People are changing their diet on behalf of farm animals and the environment:
http://www.t3v.makessense.co.uk/articles/205.html
"......Researchers at the University of Chicago have calculated the relative carbon intensity of a standard vegan diet in comparison to a US-style carnivorous diet, all the way through from production to processing to distribution to cooking and consumption. An average burger man (that is, not the outsize variety) emits the equivalent of 1.5 tonnes more CO2 every year than the standard vegan. By comparison, were you to trade in your conventional gas-guzzler for a state of the art Prius hybrid, your CO2 savings would amount to little more than one tonne per year......."