Climate change is a problem, and we need to lower our emissions as much as possible in order to tackle it. It is widely accepted that extracting and burning fossil fuels emits a lot of greenhouse gases, but what about animal agriculture? Does our appetite for animal based foods have any effect on the planet? Does eating plant based foods emit less than eating animal products? In this post, I will answer these questions based on our current scientific understanding.
How much does animal agriculture emit?
Agriculture and forest management as a whole represents 24-34% of all human caused emissions.1,2 Animal agriculture emits approximately 14.5% of all emissions.3 This is comparable to the emissions from the transport sector, including all cars, trucks, trains, boats, and planes combined.2 Some other estimates put this figure at 19-20%.1,4 So meat, dairy, eggs, and fish farms represent roughly 60% of all food based emissions. Despite this, animal foods provide only 37% of the worlds protein and 18% of the worlds calories.5
Where do the emissions from livestock farming come from? In contrast to what you might expect, most agricultural greenhouse gas emissions do not come from burning fossil fuels. Approximately 39% of animal agricultural emissions are the methane produced in ruminant animal’s stomach (such as cows or sheep) via enteric fermentation, which they burp out. Approximately 24% of these emissions are nitrous oxide and methane from the fertilisers used to grow animal feed. Approximately 13% of these emissions are the carbon dioxide emitted during the cultivation of animal feed. Approximately 9% of these emissions are the carbon dioxide emitted as a results of land use change, to grow more animal feed and expand grazing land. Deforestation leads to emissions both from the removed vegetation and the exposed soils. Approximately 10% of these emissions come from animal manure and 2.9% come from post-farm processes such as transportation and slaughter. Only 1.8% of these emissions are a result of energy use.3
Overestimates and underestimates
As mentioned, animal agriculture represents 14.5-20% of emissions. However, on the internet and in documentaries, you may see a range of statistics that are higher or lower than this. So who’s right? If we want to tackle climate change effectively, it’s important to evaluate the actual impact of livestock farming. These different estimates occur because different studies choose to include or exclude various types of emissions. For example, some assessments include greenhouse gas emissions from the use of fossil fuels during farming, or the emissions from deforestation. Other assessments only consider greenhouse gas emissions directly from animals. So, when comparing industries, the fairest approach is to refer to statistics from a life cycle analysis. A life cycle analysis considers all emissions that occur during each step of a products life cycle. In this section, we will discuss various overestimates and underestimates for animal agriculture’s emissions.
One report concluded that the livestock industry represent 51% of all emissions.6 However, this report made several invalid assumptions. For example, they included carbon dioxide emitted via the breath of farmed animals. However, the plants grown to feed animals store this carbon via photosynthesis. The carbon dioxide stored during photosynthesis and the carbon dioxide emitted during animal respiration are almost identical, so overall no net emission occurs. Additionally, the report included the opportunity cost of not reforesting the land currently used by animal agriculture, and double counted these emissions.7 The opportunity cost of land use is important, but the livestock industry does not directly emit this every year. I will discuss the indirect emission associated with land use in a future post.
Of course, claiming this 51% statistic would make it easier to convince people and politicians to change their behavior and policies respectively. However, misleading others is not a good strategy. We have to focus on the facts. Without exaggeration, the environmental impacts of animal agriculture are already serious enough to justify dietary changes.
In contrast, another article suggested that if the U.S. eliminated animal food, their national greenhouse gas emissions would only reduce by 2.6%.8 However, the simulations in this paper were also based on some impractical assumptions9-11:
- The paper assumed that if the U.S. stopped raising animals, it would continue to grow the current amount of animal feed and more. In reality, if the U.S. raised fewer animals, farmers would grow fewer crops to feed these animals and instead farmers would grow crops for human consumption.9
- The paper assumed that because there would be no animal manure available in the simulated scenario, more chemical fertilisers would have to be produced, which would lead to more emissions. However, in reality, less fertiliser would be required because less land would be used to grow animal feed, and there would also be less of a need to maximise the yield of each harvest.11
- This paper assumed that the diet of U.S. citizens would be mainly grains such as corn. Of course, this diet would be nutritionally inadequate, and so the paper concluded that nutritional deficiencies would arise. However, if we eat a variety of plants, consume vitamins B12 supplements, and plan our diet well, we can prevent these deficiencies without consuming animal products.10,12
- This paper assumed that in order to consume the large amounts of grown food, a person would have to consume over 4700 calories per day. This is almost double the recommended daily calorie intake and would lead to problems related to obesity.10
- The paper assumed that human inedible crop byproducts would simply be burned instead of fed to animals. However, these crop residues can be fed to microorganisms such as fungi to produce human edible proteins13,14 or synthesised into other useful products such as biofuels.15,16
Even in this unrealistic scenario, the result still showed a reduction in emissions. Additionally, focusing on the relative greenhouse gas emissions in the U.S. is not very relevant to the rest of the world. Because the U.S. emits a lot of greenhouse gases through industries other than animal agriculture, the emissions from livestock may seem relatively low. However, in reality these emissions are still high in absolute terms. Considering global statistics is much more informative.
