Foer relates how, one night, he sneaked onto a California turkey farm with an animal-rights activist he calls C. Most of the buildings were locked, but the two managed to slip into a shed that housed tens of thousands of turkey chicks. At first, the conditions seemed not so bad. Some of the chicks were sleeping. Others were struggling to get closer to the heat lamps that substitute for their mothers. Then Foer started noticing how many of the chicks were dead. They were covered with sores, or matted with blood, or withered like dry leaves. C spotted one chick splayed out on the floor, trembling. Its eyes were crusted over and its head was shaking back and forth. C slit its throat.-- from Elizabeth Kolbert's review of Jonathan Safran Foer's Eating Animals. Kolbert makes no mention of greenhouse gas emissions from livestock.  Does Foer?
The story goes that Franz Kafka visited the Berlin aquarium and, gazing into the illuminated tanks, addressed the fish directly. “Now at last I can look at you in peace,” he told them. “I don’t eat you anymore.”
But should we cut out meat (and fish) altogether? And, as Kolbert points out, what about all other animal products? Can one imagine a world where many fewer animals are kept in excellent conditions and only consumed on special occasions? If not, how about 'Meat 2.0?' (or its dark side 'secret burgers')?
Would a world in which humans eat no animals be palid, etiolated? A more sustainable (more plausible) alternative, perhaps, would be one with a smaller human population which both reveres and eats a limited number of animals, rather as some nomadic peoples still do today. , 
And then there is Kafka's hunger artist (with whom I have some sympathy).
Image: a lake of blood and excrement near Granjas Caroll, Mexico
 An overview from more than a year ago but still useful is Andy Revkin's Can people have meat and a planet too?
 A non-dreadful scenario for reduction in the total size of the human population would most likely be an accelerated and peaceful demographic transition: billions of freely made choices by more and more people to have just one or two children. Global population would peak at about 9 billion mid century and start to decline thereafter. Quality of life would continue to improve: 'Malthus' well and truly vanquished.
 (added 7 Nov) Or, as John Berger sees it (Why look at animals? 1977), as peasants in agricultural societies have long done:
A peasant becomes fond of his pig and is glad to salt away the pork. What is significant, and is so difficult for the urban stranger to understand, is that the two statements in that sentence are connected by an and and not by a but.