A good article in the New York Times, linked to by Bru Notes (again, thanks), shows a PR campaign by groups such as PETA and the Humane Society that states that eating meat makes you more liable for the global warming problem than someone driving a Hummer. And there is data from the United Nations that backs this up. This is something I've thought of before, when you consider the transportation and amount of fossil fuels that it must take to ship meat throughout the world. That's not counting the actual raising of cows and other animals for meat on the farm. I eat meat, as I'm sure a lot of left-leaning people do. So it makes you think.
But as Bru posted, I don't agree with PETA's insinuation that those who are already fighting against global warming, including Al Gore and others, should do even more. Global Warming is a lot to adapt to, for anyone who's serious about it. You have to sell your SUV and drive a smaller, fuel-efficient car. You have to recycle more. You have to make a lot of changes, and you can only change so much. I don't think someone who drives a Prius, lives in a small apartment or house and is a good eco-citizen in most respects is an evil hypocrite for eating a hamburger now and then. If PETA and the Humane Society wants to fight global warming on the pretense of saving the animals, have at it, it's a great and noble goal. But they shouldn't expect other environmental activists to do it.