“Ruminant methane should not be seen as emissions to be mitigated”

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 18th century
• 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.
• Because 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

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 expresses climate impact in the unit carbon dioxide equivalents (based on GWP-100 or GWP-20) which treats all methane emissions as “new”. 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 maths, computers and statistical tools.

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.

As emissions are often linked to consumption of meat and to a lesser extent milk (milk actually represents 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. 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, imports 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.

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.  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. 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 considers 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 from pastoral systems, 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. 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.

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 produces 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, 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 from a growing number of beavers also cause considerable emissions. Even forest plantations, long seen as the gold standard for carbon sequestration in landscapes come 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.

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. 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. A rich wetland can emit as much as 300kg methane per year according to the Swedish forestry agency. 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.

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, still climate policy is only about the fossil fuels and the changes in carbon stocks caused by land use changes. 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. 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 a very different story if the ruminants are fed with feed crops grown on arable land with artificial fertilisers 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 systems 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 are 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. 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. 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 the Regenetarianism blogger.

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 disputes 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 don’t graze). In addition, also the production of grass on crop lands can sequester a lot of carbon. Research from Sweden shows that croplands have increased their content of organic matter (carbon) substantially as a result of the cultivation of perennial leys. 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.

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. 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.

Read the fully referenced article in its original location here