Estimates hover around there being ~2x as many cows in North America today than there were bison in 1500, but there were also large deer and antelope population

Estimates hover around there being ~2x as many cows in North America today than there were bison in 1500, but there were also large deer and antelope populations at the time. The carbon went from atmospheric CO2 -> grassland biomass -> animal biomass + CH4 + CO2, and the CH4 was oxidized back to CO2, so this was largely a steady state situation, and it certainly can be a model for sustainable meat production. Estimates of the human population are more contentious (genocide denial is an issue) but 50 million for North America might be the upper bound. If everyone stopped eating meat, while fossil fuel production and consumption remain unchanged, there would be little or no noticeable effect on our current climate trajectory. If everyone kept eating meat, while eliminating fossil fuel use, then atmospheric CO2 and CH4 would stabilize in ~100 years. Practically, if meat was raised humanely without fossil fuels, it would be a good deal more expensive, so people would eat less of it, perhaps leading to a 50% cut in meat production.