The threat of global warming has many businesses clamoring to get carbon neutral. The Super Bowl this year, for example, was powered by wind. Airlines sell carbon offsets so we feel less guilty burning jet fuel. And the latest wrinkle is food miles: a way to assess the carbon cost of foods based on how far they travel to reach the grocery store. It’s meant with good intentions, but my next guest says these carbon calculations are not all they’re cracked up to be. Michael Specter wrote about the difficulty of sizing up carbon footprints for the New Yorker magazine, and he speaks with Faith Salie on Fair Game.