beef. It has been demonstrated to be safe for the animal, consumers, workers and the environment.

The dosage of Bovaer is recommended at 1 gram per 20 kg of feed (label recommendation). The manufacturer claims that a 45% reduction in methane emissions for dairy cows and 30% for beef cattle, is achievable, but only when the supplement is fed within a blended or total mixed ration.

Seaweed

Microalgae, commonly known as seaweed, are a large group of marine plants, made up of three relevant taxa: Rhodophyta (red), Chlorophyta (green) and Phaeophyceae (brown). Bromoform is found in the highest concentrations in red seaweed Aspargopsis, which is grown in subtropical regions around the world. Brormoform is also found in lower concentrations in the brown and green seaweed groups which are more ubiquitous and widespread in the world’s oceans. Feed additives derived from Asparagopsis have reduced methane emissions by 40+% and 90% respectively.

Bromoform (CHBR3) has proven to be highly effective at inhibiting methanogenesis along with other halogenated volatile organic compounds. These VOCs effectively bind to enzymes and reductases, reducing H2 and CO2 release and through archaeal organisms these produce CH4. 

There are some studies and claims that Bromoform promotes increases in animal productivity, but other studies report modest reductions in milk yields (-6.5%) this appears to occur when reductions in animal intakes of feed are also observed. There has also been some evidence of abnormalities of the rumen walls of participating animals in such studies, with the loss of papillae and microscopic inflammation found in two studies, although the studies were not able to directly conclude that damage to the rumen was as a result of A.taxiformis supplementation. It is clear that there are discrepancies within the results of the various studies undertaken using Bromoform and that the energy in the H2 compounds resulting from the reductase reaction is not 100% possible to be re-diverted into volatile fatty acids and appears to require the expansion of H2 sinks within the rumen and is seen as an area of further developmental work.

There are numerous other bioactive compounds within the microalgae plants / seaweeds, and are known to produce other compounds that have anti-microbial function that could modify the rumen environment and reduce methane emissions in different ways. These include; phlorotannis, saponins, sulfonated glycans and other halocarbons and bacteriocins, these are the source of ongoing research and developmental work.

Condensed Tannins

Condensed Tannins (CT’s) are commonly found in high concentrations in various UK native flora, including Greater Birdsfoot Trefoil, Birdsfoot Trefoil and Sainfoin. These are all commonly found in herbal leys. CT’s are complex plant polymers of polyphenols found in legumes and other C3-type plants. CT’s are considered to reduce methane emissions through the following mechanisms:

  • Reducing fibre fermentation
  • Inhibiting the growth of methanogenic micro-organisms
  • Acting directly against hydrogen-producing microbes.

CT’s are able to bind to proteins, polysaccharides and metal ions and inhibit fibre digestion of longer-chain starch, cellulose and hemi-cellulose. As such CT’s consequently reduce the formation of hydrogen and acetate and inhibits the growth of methanogenic microorganisms, thus reducing enteric CH4.

Excessive inclusion of biologically active Condensed Tannins within ruminant diets have been found to be detrimental if it exceeds 6% of the overall animal diet in terms of dry matter intake (DMI). Elevated levels have been found to impact negatively on animal performance in terms of growth rate or milk yield. Target inclusion of CT’s are recommended to between 2 and 4% where improvements in animal performance can be achieved. The scientific quantification of the impact of CT’s on Methane emissions is not clear, with the research inconsistent with the work that has been published to date, but it is not considered inconsequential.

From other parts of the world, studies (predominantly Australia) are being undertaken on management practices and cattle browsing legumes known to hold high levels of Tannins, Desmanthus or Leucaena species. Leuceana is a tropical and sub-tropical legume fodder crop and Desmanthus is a tropical legume. The inclusion of both crops in ruminant diets has been shown to improve live weight gains and reduce methane emissions in cattle.

Diversity and grazing diets

By embracing the diversity of grazing diets, there is potential to reduce ruminant emissions through a whole-systems approach. This involves increasing the overall dietary content of tannins coming from multiple grazed forage species, such as herbal leys, willow and other silvopastoral feeds. This can achieve a measurable and meaningful reduction in enteric methane production. However, achieving this requires investment and expansion of knowledge and empirical quantification.

