Would removing cattle from the human food chain reduce the methane? Or just displace it’s production? Most obviously to human burps and farts. But maybe in the base vegetable to more processed palatable food types. The decomposition of human waste that has not processed the vegetable matter the way grazers do?
I find it difficult to get accurate information out of the conflicting information wars on the subject. Most admit to an increase in some negative aspects of mass vegan diet. But both sides veer in opposite directions. Obviously the world got along fine with vast herds of grazers, that for some time were not food sources on a large scale. But they were numerous and eventually nature ate every one of them.
Yes, it would. Cattle produce methane from their rumen, where bacteria break down cellulose and produce the methane. (BTW, since the rumen is the first stomach, the methane usually exits via the cow’s mouth, not the other end. A lot of people get this wrong.) Cattle feed is very high in cellulose and results in lots of methane; human food has some, but it doesn’t get digested to any significant degree.
This xkcd: Land Mammals is a thought provoking graphic about the size of humans & their livestock versus the size of Nature.
Yes, we have killed off a bunch of Nature since the say, 1600s. But even if we’ve killed 3/4ths of it that means you just need to quadruple the Nature part of that graph to see what it once was.
Bottom line: The total population of people and their husbanded animals vastly exceeds the size Nature ever was on its own. The effluent consequences are likewise vastly larger than anything Nature has done in millions of years, if ever.