From the April 26th New York Times, Environmental Cost of Shipping Groceries Around the World, discusses the complexities of global food trade. Its great efficiency, the hidden subsidies to transport, and the politics of carbon footprint calculations:

Cod caught off Norway is shipped to China to be turned into filets, then shipped back to Norway for sale. Argentine lemons fill supermarket shelves on the Citrus Coast of Spain, as local lemons rot on the ground. Half of Europe’s peas are grown and packaged in Kenya. …

Increasingly efficient global transport networks make it practical to bring food before it spoils from distant places where labor costs are lower. And the penetration of mega-markets in nations from China to Mexico with supply and distribution chains that gird the globe — like Wal-Mart, Carrefour and Tesco — has accelerated the trend.

But the movable feast comes at a cost: pollution — especially carbon dioxide, the main global warming gas — from transporting the food.

Under longstanding trade agreements, fuel for international freight carried by sea and air is not taxed. Now, many economists, environmental advocates and politicians say it is time to make shippers and shoppers pay for the pollution, through taxes or other measures. …

Some of those companies say that they are working to limit greenhouse gases produced by their businesses but that the question is how to do it. They oppose regulation and new taxes and, partly in an effort to head them off, are advocating consumer education instead.

Tesco, for instance, is introducing a labeling system that will let consumers assess a product’s carbon footprint.

Some foods that travel long distances may actually have an environmental advantage over local products, like flowers grown in the tropics instead of in energy-hungry European greenhouses.

“This may be as radical for environmental consuming as putting a calorie count on the side of packages to help people who want to lose weight,” a spokesman for Tesco, Trevor Datson, said. …

Some studies have calculated that as little as 3 percent of emissions from the food sector are caused by transportation. But Mr. Watkiss, the Oxford economist, said the percentage was growing rapidly. Moreover, imported foods generate more emissions than generally acknowledged because they require layers of packaging and, in the case of perishable food, refrigeration. …

The problem is measuring the emissions. The fact that food travels farther does not necessarily mean more energy is used. Some studies have shown that shipping fresh apples, onions and lamb from New Zealand might produce lower emissions than producing the goods in Europe, where — for example — storing apples for months would require refrigeration.

But those studies were done in New Zealand, and the food travel debate is inevitably intertwined with economic interests.