For every pound of chicken meat produced, 5 pounds of greenhouse gasses are emitted. Three-quarters of that comes from commercial poultry feed—mostly cereal grains that require huge amounts of nitrogen fertilizers and water. Because free range birds have a more varied diet, it theoretically can lessen the impact, but they’re also allowed to live longer than their industrial cousins, so overall they consume more food. The other thing that drives researchers crazy is that there’s no uniform definition of “free range.” To be used on a carton of eggs, the USDA requires only that the hens have “continuous access to the outdoors during their laying cycle,” but that could mean anything from a glorious field to a concrete porch off a building where they’re packed in. Even among farms that let their chickens grow up outside in nature, there’s so much variation in how they do things that it’s difficult scientifically to pin down the environmental impact.
Free range grazing of sheep has more confirmed benefits. For example, it helps maintain soil health, reduces the risk of wildfires, and provides natural fertilizer from the animals’ manure. More exciting, it can pull carbon into the earth—and out of the atmosphere, where it’s dangerous. It can even help support endangered species like the California tiger salamander, Bay checkerspot butterfly, and the burrowing owl.