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UNITED STATES, August 31, 2007: Ever since “An Inconvenient Truth,” Al Gore has been the darling of environmentalists, but that movie hardly endeared him to the animal rights folks. According to them, the most inconvenient truth of all is that raising animals for meat contributes more to global warming than all the sport utility vehicles combined. The biggest animal rights groups do not always overlap in their missions, but now they have coalesced around a message that eating meat is worse for the environment than driving. In late November, the United Nations Food and Agriculture Organization issued a report stating that the livestock business generates more greenhouse gas emissions than all forms of transportation combined.

When that report came out, People for the Ethical Treatment of Animals and other groups expected their environmental counterparts to immediately hop on the “Go Veggie!” bandwagon, but that did not happen. “Environmentalists are still pointing their fingers at Hummers and S.U.V.’s when they should be pointing at the dinner plate,” said Matt A. Prescott, manager of vegan campaigns for PETA.

So the animal rights groups are mobilizing on their own. PETA is outfitting a Hummer with a driver in a chicken suit and a vinyl banner proclaiming meat as the top cause of global warming. It will send the vehicle to the start of the climate forum the White House is sponsoring in Washington on Sept. 27, “and to headquarters of environmental groups, if they don’t start shaping up,” Mr. Prescott warned. He said that PETA had written to more than 700 environmental groups, asking them to promote vegetarianism, and that it would soon distribute leaflets that highlight the impact of eating meat on global warming.

“You just cannot be a meat-eating environmentalist,” said Mr. Prescott. The Humane Society of the United States has taken up the issue as well, running ads in environmental magazines that show a car key and a fork. “Which one of these contributes more to global warming?” the ads ask. They answer the question with “It’s not the one that starts a car,” and go on to cite the United Nations report as proof.

On its Web page and in its literature, the Humane Society has also been highlighting other scientific studies — notably, one that recently came out of the University of Chicago — that, in essence, show that “switching to a plant-based diet does more to curb global warming than switching from an S.U.V. to a Camry,” said Paul Shapiro, senior director of the factory farming campaign for the Humane Society.