The methane ruminations

The real feat of ruminants is their methanogenic metabolism that allows them to digest things that we can’t eat and convert them into highly valuable foods. Let’s stick to that.

Methane belching by grazing ruminants should not be seen as “emissions” that have to be mitigated. The numbers of animals should be regulated by the carrying capacity of the ecosystems, with due consideration of how landscapes should be used – chopping down rainforests to convert to grassland is not a good idea, while maintaining grazing of Europe’s semi-natural grasslands is a good idea. It is very different story if the ruminants are fed with feed crops grown on arable land with artificial fertilizers and pesticides.

Perhaps you wonder why I spend time on discussing methane emissions from ruminants. Essentially, I am much more interested in discussing the commodification of food, alternative food ways, industrial agriculture, the nitrogen cycle, the materiality of economic growth and how humans interact with the rest of the living. Animal agriculture, for the better and the worse, is linked to all these as well. Methane emissions, as mostly (erroneously) calculated, represent the biggest part of livestock emissions and almost half of all agriculture emissions. Therefore, methane has been central in the debate about livestock and climate.

It is unfortunate, because the dominating narrative is based on flawed science or at least flawed perspectives and a lack of understanding of the agriculture and food systems as well as the need to adapt farming to local ecological conditions and not to global models. It is unfortunate, as it has made many food activist believe that the most important thing they can do for climate is to stop eating beef or mutton and quit drinking milk, while the real target should be industrial agriculture (monoculture, input based, commodity focus) in all its shapes, regardless if it is producing livestock or crops. It is unfortunate, because within the livestock sector it has made ruminants appear to be much worse than monogastric animals (chicken and pigs) and it is unfortunate, that within the ruminants is has made intensive production appear to be superior to extensive production.

Anyway, here we go.

My focus here is methane (CH4), but let me briefly discuss carbon dioxide (CO2) and nitrous oxide (laughing gas, N2O). Depending on how livestock is raised they emit methane, carbon dioxide and nitrous oxide in varying proportions. Methane comes mainly from the digestive system of ruminants (cows, sheep, goats, buffaloes) and to a lesser extent from manure from all livestock and from the digestive systems of non-ruminant. Carbon dioxide emissions are from the direct use of fossil fuels in farm operations (tractors, combines, pumps), but also embedded in infrastructure and machinery. In addition fossil fuels are used for the production of plastics and in chemical fertilizers. It is mainly in the production of feed that these emissions occur. Nitrous oxide emissions are from manure and from the production and application of fertilizers. Soils also emit nitrous oxide, but that is mainly as a result of the application of nitrogen fertilizers (the whole nitrogen cycle is very complex, so this is a short version. If you want to know more I can recommend this new report by Rasmus Einarsson, which I plan to write about in the future). Overall, chemical fertilizers are the main driver of nitrous oxide emissions and an important part of the carbon dioxide emissions from agriculture.  An estimated total of 5% of total greenhouse gas emissions can be traced to nitrogen fertilizers(Gao and Serrenho 2023). Both carbon dioxide and nitrous oxide emissions are thus primarily a result of industrial processes originating in fossil fuels, while methane comes from a natural process intrinsic to ruminants, wild or tame. 

The consensus

I believe there are some basic facts for which there is a fairly high level of scientific consensus*:

-Methane is a powerful greenhouse gas, i.e. increasing levels of methane in the atmosphere cause global warming.  

- Methane concentration in the atmosphere has increased with 160% since the middle of the 18^th century (UNEP 2022)

-Methane is broken down in the atmosphere by chemical processes and the ”lifespan” of methane is calculated to be around 10 years (see more below under methane sinks).

-Constant methane emissions leads to a constant concentration of methane in the atmosphere and thus to no additional global warming, but maintains the warming already caused. Emissions of carbon dioxide accumulate in the atmosphere, which means that constant carbon dioxide emissions are causing increasing global warming.** (IPCC 2021, McAuliffe et al 2023)

-Beacause of this, there is not one correct way to recalculate methane into carbon dioxide equivalents but many different ways which are all based on various assumptions and value judgements, giving widely different results (IPCC 2021, McAuliffe et al 2023).

