Sad but true. Ezra Klein:
Two researchers at the University of Chicago estimated that switching to a vegan diet would have a bigger impact than trading in your gas guzzler for a Prius (PDF). A study out of Carnegie Mellon University found that the average American would do less for the planet by switching to a totally local diet than by going vegetarian one day a week. That prompted Rajendra Pachauri, the head of the United Nations Intergovernmental Panel on Climate Change, to recommend that people give up meat one day a week to take pressure off the atmosphere. The response was quick and vicious. “How convenient for him,” was the inexplicable reply from a columnist at the Pittsburgh Tribune Review. “He’s a vegetarian.”
Looking at the chart, there are lessons for the environmentalist meat-eater beyond just "eat less meat." Switching from beef to pork cuts that part of your plate's carbon footprint in half, and switching from pork to chicken cuts it in half again. 2% milk, yogurt, and eggs are all pretty guiltless from an environmental standpoint.
All that said, once again the evidence is in: cutting your consumption of meat in general, and red meat in particular, is good for you, your family, and your planet. I can say, too, that I've significantly decreased the amount of meat I eat over the couple of years, especially beef, and it hasn't been nearly as bad as I thought it would be. A bean and cheese burrito, yogurt with blueberries, and an apple isn't a bad lunch!