Let's Make Some Sweeping Statements

I thought it would be easy to create a sweeping statement first blog post:
..."Going Vegan Will Cut CO2 Levels by 62.3% and Save The World"...
but early research attempts have already confounded me slightly.

I suspect there are two main issues I'll try and consider, though others will have different priorities:
1) the environmental impact of food production, and subsequent affects - mainly through greenhouse gases and water resources
2) the issues of simply creating enough food for the growing population with changing diets over the next few decades.

(...and the ethics of eating little cows and sheep, battery farming, GM crops, agricultural subsidies, fisheries...this is fairly complex.)

But measuring the environmental impacts of different foods is tricky. Do you consider transport? The resources that grew the grain that fed the cow? What about packaging? Making overview statements about food security and the impacts of diet is difficult. Yes, all other things being equal, creating a steak will have required more water and have a higher carbon dioxide footprint than the equivalent weight of potato or wheat. Its easy to find statements on the internet from environmental groups and vegan societies saying exactly what you'd like them to say - but finding recent and reliable sources that back these quotes up is difficult. There's a lot of assumptions and a lot of subtleties. And that's one of the areas we'll be exploring during February.

But just to create food for thought, and squeeze in one little sweeping and debatable statement:
“The world must create five billion vegans in the next several decades, or triple its total farm output without using more land.” Dennis Avery, Center for Global Food Issues
Opinions?