Different perspectives

The main difference is about the perspective and context. The general public gets fed with statements such as eating so much beef equals driving a car so far. Not only is the comparison unfair because the emissions from the car are just what comes out of the exhaust pipe and not the enormous emissions embedded in the cars themselves, the roads, the garages, the factories and hospitals which are all part of the automobile infrastructure. It is even more unfair because it express climate impact in the unit carbon dioxide equivalents (based on GWP-100 or GWP-20) which treats all methane emissions as “new” (McAuliffe et al 2023). The GWP metric is based on the comparisons of the warming potential of a pulse of methane and a similar pulse of carbon dioxide. By this method all emissions of methane will cause marginal warming and by inference every day a cow lives it will add to global warming and every glass of milk will also add to global warming. But that is only correct if methane emissions have increased with the same quantity as that in the pulse. Most cows were there also yesterday and the year before. A reduction of methane emissions also have another effect than a reduction of carbon dioxide emissions. Reducing carbon dioxide emissions just means that global warming will progress slower than without the reduction, while reducing methane emissions actually leads to a lower temperature***. To deal with those flaws other metrics, e.g. GWP*, have been developed and the application of them leads to very different results. If you really want to dive into these issues, I can recommend this technical report by the UNFCC secretariat (2023). The main point to keep in mind is that constant emissions of methane cause no additional global warming, and that the LCA values of beef, mutton, wool, milk or cheese are not giving a correct picture of the climate impact as long as GWP100 or GWP20 are used.

It should be noted that the debate is rarely between climate scientists in the sense of people that actually have expert knowledge of the climate and Earth systems but by people and scientists with other expertise. For example, most of the popular debate about the impact of livestock is derived from life cycle analyses using the metric GWP100 or sometimes GWP20. But those making life cycle assessments are mostly no more climate experts than I am (or you are) even if they often are portrayed like that in media. For making a lifecycle assessment you need as little understanding of climate science as you need to understand the metabolism of the human body to calculate your intake of food energy. And for making a meta-analysis of thousands of lifecycle analysis you just need math, computers and statistical tools (I was tempted to link to an article where one such pseudo climate expert claimed that “Avoiding meat and dairy is ‘single biggest way’ to reduce your impact on Earth”, but I don’t want that article to get more clicks than it already has got).

Methane from ruminants

I will primarily discuss cattle and buffalo here as they are the dominating ruminant species. The methane emanations from ruminants have undoubtedly increased. Between 1961 and 2019 the yearly emissions from cattle and buffalo increased from 59 Mt CH4/year to 89 Mt CH4/year, i.e. an increase with 50% over almost 60 years. The effect on global average temperature of the methane from an increasing number of cattle has been estimated to 0. 028 ̊C from 1981 to 2019 and 0.15 ̊C since 1750. Emissions from cattle represent a minor share of the increase in anthropogenic methane emissions in recent decades (del Prado et al 2023).  

As emissions are often linked to consumption of meat and to a lesser extent milk (milk actually represent a larger share of the methane emissions) it is worth while noting that global per capita beef consumption has not increased at al since 1961, milk consumption just little. Meanwhile the global population has increased with 151% which means that the increase in methane emissions of 50% can fully be attributed to population growth and not to increased consumption. Per capita, methane emissions from ruminants have been substantially reduced (FAOSTAT 2024). Any increase in methane emissions from ruminants should thus not be framed in the context of “increasing meat consumption” but in the frame of growing population. Meat consumption per capita has increased but that is attributable to the increase of the monogastric animals, in particular chicken and not beef or mutton. It is quite surprising that in the heated “meat” debate, articles are mostly illustrated with cows or a steak when the share of consumption is around 20%.

Of course, this can differ between countries. In Sweden the emissions from cattle is now lower than it was 1870 (Danielsson 2023). Sweden can thus have the same number of cattle for thousands of years without them causing any additional warming. The consumption of ruminant meat per capita has increased somewhat but the consumption of dairy products has decreased considerably. Sweden, however, import beef corresponding to 45% of the consumption, but that equals more or less an increase of population with 40% since 1960. Studies from Germany show a similar pattern as Sweden (Kuhla and Viereck 2022)

