The Global Warming Diet

The source: “Food-Miles and the Relative Climate Impacts of Food Choices in the United States” by Christopher L. Weber and H. Scott Matthews, in Environmental Science and Technology, May 15, 2008.

Worried about the environmental cost of eating Chilean grapes in January? Eager to help curtail global warming by grilling only locally grown beef? Then pay more attention to what you eat and less to geography. Surprisingly, write two engineers at Carnegie Mellon University, consumers can do more to reduce greenhouse gas emissions by shifting family menus one day a week from red meat and dairy products to chicken, fish, or vegetables than they can by buying 100 percent locally grown food.

Christopher L. Weber and H. Scott Matthews found that the delivery of food from producers to grocery stores accounts for only four percent of America’s food-related greenhouse-gas emissions. Most of the environmental impact of food is the result of things that happen during the production phase. Transportation as a whole accounts for only 11 per-cent of food’s life cycle emissions, and international air freight only two percent of that.

No matter how it is measured, Weber and Matthews write, “red meat is more greenhouse–gas -intensive than all other forms of food,” because of the long supply chains of animal feed. Dairy products are second. They are about half as intensive as red meat, calorie for calorie. Fruits and vegetables take about the same toll on the environment as chicken, , fish, eggs, and nuts. The impact they have on the environment is less in the production phase, but greater in delivery and transportation.