Other options

Other options for exploring enteric methane production, including but not exhaustively:

  • Genetic selection 
  • Vaccination
  • Feeding of grape marc (which is high in Tannins)
  • Adding nitrate or biochar to feed

Conclusion

This is a dynamic area of development and knowledge exploration on GHG emissions, with many complex interconnections to broader environmental concerns. It is important to recognise these links, which include, but are not limited to, animal welfare, animal longevity, as well as other sustainability factors such as biodiversity, water quality, air quality. These, along with other far-reaching sustainability goals, must be carefully balanced to inform the best possible decisions.

Methane Capture from Slurry

Posted on April 20, 2023 by - Insights, Farm Net Zero

A Farm Net Zero (FNZ) event held in March 2023, Trenance.

Methane emissions from livestock make up a large part of a farm’s carbon footprint, capturing and processing these emissions can help to reduce the carbon footprint. Farm Net Zero Monitor Farmers, Katie and Kevin Hoare, milk 120 cows on a 130-acre Cornwall Council holding which required investment to improve slurry storage. They have worked with Cornish company Bennamann as part of a pilot with Cornwall Council to install a covered slurry lagoon that captures and processes methane gas for use as a fuel. A group of farmers met to learn more about the system, with talks from Dr. Chris Mann, co-founder of Bennamann, and George Mills, Area Sales Manager at New Holland who supply methane-powered tractors. This event was made possible with thanks to the National Lottery Community Fund who fund the Farm Net Zero project.

Chris Mann explained how the Bennamann system works, and how it can allow slurry pits to become mini power stations. Slurry is scraped into a reception pit where it is macerated to enhance breakdown and then into a well-insulated lagoon where microbial activity produces methane and other gases, as it does in an uncovered pit. The gases are collected by the cover, processed in a shipping container-sized plant unit with the cleaned methane pumped into another reception chamber sitting above the slurry pit. This processed methane can then be bottled and used as fuel in New Holland’s methane-powered tractor, or in a Bennamann methane-powered generator to provide electricity either for on-farm use or sold to the grid. 

George Mills showed the group around New Holland’s methane-powered tractor. Currently, this is able to do four hours of work on a single tank, with a range-extending fuel tank/front weight increasing this to twelve hours. Although slightly more expensive than a diesel tractor, the ability to run on home-produced gas can mean it is cheaper to run in the long-term by avoiding fluctuating fuel prices. Plus, the reduction in diesel use can have major benefits to reducing the farm’s carbon footprint.

Kevin and Katie say the covered and processed slurry is a better product to use as it is almost like digestate, allowing them to apply it with a trailing shoe between grazings and reduce the amount of artificial fertiliser they require. They are now able to meet all the grassland’s P and K needs from slurry, which has clear financial benefits and also helps their carbon footprint by reducing demand for carbon-intensive artificial fertiliser. A grass yield trial is in development to quantify the benefits of the new slurry.

The ultimate aim for Trenance is to go off-grid, with the methane capture system providing all the fuel for machinery and electricity. Katie and Kevin are keen advocates for agriculture’s role in providing climate change solutions and feel it is important for farmers to tell their story to the public to demonstrate their commitment to the environment. Using the Farm Carbon Calculator for Trenance through the Farm Net Zero project shows that the new slurry store is capturing around 600 tonnes of CO₂e from methane, putting the overall carbon footprint at 0.13 kg of CO₂e per kg Fat- and Protein-Corrected Milk (FPCM).

Key takeaways:

  • Methane capture from slurry reduces the farm’s carbon footprint by preventing methane entering the atmosphere
  • Using processed methane as fuel also reduces emissions from red diesel and electricity use
  • The methane capture system has financial benefits through reductions in fuel/electricity purchases, the option to sell gas and the ability to use slurry more effectively and replace bought-in fertiliser.

Farm Net Zero resources, events, newsletter

  • To find out more about other previous events, trials and resources produced from the Farm Net Zero project head here.
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