I recently read a report that concluded that buying lettuce from Morocco in London resulted in a smaller carbon footprint than buying local lettuce grown outside London. The conlcusion being that we really shouldn't use food-miles as a measure of sustainability, that the free market has worked all this out for us. What's wrong with this picture?

Well, first of all a little digging dispelled the conundrum. The study assumed a consumer bought the lettuce in January. It assumed that the local English lettuce grew in a heated greenhouse under artificial lighting using conventional (fossil fuel based) fertilizers and pesticides.

Given that situation, I guess I would have concluded that England isn't a good place to grow commercial lettuce in January, and that we probably shouldn't try. But that's just me.

More broadly, there are a lot of efforts right now to debunk the use of food-miles as a measure of sustainability. I'll admit that food-miles are a pretty broad brush. But as a general rule, I think it's a perfectly good one. Here's why.

First of all, even if we accept the premise in the above comparison, emissions are not created equal. We can control emissions from a power plant more easily than emissions from an airliner or truck. It's a point source, and doesn't move. In addition, airline emissions at 10 kilometers altitude hang around longer and do more climate damage than those at ground level. So local buying shows an advantage even if emission amounts are equal.

But more importantly, shopping by lower food-miles insulates us from higher energy costs. If the cost of oil doubles - a not unlikely scenario in the next 3-5 years - then the cost of Moroccan lettuce will rise accordingly. The cost of the local lettuce, even in the preposterous situation described above, will be less sensitive since it can be accomplished using other energy sources. Multiply this by all the other foods migrating from other continents, and you can see what kind of dent it would make in your food budget. Or the food budget of someone on a fixed income. This is in fact what happened in some developing nations in 2008.

Even better than eating locally, eat seasonally as well. Support your local grower network all through the year. A local grower network is our insurance against spiraling energy prices, and a fundamental piece of our emissions control strategies. Get your schools and your company cafeteria buying locally and reinforcing this network. The network itself, and the community structure that comes with it, are just as important as the food passing through it when it comes to resiliency. Building a local food network should be seen as a personal and governmental responsibility. It should also be accepted as a Corporate Social Responsibility goal. Building a local food network is a lot harder without the corporations on board.