There is a widespread opinion that industrial animal agriculture emits more methane than traditional livestock systems, but, unfortunately, that is not at all correct. On contrary, the increase in livestock methane emissions is mainly from developing countries and the methane emissions per kg meat or milk is considerably higher in extensive livestock production. For example, African cattle in grazing emits six times more methane per kg meat or milk than European ones (GLEAM 2024).  On the other hand, intensive livestock production leads to a more intensive feeding and higher emissions of carbon dioxide and nitrous oxide. In the USA almost three quarters of all methane emissions are from cow-calf operation which are based on grazing and some winter forage with very small quantities of supplement feeding. Just 13% of the emissions came from feedlots (Rotz et al 2019). With the dominating way of calculating carbon dioxide equivalents as a measure of global warming intensive livestock production is “better” while the opposite is true if one consider that most of the methane emissions are not new. Notably, from what I can understand there have actually been no measurement at all of the actual emissions form pastoral system instead figures are derived from standard emission factors. Some recent research from the Netherlands and Denmark indicate that methane emissions from grazing cows might have been overestimated.

A fair consumption?  

Some agree that the total number of livestock doesn’t necessarily have to be reduced, but that those having much livestock and therefore high historical emissions should reduce the numbers to allow others to increase their production or consumption (Rogelj and Schleussner 2019). But that argument misses some pertinent points. First, the notion that consumption and production patterns should be very similar in all parts of the world is mistaken. There are ecological reasons for why ruminants have been very important in the agriculture and food systems in many parts of the world, but not in others. In cold and dry climates, ruminants have been very important and constituted staple foods. When I visited Mongolian herders some ten years ago a family I visited ate 2 cows, 10 sheep and one horse and enormous quantities of milk. Meanwhile the agriculture and food systems of the fertile river plains in Asia have had a very small role for ruminants.

If I, again, look into the Swedish situation we have 0.9% of all cows and 0.03% of all sheep in the world while our population is 0.13% of the global (FAOSTAT 2024). So not even with a fairness argument there would be any need to reduce the number of cows here. Having said that, there are countries with totally oversized livestock sectors including many European countries, even if it is mostly pigs and chicken that are too many. Several of them, e.g. Denmark, Germany and the Netherlands, have lately taken steps to reduce the numbers. New Zeeland has a totally disproportionate dairy sector as well as a big production of beef, sheep and even deer (!) and there may be many valid reasons to shrink the livestock. Brazil is another country with an oversized livestock sector, not only cattle but also chicken that now is even bigger than beef in the export market.

An ecosystem without cows is not a methane-free ecosystem

The methane climate calculations are based on the assumption that a reduction of cows will mean a corresponding reduction in emissions. But that is based on the assumption that the biomass that is now consumed by cows will not be transformed by any processes that produce methane. Clearly that is a flawed assumption. If we limit the discussion to the grasslands, which do provide most (at least 55%) of the feed of cattle and sheep alike (Mottet et al 2017), it is apparent that if all domesticated animals were culled, the number of wild animals would increase, and most of them would be ruminants. The grass not eaten by animals would be eaten by insects such as termites or grasshoppers, rot or burn depending on climatic factors. In all cases the land will emit methane.

As cattle use a lot of land, rewilding of various sorts are often proposed as a better alternative than grazing cattle or sheep. While re-wilding can have considerable merits from a biodiversity perspective (but there are also considerable problems associated with rewilding) it is not at all apparent that new landscapes will emit less methane. Dams by a growing number of beavers also cause considerable emissions (Colin at al 2014). Even forest plantation, long seen as the gold standard for carbon sequestration in landscapes comes with their own problems. First,the carbon stock is mainly in the wood above ground and is there very vulnerable to fires, storms and insects and secondly, recent research show that the reduction in albedo can turn forests into net warming ecosystems compared with grasslands or other more open landscapes (Hassler et al 2024).

Missing baselines or alternative land uses

There are many efforts to calculate the number of wild animals before humans reduced their numbers as well as their methane emissions (Pedersen et al 2023,  Manzano et al 2023) Of course we can’t know for sure and it also depends on at what time we set the baseline, but it can safely be assumed that the biomass of wild mammals and their methane emissions were***** in the same order of magnitude as the biomass and emissions from domestic ruminants. The methane emissions from wild animals even today are considered to be “natural” while emissions from domestic ruminants are classified as “anthropogenic”. This is hardly “fair”.

