How does the environmental impact of a dog compare to that of an SUV? Via Robert Nagle in the MR comments section, here is one article defending the dog. It makes many good points but right now I am especially interested in this passage:
…most dogs DO NOT eat meat and cereals. With a few exceptions, they eat “meat” and “cereals.” The “meat,” in particular, tends to be byproducts–things that people in the US simply won’t eat, even in hot dogs.
Does that mean that the cow parts are a "free lunch," environmentally speaking? Let's say you have a dogless world and the cow organs are thrown away. Dogs come along and suddenly those organs are sold to dog food companies. The profit margin on cows increases. The supply of cows goes up, as more resources are put into raising cows, and that means more cow emissions. This process continues until the (private) costs of cow production rise, and/or the prices of cow products fall. In other words, it depends on elasticities but the dog diets do have an environmental impact.