The romantic notion of buying local fruits and vegetables from your friendly farmer down the red dirt road might makes excellent fodder for a marketing campaign, however it has little basis in fact. Walmart and others have announced an initiative that whenever possible they will source local. If you have a distribution system better than the federal government it is easy to make that type of pronouncement. It is more carbon efficient for Walmart to move produce than for a local farmer to bring a product to the weekly farmers market. The problem is if Walmart is sourcing all the local produce, you Mr. & Ms. Average Consumer have no chance. The supply simply is not there. Also, the whole point of this exercise is to reduce the total carbon footprint on the planet, it is not at all clear that buying local helps the environment.
Marketing of buying local is a great driver because it makes everyone feel good that they are helping the merchant down the street and reducing pollution along the way. It is ironic that Walmart is now seen as helping local merchants. Walmart has done more to put whole sectors out of business than any organization in history. (that however is fodder for another post, think pizza from Walmart and be very afraid)
The feel good notion of buying local has caught on and will be with us for a while.