LIFECYCLE ANALYSIS OF ENTERIC METHANE MUST BE REVISED.

Introduction: Methane produced by ruminants (also called enteric methane) is in the spotlight because of assumptions about its high global warming potential. This has resulted in perceptions and policies with profound effects on worldwide ruminant, especially cattle, keeping and production. This article will show that methane emissions should be seen in context with different fates and timelines in the atmosphere and its warming effects, and the limitations caused by counting only carbon (methane) emissions in Life Cycle Analysis (LCA), instead of carbon in and out.

Sources of methane (CH₄) and their definitions: Methane is released from many sources apart from ruminants, e.g. below ground fauna, shell fish, blue green algae, saprophytic fungi, wetlands, lakes, landfills, rice paddies, fossil fuels and fires. It is classified into biogenic and anthropogenic sources, the latter two being thermogenic and pyrogenic. Biogenic are from naturally occurring sources, thermogenic are from fossil fuels and pyrogenic is methane released from fires. It is important to note that these forms have different atmospheric lifespans and global warming potentials due to different breakdown rates which are discussed below.

Methane in the atmosphere: Methane accumulates primarily in the troposphere section of the atmosphere. It’s activity there is expressed in one of three ways: half-life, lifespan and perturbation time. The half-life is the time it takes for 50% of the methane to break down in the troposphere. The lifespan is the average time it takes for methane to break down in the troposphere, and the perturbation time is the time it takes for all the lingering effects of methane to subside.

Currently, the half-life is about 7 years, the average lifespan 9 to 12 years, and the perturbation time around 13 years. So, if 100 units of methane are emitted at one time, 50 would have disappeared in 6 to 7 years. The break down, however, occurs along an exponential curve, so some methane will break down very quickly within a few minutes, while others that escapes into the stratosphere can last as long as 144 years. The average of 9 to 12 is the median point of the exponential curve.

Break down of methane: Methane is oxidised by hydroxyl radicals in the atmosphere to carbon dioxide (CO₂) and water vapour (H₂O), the extent of the process being referred to as the atmospheric oxidation capacity. A hydroxyl radical is an OH molecule with an unpaired electron, and which is primarily formed from ozone (O₃) photolysis, although there are other ways as well. The hydroxyl radical is super reactive, and is referred to as the ‘’atmospheric cleaner’’ which removes or break down numerous trace gases; the most important being carbon monoxide (CO), methane, numerous anthropogenic volatile organic compounds from industrial processes and burning of fossil fuels, and biogenic hydrocarbons from plants, phytoplankton and algae.

The removal of methane is influenced by both the staying time and the amount in the atmosphere. Since the start of the industrial revolution, the half-life, average lifespan and perturbation time of methane has all increased. The half-life has increased from approximately 4 to 7 years, the average life span from about 6 to 9 - 12 years, and the perturbation time has also increased significantly. There are several reasons why, the most obvious being the burning of fossil fuels. Burning fossil fuels does three things: firstly, it releases a lot more methane that hadn’t been part of the biogenic cycling of methane; secondly, burning fossil fuels also releases carbon monoxide. Carbon monoxide reduces the atmospheric oxidation capacity for methane since it uses up the hydroxyl radicals needed to break down methane, and thirdly, the added air pollution and smog interfere with the wavelengths of light needed for ozone photolysis. Thus, with a longer half-life and lifespans of methane, more methane accumulates in the atmosphere, which increases atmospheric warming.

Biogenesis and methane: The earth harbours a mostly closed and repetitive system with a finite number of elements, including carbon, that exist in molecules or radicals as either a solid, liquid or gas. These elements cycle and recycle through these phase changes in various molecules at different rates of speed at varying rates of time. With carbon (methane in this case), the problem has been that science has concentrated mainly on emissions rather than on total carbon accounting analysis, obviously because of the scare of global warming. However, with recent introduction of isotope and satellite methodology and using carbon budget analysis, it has been shown that the amount of methane emitted is closely matched by the amount of methane oxidized. If the amount emitted  exceeds the amount oxidized, the excess persists and accumulates in the atmosphere. The biogenic cycle shows the balanced carbon budget, because the biogenic is the same carbon being cycled, whereas carbon (methane) accumulates with thermo- and pyrogenesis. This results because OH is largely consumed by the extra anthropogenic emissions of CH₄ as well as the CO produced by the combustion of fossil fuels and fires.

A further reason for the balance being disturbed is that atmospheric carbon has also increased due to the reduction of photosynthetic carbon cycling capacity through industrial and tilled agricultural practices, degradation, desertification and deforestation, and also because of the weakening of soil and tropospheric sinks. Soil sinks rely on microbial and chemical processes, while tropospheric sinks rely upon hydroxyl radical availability (i.e. the atmospheric oxidation capacity). Agriculture practices and livestock production have been implicated in all of these, and therefore there is a responsibility for reversal and regeneration. This is the topic of the next sections.

