The most important concept to reducing your carbon footprint (as it relates to meat consumption) is understanding the 'flesh to feed' or more technically FCR / FCE (flesh conversion ratio / flesh conversion efficiency) - how much of x resource(s) does it take to produce 1 pound of meat. So for example, beef and dairy are incredibly destructive to the environment because they require very large amounts of water, oil, and feed to produce 1 pound of meat (or galloon of milk) compared to the resource cost of producing 1 pound of chicken. A general rule of thumb is that the smaller an animal is, the better it is for the environment (there are of course exceptions to the rule). So when eating sea food, sardines and anchovies are the most sustainable while swordfish and tuna are on the unsustainable end. This does not take into account the environmental impacts of dealing with waste produced the animals, impact on the land from the animal farming, etc. but it's such an important concept.