The sustainability issue surrounding meat consumption is an important issue. It should be noted that nearly all of those problems arise from current industrial agricultural practices. By consuming grass fed, pasture raised animals you are supporting a sustainable model where animals feed off of the land, and their waste fertilizes the ground for perennial plants to grow, year after year.
That stands in contrast to vast farms of annual grains draining the ground of all nutrients, turning the soil to dust, and only propped up by petroleum-based fertilizers obtained from war-torn regions halfway around the world. Those grains are then fed to animals in feed lots, under horrid conditions, making sick animals, and sick people that eat those animals.
To my knowledge, all large-scale grain agriculture is destructive to the environment. And, the only true perma-culture includes animals in the mix, because key nutrients for the plants, such as Nitrogen, only come from animal sources. This is why petroleum -based fertilizers are used to support agriculture currently: Petroleum is liquefied dinosaurs. So, vegetarian solutions to the sustainability issue will always fall short, because they lack the key animal component in the natural cycle of soil preservation. That is my understanding, anyway.
Some will object to any consumption of animals, as immoral exploitation of those animals. I am a former vegan, and understand those feelings, as that was my motivation. However, the reality of the world seems to be that optimal human nutrition includes consumption of animals, and sustainable agriculture requires it. By purchasing local, pasture raised meat, you are providing a much better life for the animals, while preserving a sustainable ecology.
Of course, as a couple of people mentioned, hunting wild game is a great solution.