Over at Environmenal Economics, a reader writes:
I am curious about might be called the “carbon economics” of buying local food. Here’s the deal…
I read everywhere that most food sold at my nearby grocery store travels thousands of miles to get here. The implication is that all those travel miles results in lots of fuel burned and lots of CO2 released into the atmosphere. Does it really?
I live in Raleigh, so a tomato grown in Sacramento, CA travels 2,800 miles to get here. Let’s say an 18-wheeler filled with 20,000 pounds of tomatoes, gets 6 mpg, travels 2,800 miles and emits 23 pounds of CO2 for every gallon of diesel fuel burned. By my calculations, that’s .53 pounds of CO2 emitted per pound of tomato delivered. (My assumptions warrant checking but seem reasonable to me.)
Conversely, say my local farmer travels 40 miles in a gasoline powered truck that gets 10 mpg and emits 18 pounds of CO2 per gallon burned, to deliver 2,000 pounds of tomatoes to my local farmer’s market. That’s about .04 pounds of CO2 released for every pound of tomato delivered. Pretty good! Except for one thing; I’ve got to drive 15 miles to get to the farmer’s market and I’m not likely to buy more than 5 pounds of tomatoes; my car gets 25 mpg and emits 18 pounds of CO2 per gallon of gas burned. So my trip to buy 5 pounds of the locally grown tomatoes emits 2.16 pounds of CO2 for every pound of tomato I buy.
Ooh, what a tantalizing question. Lot’s of interesting comments have been posted there, so you can check it out. A couple quick thoughts: what would the farmer be doing without the farmers’ market? Their different driving pattern will play a role in the final carbon tally. Over time, as more farmers’ markets are established, consumers shouldn’t have to drive much farther than the distance to their standard grocery store; while going a relatively long distance now might be a net-carbon no-no, supporting farmers’ markets could encourage more of them, thus reducing distances.
This is something I’d love to put some more thought into, but I’m out of time. Join the fray and I’ll get back to this later.