Increasing atmospheric oxidation capacity: All pathways of OH formation are directly and indirectly tied to moisture and biogenic activity. In ecosystems rich in vegetation, organic volatiles, soil microbes, and photochemical flux — essentially “alive air” — OH production can be orders of magnitude higher than in dry or desert-like air. More humid ecosystems produce a lot more hydroxyl radicals during both day and night. So, when the hydroxyl radical concentrations are increased, the half-life and life span of methane and other hydrocarbons are reduced, even though the rate constants (reactivity of the molecule) of the various gases stay the same. Thus, biogenic methane emitted into the troposphere in an ecosystem context where the precursors for hydroxyl radical formation exist will be oxidised faster than the average lifespan of 9 – 12 years. This is due to the greater availability of hydroxyl radicals and therefore increased atmospheric oxidation capacity than in other systems. To bring this into a methane management context: reducing thermogenic and pyrogenic methane emissions should be first priority. Reducing deforestation, degradation and desertification should be a further priority.

Rehydration of degraded landscapes: This is primarily related to soils and soil function:

• Increase soil carbon through increasing organic matter via decomposition and microbial carbon metabolites and necromass (dead microbes)
• Improve soil structure via mycorrhizal (fungal) associations, which will increase oxygen, water infiltration and retention, root zones for water, phosphorus and micronutrients, and photosynthetic rates and root exudates
• Increase above and below ground biomass (plant and microbial), which will increase plant transpiration, biogenic volatile organic compounds (BVOCs), microbial diversity, and the diversity of fungi etc. that live in a plants (endophytes). The BVOCs have two functions: Together with nitric oxides in the soil, they form OH via O₃ photolysis, and in combination with OH they form secondary organic aerosols which can seed clouds and consolidate water vapour into rainfall. An increase in endophyte diversity results in a reduction of micro-organisms that produce methane in the soil, thereby limiting the total load of methane entering the troposphere.

Implications to agricultural practices: In crop production, soil organic matter and carbon must be protected and maximised. This requires minimal or no tilling, use of cover crops, and where appropriate, livestock introduction, i.e. regenerative (RA) practices. Here, and in sole ruminant livestock systems, well managed rotational grazing programs such as adaptive management or quick rotation high intensity systems, the following benefits may accrue:

• Grazing redirects photosynthetically fixed carbon in plant vascular tissue from going to the leaves and seeds down to the roots and being exuded as exudates for minerals. This action will increase soil organic matter
• Grazing causes the release of BVOCs
• Breakdown and decomposition of plant material will be promoted, particularly in semi-arid and arid environments with less moisture. Decomposed materials will increase organic matter via the decomposition pathway.
• Manure, which is approximately 30% microbes (bacteria, fungi, protozoa), contributes to soil organic matter also as microbial necromass, especially in ecosystems with lots of soil fauna (e.g. dung beetles, worms, termites) that quickly breakdown and mix manure into the topsoil, subsoil and further down.

Implications to LCA accounting: Well managed RA practices will improve soil health and structure, thereby increasing water infiltration and retention. Such practices will also increase plant growth plus water vapour and BVOC emissions. This will increase the relative humidity on such managed farms due to increased evapotranspiration from a greater plant biomass, which in turn will lead to greater OH formation and availability. Therefore, the atmospheric oxidation capacity will increase, resulting in faster oxidation of biogenic methane.

So, in terms of RA grazing, it doesn’t just offset enteric methane via soil carbon sequestration; it also offsets enteric methane via enhancing the atmospheric oxidation capacity of the troposphere due to the increased OH formation and availability. To a lesser extent, there is also an increased capacity of the soil to oxidize methane via both the methanotrophs and chemical processes.

In addition, with all the increased biomass/biodiversity (plant, animal, micro fauna etc.) above and below ground with RA management, there is further a lot of photosynthetic fixed carbon transfer to higher trophic levels that should also be taken into account in the LCA accounting models.

Concluding remarks: The international LCA counting methodology, calculating only methane emissions is inadequate and is harmful to ruminant production, particularly cattle accounting for 70% of the global ruminant enteric methane emissions. This should be revised, taking into consideration biogenesis and how OH oxidation can be enhanced at the farm, ecosystem and global levels. Some of these principles and counting methodologies have been implemented in published models for dairy and wool farming by South African scientists, which are referenced below.

References:

Reinecke, R., Blignaut, J. N., Meissner, H. H., & Swanepoel, P. A. (2025). DESTiny, an online farm-wide tool to estimate the net carbon emissions of a pasture-based dairy farms in South Africa. Frontiers in Sustainable Food Systems, 9, 1491973. https://doi.org/10.3389/fsufs.2025.1491973.

Blignaut, J., Swan, P. & Blignaut, L. (2026). A biogenic life cycle approach towards estimating the carbon intensity of wool production: Evidence from six Australian case studies. Agricultural Systems https://doi.org/10.1016/j.agsy.2025/104631