So avoiding beef and dairy products helps reduce your contribution to global warming by reducing the need for as many cows in the world. Of course, one person boycotting the beef industry for a day won't do much, but if hundreds or thousands of people did, the need for beef and dairy would reduce and there'd be less cows polluting the skies.
In fact, all animals raised for food contribute to the use of resources and water--everything does, of course. So reducing the consumption of chicken, turkey, and other farmed animals again reduces your environmental impact. And if you generally buy your meat from Safeway rather than locally, you decrease your carbon footprint by avoiding meat because you aren't consuming something that was driven from far away.
During World War II, Meatless Mondays came into effect to conserve meat to send to the troops overseas. Today, the environmental movement and those concerned with their health (and their wallets) have taken that alliterated term and used it to reduce meat consumption. Back then, they were more concerned about conserving beef, as you can see below in the old poster from the U.S. Food Administration, but for today's purposes, why not eliminate poultry and all meat and dairy products?
I started participating in Meatless Mondays two weeks ago and found that it isn't very difficult. For one day in the week (doesn't have to be Monday), just opt for a vegetarian or vegan diet, depending on how far you want to take it. Here are the official guidelines set out by the Meatless Mondays organization.
If you want to go for completely zero-dairy, zero-meat, like I've been doing, try these options: For breakfast, pull out that cereal box and pour some soy or rice milk on it. Or slap some Earth Balance buttery spread (dairy-free!) onto some toast. Before you make that turkey sandwich for lunch, how about classic PB&J? Rather than have chicken or beef for dinner, have beans or opt for a no-protein dinner and stick to the veggies and starches.
It can be fun to try out interesting meatless meals. The Meatless Mondays website has a bunch of recipes you can try, as well as additional information about the organization. The website's focus is more on health than environment, but reducing meat consumption helps both. And if you're feeling adventurous, why not try to make Meatless Monday extend into Tuesday, or even Wednesday? Who knows, perhaps you'll find the vegetarian or vegan lifestyle is for you! (Just be sure you get enough protein and supplements so you stay healthy.)