National Geographic wrote an assessment of cows several years ago as part of a future of food series. They concluded that cows/climate were currently about a 50/50 environmental wash, which I thought was fair (I'm the son of a large animal vet, also concerned about the environment). People don't realize the value of ruminants, as they are uniquely able to convert grass into fertilizer which nourishes other plants/birds which offsets some of their impact (high water/grain use, methane). Their product is also generally healthy when used wisely. That said, I believe it would also be wise to graze cattle in less arid marginal lands (ie foothills, maybe not so much in arid West coast) rather than feed them so much grain from valuable farmland. We don't have to convert to veganism, simply eat more fruits/veggies to improve our diets and environment (in a Michael Pollan/Joel Salatin sense). I just had lunch w my Dad's 85 yr old dairy vet partner who became almond rancher. Even he's a bit disgusted with the rise of "superdairies" that use so many resources.