Everyone loves the fresh produce at a Farmers Market. And we love that it traveled a minimal distance to get here, thus being as environmentally friendly as possible. Right?
Wrong. It turns out that driving small trucks on individual routes between every farm and every store burns far more diesel fuel than combining routes and using distribution centers. Compare the tangled spider web of redundant routes when you deliver locally grown food between the closest farm and store, to the much simpler model of using a distribution center. Retailers use this model for a reason: it saves money because it burns much less fuel. And it usually accomplishes same day fresh delivery between farm and market. Many of the individual routes taken are indeed longer, but the overall mileage traveled is way, way less.
Economies of scale also play an important role. A big truck burns less fuel per pound of cargo than a small truck. A train burns even less, and it delivers at a faster average speed. The king of efficiency is a container ship. If the product can tolerate the slower delivery, it's the environmentally cleanest way to deliver anything.
You also need to consider the complete energy cycle: Not just the delivery of the food, but its production as well. In the case of meat, whether the animals can graze or have to be given feed has a huge impact. Lamb raised in New Zealand, where they can graze year-round, have to be shipped 11,000 miles to the UK. But lamb raised in the UK have to be given feed. The difference? Four times more carbon dioxide is emitted, in total, eating locally raised lamb.
Tomatoes grow like crazy in sunny Spain, but to grow them in the UK requires heated greenhouses that suck power from the grid. Shipping tomatoes from Spain to UK markets uses only half the total energy, compared to those shoppers who prefer locally grown tomatoes.
Enjoy Farmers Markets for what they are: A premium boutique experience. The tomatoes might be fresh and huge, but it's not necessarily an environmentally friendly way to get food to consumers.
Energy efficiency and local production are sometimes the same thing, but often they're not. Consider the efficiencies that can be gained growing food in a better location, reducing animal feed production, and using transportation that benefits from economies of scale. That's being truly green.