Earth Day is a week away, so brace yourself for cuddly, hug-the-planet blubbering from the presidential candidates. John McCain will tell you we must be the "caretakers of creation." Hillary Clinton will talk of recycling and efficient light bulbs. Barack Obama will surely tell us we "cannot afford more of the same timid politics when the future of our planet is at stake." Ah, but what about hamburgers? When the candidates tell us to stay out of McDonald's, then we will know their light bulbs are on. The end of timid politics is when they say that with the planet at stake, you must eat less steak. With fatal food riots in poor nations, and with China rapidly approaching Western levels of consumption, we in these obese United States must redefine what constitutes, to borrow from McDonald's, a "happy meal." Scientists are concluding that along with more fuel-efficient cars and curbing industrial pollution, the simple act of eating less meat could help slow global warming. "For the world's higher-income populations, greenhouse-gas emissions from meat eating warrant the same scrutiny as do those from driving and flying," according to the authors of a study last fall in the medical journal Lancet. Those authors, from Britain, Australia, and Chile, found that with global meat and milk production being on course to double by mid-century, the methane and nitrous oxide being released (that includes flatulence and gases from manure) is significant. Livestock occupy nearly a third of the land on earth. Agricultural greenhouse gases are about 22 percent of all emissions around the world. The study said that stabilizing agricultural emissions would require a 10 percent cut in global meat consumption. There would likely be other benefits, such as lower rates of heart disease, colorectal cancer and obesity, and preservation of the habitat for all kinds of species. "Today, as Chinese, other Asian, European, and U.S. farmers begin to run short of land for crop expansion," the study said, "the increasing demand for meat in developing economies is forcibly extending intensive agriculture into the tropical rain forests of South America." Similarly, the 2008 "State of the World" report from the Worldwatch Institute calls meat and seafood "the global diet's most costly ingredients." A huge problem in wealthy nations is that even when people cut down or give up meat for health reasons, they often substitute increasingly endangered fish near the top of the oceanic food chain such as swordfish, tuna or shark or create a demand for shrimp and salmon that overwhelms the environments they are being raised in. The report noted that consumer pressure for "sustainable" varieties of seafood and more humanely grown meat has already resulted in pledges by corporations to provide such products, even by fast-food chains. But that does not get away from the ultimate realization that wealthier people at some point have to move "down the industrial food chain," choosing less of products that are disappearing or particularly damaging in their production. "Eating less of these foods," the report said, "is a sort of investment in the future, since it will mean saving family farms, improving rangeland, reducing water pollution, and, in the case of wild fish, preserving a catch that is increasingly scarce." In 1928, the Republican Party promised a chicken in every pot. In a 1984 Democratic presidential debate, Walter Mondale chided Gary Hart's "new ideas" by asking, "Where's the beef?" Now the next president needs to put meat on the bones of environmental policy - by telling us to eat less of it. Derrick Z. Jackson is a columnist for The Boston Globe.