Proper estimation of GHG  from food production and consumption is notoriously complicated: livestock emit methane, a much more potent greenhouse gas than carbon dioxide; commercial meat production is disproportionately grain-intensive, and so the more meat is eaten, the greater the climate burden in terms of fertilizer and fuel inputs; finished food products, whether meat or grain, have to be transported, packaged, and sold, involving still further burdens. Several years ago,  a University of Chicago study found that in a typical household, GHG emissions connected with food can be as important as those associated with the home's car or cars.
A new report in World Watch Magazine argues that a previous study done under the auspices of the Food and Agriculture Organization radically underestimated the emissions from meat and poultry production. The FAO estimated in 2006 that such emissions amount to about 18 percent of total world GHG emissions; but World Watch puts them at 51 percent.
