One of my all time favorite books is called "How to lie with statistics." Your source in no way rebuts my comment.
First, one of the reasons humans consume beef (as well as certain other kinds of meat) is that cows can convert grass to protein, something humans cannot do. So in savannas, eating animals that convert the grass to protein is one of the ways humans make life work at all.
Second, much of the world's beef supply is not grass fed. It is corn fed.
This gets done in part because it makes the beef fattier and thus makes it more profitable. It also makes it less healthy to eat and much more land intensive and wastes the thing that historically made cows valuable to humans.
In a scenario where we raise products like corn -- that the human body can already use for its protein content -- and feed it to cattle to produce beef, yes, that's hugely, hugely wasteful. It's also problematic that we ship so much beef long distances because of the energy costs involved.
If you work on moving towards grass fed beef and local consumption, you begin to dramatically reduce the resources involved in consuming beef.
Additionally, I am not advocating for the entire world to move to a 100 percent beef diet. That's crazy talk on the face of it.
Most religions advocate for a vegetarian or semi-vegetarian diet. Religion tends to contain historic wisdom concerning what works well for humans based on firsthand observation.
But there is plenty of room for the occasional human "carnivore" as well as for some people continuing to eat beef regularly. We don't need to vilify the consumption of meat in order to pursue environmental goals.
If eating beef helps eliminate health issues in some people, then letting those people eat beef is likely to be less resource intensive than insisting they eat a vegetarian diet and take a boatload of drugs.
This is a problem space I've thought about a whole lot. I have a serious medical condition that I control with diet and lifestyle. I wanted to be vegetarian and I tend to eat less meat most of the time than most Americans, but I also sometimes eat beef for medicinal purposes and I eat bacon somewhat regularly because bacon fat is one of the fats I tolerate well. My body misprocesses fats and there is a somewhat long list of plant oils I actively avoid.
I am supposed to be on thousands of dollars of drugs every month even when I'm not actively sick, just as "maintenance," and more when I'm actually sick. If the dollar value of the drugs I'm supposed to be taking is any measure at all of their environmental impact, then eating some meat is vastly less environmental burden than the drugs I am supposed to be on.
No one but you is saying "We should all just eat like carnivores" and you said it sarcastically. That extremist scenario is nothing anyone is genuinely advocating for.
I am all for making it easier and "cooler" for most Americans to eat less meat on average than they currently do. I am also for letting a small number of weirdos peaceably coexist with the rest of us who choose to eat nothing but meat because they find it beneficial to stubborn health issues that doctors don't know how to fix.
The way you lower our aggregate carbon footprint with regards to diet is you make it easier to find good vegetarian options. I don't eat hamburgers. Finding some source of protein at a fast food joint that isn't a fucking hamburger can be challenging.
Fortunately, affordable and convenient vegetarian options are somewhat easier for me to find than they used to be, such as vegetarian pizza and bean burritos. So my life works better than it used to because it's so much easier than it used to be to find something cheap and readily available wherever I go that isn't a fucking hamburger.
Hamburgers tend to be pretty goddamned disgusting, in part because we typically use the lowest quality beef to make them on the theory that we can just grind it up and turn it into a patty and la la la not listening on that detail of "garbage in, garbage out."