Another missing baseline is that the reduced methane emissions from the draining of natural wetlands is not counted as a reduction of emissions while the emissions of carbon dioxide and nitrous oxide from these wetlands are classified as anthropogenic. Historically has at least 20% of all wetlands in the world been drained for agriculture purposes, and even far higher share in the temperate zones (Paudel et al 2016). A rich wetland can emit as much as 300 kg methane per year according to the Swedish foresty agency (2021). If such land is grazed by cattle, which we do on a small scale on our farm, the corresponding emission will be considerably less, but the emissions from the cattle are now suddenly anthropogenic. There is a similar issue around rice cultivation which often take place in former wetlands.  

All this makes the net effect of a mass culling of domestic ruminants highly uncertain. Considering that it is also the livelihood and an integral part of their culture of many hundred million people it is simply insane to consider that under the umbrella of climate policy (Houzer and Scoones 2021).

Are the emissions natural or anthropogenic? Are they even emissions?

One could discuss if it is reasonable that the methane emissions from ruminants is classified as anthropogenic. Of course, for the climate, it makes no difference if methane comes from natural sources or from fossil emissions. But it makes a big difference for climate policy because climate policy and the climate debate is all about regulating anthropogenic emissions.  Natural processes emit approximately 20 times more carbon dioxide than the combustion of fossil fuels (Friedlingstein et al 2022), still climate policy is only about the fossil fuels and the changes in carbon stocks caused by land use changes (LULUCF). Natural systems are assumed to be in balance and this includes the emissions of carbon dioxide by humans, farmed animals, plants, and the whole micro life in soils. It is very hard to see why the carbon dioxide emitted from the metabolism of a cow is considered natural but not the methane (even if the scandalous movie Cowspiracy did count carbon dioxide exhaled by livestock as emissions).  In that vein, I think it is rather dubious to even to call the methane emanating from cows for “emissions”.

From what has been discussed above, I don’t think we should see methane belching by grazing ruminants as “emissions” that have to be mitigated or reduced. The numbers of animals should instead be regulated by the carrying capacity of the ecosystems, with due consideration of how landscapes should be used – chopping down rainforests to convert to grassland is not a good idea, while maintaining grazing of Europe’s semi-natural grasslands is a good idea. To ensure more space for wild life is also a good idea, even if the competition between wild and domestic herbivores is overstated. It is very different story if the ruminants are fed with feed crops grown on arable land with artificial fertilizers and pesticides. The real feat of ruminants is their methanogenic metabolism that allows them to digest things, grass, leaves, and straw, that we can’t eat and convert them into highly valuable foods. Let’s stick to that.****

Methane sinks

Natural system tend to have self-regulating processes, where the output of one process is the input to other processes. Considering that there has been a lot of methane emitted over the years it is apparent that methane is also taken care of, that is what is behind the quoted “lifespan” of methane. This must be understood as an average and not as an aging process of each methane molecule. Some methane molecules will degrade in seconds after they were formed while other will be around for centuries.  I will just briefly mention what is often called methane sinks. In reality they are not sinks in the sense that they will store methane. Instead they will break down methane into simpler forms. As a young boy I was very interested in chemistry but I must admit that I can’t totally follow all the ins and outs of methane chemistry, please check the references for a more complete and accurate picture. Anyway, here is my rough sketch: 

Some methane, but not a very big share, is eaten by methanotrophs (sometimes called methanophiles), bacteria or archaea that use methane as their source of carbon and chemical energy (Friedlingstein et al 2022). There is also some reactions with chlorine (Cl) that can convert methane but it seems to be of limited importance. Most methane is broken down in the troposphere by reacting with hydroxyl radicals (Stevenson et al 2020). The limiting factor here is the availability of hydroxyl radicals. Increased hydroxyl radical formation would act as a “sink” while decreased hydroxyl radical formation means that methane stays longer in the troposphere. Hydroxyl radical formation is influenced (negatively or positively) by other gases such as carbon monoxide, nitric oxide, ozone, water vapor and volatile organic compounds. Many of these gases have both man-made and natural sources. There is the hypothesis, probably hard to prove, that the emissions of some of these gases from grasslands may create sufficient hydroxyl radicals to actually break down the methane emitting from the animals grazing the same grasslands. Considering that methane levels were fairly stable for a long time, despite many factors influencing emissions, it seems plausible that there would be such mechanism or other natural regulating mechanisms. If you want to dive more into this topic, please follow this link to Regenetarianism, an anonymous, non peer-reviewed source (with many peer-reviewed references to follow).

