At what point will people realize that it is impossible to measure the carbon footprint of the food they buy? The concept of “food miles” is only a small part of the story. Consider this case of the potato chip, which is discussed in an op-ed in today’s New York Times:

And while it might seem logical that the further an item of food journeys, the more carbon emissions it generates, this turns out not to be the case. When you count the energy used by harvesting and milking equipment, farm vehicles, feedstock and chemical fertilizer manufacture, hothouses and processing factories, transportation emerges as just one piece of the carbon dioxide jigsaw puzzle.

Take the potato chip, for instance. When Walkers, a British snack manufacturer, studied the carbon footprint of a packet of its chips, distribution represented just 9 percent of the total. The greatest emissions came in storing and frying the potatoes. Farmers store potatoes in artificially humidified warehouses, which take energy to run, generating emissions. Because of the way they’re stored, the potatoes contain more water and take longer to fry, generating more emissions. And since farmers sell potatoes by weight, they have no incentive to drive off excess water. Changing the way potatoes are warehoused and sold could therefore significantly cut the carbon footprint of chips.

Obviously, calculating the carbon footprint of food is an extraordinarily tricky business. But only when we understand a food’s energy use throughout its life cycle from seed to kitchen can we make intelligent decisions on where to start on cutting the greenhouse gas it generates.

These sorts of anomalies are likely to be pervasive in the production process. As a result, “we” can’t really make intelligent decisions as consumers on cutting greenhouse gas emissions in the food production cycle — producers can, but only if they have an economic incentive to do so. That’s why we need a carbon tax. If the price of storing and frying potatoes reflects the damage it does to the environment, then producers will have an incentive to figure out a better way. Consumers won’t have to worry about “food miles” and government won’t have to try to calculate “carbon footprints” of various industries. The same principle applies to the production of any sort of commodity good.