There is an interesting article in the recent issue of the Journal of Environmental Science and Technology titled "Food-Miles and the Relative Climate Impacts of Food Choices in the United States".
Recently, people who are environmentally conscious and who also believe that organic food is more healthy have had to start balancing their desire to buy organic food (which might not be locally produced) with their desire to fight climate change by buying locally (and thus minimizing transportation-related greenhouse gas emissions).
As I read it, this article addresses two big questions: how much does distance and transportation add to the carbon emissions related to food in the US? and what are the differences in total emissions (production and transportation) between food categories in the US?
The answer to the first question is not all that much. Total transportation only contributes 11% of the life-cycle greenhouse emissions of a product (4% of which is final delivery). Therefore savings can be made by buying locally, but not all that much. (I would add that buying locally, might very well involve less efficient production.)
To answer the second question, the data was broken down into seven groups:
2) Cereals, Carbohydrates
3) Chicken, Fish, Eggs
5) Fruit, Vegetables
6) Oils, Sweets, Condiments
7) Red Meat
The emissions of each these categories was measured four different ways: CO2/household, CO2/dollar, CO2/kCal and CO2/kg.
Red meat comes out as the largest contributor by a large margin using any of these measures (the authors estimate that red meat contributes 150% more greenhouse gases than chicken or fish). Dairy comes out high based on CO2/dollar (I would think this is because milk is historically very inexpensive relative to its nutritional value). When CO2/household and CO2/kCal are used, the contribution from dairy falls back a good deal, and when CO2/kg is used dairy falls in line with the minor contributors.
The authors suggest that replacing some red meat and dairy intake with chicken or fish, say once a week, would have a greater positive impact on the environment than buying locally.
It still looks to me like dairy should not be in the same category as red meat. Nevertheless, this is an interesting study and will surely invite similar analyses in other countries.