Hopefully you know that the environmental benefits of local food are highly questionable (here’s one summary–note that the moron promoting local food is eating local meat!). If you want to reduce the environmental impact of your food, go vegetarian and stop thinking about the issue. However I suspect that certain types of local food will become much more important over time–specifically the contrast between food that is flown overseas, and food that only travels by land. As far as I know, there are no really good proposals for reducing the carbon emissions of air travel, whereas there are real ways to reduce the impact of ground transport. So that should partially change the balance.
The article mentioned above notes the difficulty of figuring out which foods are actually the best in terms of carbon emissions–one reason to think that carbon taxes are essential, since they more effectively process information than we can.