I'd heard and read a lot about carbon footprints, but never understood it very well until I heard a presentation by Jude Capper, now a new Ass't Professor at Washington State Univ. She summarized some work that she had done in conjunction with Dale Bauman and Euridice Castaneda-Gutierrezof Cornell Univ and Roger Cady, now of Elanco. The fundamental component of their work was published in the Proceedings of the National Academy of Sciences in 2008, but they have expanded it and continued their analysis.
If you haven't heard Jude speak on the topic or are confused about carbon footprint and animal agriculture I suggest that you participate in the eXtension webinar hosted by the Livestock and Poultry Environmental Learning Center. Both Jude and Roger will be presenting. Just click on the "Live Webcast" link and then the "Connect Now" link. The webinar room will open about 15 mintues before the start.
The webinar will be at 2:30 PM EDT on 31 July 2009. Let your friends and neighbors know.
Hope that helps.
Disclaimer: Roger Cady and I are old friends. We started Dairy-L, the listserv-software-based virtual community together now 20 years ago. That doesn't mean that I don't chastise him when he needs it, ( :-) ) but he doesn't on this. It's good work.