Sunday, August 07, 2005

Food miles

A hilly 13km cycling trip carrying a couple of melons on a hot summer's day really brings home the meaning of food miles!

Perhaps I should explain. There's a roadside fruit stall that sets up once a week on the route we cycle to work. Japanese fruit is really good, and we like to pick up a selection of whatever is in season. The stall mostly sells fairly local produce which seems to cover a wide range of items, but grapefruit is strangely absent - they are all imported from Florida, which seems odd for a country with such a strong tradition of citrus growing (eg satsuma). There also don't seem to be any local suppliers of that staple food of cyclists, the banana.

This NewScientist article from a few months back describes some interesting research on the hidden environmental costs of food production in the UK. It demonstrates that the total air and ship miles of imported food is actually an extremely small part of the overall problem, with lorry transport in the UK doing the lion's share of the damage. The real surprise to me, though, was the fact that the average person's shopping trips, 221 per year of 6.4km length (and almost all by car) causes about half as much harm as the lorries do. On reflection though, a 40-tonne lorry has a much larger payload as a proportion of vehicle weight than a 1-tonne family car with a bag of shopping, and the car trip will also take place in congested urban environments, so the per-tomato environmental cost of each mile in the car will be much higher than for the lorry.

Back to the melons. The sheer effort of transporting them a few miles also made me think about the extent to which agriculture relies on oil as a raw input. A bit of surfing finds energy input:output ratio estimates of about 10:1 overall from some alarmist "peak oil" type sites (ie 10 times as much fossil fuel energy is used in production as is created in food calories), and more industry-friendly estimates for the most efficient foods (bread) give a more optimistic picture, such as this estimate of an energy ratio of 1:5 in favour of food output. Probably the truth is somewhere between the two. In any case, even the most optimistic estimates underline to what extent our society has been based on ever-increasing increasing supplies of cheap energy.


Anonymous said...

I recently read a fascinating account of food production and transport in classic Mayan culture. I'm going from memory here, so I'll likely mangle the details a bit, but it's possible to calculate firm limits on the range of food trade in Mayan culture. They had no vehicles or beasts of burden, so any food - maize and the like - had to be carried by humans. Since the human carrying the food needs to eat, one can calculate a fixed range beyond which trade is no longer possible, because the person carrying the food will end up eating it all before he gets there. I don't remember the resulting range, but I think it was something like 50 miles.
- John Fleck

Anonymous said...

Re: the energy ratio of food production.

I wonder if the lower estimates are looking at only the direct inputs? Any sensible calculation has to look at the transport etc costs as well.

I also wonder if an average is a useful figure here. The varience between an organic apple grown a few miles away and sold in a local shop and a processed apple pie made from New Zealand apples and bought from a supermarket must be huge.


James Annan said...


Interesting approach. The energy cost couldn't quite prohibit long-distance trade (well-known maths/logistics puzzle: how to cross a desert with a vehicle that can only carry enough fuel to go half way) but the sharply increasing inefficiency of such trade over large distances would certainly militate against it for exchanging fungible calories, at least.


I don't know the details of the various calculations, but would not be surprised to find people using definitions which are convenient for their purposes...AIUI a lot of the UK's organic food is imported, which brings another twist to the organic v conventional debate.