On average each of us humans breathes out 1kg of carbon dioxide (CO2) every day, the larger you are or the more you exercise, the more CO2. So why don’t we consider human metabolism to be a cause of climate change? After all, there are 7.6 billion of us, that’s a lot of CO2 hitting the atmosphere each day (1).
It’s because the carbon dioxide we breathe out originally came from the air, so when we exhale we’re simply putting it back from whence it came: we are part of a continuous carbon cycle, we are not adding new carbon. The same is true for anything that respires, including cows, each of which breathes out a whopping 10kg of carbon dioxide per day! So whether you are a cow, dog, human, ant or elephant, your breathing does not increase CO2 in the atmosphere.
The basic carbon cycle goes like this: plants photosynthesise using energy from the sun to take CO2 from the air, split it into carbon and oxygen, release the oxygen back into the air and use the carbon to grow. Humans and animals eat the plant (or animal in the food chain that originally ate the plant), metabolise the carbon, use it for their own growth and repair, and breathe out as CO2 or excrete the rest.
Carbon also cycles via the gas methane (CH4), burped by cattle and for which they are much vilified. Yet the carbon in methane from cows, just like that in their breath, is being recycled from the plants they ate, which originally took it from the air.
This blog aims to clear up the confusion often caused by the conflation of two quite distinct sources of carbon, which has led to the common belief that all cows are bad for the environment. And to explain how cows raised in a particular way not only have a positive impact on the planet by helping reduce atmospheric carbon but are actually essential to rebuilding and restoring the health of the world’s depleted soils.
But in order to get to grips with that, we first need to take a look at how carbon mooooves….
Carbon: cycling or stored
There’s a finite amount of carbon in the earth’s biosphere, which is either cycling or stored.
As a basic building block of all life on earth, carbon is continuously cycled (and recycled) in many guises. It may be cycling as a gas (CO2 or CH4) in the atmosphere and absorbed into oceans, or as a liquid or solid when part of living things or recently living things, such as plants, animals, microbes, soil humus and wood. Carbon moves easily and constantly between its gaseous, liquid and solid forms as it is cycled by plants and animals through respiration, rumination, reproduction and all other processes of life. This is naturally cycling carbon.
On the other hand, the majority of stored carbon was removed from the atmosphere and laid down during the carboniferous period 300-360 million years ago, a time when atmospheric CO2 levels were much higher than now (2). Over the millennia, this has formed into the fossil fuels oil, coal and natural gas. Whilst undisturbed, this carbon is locked away: stored and not part of the moving carbon cycles.
Natural carbon cycles all start with photosynthesis
There are many different natural carbon cycles, each of different complexity and duration, but they all start with photosynthesis – the capturing of sunlight energy by green growing plants. Some carbon recycles from the air through a plant and back to the air in as little as 24 hours as plants photosynthesise during the day and respire at night. Some cycles take weeks or months, such as when a plant grows and is eaten by an animal that metabolises its carbon and then breathes it out as CO2 once more. Other cycles last many, sometimes hundreds of years, for example when a tree grows to maturity, then is burned in a forest fire, which releases carbon back into the atmosphere.
There’s an annual cycle as CO2 levels in the atmosphere ebb and flow each year with the seasonal ‘breathing’ of the world’s vast boreal forests in North America, Alaska and Russia: levels are lowest in late autumn after a summer of rapid photosynthesis when CO2 is removed from the air - a long, slow global inhale; then, as leaves fall and photosynthesis declines, atmospheric CO2 levels gradually rise over the winter peaking again in May - a long, slow exhale.
A less well known carbon cycle, but one that is fundamentally important for all life on earth, is the capacity of soils to absorb carbon. The soil is alive with micro-organisms and when plants take carbon from the air, as described above, as well as for their own growth, they use it in a symbiotic relationship to feed the soil microbes in exchange for nutrients and other ecological functions. Plants do this by releasing exudates via their roots in the form of many different carbon compounds; in effect they are exuding liquid carbon.
The energy provided by liquid carbon in plant exudates drives a multitude of interactions within soil, including the reproduction and life-cycles of many different soil microbes. Organic matter from the biomass of plant roots as they grow and die, plant matter trodden into the soil by grazing cows, along with the fertiliser they leave behind, all adds carbon (and other nutrients), which the microbes ultimately convert into complex and very stable carbon compounds called humus. Humus is the building block of soil and building new soil, by storing carbon in this stable form, is called carbon sequestration. Under healthy aerobic soil conditions, up to 40% of the carbon captured from the air by plants can be sequestered in the soil in this way (3).
Sequestered carbon can stay locked in the soil for many, hundreds and potentially thousands of years, as in old growth forest soils and the last of the unploughed American prairies. And although there is a limit to the amount of carbon a soil can hold, there is no limit to the volume of soil that can be built, with some prairie soils reaching over six feet deep (4). Managing pastures in a way that replicates how the prairie soils were built plays a vital role in this process of carbon sequestration.