How much do animal products emit compared to plants?
A meta-analysis analysed data from 38700 farms and 1600 food supply companies. To date, this study is the largest food life cycle analysis ever conducted, summarising all of today’s evidence related to the topic. Are meta-analyses perfect? Not quite. However, among the different types of scientific evidence, in general meta analyses are one of the highest-quality and least biased studies.17
Approximately 90% of the protein and calories consumed worldwide come from only 40 unique foods. From this, the meta-analysis focused on these foods in particular. The study considered greenhouse gas emissions, eutrophication, acidification, and land use. However, this post will focus on greenhouse gas emissions alone. Future posts will look at these other environmental effects. The key take away from this meta-analysis is that the most sustainably produced animal foods consistently have a more negative effect on the environment than plant based proteins such as tofu, legumes, and grains. No matter how sustainable we try to raise cows, eating plants directly emits less greenhouse gases. For example, the table below compares the most sustainable beef, cheese, pork, seafood from fish farms, chicken, and eggs to the most sustainably produced tofu.5
Comparison of greenhouse gas emissions from animal foods and tofu per unit of protein.5
As you can see, animal foods emit more greenhouse gases than tofu. Red meat, such as beef and lamb, emit the most by far. So when it comes to reducing climate change, consuming less food from ruminants such as beef, dairy, and lamb is most important.18,19 Even if we do the comparison per unit of calorie, per serving, or per unit weight, animal foods consistently emit more than plant based foods.20 We also observe similar results even if animal products are compared with the most unsustainably produced tofu. In addition to tofu, other legumes, plant based meats, fruits, vegetables, and grains are also low emitters. Similarly, the most sustainable dairy milk emits 2.8 times more than the most sustainable soy milk per litre.5
So why do animal foods emit more greenhouse gases than plants? First of all, animals are energetically inefficient. When an animal eats food, only a small percentage of the calories and protein in the food remains in the final animal product.5 This efficiency is often referred to as the feed conversion ratio. For example only 5% of the protein, and only 3% of the calories that a cow eats ends up in the final beef product.20,21 As an animal grows, protein and calories are used to grow organs other than muscle, and energy is used to stay alive. So, if we eat animal products rather than eating plants directly, a lot of nutrients are wasted.
In addition, because we grow more crops in order to produce food for animals, the greenhouse gas emissions associated with crop cultivation are higher. The most common animal feeds are soybeans, corn, and grass. Growing this feed represents 67% of the deforestation caused by agriculture. When a forest is cut down, carbon is released from organic matter both above and below the ground. As previously mentioned, ruminants such as cows burp methane through enteric fermentation and animal fertilizers also release methane and nitrous oxide. Furthermore, because animal foods typically spoil more easily than plants, the emissions associated with food waste are higher.5 Eating plants directly can either eliminate or reduce these problems.
Conclusion
Animal agriculture represents 14.5-20% of all human caused greenhouse gas emissions. In general, eating plants directly emits significantly less greenhouse gases than eating animal products, even if the animal products are produced “sustainably”. Therefore, in order to reduce our dietary carbon footprint, replacing animal products with plants is effective. In particular, eating less beef and lamb is most important. If you want to know more about climate change in general and the issues related to it, you can check out this post. In the next post I will discuss in more detail some of the common misconceptions related to methane emissions and climate change.
References
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