The "food miles" concept was almost too good to be true–buying locally-grown food supported neighborhood merchants, preserved scenic farmland, required trips to quaint farmers markets, offered great dinner party bragging rights, and, perhaps most important, slowed global warming by saving all the fossil fuel required to fly produce and meat around the world. As it turns out, the last bit really is too good to be true:
Instead of measuring a product's carbon footprint through food miles alone, the Lincoln University scientists expanded their equations to include other energy-consuming aspects of production — what economists call "factor inputs and externalities" — like water use, harvesting techniques, fertilizer outlays, renewable energy applications, means of transportation (and the kind of fuel used), the amount of carbon dioxide absorbed during photosynthesis, disposal of packaging, storage procedures and dozens of other cultivation inputs.
Incorporating these measurements into their assessments, scientists reached surprising conclusions. Most notably, they found that lamb raised on New Zealand's clover-choked pastures and shipped 11,000 miles by boat to Britain produced 1,520 pounds of carbon dioxide emissions per ton while British lamb produced 6,280 pounds of carbon dioxide per ton, in part because poorer British pastures force farmers to use feed. In other words, it is four times more energy-efficient for Londoners to buy lamb imported from the other side of the world than to buy it from a producer in their backyard. Similar figures were found for dairy products and fruit.