Very good presentation in the Scientific American in 5 color slides of how beef contributes to global warming.
The only issue I have with this article, is that it is strictly from a CO2 generation point of view. And the thing with the environment and eating meat, is that you have also to take into account the water consumption of cattle. You need water to grow cereals to feed to the cattle, who also drink water. So besides the amount of CO2 that the cattle produce, you also need to take into account the water consumption. At the end of the day there is a factor of 50 between the water needed to "produce" one kilo of meat and one kilo of bread. This is a complex problem, and we need a systems dynamics approach to it, not just looking at one parameter. And yeah, we should all eat less meat - it is also healthier