Megan is pondering an interesting question. Apparently some contrarians have begun trying to convince her that the carbon cost of transporting non-local food is so high that the metabolic energy she expends by biking to work may come at a larger carbon cost than just taking a cab. That is, a distantly-grown apple takes so much energy to grow, produce and deliver that we’d be better off burning fossil fuels rather than expending human effort.
Two things. First, as Megan points out, gasoline has to be transported, too. Second, not too long ago Drake Bennet pointed out some good reasons for wondering whether local food is actually environmentally friendly: it doesn’t take too many trips to the farmer’s market in a mostly-empty car for the tomato you just bought there to represent more energy use than the one shipped across an ocean in a massive container ship, then packed into a fully-loaded diesel semi.
But I’m still curious about how the energy use breaks down. Some figures arrived at via quick googling:
- One gallon of gas contains 121 MJ of energy, or 28,920 kilocalories (1 dietary calorie = 1 kilocalorie)
- A 175 lb bicyclist traveling at 15 mph expends about 34 calories per mile
- The highest average fuel economy in US history was 26.2 mpg. Depressingly, this occurred in 1987, according to Wikipedia.
- Fight with Quicksilver’s calculator functions a little and you get… let’s see here… *whirring noises*… 1103.81 kilocalories per mile of travel by car.
So bicycling is 32.4 times more efficient, in terms of pure energy use, than driving an average car (from 1987). Making energy by growing and harvesting food certainly takes a lot more energy than making it by pumping oil out of the ground and putting it through a fractionating column. But 32 times more per unit of produced energy? Well, maybe.
At any rate, the difference in locally- versus distantly-grown food seems unlikely to be the deciding factor. The real question is whether, carbon-wise, you should be making that bike ride at all, regardless of where your groceries began their journey. I can easily imagine a tomato requiring 32 times more energy to grow, harvest and deliver than it provides in food energy.
But who knows? It’s all very confusing, and the concerned individual taking deliberate action to save the environment through carefully researched lifestyle changes seems to me to be embarking on such a crapshoot that they’ll be very lucky if, when all is said and done, they’ve managed to even offset the carbon cost incurred by their EnergyStar LCD monitor’s daily display of Treehugger.
OR: What Ezra said.