I think the focus on cows is kind of ridiculous. Our world's natural balance before humans included vast numbers of ruminants over vast expanses of the world. (e.g. huge populations of forest buffalo in Europe, vast Mammoth and Bison herds in North America). This is an issue being pushed with the intention of distracting from the real issue: fossil fuel use.
Here's the math: https://mrdrscienceteacher.wordpress.com/2019/09/21/bison-vs...
There weren't just Bison though. Before humans came to North America there were vast herds of many other megafauna species out there too.
> What percentage of land use for dairy cows is arable? Pretty much all of it. It's either being used directly for grass, or indirectly to grow grains which are fed to the cows. > What percentage of greenhouse gas emissions are added to the environment over already existing in the environment and just being moved? I think the number itself is the amount over what already existed.
You must consider other factors as well. The grass where cows are feeding is also a home and food for many other species. Making the land arable makes that void. Add pesticides, add other things to fight animals eating crops and the picture you get is just another extreme.
Not really. First, most beef isn't grass fed. By and large most cows are fed corn and soy, which means most of the land used producing beef already has those bad side effects. Second, if you grow food directly, you actually need less land to produce the same number of calories in plant material instead. So, you'd actually be able to creat more wild grassland without beef than with it.