I once read that if everyone on the planet were vegetarian it would require farming every inch of soil on the planet to feed them.
You may have read that, but it doesn't make any sense. Eating lower on the food chain is way more efficient. Remember that ten pounds of vegetable protein to make one pound of animal protein?
Remember that humans are animals so they also have to make pounds of animal protein out of plant protein in order to grow and survive. But, unlike ruminants such as cows, goats, and sheep, a vegetarian human must get all of their protein from the plant so will have a higher requirement than a strict herbivore for those pounds of plant protein.
Ruminants get most of their protein from digestion of rumen bacteria, not from plants. These bacteria are unique in that they can make use of plant cellulose, breaking it down and fermenting it for their own use. The byproducts of this fermentation in turn provides energy for the animal as well as all of its B vitamins and protein. Ruminants can live very nicely on very little plant protein. In fact studies were done on mature ruminants fed diets with no protein and they did just fine for a long time.
Plant cellulose (which consists of long chains of glucose molecules) is completely wasted on humans and other single stomached omnivores because they do not have the enzymes to break it down. Humans are much less efficient at using plants as food than ruminant herbivores -- they have to eat much more to get the same results. I'd like to see a human grow from 50 pounds at birth to close to 1000 pounds at 14 months old on grass alone.
When a creature that exists at the top of the food chain (a primary consumer which produces no food itself) eats only those organisms at the bottom of the food chain bypassing the natural steps of the food chain supply, the efficiency of converting food to energy is lost. I can't see how this saves the planet.
I would like to see a citation about how the majority of cattle are farmed, but even if you are right about them being free ranged, that takes up huge amounts of land.
I don't have a citation, I just live in the west in the middle of cattle country so I see, experience and understand how much these animals eat and drink and how the land is used. Cattle are free-ranged on private, state and federal land (millions of square miles of it). The ranchers pay for grazing leases. If you want to accuse domestic grazers of causing climate change it would be hard to explain how the massive herds of buffalo, antelope, deer and elk would not have caused the same problem when they existed in herds of millions on US plains (far more than the number of cattle that now graze on the same land) hundreds of years ago.
In fact a ruminant that feeds on grass produces little methane and their rumens have a type of bacteria that utilizes the tiny amount of methane produced. Ruminants fed on grain produce more methane which escapes into the atmosphere.
Much of the science behind the global warming (climate change) scare is flawed, the data often hyper-inflated and not without its own political agendas (erosion of private property rights and other individual freedoms among them).