“Sushi tastes amazing. A great steak is just amazing.” Those are not the words you expect to hear from a leader of the vegetarian movement. But that’s how Graham Hill, founder of the sustainability website TreeHugger, feels about the fleshier components of his diet. He is a self-described “weekday vegetarian,” a compromise that came about after years of trying–and failing–to adhere to a strictly vegetarian diet. For the past year, Hill has preached the cause of partial vegetarianism to help fight global warming. According to the U.N., the livestock industry produces 18% of the world’s greenhouse gases. Part-time vegetarians, a.k.a. flexitarians, choose what to eat and when. The popular Meatless Monday movement, which began in 2003, has been backed by many celebrities, including Paul McCartney, who has spearheaded his own Meat Free Monday campaign. Last year the Belgian city of Ghent picked Thursday as its Veggiedag, calling for meat-free options to be served that day in schools and public institutions. The drive to avoid eating meat on certain days is not new. Catholics have long been urged to abstain on Fridays. But environmentalists have only recently caught on. “The surge is due to a sense of a plateau. You’ve already reached out to the base of strict vegetarians, and it’s hard to get beyond those numbers,” says Peter Singer, a Princeton philosophy professor and the author of Animal Liberation. “People should go further, but it’s progress in the right direction.” Although the American Dietetic Association doesn’t track the number of part-timers, the group says roughly 2.5% of Americans are strictly vegetarian, a diet that poses no health risks as long as practitioners get enough protein from beans and other nonmeat sources. “A partial-vegetarian plan is a little more user-friendly,” says Dawn Jackson Blatner, a flexitarian and ADA spokesperson. The goal for many activists is simply to get more people to eat less meat. “Absolute purists should be living in a cave,” says Ingrid Newkirk, president of People for the Ethical Treatment of Animals . “Anybody who witnesses the suffering of animals and has a glimmer of hope of reducing that suffering can’t take the position that it’s all or nothing. We have to be pragmatic. Screw the principle.”