"The significance of this opportunity was emphasized in a recent presentation at the World Bank by Jonathan Foley, director of the University of Minnesota Institute on the Environment. According to analysis by the Institute, every pound of meat is equivalent to about 30 pounds of grain production in its contribution to climate change when allowance is made for the full life cycle of livestock production. This is primarily because methane emissions from ruminants have a GHG impact roughly 25 times that of carbon dioxide.
...Another expression of the resource intensity of meat production, Foley explained, is that even highly efficient agricultural systems like that in the US only deliver about the same calories per hectare in human consumption terms as poor African countries with more grain based diets."
Alan Miller, "Diet for a Low Carbon Planet," World Bank Blog, last modified May 3, 2011, accessed May 28, 2014, http://blogs.worldbank.org/climatechange/diet-low-carbon-planet.