The best documentary you could possibly watch to educate yourself on the environmental issues animal agriculture is responsible for is COWSPIRACY. Cowspiracy is on Netflix which makes it very easy for many to watch, it's not a boring documentary at all. Trust me your mind will be blown. Seaspiracy if you haven't already seen in the chapter talking about fish focuses on the sea side of things however cowspiracy touches on this as well a little.

Just go watch it!

http://www.news.cornell.edu/stories/1997/08/us-could-feed-800-million-people-grain-livestock-eat
http://www.globalissues.org/article/240/beef
http://m.ajcn.nutrition.org/content/78/3/660S.full
http://www.cowspiracy.com/facts/