[Kalium]

Trans-oceanic shipping and trains are surprisingly low-impact per unit of food. When you add in the environmental impact of things like growing rice in Texas deserts and almonds in California, the results can easily come out in favor of trade.

There are other considerations, too. Favoring local products is a good way to keep poor food-exporting countries poor. I don't want that, though I understand some people have different priorities from me.