To Kami: A Response

Hey Kami! Thanks for your comment. I'm always a little leery of putting stuff like this on my blog, so thanks for writing and asking about it!
I'm trying to think of a good way to write an answer, but it might be a little long. I hope you don't mind.;)
When people talk about animal agriculture increasing the amounts of greenhouse gases, they are primarily talking about methane produced by the animal. (Here's another website you can read more about it if you want to. ) Methane is bad because it actually absorbs more heat than CO2, so even though there might be lower levels of it in the atmosphere, it actually (from what I understand) is more harmful to the environment. The levels are high enough that it is more of a problem than CO2. Of course, there is also the environmental cost of producing and shipping as well, but those are more along the lines of carbon monoxide.
There are several answers (I think) as to what would happen if we stopped killing the animals in agriculture. For one, there is the law of supply and demand. If the demand for these animals goes down, they just won't be born to be killed.
Also, when our ancestors domesticated the animals that are commonly used in agriculture, they bred them specifically to meet certain requirements (such as producing more milk, more meat, etc.) That is actually one of the reasons why cows were domesticated. The animals that we know today are different in some ways to their wild ancestors. So chickens would be like the wild fowls (like grouse and pheasants) And these animals have predators anyway, like wolves, cougars, and in the case of chickens, dogs, foxes, etc.
I think that animals have enough predators in the wild that either a. the predators would eat the animals, overpopulate, and the ecosystem would balance itself out. Or there's b. the animals would not have enough food, water, or shelter and simply die, just as if another animal in the world was overpopulated (or, people might kill them for food in the wild as well).
I think one of the big factors to take into account is the fact that most of the animals that we eat for meat have been altered in some way or another to grow as big as possible as fast as possible, especially chickens. Usually when chickens are big enough to be killed, they are almost crippled because they can't walk. (This was the case for the chickens that we raised on our farm too, crazy huh?) But the same is true for cows and pigs. So when they aren't very old, the body that they were born with and have grown into wouldn't be the ideal body to survive in the wild.

So these are my thoughts on the topic. I love to talk about this stuff, and thank you for talking about it with me! Feel free to write back. :)