There’s been no shortage of talk about listing carbon footprints on food labels. The British supermarket Tesco has already added a carbon emissions number to 20 of its products; it had hoped to label more, but figuring out what that footprint should be was tougher than expected. Now there’s an even less practical idea: Professor Tim Lang of City University–London has proposed embedding computer chips in food labels so shoppers can instantly use their cell phones to look up products in a sustainable food guide.

Of course, as Lang himself admits, since the criteria for judging sustainability are still being argued over, the concept of a single, broadly accepted sustainable food guide is highly conceptual. But that’s shadowed by a far more significant obstacle: Most food isn’t produced sustainably, so manufacturers have no interest in giving consumers more information about it.

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