There's also a total absence of data.

Had the author consulted the literature, he'd know that the environmental credentials of grass-fed beef are extremely suspect; some studies suggest that the carbon footprint is actually greater than intensive feedlot beef and the land use is absolutely vast. He'd know that only a handful of animal sources of protein have equivalent CO2 emissions to plant sources - intensively reared poultry, eggs and some inshore seafoods.

https://www.researchgate.net/publication/257160858_The_price...