Not the first. Sounds like we're not consuming our entire food supply, but rather generating more as we need it.
And there's a lot of other things besides cow farts contributing to global warming, which can have a much bigger effect for much less effort than making the world vegetarian.
Clearing huge swaths of Brazilian rainforest, “the lungs of the planet”, to make way for cattle seems like a pretty significant contributing factor though, would you agree? Less demand for meat, less demand for eliminating large pieces of a rather important natural carbon sink.
And there's a lot of other things besides cow farts contributing to global warming, which can have a much bigger effect for much less effort than making the world vegetarian.