Humans took pigs with them to the Americas, and Oceania including Australia. These intelligent, creative but aggressive people escaped, and have been breeding in the wild. They are a major problem wherever they live, and have caused the extinctions of many local species.
Unlike the poor creatures kept in factory farms, wild pigs eat by ploughing up the soil with their tough snouts. This exposes organic matter, which is of course the idea: they eat some of it. But all the little stuff like fungi and plant bitses left are exposed to oxygen, and rapidly decay to release carbon dioxide.
The scale of their contribution to climate change is staggering. (Sorry, I have a vision of a scale, you know, for measuring weights, staggering around, but then that’s why I love clichés.) In just the areas where they are invasive rather than native, they generate as much carbon dioxide annually as 1.1 million cars.
Maybe we need to electrify our global wild pig population?
Actually, there is a better method, developed in Australia: Hoggone. Sodium nitrite is not that good for humans, but is fatal for pigs, and the resulting death is free of suffering. It makes them feel like a nap, and they wake up dead.