Agriculture is responsible for up to one third of the world’s greenhouse gas emissions and the majority of this comes from animal farming¹. It’s estimated that animal products account for 83% of the emissions caused by EU diets².
The largest share of direct greenhouse gas emissions from animal farming is in the form of methane, mostly from the digestive processes of ‘ruminant’ animals like cows and sheep. But nitrous oxide from wastes and manures and carbon dioxide from land use change are also major sources of emissions.
Methane CH₄ – This primarily comes from the digestive processes of ruminant animals, such as cows and sheep. The population of farmed ruminant animals worldwide numbers over 2.5 billion. Each one is busy eating as much grass, or feed, as possible and digesting it in a process called “enteric fermentation”. This fermentation process allows cows and sheep to eat plant material that most other mammals could not digest – such as grass – but it releases large amounts of methane. Methane is shorter lived than carbon dioxide, but its impact on atmospheric temperatures is 28 times higher.
Nitrous oxide, N₂O – Nitrous oxide is also a highly potent greenhouse gas and its global warming potential is even higher than that of methane. Animal manures and the application of synthetic fertilisers lead to high levels of microbial activity which is the source of Nitrous oxide. Not only does animal farming generate huge amounts of animal waste and manure but the high-yield crops needed to feed factory farmed animals also creates huge demand for synthetic fertilisers. These are also applied to grazing pastures to make them more productive. Emissions from the meat and dairy sector alone are enough to reach the ‘planetary boundary’, or safe global limit, for nitrogen emissions³.
Carbon dioxide, CO₂ – This is released by agricultural soils and a huge amount is also released when land is converted, often from more biodiverse natural habitats, into farmland.
When thinking about carbon emissions from food, people often think about ‘food miles’, but the processing, packaging, transport, and retail of food combined represents only a tiny fraction of food emissions. The farming stage is where most of the direct emissions come from and that’s why the types of food we choose to eat make such a big difference².
But looking only at these ‘direct emissions’ from animal farming misses an important part of the picture as it doesn’t account for the carbon ‘opportunity cost’ of land use. This involves asking not only how much greenhouse gas is released from a farming system, but how much carbon could be absorbed by using the land differently. For instance, by restoring forest or peatland habitats that have been lost to agricultural expansion research from the University of Harvard found that reforesting farmland that is currently used for animal farming in the UK would absorb the equivalent of 12 years of total UK emissions⁴.