Beef is the big bugaboo when it comes to climate-altering foodstuffs--but that's only because we eat so much of it. When the Environmental Working Group dug into the numbers (in its report Meat Eater's Guide to Climate Change and Health), it found that lamb was an even worse offender. It turns out that sheep produce less meat per pound of "live weight" than cattle, yet emit similar amounts of methane. An even bigger surprise is the number-three offender: cheese.

Its production entails many of the same greenhouse sins as beef's (feed, fertilizer, manure, etc.) and isn't very efficient—it takes nearly 10 pounds of milk to produce a single pound of cheese. If everyone in the country abstained from meat and cheese one day a week, the report calculates, it would be the same as taking 7.6 million cars off the road. Figures below are kilograms of CO2-equivalent per kilo of food consumed.