Barbarian asks:
You don't think agriculture is done by humans? Who, then?
No. In fact, most cattle are not grazing, but in feed lots. Last year, there were about 92 million cattle in the United States:
http://usda.mannlib.cornell.edu/usda/current/USCatSup/USCatSup-06-24-2016.pdf
On the other hand, in pre-Columbian United States, there were about 30 million bison. So a three-fold increase. This doesn't touch the other agricultural sources of carbon dioxide, such as gasoline and diesel engines, chemicals, and so on.
See above. Do we have to abandon meat? No, but we need some fixes if we want to continue as we do. That can be either finding a way to reduce usage, or technology to deal with the waste in a save manner.
Or we could just let nature do it for us. That's probably not a very good idea in the long run. Nature's way tends to be drastic cuts in population.