When discussions turn toward reducing agriculture’s greenhouse gas emissions, less livestock and moving toward a plant-based diet is the common wisdom. However, perhaps eliminating livestock altogether – as some activist groups would argue perhaps not the optimal strategy.
A study published in the Proceedings of the National Academy of Sciences in the US modelled the country’s agriculture sector to determine the impacts of removing farmed animals – not just on greenhouse (GHG) emissions, but also on food supply adequacy. The analysis, undertaken by USDA researchers, found that animal-derived foods currently provide 24% of energy, 48% of protein, 23% to 100% of essential fatty acids and 34% to 67% of essential amino acids available for consumption.
Although a modeled plants-only agriculture scenario produced 23% more food, the researchers found fewer of the US population’s requirements for essential nutrients were met. When nutritional adequacy was evaluated by using least-cost diets produced from foods available, more nutrient deficiencies, a greater excess of energy, and a need to consume a greater volume of food solids were encountered in plants-only diets. In the simulated system with no animals, estimated agricultural GHG decreased by 28%, but did not fully counterbalance the animal contribution of GHG (49% in this model). The researchers concluded that removing animals from US agriculture would reduce agricultural GHG emissions, but would also create a food supply incapable of supporting the US population’s nutritional requirements.
Nutritional adequacy was evaluated using least-cost diets produced from foods available. Researchers found that more nutrient deficiencies, a greater excess of energy and a need to consume more food was necessary in people consuming plant-only diets. So while removing animals from agriculture in the US would reduce agricultural emissions, it would also create a food supply incapable of supporting the US population’s nutritional requirements. The results give valuable insights into why decisions on modifications to agricultural systems should be made based on direct and indirect effects on diets, rather than changes in individual nutrients.
While adequate nutrition is one consideration, the opportunities for carbon mitigation could be another to consider in this equation. The National Academy of Sciences and the Intergovernmental Panel on Climate Change (IPCC) both say that sequestering carbon in the soil offers almost 90% of the mitigation potential for all of agriculture’s greenhouse gases. While the science is still emerging its seems composting, no-till cultivation and improving soil structure help encapsulate carbon.
UK Soil Association has produced a climate change study that found grass is uniquely capable of forming soil carbon thanks to its high root densities, fine root hairs, and high levels of fungi living with its roots. Grasses take up CO2 from the air during photosynthesis. In symbiosis with root-dwelling fungi and with a substance called glomalin, plants then exchange carbon for nutrients within the soil. Glomalin assists these transactions and aids in forming carbon-filled soil aggregates, which appears to effectively sequester the carbon.
When it comes to soil, author Maia Reed maintains grazing animals are “indispensable partners”. Grazing prunes plants, stimulating vegetative growth and assisting light in reaching seedlings; hooves press seeds and plant litter into the ground, aiding seed germination and litter decomposition; and animal digestion speeds the cycling of nutrients through the system, adding valuable organic matter to soil, ultimately enhancing nutrient exchange and the soil’s water holding capacity. Well managed grazing, according to Reed, bolsters soil regeneration and supports grass’s diverse functions, from the microscopic to the ecosystem.
These types of analyses indicate the complexity of dealing with the challenge of climate change for food production systems. When a holistic approach which takes into account dietary requirements and sequestration options, the argument for eliminating animals from agriculture is less compelling.