Grasslands’ unique ability
Fossil records show us that 55 million years ago grasslands and ruminants co-evolved (5) (2) and grasses have evolved to be grazed. When combined with appropriate grazing, grasslands are the key to carbon sequestration on a rapid scale. Unlike bushes and trees that store the majority of their biomass above ground and do not respond to repeated browsing with rapid re-growth, evolution has bestowed grasslands with the unique ability to not only withstand repeated grazing but to positively benefit from it. Grasses also benefit from disturbance and fertilisation by ruminants as well as their role in preventing the plains and prairies progressing into forest.
Each bite primes the carbon pump
Through the perfection of evolution, each time a cow takes a bite of grass it triggers the plant to release exudates in order to receive in return the nutrients needed for rapid regrowth. The grass’s rate of photosynthesis goes up, more grass (biomass) is grown and more carbon is removed from the air and pushed down into the soil. The action of grazing repeatedly pushes the grass back into it’s growth stage and as long as grass is actively growing, not senescing, carbon is being removed from the atmosphere and sequestered into the ground. In a positive feed-back loop, this liquid carbon pathway supports a healthy underground ecosystem, building soil organic matter, creating humus and soils that are deep, well-functioning and fertile (3). When cows graze, the carbon cycle is boosted and each bite primes the carbon pump.
Roaming, grazing cows sequester carbon
Once you understand this process, it becomes clear that although the cow is breathing or belching as she grazes, for all the carbon she cycles through her metabolism, there is carbon also being removed from the air and sequestered into the soil. This means that, when she is exclusively fed her natural diet of grass, there is a net reduction in atmospheric carbon. Roaming, grazing cows sequester carbon.
There is much debate, though limited scientific evidence, about the size of the vast herds of herbivores that roamed the grasslands of the world up to pre-industrial times (6). But one thing is for sure: the hundreds of millions, or billions, of them were not causing any climatic problems. In fact, quite the reverse. By grazing and stimulating rapid photosynthesis, they, along with the herbivorous megafauna before them, played a pivotal role in the reduction of atmospheric carbon that brought CO2 down to pre-industrial levels (2). And when grazed appropriately, cattle will continue to do this.
Cows produce nutritious food powered by the sun
The beauty of working with natural systems in this way is that not only does a cow’s grazing stimulate and speed up carbon sequestration in the soil, but she also provides us with a nutritious by-product to her helpful environmental services in the form of meat or milk. And all achieved with no inputs other than the free, perennial energy source of sunlight.
But we can’t talk about ruminants without a bit more on methane, so let’s continue the journey into how carbon mooooves….
Carbon cycling through methane
Another natural cycle occurs when carbon is used to produce methane in the metabolism of microbes known as methanogens. The main natural sources of methane are wetlands and forest fires as well as the guts of ruminants and termites. It is the same microbial action and associated release of methane that finalises plant decomposition, be it on the ground in the rotting of uneaten plant biomass or in the gut of an animal that is digesting plant matter, called enteric fermentation.
As discussed, what is important about methane being produced by microbes in a cow’s rumen rather than from microbes on the ground, is that the cow is also providing us with food by turning grass, something we can’t eat, into something highly nutritious that we can.
As with other natural cycles, the movement of carbon through methane and back to CO2 can take different lengths of time. The short route involves methanotrophs, methane oxidising bacteria, which have been shown in studies in Australia (7) to oxidise more methane than cattle produce. The action of methanotrophs also causes methane to diffuse from the atmosphere into soils to be oxidised (4). The slightly longer route is when methane in the atmosphere is oxidised by hydroxyl radicals back into water and carbon dioxide (8), which can take up to 12 years. The hydroxyl radical is nature’s main methane sink, oxidising 90% of methane emissions.
It is critical to understand that methane, produced by methanogens either in boggy soils or the guts of termites or ruminants and then oxidised back to CO2 either by methanotrophs or by the hydroxyl radical, is part of the cycling and recycling of carbon. No new carbon is added to the system. While the number of cattle on the planet remains constant, there is no increase in atmospheric methane as a result of their enteric fermentation because nature’s methane sinks balance production.
Furthermore, cows kept on pasture convert into methane just 1% of the carbon taken in by plants during photosynthesis (12). And whilst this may have a global warming potential 25 times greater than CO2, it is still considerably less than the carbon sequestration benefits of well-managed grasslands previously noted (13).
Throughout history, there have been significantly more ruminants on the planet than now which played an active role in reducing atmospheric greenhouse gases (GHGs) through their grazing and subsequent carbon sequestration (2). When in balance, methane is not the evil it’s made out to be – as with most things in nature, it’s only a problem when it gets out of balance.
