While the climate impact of livestock could not be reduced much if the some 60 billion farm animals worldwide were moved from intensive to extensive farming operations, livestock pollution could be greatly reduced in such a shift. While net greenhouse gas emissions are mostly a factor of global herd size, livestock pollution only becomes a major issue when animals are densely confined in large numbers.
When there is a low density of animals on the land, manure can be absorbed into the soil, acting as a natural fertilizer. With modern factory farming, this is not the case, as there may be up to 10,000 hogs, 20,000 dairy cows, or 100,000 broilers (meat chicken) in one operation, so manure goes from being a light fertilizer to being a massive waste-management liability.
Concentrated animal feeding operations – CAFOs, as they are commonly called – typically use large quantities of water to flush manure into large open lagoons from out of the barns where the animals are confined. The millions of gallons of urine, feces, and water in the lagoons are typically sprayed onto surrounding crops as fertilizer. But at large operations, the fields are only able to absorb a portion of the quantities of the waste created, leading to nutrient overload, a build-up of heavy metals in the soil, and the overfilling of lagoons.
Manure saturation can lead to run-off into waterways, which can cause algal blooms that kill marine life by reducing oxygen levels in the water. The FAO sites CAFO effluence as a major cause of the 1998 algal bloom in the South China Sea that killed 80% of marine life in a 100 square-kilometer area. Today, the many dead zones in Chinese rivers are a direct cause of CAFO pollution. Beyond devastating marine life, when CAFO waste makes it into waterways through rain run-off or lagoon overflow, heavy metals and antibiotic-resistant pathogens are also released into the water, posing health risks to those who come into contact with them.
The USDA estimates that livestock in America produces 500 million tons of manure annually, over 3 times the waste created by all humans living in the country (to wit, an EPA study claims that a dairy operation of about 25,000 cows creates as much liquid waste as a city of 411,000 people). Under the provisions of the Clean Water Act of 1972, it is illegal for CAFOs to discharge effluence into US waterways, though it was only in 2003 that the EPA started to get serious about requiring farms that manage large quantities of manure to apply for permits.
But even if CAFO waste is kept away from waterways and aquifers, the heavy build-up of gases such as ammonia, methane, and nitrous oxide – along with fine dust particulates — can cause acid rain and upper-respiratory problems for surrounding populations. In warehouses that confine large numbers of animals, fans must be kept running non-stop so that the gas build-up does not asphyxiate the animals and the workers inside. Some farms have started to use biogas generators that capture and harness this gas to help power their operations. While this cuts down on air pollution and provides energy, it does not solve many of the other environmental externalities caused by CAFOs.
Although CAFOs are livestock operations, and until the mid-twentieth century most livestock has taken place exclusively on farms, it is hard to consider CAFOs farms in the traditional sense, given that they often involve raising tens of thousands of animals crammed together in closed buildings, away from sunlight and soil. In terms of pollution, they must be treated as industrial operations, for the air and water pollution that they create often exceeds that of large manufacturing plants. In order to mitigate the environmentally destructive effects of CAFOs, policy makers must update their thinking towards animal agriculture to reflect the drastic changes that have occurred in the sector worldwide over the last half-century.