Clearly there are still many gaps in our knowledge of the methane cycle. For me that is yet another argument for why we should be careful of not jumping into actions and policies which later on may show to be misdirected.

Mitigating methane emissions with carbon sequestration in soils

There is also the possibility to sequester carbon in grasslands. While nobody dispute that carbon can be sequestered in grasslands, there has been considerable controversy about to what extent, for how long and how grazing can contribute to this. On average, it seems that grassland carbon sequestration can be very substantial for grazing livestock (It has obviously no relevance for livestock that doesn’t graze). I recently wrote an article on the topic (Rundgren 2024). In addition, also the production of grass on crop lands can sequester a lot of carbon. Research from Sweden show that croplands have increased their content of organic matter (carbon) substantially as a result of the cultivation of perennial leys (Poeplau et al 2015). There are similar results from other agriculture systems as well.

In general, the narrative of “the climate” being primarily a physical system that is regulated by emissions and sinks of a number of greenhouse gases is a far too simplistic view as the ecological systems also are co-creators of the climate (Pielke et al 2022).

Fossil methane emissions are relatively easy to fix and will disappear

Considering that methane levels in the atmosphere are high and increasing, should we not do anything? For sure, there is a very low and big hanging fruit in the reduction of methane from fossil fuels. Those emissions are also much bigger than mostly assumed (IEA 2022). Ultimately, if fossil fuels are phased out, which they will be either because of climate policy or because of economic reasons, those methane emissions will also disappear. In addition, reduced emissions of other gases will probably also improve the methane sink. But even in the shorter term a huge share of the fossil methane emissions are about leaks in the fossil gas chain and they could quite easily, and even profitably, be plugged (IEA 2022).

References

Colin J. Whitfield, Helen M. Baulch, Kwok P. Chun, Cherie J. Westbrook. Beaver-mediated methane emission: The effects of population growth in Eurasia and the Americas. AMBIO, 2014

Danielsson, Rebecca 2023, Nötkreaturens metanproduktion i Sverige – en jämförelse mellan 1937 och 2019, SLU rapport 310.     

del Prado A, Lindsay B, Tricarico J (2023) Retrospective and projected warming-equivalent emissions from global livestock and cattle calculated with an alternative climate metric denoted GWP*. PLoS ONE 18(10): e0288341.

FAOSTAT, https://www.fao.org/faostat/en

Friedlingstein et al, Global Carbon Budget 2022, Earth Syst. Sci. Data, 14, 4811–4900, https://doi.org/10.5194/essd-14-4811-2022, 2022.

Gao, Y., Cabrera Serrenho, A. Greenhouse gas emissions from nitrogen fertilizers could be reduced by up to one-fifth of current levels by 2050 with combined interventions. Nat Food 4, 170–178 (2023)

GLEAM, Global Livestock Environmental Assessment Model, FAO 2024, https://www.fao.org/gleam/dashboard/en/

Global Methane Assessment (PDF). United Nations Environment Programme and Climate and Clean Air Coalition (Report). Nairobi. 2022.

Graham A McAuliffe et al 2023 Environ. Res. Lett. 18 084014

Hasler, N., Williams, C.A., Denney, V.C. et al. Accounting for albedo change to identify climate-positive tree cover restoration. Nat Commun 15, 2275 (2024).

Houzer, E. and Scoones, I. (2021) Are Livestock Always Bad for the Planet? Rethinking the Protein Transition and Climate Change Debate. Brighton: PASTRES.

IEA 2022, Methane emissions from the energy sector are 70% higher than official figures https://www.iea.org/news/methane-emissions-from-the-energy-sector-are-70-higher-than-official-figures

IPCC 2021 IPCC Sixth Assessment Report—Working Group 1: The Physical Science Basis

Kuhla, B and  G. Viereck, Enteric methane emission factors, total emissions and intensities from Germany's livestock in the late 19th century: A comparison with the today's emission rates and intensities, Science of The Total Environment, Volume 848, 2022.

