First off, I liked the article because I think its great when Steve explores other topics other than the standard "getting things done", "getting out of bed", etc personal development things. I totally agree that factory farming methods are a major problem in this country and one that needs to be dealt with if we want to slow down climate change. We have to move to much more sustainable methods and decreasing or eliminating the meat from our diets is a great step.
Steve, could you point me to the United Nations report that you referenced saying that agriculture is the largest C02 emitter?
A little searing got me the following data from the International Energy Agency that shows agriculture as 4.7% of the total with the majority coming from Public Electric and Heat Production.

I'm sure politics influences these statistics to an extent, but wouldn't the UN also have a bias?
International Energy Agency (IEA)
2001 data: Percent of Carbon Dioxide (CO2) Emissions by Sector
Public Electricity & Heat Production: 42.3 %
Other Energy Industries:4.6%
Manufacturing Industries and Construction: 11.5%
Internal Transportation:30.3%
Residential:7.8%
Other Commercial,Public, and Agricultural Sectors: 4.7%
Source:
http://earthtrends.wri.org/pdf_libra.../cli2_2005.pdf