When I am in Charlottesville, I always try to get my produce from the local markets. When I came home I told my dad that he should start buying local at home, he asked me “Why should I, when it’s more expensive?” I told him that buying local not only keeps his money in the local economy, but it is much more sustainable; the little effect a single piece of fruit can have adds up and can have a big effect on the environment.
If he buys his strawberries from California, they have to travel from thousands of miles away to reach the grocery store. That involves shipment on a truck, if not multiple, using diesel and refrigeration on the truck. This emits gases and depletes the ozone layer.
Buying local also cuts out the travel time from the field to your home, meaning it is much fresher.
The explanation of the systems involved with buying local produce that I gave him definitely changed his mind about buying local and I think once other people learn about it, it will change their minds too. I definitely believe that making small changes everyday can allow us to become more sustainable.
kaitybadlato 
I really love the way you expain it. It is brief but perfectly well defined reason why we should support the local economy by buying local. I am sure your friend changed his mind and many people will once they are aware of the reasons.