Gases collectively known as Green House Gases (GHG) are responsible for climate change; the main ones are carbon dioxide (CO2), methane, nitrous oxide and F-gases. How does agriculture – livestock farming – contribute GHGs to the atmosphere? Where does the carbon come from, and where does it go?
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Agriculture is a large producer of GHGs but it only accounts for 10% of the UK national emissions; transport, energy supply, residential use and business all produce larger amounts.
Within the agricultural sector, livestock play their part both directly (their methane emissions due to rumination account for 56% of the agriculture contribution). And indirectly (nitrous oxide emissions from fertilisers, 31%, many tons of which are used to produce animal feed). Energy and fuel usage within agriculture make up 13% of GHG, primarily as CO2. Overall, agriculture produces nearly half the amount of the UK’s methane; and 68% of the nation’s nitrous oxide, but only 2% of the CO2. Only waste management processes produce nearly as much methane as agriculture. And even then both of these put together don’t produce nearly as much GHGs as transport and energy supply.
The carbon cycle
Much simplified, carbon found as atmospheric CO2 is used by plants for photosynthesis, to grow and reproduce. The process of storing carbon within the plant itself is called sequestration; the plant releases oxygen back into the atmosphere. A large part of the carbon sequestered by plants is incorporated into the plant molecule cellulose. (This is also what paper is made of, amongst other things). If the plant doesn’t get eaten, dies (and rots) or burnt to release the carbon, it remains sequestered for years. Woodland, forests, permanent grazing and moorland are all areas of carbon sequestration. Many of these areas are classed as marginal, because here for various reasons growing crops for human food is not possible. This may be due to terrain, exposure, climate or other reasons. Two thirds of marginal land grows vegetation rich in cellulose that is easily digested by cattle and other ruminants.
The carbon sequestered in this kind of cellulose rich vegetation can be used by animals for growing and producing high quality protein for our nutrition; part of it will be released as methane during rumination. After approximately 10 years in the atmosphere more chemical reactions will return the carbon to plants in the form of CO2 for photosynthesis. As the carbon started as CO2 in the first place before being eaten by animals, and given that ruminants are not creating new carbon atoms in their digestive system, the cycle continues in order to grow and renew plant life. The carbon released by ruminants is no more than it would be released if the plants just died on their own and rotted away – albeit slower.
What does not form part of the “normal” carbon/methane cycle is the CO2 released from using fossil fuels.
Ruminants have lived on this planet for far longer than we have been using fossil oil to power our civilisation. It is reasonable to think that fossil fuels have a much greater impact on the world’s changing climates than livestock. Especially cattle that are extensively grazed and make use of the poorest, most marginal types of land that we could never convert to producing crops for human consumption.
Different livestock systems
As we become more conscious of the origins of the food we eat, open scrutiny becomes the norm on the production systems. We talked in a previous article about intensive and extensive livestock systems. Cattle reared very intensively, in feedlots (mostly abroad) where the fast turnaround is guaranteed by large amounts of grains grown specifically for them (at the environmental cost of monoculture) must account for a far larger proportion of GHGs due to their own digestion; but also the really high inputs such as fuels and fertilisers needed to support this kind of pyramid.
On the other hand, more extensive systems that effectively make use of neglected land to graze both sheep and cattle like those in the UK with minimal input of artificial feeds – reiterate, land that would be inadequate for turning into crops – are able to significantly reduce the total of GHGs implicated by not needing all the fuels and fertilisers. In addition, they are providing us with high quality protein practically on our doorstep.
There is no need to look for beef, lamb, pork coming from abroad, having travelled sometimes thousands of miles (= more CO2 released), in certain cases produced under welfare-dubious conditions, when we have excellent local produce in the UK that is of high welfare and supports our local economy. British grass-fed beef is not only higher welfare than in other more intensive systems. (As cattle get to spend a good part of the year grazing outdoors – compared to all year round housed). The environmental cost is also much, much lower, due to grass management practices and the heavy use of manure (both carted through from winter housing and naturally deposited); which helps reduce the use of fertilisers and especially grains.
Soil health
As the human population in the world keeps growing and the drive for more efficient food production becomes stronger, we must not forget that farming of any kind cannot exist in a desert. Even if we all decided to do away with livestock farming and switch to a complete plant based diet, we would still have to farm crops for us to eat. How are the fields going to cope without animal manure? Chemical fertilisers replenish the bare minerals that are needed by the plants. But they do nothing for soil texture, composition and biodiversity – all the factors that keep it healthy and thriving.
In each cupful of healthy soil there are billions of organisms, all contributing to the plant crop above. Animals and their manure, ruminants especially, have always added extra nutrition back to the soil. When farming efficiency and monocultures have progressed alongside for a few generations, field sizes increased exponentially, fertiliser use skyrocketed and the general soil health perished.
A peer reviewed study published in 2019 showed how pasture management affected the soil composition, and varied year by year. For example, continuously grazed fields had the richest soil communities thanks to the continuous application of nutrient rich manure. Whereas at the other end of the scale those fields that received no manure (poultry or cattle) had the lowest richness of diversity. Above ground plant populations and water quality need to be taken into consideration when approaching different pasture systems; as some, such as continuous grazing. may have negative effects on these. However, rotational grazing and buffer zones of un-fertilised land may be a useful consideration.
Overall, each farm is different
Every UK farmer working alongside agronomists, biodiversity specialists and their vets (for the animal welfare input) is trying their best to produce high quality meat over land that would otherwise have little use and that if left to rewilding would not contribute anything to feeding the world’s growing population.
Discussion