To recap, a range of naturally occurring processes have cycled and recycled a finite amount of carbon for millennia, and will continue to do so. Many of the environmental problems we are now experiencing result from human activities that have added – and continue to add - ‘new’ carbon to the system.
The exponential increase of the human population and our seemingly unquenchable thirst for growth in all aspects of life, has resulted in our blindly burning through vast quantities of stored carbon in the form of fossil fuels. We are on course to release into the atmosphere 60 million years’ worth of this long since sequestered carbon in just 150 years. Once released into the atmosphere, it becomes part of the cycling carbon, putting enormous pressure to the earth’s ability to cycle it through natural processes. When those processes are overloaded, the levels of CO2 and methane in the atmosphere rise.
150 years ago, CO2 levels were a comfortable 280 parts per million (ppm); in 2017 they peaked at 410ppm, a dramatic increase (2). Methane levels too have seen a rapid rise, doubling since the industrial revolution (9). These increases in carbon dioxide and methane, resulting directly from human activity, are having significant consequences for the climate because of their role as greenhouse gases (GHGs).
Greenhouse gases: from protection to poison
The part of the atmosphere nearest earth, the first 10km or so, known as the troposphere, is made up of around 78% nitrogen and 21% oxygen, with small concentrations of other trace gases, important ones being carbon dioxide and methane. These are important because, along with water vapour and nitrous oxide, they are greenhouse gases. Vital for keeping the earth inhabitable, GHGs create a protective shield (‘greenhouse’) around the troposphere that keeps the earth warm enough to sustain life as we know it.
Yet what has been protecting us is now in danger of poisoning us. The concentration of GHGs is increasing so that instead of ensuring the essential warming of the earth, they are causing overheating… and climate change.
Cows cycle carbon: fossil fuels add carbon
Those seeking to influence our food choices away from animal products often report on climate change by conflating the carbon that is already in the atmosphere with the carbon that is being added to the atmosphere as a result of human activity. While cows cycle carbon, fossil fuels add carbon. It’s essential to understand the difference.
Pie charts representing global methane emissions frequently show one 25% slice for methane from enteric fermentation in cattle and then equate it with another 25% slice for methane from the mining and burning of oil, coal and natural gas. This is either a gross misunderstanding of the carbon cycle or a deliberate attempt to confuse the public.
Methane from cattle is made from carbon taken from the atmosphere. It is not biochemically possible for cattle to emit more carbon than they consume in their diet. Cows can only cycle carbon. In contrast, methane from the mining and burning of fossil fuels is made from stored carbon and it adds carbon to the atmosphere. This makes the size of the whole pie chart bigger, not just a slice.
It’s not the cow, it’s the how
This is not to say that all cattle farming is harmless. Quite the contrary, modern intensive livestock farming practices use large amounts of fossil fuels and feed animals human-edible crops, like grains and soya, with the aim of producing more output more ‘efficiently’. This approach to ‘efficiency’ measures litres of milk or grammes of protein produced per area of land in the shortest possible period of time. However, when all external costs are taken into account - the fossil fuels used; the soils damaged; the carbon released in the production of crops to feed the animals; the greenhouse gases emitted and the chemicals released into the natural environment - such modern, intensive farming practices can be seen as inefficient and unsustainable (11).
Again, it is the conflation of carbon sources and disregard for the off-setting of carbon sequestration, that bury the sustainable farming practices within the general criticism of industrial practices. And so for cows: it’s not the cow herself but the how she is raised that turns her from a roaming, grazing, carbon sequestering, nutritious food giving, environmental saviour to a fossil fuel driven, grain-chomping, environmental disaster.
This conflation of carbon cycles and carbon sources is blindly repeated as a mantra in much of the media, causing confusion amongst many who don’t have the time or inclination to study climate change for themselves. The general population is left believing that methane from cows is adding just as much to the atmospheric load as methane from natural gas production and other human activities. Nothing could be further from the truth.
It is no coincidence that the amount of carbon released from fossil fuels corresponds with the dramatic increase in carbon dioxide and methane in the atmosphere over the past 150 years. This is made worse by our increasingly industrialised food systems, where rainforests have been cleared to make way for food production on an unsustainable scale. This not only uses fossil fuels and releases carbon that was stored in the forest biomass and forest soil, but the impact is further exacerbated by the loss of forested land as natural carbon sinks. Since the industrial revolution, the burning of biomass (forests) to make way for agriculture has contributed 10% of the annual methane emissions (9) and has been the main contributor to a further recent increase (10).
