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Crunching the numbers on a vegan in a Hummer
(Updated below with Michael Pollan’s response)
You want some petroleum with that Big Mac?
Journalist and food writer Michael Pollan broke down the hidden cost of America’s best-known burger on Saturday to an eager audience at the Poptech conference. He traced the Big Mac’s origins all the way back to the oil fields, used to make fertilizer that is crucial to the corn grown for cows in massive feeds lots.
“Our meat eating is one of the most important contributors we make to climate change,” said Pollan, who is best known for his book “The Omnivore’s Dilemma.”
“A vegan in a Hummer has a lighter carbon footprint than a beef eater in a Prius.”
Gidon Eshel and Pamela Martin of the University of Chicago published a 2005 paper in the journal Earth Interactions that looked at the relative carbon footprints of plant-based and red-meat diets.
They found that the difference between an heavy meat-eating diet and a vegan diet was about 2 tons of carbon dioxide equivalent per person per year. The difference between a Prius and an SUV (they used a Suburban, which gets about the same mileage as a Hummer) was 4.76 tons per year.
Pollan’s claim, said Eshel, “is emphatically wrong. If you’re looking at the mean American driving habits and eating habits, it’s not even close.”
“In my heart I’m flatly on the Pollan side, but I’m a scientist and I don’t like to play fast and loose with numbers,” he added. “It’s like death panels in the healthcare debate. We don’t want to get into hyperbolic statements that are numerically unsound.”
To be sure, the calculations behind food-related carbon footprints can be complex. The impact of a Big Mac includes the carbon footprint of the cattle feed and the fertilizer used to grow it, the fuel burned to get the animal to a feedlot and then to market, and the animal’s emissions of methane gas, which can be 20 times more potent than carbon dioxide as a greenhouse gas.
UPDATE: Michael Pollan has asked Poptech not to post his presentation without removing the statistic about the vegan Hummer driver.
“After digging in to it further, and consulting Gidon Eschel, I don’t feel comfortable defending it,” he wrote to Reuters in an email. “It’s much more important to keep the focus on the central thrust of the environmental case against eating industrial meat, which is not in dispute and certainly does not stand or fall on the case of the vegan Hummer driver.”
“Thanks for your doggedness on this matter, which we can hope will stop this meme before it hurts somebody,” he added.
The blogger Fat Knowledge did a separate calculation of the numbers after Eshel and Martin’s paper was published, and concluded:
Going from a Mad Meat Eater diet to a Vegan diet saves 6.5 tonnes of CO2 a year while going from a Hummer to a Prius saves 6.4 tonnes. Given a margin of error on the values, I call that a tie.
The numbers have also shifted as gas mileage improves. Using Eshel and Martin’s calculations with the current EPA mileage statistics, a 2010 model Hummer getting 14-15 miles per gallon has a carbon footprint of 4.3 to 4.7 tons per year, depending on whether it’s an automatic or manual transmission model. (The EPA’s own carbon footprint calculations, which include the manufacture of the vehicle, are significantly higher)
A 2010 Prius getting 50 miles per gallon has a footprint of 1.4 tons. The difference is 2.6 to 3.3 tons per year — not very far from the 2 ton difference between a meat-eater and a vegan.