Environmental Impact of Animal Agriculture

The environmental impact of animal agriculture refers to the effects of raising animals for meat, dairy, eggs and other products on the climate, land, water, air and biodiversity. Animal agriculture is widely recognised by scientists and international bodies as one of the largest human influences on the environment. Environmental concerns are among the main motivations for veganism and for reducing consumption of animal products.

Greenhouse gas emissions

Livestock contribute to climate change through several pathways: methane from enteric fermentation in the digestive systems of ruminants such as cattle and sheep; methane and nitrous oxide from manure; nitrous oxide from fertiliser used on feed crops; carbon dioxide from energy use; and carbon dioxide released when forests and other ecosystems are cleared for pasture or feed crops.

Estimates of the sector’s total contribution have varied with methodology and data:

The FAO has noted that differences between its estimates largely reflect updated methods and data rather than a real decline in emissions. The 2013 report attributed roughly two-thirds of the sector’s emissions to cattle raised for beef and milk. Some independent researchers have argued that these figures underestimate the full impact because they do not account for the “opportunity cost” of land that could otherwise store carbon if restored to forest or other natural vegetation. For further discussion, see veganism and climate change.

The Poore and Nemecek study

A widely cited 2018 study by Joseph Poore and Thomas Nemecek, published in Science, compiled data from around 38,700 farms in 119 countries covering about 40 food products. Its main findings included:

• Food production was responsible for around 26% of global anthropogenic greenhouse gas emissions.
• Meat, aquaculture, eggs and dairy used about 83% of the world’s farmland and produced 56–58% of food’s emissions, while providing about 37% of protein and 18% of calories.
• Environmental impacts varied greatly between producers of the same product, but the impacts of the lowest-impact animal products typically exceeded those of plant-based substitutes.
• Shifting from current diets to a diet that excludes animal products was estimated to have the potential to reduce food’s land use by about 76% and food-related greenhouse gas emissions by about 49%.

The authors concluded that dietary change could deliver environmental benefits on a scale not achievable by producers alone.

Land use

Animal agriculture is the largest user of agricultural land worldwide, through both grazing land and cropland used to grow animal feed. Because animals convert only a fraction of the calories and protein in their feed into food for humans, producing animal products generally requires more land than producing equivalent plant foods. Expansion of pasture and feed crops, particularly cattle ranching and soy cultivation in South America, has been identified as a major driver of tropical deforestation, including in the Amazon.

Water use and pollution

Agriculture accounts for around 70% of global freshwater withdrawals, according to the FAO. Research by Mesfin Mekonnen and Arjen Hoekstra of the Water Footprint Network estimated the global average water footprint of beef at around 15,000 litres per kilogram, although most of this is rainwater used by pasture and feed crops rather than irrigation water. Animal products generally have larger water footprints than plant foods of equivalent nutritional value.

Livestock also contribute to water pollution. Runoff of manure and fertiliser can carry nitrogen and phosphorus into rivers and coastal waters, contributing to eutrophication, algal blooms and oxygen-depleted “dead zones”. Concentrated operations associated with factory farming can also cause local air pollution, including ammonia emissions.

Biodiversity

The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), in its 2019 global assessment, identified changes in land and sea use as the leading direct driver of biodiversity loss, with agricultural expansion a major component. Livestock contribute through habitat conversion, overgrazing, feed crop production and pollution. Fishing and aquaculture, which also supply animal products, have additional impacts on marine ecosystems.

Variation and debate

Impacts differ considerably between products and production systems. Ruminant meat such as beef and lamb generally has the highest emissions and land use per unit of protein, while poultry, pork and eggs are lower, and legumes, tofu and other plant proteins are typically lowest. Some researchers and farmers argue that well-managed grazing can improve soil carbon storage and that animals can use land unsuitable for crops; others contend that such benefits are limited and often temporary. Debate also continues about the most appropriate way to compare the warming effect of methane with that of carbon dioxide.

Key areas of ongoing research include:

1. Methods for accounting for land-use change and carbon opportunity costs.
2. The potential of feed additives and breeding to reduce enteric methane.
3. The environmental performance of alternative proteins, including plant-based milks and meat alternatives.

See also

• Dairy Industry
• Egg Industry
• How to Go Vegan