Fossil fuel fools
It’s easy to be hoodwinked by reductionist research reports that purport to study sustainable farming methods. The idea, for example, of reducing methane production in cattle through feeding them particular diets lacks consideration for the fossil fuel used to sow, spray, grow, harvest and transport such special feeds. These studies are misleading although sound-bites like “Feeding cows linseed reduces methane” make seductive media headlines.
There is no upside for the fossil fuel industry of exposing this carbon conflation and it is certainly in their interest to perpetuate the confusion caused. They are making fossil fuel fools of all of us. They realise that human nature is such that we won’t want to reduce our energy use if we believe an easier option will have the same effect on climate change, like cutting down, or even cutting out, our meat consumption.
Rice production in flooded paddies produces 10% of global man-made methane, yet those cutting down on meat may eat more rice in the belief that it’s more environmentally sustainable, not realising its carbon footprint from the fossil fuels used to transport it from the other side of the world or that it has none of the carbon sequestration benefits of grazing cattle.
And this, of course, plays perfectly into the hands of those with an animal-meat-free agenda, be that for ideological reasons or for the less altruistic, as in the behemoths that are putting enormous resources into growing ‘animal-free’ protein in petri-dishes (and using lots of fossil fuels in the process).
While people should be free to choose the food they eat, it is wholly unethical for vested interests to try to influence those choices through misinformation and biased reporting, putting their profits and personal agendas before the future health of the planet and its growing population.
Any animal or plant-based food production that uses fossil fuels from soil to sale without a net off-set of carbon sequestration is inherently unsustainable.
One solution may be if technology reaches the point where protein can be grown in labs at suitable scale and cost, using renewable energy sources. This would be an amazing achievement that could provide protein for many people. However, unlike the protein produced from grazing cows, there is no carbon sequestration in the process. And the potential for further loss of food security should not be underestimated if food sources consolidate into the hands of a few global players and corporate profits take precedence over human welfare. Animal products provide much more than just protein and it is the multitude of balanced micro-nutrients that are essential to good health. Placing food supply with a few giant corporations increases the chances of micro-nutrient malnutrition on a global scale.
Become a carbon-friendly omnivore
Roaming, grazing cattle can provide the same solution to reducing atmospheric carbon as the herbivorous megafauna did since their evolution alongside grasslands 55 million years ago. Recently revived traditional practices such as mob grazing cattle on healthy grasslands demonstrates that it’s possible for farming to have a positive influence on the planet by turning sunlight energy, through photosynthesis and carbon cycling through 100% grass-fed ruminants, into nutrient-rich, flavoursome, high welfare, ethical meat and milk.
Become a carbon-friendly omnivore. Vote with your fork to encourage more farmers to make the switch: support carbon sequestration by only eating meat or drinking milk from animals certified 100% grass-fed. To find such food go to the website of the Pasture Fed Livestock Association, which is the only UK organization to certify meat and dairy as 100% grass-fed. Eat your beef and drink your milk guilt-free.
See our Courses page to learn more about grazing cattle for soil health and carbon sequestration as well as productivity, animal and human health.
Artwork: with thanks to the amazingly talented Emily Chappell for turning an idea, presented on a flow chart with some captions, into a the beautiful artwork which accompanies this blog.
(1) Humans breathe out 1kg CO2 per day http://www.sciencefocus.com/qa/how-much-does-human-breathing-contribute-climate-change
(2) Dr David Johnson - Carbon Underground https://www.youtube.com/watch?v=LFoVVA2eZxA
(3) Liquid carbon pathway http://www.amazingcarbon.com/PDF/JONES-LiquidCarbonPathway(July08).pdf
(4) Growing a Revolution by David Montgomery
(5) Co-evolution of grasslands and herbivores https://www.fws.gov/southwest/es/documents/R2ES/LitCited/LPC_2012/Stebbins_1981.pdf
(6) Pre-Industrial revolution ruminant numbers https://journals.uair.arizona.edu/index.php/rangelands/article/viewFile/11258/10531
(7) Soils absorb methane http://www.abc.net.au/site-archive/rural/nt/content/200908/s2649444.htm
(8) Methane sinks http://www.ghgonline.org/methanesinkatmos.htm
(9) GHG increases since the industrial revolution https://earthobservatory.nasa.gov/Features/GlobalFire/fire_3.php
(10) Natural gas the cause of increased methane https://www.ecowatch.com/nasa-study-methane-spike-2526089909.html
(11) Sustainable Food Trust: the True Cost of Food http://sustainablefoodtrust.org/articles/hidden-cost-uk-food/
(12) Methane production from grazing livestock (does not include the carbon sequestration) https://www.niwa.co.nz/atmosphere/faq/is-pastoral-agriculture-carbon-neutral
(13) Mob grazed (AMP grazed) cattle sequester more carbon than they emit in GHG equivalent per kg beef https://www.sciencedirect.com/science/article/pii/S0308521X17310338