One of the arguments that Locavore's make for why you should buy locally is that by doing so you will reduce the amount of "food miles", and by implication, the amount of greenhouse gases created to feed yourself. This argument has been persuasive to many consumers as indicated by popularity of the "100-mile diet" concept which basically advocates sourcing your food from within a radius of 100 miles. Doing so will reduce your "food miles" and in this way you can help the environment. If everyone followed suit it would make a huge difference in terms of greenhouse gas emissions (and the vitality of your local economy but I will not address this aspect of locavorism in this blog).

The main problem with the "food miles" argument for locavorism is that it only looks at greenhouse gas consumption from the retailer (i.e., farmer) to the consumer (i.e., the "distribution" component in table below), and does not address greenhouse gas consumption from a life cyle perspective which would include the greenhouse gases consumed to plant, harvest, package, store, distribute, consume, and dispose of the food items. When this broader perspective is taken into account, the "food miles" argument for locavorism can be contradicted by the facts (i.e., buying local can produce more greenhouse gases than buying from the global supply chain).

Source http://www.globavore.org

If a farmer is producing and selling food that is in season to local consumers, then this is the best case scenario for locavorism. If the food producer needs to consume energy to heat a greenhouse to get a jump start on the growing season or to extend the season, or needs to consume energy to maintain a cold storage to preserve their harvest, then this energy is being consumed where it would not have been had the food been imported from a different food producing region at a different latitude where the product is in season or not subject to heating or cold-storage requirements. Transporting food in bulk via a container ship from one region to another region where it is supplied to consumers via transport to a grocery outlet, has been calculated to consume less greenhouse gases than consumers driving en-masse to a local producer to pick up out-of-season food items (e.g., local apples from the UK versus apples imported from New Zealand). Consumers are likely to pick up more of the food items they need at the local grocery store than they will be able to at a local producer so less trips are required. In some respects, Locavore's have it right that the drive from your residence to the food retailer is a big culprit in green house gas emissions, however, the argument can be turned against a Locavore when it is pointed out that the cost of transporting food from one region at latitude A to another region at latitude B via a container ship is so efficient that it accounts for a very small fraction of the overall greenhouse gas emissions produced relative to the amount of emissions produced when consumers drive en-masse from their residence to a local food producer who may be supplying only a fraction of their food requirements and thus not negating a trip to your local grocery store.

The "food miles" argument is only one of the arguments for buying food locally. For a food producer to extoll the lack of green house gas emissions produced by consumers buying locally, they will need to find innovative ways to make that statement true relative to the efficiency of the global food supply chain coupled to a big box grocery outlet. One simple innovation is delivering the food to consumers individually or at centralized pickup points, rather than having consumers drive to the local food producer to pick up their goods. Other innovations would involve improving the efficiency of other parts of the food life cycle: production innovations, heating innovations, cold-storage innovations, packaging innovations, and disposal innovations. Doing so would give more force to the argument that buying local helps the environment by reducing green-house gas emissions. I don't think these arguments against buy-local are fatal, but they do require locavore's to step up their game if they want to use a reduced food miles argument in an honest manner to promote their food products. There is room for local innovation here, but it is an innovation that looks at greenhouse gas consumption from a life cycle perspective rather than just how much is consumed in the distribution component.