Carbon Footprints

A very interesting article in this week's New Yorker about the complexities of measuring something's (or someone's) carbon footprint. Turns out "food miles" is a pretty darn inadequate way to think about how what we eat or buy affects the environment:

“People should stop talking about food miles,” Adrian Williams told me. “It’s a foolish concept: provincial, damaging, and simplistic.” Williams is an agricultural researcher in the Natural Resources Department of Cranfield University, in England. He has been commissioned by the British government to analyze the relative environmental impacts of a number of foods. “The idea that a product travels a certain distance and is therefore worse than one you raised nearby—well, it’s just idiotic,” he said. “It doesn’t take into consideration the land use, the type of transportation, the weather, or even the season. Potatoes you buy in winter, of course, have a far higher environmental ticket than if you were to buy them in August.” Williams pointed out that when people talk about global warming they usually speak only about carbon dioxide. Making milk or meat contributes less CO₂ to the atmosphere than building a house or making a washing machine. But the animals produce methane and nitrous oxide, and those are greenhouse gases, too. “This is not an equation like the number of calories or even the cost of a product,’’ he said. “There is no one number that works.”

Many factors influence the carbon footprint of a product: water use, cultivation and harvesting methods, quantity and type of fertilizer, even the type of fuel used to make the package. Sea-freight emissions are less than a sixtieth of those associated with airplanes, and you don’t have to build highways to berth a ship. Last year, a study of the carbon cost of the global wine trade found that it is actually more “green” for New Yorkers to drink wine from Bordeaux, which is shipped by sea, than wine from California, sent by truck. That is largely because shipping wine is mostly shipping glass. The study found that “the efficiencies of shipping drive a ‘green line’ all the way to Columbus, Ohio, the point where a wine from Bordeaux and Napa has the same carbon intensity.”

The environmental burden imposed by importing apples from New Zealand to Northern Europe or New York can be lower than if the apples were raised fifty miles away. “In New Zealand, they have more sunshine than in the U.K., which helps productivity,” Williams explained. That means the yield of New Zealand apples far exceeds the yield of those grown in northern climates, so the energy required for farmers to grow the crop is correspondingly lower. It also helps that the electricity in New Zealand is mostly generated by renewable sources, none of which emit large amounts of CO₂. Researchers at Lincoln University, in Christchurch, found that lamb raised in New Zealand and shipped eleven thousand miles by boat to England produced six hundred and eighty-eight kilograms of carbon-dioxide emissions per ton, about a fourth the amount produced by British lamb. In part, that is because pastures in New Zealand need far less fertilizer than most grazing land in Britain (or in many parts of the United States). Similarly, importing beans from Uganda or Kenya—where the farms are small, tractor use is limited, and the fertilizer is almost always manure—tends to be more efficient than growing beans in Europe, with its reliance on energy-dependent irrigation systems.

Williams and his colleagues recently completed a study that examined the environmental costs of buying roses shipped to England from Holland and of those exported (and sent by air) from Kenya. In each case, the team made a complete life-cycle analysis of twelve thousand rose stems for sale in February—in which all the variables, from seeds to store, were taken into consideration. They even multiplied the CO₂ emissions for the air-freighted Kenyan roses by a factor of nearly three, to account for the increased effect of burning fuel at a high altitude. Nonetheless, the carbon footprint of the roses from Holland—which are almost always grown in a heated greenhouse—was six times the footprint of those shipped from Kenya. Even Williams was surprised by the magnitude of the difference. “Everyone always wants to make ethical choices about the food they eat and the things they buy,” he told me. “And they should. It’s just that what seems obvious often is not. And we need to make sure people understand that before they make decisions on how they ought to live.”

(read the whole thing here)