What's the true cost of the emissions from every gallon of gasoline, when you add up all the negative environmental impacts they'll lead to, from poor air quality to catastrophic climate change? Nine dollars a gallon. Add that to what you're typically paying at the pump right now, and it means that the real cost of a gallon of gas to the planet and our future is easily into double digits.

So says a pair of new analyses by big-shot economists, who think that telling people the true cost of carbon might make us stop mortgaging our children's future just so we can drive that Escalade to the air-conditioned gym. They argue that the federal government has assessed the "social cost" of carbon (that's the cost of all its environmental impacts, present and future) at $21 a ton, but that the actual cost is oh, about 45 times as high, or $900 per ton.

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Viewed another way, with the U.S. emitting the equivalent of close to 6 million tons of carbon dioxide annually, the higher figure suggests that avoiding those emissions could save the nation $5.3 trillion annually, one-third of the nation's economic output.

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