You probably already know that cheap feedlot beef is not really cheap. Its carbon / methane footprint is sky-high, not to mention how much water these operations require. Plus the treatment of the animals is often inhumane.
So when you do eat beef, try to buy the expensive grass-fed kind. They lead pretty good lives, grazing on pastures and turning grass you cannot digest into protein you can. Free-range cows are better for the environment, but they do still emit methane, of course.
Lamb, beef, cheese, and pork are the four most carbon intensive sources of protein to produce.
Eat chicken. Chickens are very efficient at converting small amounts of grain into large amounts of protein. Unlike cows, they don’t burp methane, and their poop contains one-tenth the methane of cows’. But once again, you have to make the difficult choice of whether or not to buy the expensive cage-free brands because these chickens lead better lives.
Even the brands in supermarkets that say cage-free are a very marginal improvement on the dismal lives chickens lead. I know it’s easy to say, “Buy the expensive, humane brand (like Mary’s at natural food stores) and eat less of it.” But that’s my ideal, which I don’t always accomplish.
Fish would be an almost ideal protein food except that everyone else agrees. Consequently, fisheries all over the world are crashing. This is really scary. The carbon emissions of farmed fish are pretty high because of the manufacture of the feed, but we have to eat! Bring a current sustainable fisheries guide with you when you buy fish.
Eggs are an excellent source of protein. Even if you buy cage-free (a marginal improvement, once again, over conventional eggs, but I look at it as mainly a market vote for more humane conditions), a serving of two eggs cost less than a dollar. That compares really well to other high-protein sources.
Maybe we should question at this point how much protein we actually need. Plant foods are a lot less carbon intensive. Eat lentilburgers. Seriously! They’re good! You want my recipe? Beans are cheap and nutritious.
I don’t eat bugs yet, but they may be the protein of the future. (Sorry, no recipes.)