Ask a Scientist – June 2018
N. from Sun City, AZ, asks “I have read that industrial agriculture, especially animal agriculture, creates nearly as much air pollution and water pollution as vehicles. What are the facts about this?” and Marcia DeLonge, Ph.D., senior scientist with the UCS Food and Environment Program, answers.
Agriculture in the United States accounts for only 9 percent of the nation’s global warming emissions, less than half of that of cars and trucks. In some cases, however, the US agricultural sector is responsible for even more air and water pollution than vehicles. For example, agriculture is the biggest source of fine-particle air pollution in much of the country and the biggest polluter of rivers and streams.
That’s the bad news. The good news is there are several cost-effective solutions to clean up the agricultural sector. But before we talk about them, let’s take a closer look at the problems.
Air (and global warming) pollution
Vehicles and farms are both responsible for similar types of air pollution. They both emit pollutants that harm health and cause climate change, including particulate matter (soot), nitrogen oxides, carbon monoxide, carbon dioxide, and methane.
Transportation-related air pollution comes from not only driving, but also manufacturing, maintaining, and disposing of vehicles. The Environmental Protection Agency (EPA) estimates that the transportation sector, which includes airplanes, trains, and ships, emits more than half of all carbon monoxide and nitrogen oxides nationwide and—as of 2016—28 percent of all US global warming pollution, more than any other sector.
Agricultural air pollution comes from both farm equipment and farming itself—the soil, plants, animals, fertilizers, and so on. A 2016 study found that agriculture is the largest global source of fine particulates, which result from ammonia emitted to the air combining with other chemicals, sunlight, and volatile organic compounds from trees, plants and vehicle and industrial emissions. In the United States, farms are responsible for more than 90 percent of airborne ammonia pollution, mostly from fertilizers and livestock manure.
Meanwhile, the EPA estimates that the agricultural sector contributes about 9 percent of total US global warming emissions. Soils used for grazing and crops account for more than half of the sector’s global warming emissions, livestock methane emissions account for about a third, and manure management accounts for about a sixth.
Vehicles and farms are also responsible for water pollution that causes algal blooms and aquatic dead zones, contaminates drinking water, and damages aquatic habitat.
When it comes to the transportation sector, runoff from paved roads and parking lots picks up leaked motor oil, spilled fuel and other pollutants and carries them into waterways. As for the agricultural sector, water pollution comes from livestock manure (and the antibiotics and hormones it contains) as well as fertilizers and pesticides. Extensive plowing and other practices also have eroded the soil on many farms, reducing its “spongy” qualities and allowing more soil, nutrients, and chemicals to be washed away.
There’s a better way
It’s obvious that it would be good to reduce pollution from the US food and farm system. So, what can be done?
One approach is for farms to integrate more agroecology practices and work with nature to protect natural resources. For example, farmers can grow plants on fields year-round, keeping living roots in the ground to soak up more nutrients before they become pollutants. And they can rotate their crops and increase crop and animal diversity in ways that boost soil fertility and break up pest cycles. Such practices also can help farmers reduce their reliance on chemicals, which would protect the environment—and farm profit margins. And healthier soil tends to store more carbon, emit less carbon dioxide into the atmosphere, and absorb more water to bolster resilience to floods and droughts.
It can be challenging for farmers to adopt agroecology practices, but but that’s why we need a farm bill that creates incentives and supports the transition. Ultimately, the more—and the faster—the agricultural sector can incorporate and improve upon these innovations, the better off all of us will be.
Marcia DeLonge is a senior scientist in the Food & Environment Program. Dr. DeLonge conducts scientific research and analyses identifying practices that lead to healthy, sustainable food and farming systems. Her work seeks viable opportunities within agriculture to both adapt to and mitigate climate change.Dr. DeLonge has a Ph.D. and M.S. in environmental science from the University of Virginia, where she developed expertise in atmospheric science, hydrology, ecosystem science, and numerical modeling. She also earned a B.A. in environmental science from Northwestern University.