Manzano, P., Pardo, G., Itani, M.A. et al. Underrated past herbivore densities could lead to misoriented sustainability policies. npj biodivers 2, 2 (2023). https://doi.org/10.1038/s44185-022-00005-z

Mottet, A Cees de Haan, Alessandra Falcucci, Giuseppe Tempio, Carolyn Opio, Pierre Gerber, Livestock: On our plates or eating at our table? A new analysis of the feed/food debate, Global Food Security, Volume 14, 2017.

Paudel, Rajendra & Mahowald, Natalie & Hess, Peter & Meng, Lei & Riley, William. (2016). Attribution of changes in global wetland methane emissions from pre-industrial to present using CLM4.5-BGC. Environmental Research Letters. 11. 034020. 10.1088/1748-9326/11/3/034020.

Pedersen, R. Ø., Faurby, S., & Svenning, J.-C. (2023). Late-Quaternary megafauna extinctions have strongly reduced mammalian vegetation consumption. Global Ecology and Biogeography, 32, 1814–1826. https://doi.org/10.1111/geb.13723

Peng, S., Lin, X., Thompson, R.L. et al. Wetland emission and atmospheric sink changes explain methane growth in 2020. Nature 612, 477–482 (2022). https://doi.org/10.1038/s41586-022-05447-w

Pielke, R.A., Sr.; Peters, D.P.C.; Niyogi, D. Ecology and Climate of the Earth—The Same Biogeophysical System. Climate 2022, 10, 25. https://doi.org/10.3390/cli10020025

Poeplau, C., Bolinder, M. A., Eriksson, J., Lundblad, M., and Kätterer, T.: Positive trends in organic carbon storage in Swedish agricultural soils due to unexpected socio-economic drivers, Biogeosciences, 12, 3241–3251, https://doi.org/10.5194/bg-12-3241-2015, 2015.

Rogelj J and Schleussner C-F 2019 Unintentional unfairness when applying new greenhouse gas rmissions metrics at country level Environ. Res. Lett. 14 114039.

Rotz, C. A., S. Asem-Hiablie, S. Place, and G. Thoma. 2019. Environmental footprints of beef cattle production in the United States. Agric. Syst. 169:1–13. 

Rundgren, G, A nail in the coffin? Not really, Garden Earth – beyond sustainability 7 March 2024.

Skogsstyrelsen, Klimatpåverkan från dikad torvtäckt skogsmark – effekter av dikesunderhåll och återvätning, RAPPORT 2021/7. https://www.skogsstyrelsen.se/globalassets/om-oss/rapporter/rapporter-20222021202020192018/rapport-2021-7-klimatpaverkan-fran-dikad-torvtackt-skogsmark--effekter-av-dikesunderhall-och-atervatning.pdf

Stevenson, D. S., Zhao, A., Naik, V., O'Connor, F. M., Tilmes, S., Zeng, G., Murray, L. T., Collins, W. J., Griffiths, P. T., Shim, S., Horowitz, L. W., Sentman, L. T., and Emmons, L.: Trends in global tropospheric hydroxyl radical and methane lifetime since 1850 from AerChemMIP, Atmos. Chem. Phys., 20, 12905–12920

UNFCC, In-session technical workshop on findings on emission metrics contained in the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, 15 June 2023.

* Clearly, consensus, is no guarantee for that something is accurate. For a lay person (like me) it is a reasonable stance to accept scientific consensus as being the best we can know for the time being.

** This is, of course, time dependent, with a very long term perspective (thousands of years), also the effect of constant carbon dioxide emissions will cease to accumulate and carbon dioxide levels will stabilize.

*** This is used by some as an argument for why it is so very important to reduce ruminant methane emissions now. Meanwhile, the implication is also that it really doesn’t matter if you do it now or 100 year later, the effect will be the same – unless there are tipping points. This effect is also used by some proponents of industrial farming to claim that a more intensive livestock is preferred as we can get the same quantity of meat with lower methane emissions. I have also seen it used by the livestock industry as a way to get carbon credits for mitigating methane emissions with feed supplements, methane recovery or intensified production!   

**** This doesn’t mean that it is always “wrong” to use feeds from croplands or grain in reasonable quantities e.g. in dairy production. 

***** I had mistakenly written “are” instead of “were” in the first version published.