What is the connection between energy consumption, CO2 emissions, and living standards?

What would be the effect on co2 emissions and energy consumption if everyone became vegetarian?

• Answer:

  Just for a little perspective on this question. It takes the following approximate dry weight quantities of feed (mostly grain, some anchovies, etc. or other depending on the animal) to produce one wet unit weight of edible meat (fat fraction depends on the animal) for the following animals:   Chicken  --  1.5 to 2 kg Salmon  --  1.2 to 3 kg Tilapia  --  1.6 to 1.8 kg Pig  --  3 to 4 kg Cattle  --  10 (5 to 20 by various claims) kg   That is dry feed to wet (mostly water) meat. Also called the feed conversion ratio (FCR). See http://en.wikipedia.org/wiki/Feed_conversion_ratio  So, now why would a vegetable diet* be more energy efficient?   There has been some controversy over whether one can have a balanced vegetable only diet. A good deal of research has gone into this. On the protein side, the answer is yes. This hinges on the essential (for us 20) amino acids complement. It can be achieved reasonably well by combination of unhulled rice and beans with some variation. There is also opaque-2 hybrid corn (maize) with a better amino acid complement than other corn varieties. Meat has a better balanced amino acid complement (no surprise) but you can get it from a well designed vegetarian diet although you may waste some amino acids that are in oversupply when you are getting enough of all of them. Vitamins and minerals? The vegetables do much better than meat on this aspect of nutrition. See http://en.wikipedia.org/wiki/Protein_combining , http://pubs.acs.org/doi/abs/10.1021/jf60163a029?journalCode=jafcau   In any event, CO2 emissions and energy consumption would go down if everyone  became a vegetarian but it is unlikely to happen. If anything, beef, the worst life cycle emitter, is trending upward. *Full disclosure -- I do eat meat.