Specifically with respect to the methane cow farts, yes. That carbon comes from their plant diet (be it grass in a field or grain in a feeding lot), and the carbon in those plants came from the atmosphere.
This isn't counting the fossil fuels the industry also burns, or the carbon released during the production of fertilizers used when growing that feed. But the carbon in the feed itself all comes from the atmosphere, and therefore the carbon in the methane emitted by cows comes from the atmosphere.
The argument I’ve heard is that with more demand for meat comes more clearing of forested land that’s turned into pasture. So instead of storing atmospheric carbon long term in trees, you take much of the carbon absorbed by the grass and release it right back.
What about when seaweed is added to the feed which reduces methane emmission by 70%?
The numbers that go into these approximations are not reliable and that's the problem with trying to have some exacting figure 20-28 and use that to create policy.
Which is why we can know that it is just about creating policy.
Seaweed in a cows diet either: increases the CO2 the cow emits, increases the mass of carbon the cow shits, or increases the mass of the cow. The carbon has to go somewhere. I don't know where it goes, but regardless of where it goes, there's no doubt about where it came from to begin with. Virtually all the carbon cows eat was pulled out of the atmosphere by plants.
On the one hand yes, on the other hand the immense amount of land set aside to produce cow feed could be used to produce much more human food, and the extra land could be used to plant forests.
