We know we need to reduce our meat consumption. Livestock farming accounts for almost 15% of all manmade greenhouse gas emissions (GHG) and around 60% of global biodiversity loss. However, solving climate change is urgent and cultural change is slow – we just don’t have time to wait for everyone to become vegetarian. Cultured meat shows potential but is still expensive and unlikely to fully replace animal-derived meat anytime soon. So, what realistic way do we have to substantially reduce GHG emissions from this sector in the next 10-20 years?
One option is to replace soy in animal feed with alternative, low-carbon protein sources: primarily bacterial protein and/or insects fed on food waste. This doesn’t solve all the problems, and we should continue to reduce our meat consumption, but it could be a rapid and substantial step in the right direction.
Soy what?
Eating animals that are fed on plants requires more land than eating plants themselves, which means that less land is available for other uses, including being left to nature. Roughly 77% of global agricultural land is used for either grazing livestock or growing animal feed, yet meat and dairy only contribute 18% of our calories and 37% of our protein. More specifically, a third of land suitable for growing crops is used to grow animal feed.
Image: Our World in Data
Soy is used as animal feed because it is high in protein (around 36% wet weight). Globally, 337 million tonnes of soybeans were produced in 2019, which equates to 121 million tonnes of soy protein. Approximately 90% of this soy protein is used as animal feed, and growing it requires a land area roughly 4 times that of the UK. More locally, the UK imports around 1.3 million tonnes of soy protein each year, which requires a land area greater than Northern Ireland.
A paper in Nature recently estimated that each tonne of soy protein gives rise to 17 tonnes of CO2e emissions. Some of this is direct emissions from farming, but most is indirect emissions from deforestation, or the opportunity cost of not reforesting the soy-producing land (most emission estimates are lower because they do not include opportunity cost). If we could replace soy protein in animal feed with low-emission alternatives, we could save up to 1.8 billion tonnes of CO2e per year. This is almost 4% of total global CO2 emissions!
What the cluck?!
Contrary to common perception, very little soy is fed to cows (<3% of soy cake fed to animals). The majority goes to chickens, (~50%), pigs (~30%) and fish (~8%). Cows are ruminants, and their digestive systems can break down cellulose. This lets them eat grass and crop residues and access the proteins they contain. Chickens, pigs, and fish are monogastrics, whose digestive systems cannot break down cellulose, so they need to eat more accessible proteins, such as those in grains and soy.
This is not an argument for eating more ruminants, though, because a lot of pasture would be better left to become natural forest. Furthermore a by-product of rumination is methane, an extremely potent GHG.
Grub’s up
Proteins are made of amino acids which in turn are made from carbon, hydrogen, oxygen and nitrogen. Therefore, we need to find a low-emission, low-cost source of each of these elements and an efficient means of building them into proteins.
These elements could come from food waste. Food waste can be fed to insects, particularly black soldier fly (BSF) larvae, which recycle the amino acids it contains into new protein. They are much more efficient at converting feed to protein than livestock, yet they still produce less protein than they are fed because they do not synthesise new amino acids. Although a third of all food globally is wasted, not all of this is captured and with conversion losses insects are unlikely to generate enough protein to replace soy. Nevertheless, this is still a great use of our food waste and a promising option.
Unlike insects, micro-organisms can synthesise new amino acids and thus additional protein, via fermentation, if a suitable source of nitrogen is added to food waste. However, most suitable bacteria require a soluble substrate, so food waste would have to be hydrolysed. The variable nature of wastes leads to separation and concentration problems in that process that have yet to be solved.
Something in the air and water
Alternatively, a number of key elements could be extracted from air and water, and fed to micro-organisms in solution. Oxygen can be provided from the air; green hydrogen can be produced by electrolysis of water using renewable electricity, which is rapidly decreasing in cost; and bio-available nitrogen can be produced by extracting nitrogen from air and then converting it to green ammonia.
Carbon, however, is more challenging because it makes up such a tiny proportion (0.03%) of air. Direct Air Capture (DAC) of CO2 produces a concentrated CO2 stream, but you need to process almost 6,000 tonnes of air to extract one tonne of carbon (for contrast, you only have to process about 1.28 tonnes of air to extract a tonne of nitrogen). This requires substantial space, energy and equipment and therefore is currently too expensive to produce commercial quantities of protein. Nevertheless, bacterial protein from DAC is being pioneered by the Finnish company ‘Solar Foods’ and merits further investment to try to bring down costs.
A cheaper alternative to DAC is to use the CO2 produced from burning fossil fuels, which can be found concentrated in flue gas. This could be a revolutionary short-term option, which is being pioneered by the biotech company Deep Branch. A pilot project at the Drax power plant in Yorkshire recently secured £3 million in government funding. However, its long-term future is limited because as we move towards a zero-carbon world, which we need to achieve in the next 20-30 years, the availability of waste CO2 will rapidly decrease.
Producing low emission animal feed using bacterial fermentation. Image: Rebecca Mason.
A new CAM-paign
Finally, these key elements could come from plants that grow in areas that would not naturally be forest and are not suitable for arable agriculture. Plants that use the Crassulacean Acid Metabolism (CAM plants) fit these criteria because they are hyper water- and nutrient-efficient, enabling them to grow in arid and semi-arid areas, which account for a third of global land area. Examples of CAM plants include cacti, aloes, and agave.
Their low lignin content makes them easy to hydrolyse and the resulting clean, uniform feed makes separation issues much more tractable. If solved, bacterial fermentation of CAM plants, with some form of additional nitrogen, could be a globally significant source of sustainable protein. More research and development is urgently needed in this space.
Soy long
We need to reduce the GHG emissions and biodiversity loss caused by livestock farming, and we need to do it fast. Eating less meat should form part of this, but it is unrealistic that everyone will turn vegetarian sufficiently quickly. Whilst not solving the entirety of the problem, finding new, low-emission sources of protein to replace soy in animal feed could be done relatively rapidly and have a substantial impact.
The biggest challenge in this process will be the supply of carbon. In the short term, converting flue gasses into bacterial protein could be revolutionary, but as we decarbonise, we are going to need to find further alternatives. Food waste fed to insects is a good option but is unlikely to produce enough protein to replace soy.
We urgently need to invest in research and development to reduce the costs of DAC and establish the potential of novel crops such as CAM plants if we are to put meat on the bones of our efforts to decarbonise livestock farming.
Featured image: United Soybean Board (CC BY 2.0), via Flickr
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