Grazing ruminants (animals that are meant to eat grass and grass alone, like cattle) produce methane as a bi-product of digestion. Much has been written and analyzed regarding the climate impact of this activity. “Big beef” tells us that industrial feedlot beef actually produces less GHGs than grass-fed, for the simple reason that the animals are sent to market at 16 months instead of 20-24 months of age. They are alive longer, so they produce more GHGs – simple!
This is much like arguing about the various levels of flatulence between two people based on their diets and how these farts contribute to climate change, but ignoring the fact that one drives a Suburban and one rides a bike. You’re missing the forest for the trees.
There is substantial evidence that properly managed grass-fed cattle more than offset their methane emissions through carbon sequestration in the soil. When moved daily through a productive perennial pasture (like those we have here in New England and New York!), grass-fed beef production becomes a net carbon sink.
Two studies for those who want to go a level deeper:
Journal of Soil and Water Conservation: http://www.jswconline.org/content/71/2/156.refs
(0.89 metric tons per hectare are required to offset methane completely, this study finds an 8 ton increase over 3 years on conversion of degraded cropland to grazing land in Georgia)
And finally the NYTimes article that provides some context on industrial meat production impacts, but does not address the nascent pasture-based systems we are trying to help build: https://www.nytimes.com/2018/01/25/climate/cows-global-warming.html?emc=edit_tnt_20180125&nlid=63070982&tntemail0=y