....direct carbon dioxide emissions are only part of the story when it comes to food's eco-impact. You also have to look at the issue of land use—specifically how much and what sort of land is required to sustain an agricultural enterprise. In a region with poor-to-mediocre soil, for example, it may be more efficient to operate a well-managed egg farm than to try growing vegetables that can't flourish under such conditions. And animals are handy at consuming low-quality grain that isn't necessarily fit for human consumption. (Rather than going to waste, that grain can help create nutrient-rich dairy products.) In fact, a recent Cornell University study concluded that modest carnivorousness may actually be better for the environment than outright vegetarianism, since cattle can graze on inferior land not suitable for crops. Squeezing more calories out of the land means that less food needs be imported from elsewhere, thereby reducing the burning of fossil fuels.
So, although this is not an excuse to keep consuming meat at our current rate (as meat processing constitutes a huge drain on resources and accounts for massive amounts of greenhouse gases)....it certainly makes me feel better about eating cheese. Mmmmmm, cheese.