Environmental impacts of animal agriculture

The environmental impacts of animal agriculture vary because of the wide variety of agricultural practices employed around the world. Despite this, all agricultural practices have been found to have a variety of effects on the environment to some extent. Animal agriculture, in particular meat production, can cause pollution, greenhouse gas emissions, biodiversity loss, disease, and significant consumption of land, food, and water. Meat is obtained through a variety of methods, including organic farming, free-range farming, intensive livestock production, and subsistence agriculture. The livestock sector also includes wool, egg and dairy production, the livestock used for tillage, and fish farming.

Animal agriculture is a significant contributor to greenhouse gas emissions. Cows, sheep, and other ruminants digest their food by enteric fermentation, and their burps are the main source of methane emissions from land use, land-use change, and forestry. Together with methane and nitrous oxide from manure, this makes livestock the main source of greenhouse gas emissions from agriculture. A significant reduction in meat consumption is essential to mitigate climate change, especially as the human population increases by a projected 2.3 billion by the middle of the century.

Multiple studies have found that increases in meat consumption are currently associated with human population growth and rising individual incomes or GDP, and therefore, the environmental impacts of meat production and consumption will increase unless current behaviours change.

Changes in demand for meat will influence how much is produced, thus changing the environmental impact of meat production. It has been estimated that global meat consumption may double from 2000 to 2050, mostly as a consequence of the increasing world population, but also partly because of increased per capita meat consumption (with much of the per capita consumption increase occurring in the developing world). The human population is projected to grow to 9 billion by 2050, and meat production is expected to increase by 40%. Global production and consumption of poultry meat have been growing recently at more than 5% annually. Meat consumption typically increases as people and countries get richer. Trends also vary among livestock sectors. For example, global pork consumption per capita has increased recently (almost entirely due to changes in consumption within China), while global consumption per capita of ruminant meats has been declining.

About 85% of the world's soybean crop is processed into meal and vegetable oil, and virtually all of that meal is used in animal feed. Approximately 6% of soybeans are used directly as human food, mostly in Asia.

For every 100 kilograms of food made for humans from crops, 37 kilograms byproducts unsuitable for direct human consumption are generated. Many countries then repurpose these human-inedible crop byproducts as livestock feed for cattle. Raising animals for human consumption accounts for approximately 40% of total agricultural output in industrialized nations. Moreover, the efficiency of meat production varies depending on the specific production system, as well as the type of feed. It may require anywhere from 0.9 and 7.9 kilograms of grain to produce 1 kilogram of beef, between 0.1 to 4.3 kilograms of grain to produce 1 kilogram of pork, and 0 to 3.5 kilograms of grains to produce 1 kilogram of chicken.

FAO estimates, however, that about 2 thirds of the pasture area used by livestock is not convertible to crop-land.

Major corporations purchase land in different developing nations in Latin America and Asia to support large-scale production of animal feed crops, mainly corn and soybeans. This practice reduces the amount of land available for growing crops that are fit for human consumption in these countries, putting the local population at risk of food security.