December 14, 2006
The food-energy equation
In his February 2004 Harper's essay The oil we eat, Richard Manning lays out the basic energy equation that underlies food.
All animals eat plants or eat animals that eat plants. This is the food chain, and pulling it is the unique ability of plants to turn sunlight into stored energy in the form of carbohydrates, the basic fuel of all animals. Solar-powered photosynthesis is the only way to make this fuel. There is no alternative to plant energy, just as there is no alternative to oxygen. The results of taking away our plant energy may not be as sudden as cutting off oxygen, but they are as sure.
Scientists have a name for the total amount of plant mass created by Earth in a given year, the total budget for life. They call it the planet's "primary productivity." There have been two efforts to figure out how that productivity is spent, one by a group at Stanford University, the other an independent accounting by the biologist Stuart Pimm. Both conclude that we humans, a single species among millions, consume about 40 percent of Earth's primary productivity, 40 percent of all there is. This simple number may explain why the current extinction rate is 1,000 times that which existed before human domination of the planet. We 6 billion have simply stolen the food, the rich among us a lot more than others.
. . .
Part of that total—almost a third of it—is the potential plant mass lost when forests are cleared for farming or when tropical rain forests are cut for grazing or when plows destroy the deep mat of prairie roots that held the whole business together, triggering erosion. The Dust Bowl was no accident of nature. A functioning grassland prairie produces more biomass each year than does even the most technologically advanced wheat field. The problem is, it's mostly a form of grass and grass roots that humans can't eat. So we replace the prairie with our own preferred grass, wheat. Never mind that we feed most of our grain to livestock, and that livestock is perfectly content to eat native grass. And never mind that there likely were more bison produced naturally on the Great Plains before farming than all of beef farming raises in the same area today.
Humans cannot eat most of the naturally produced biomass each year since it is in the form of grasses and trees, so we destroy that biomass by clearing those fields and planting crops that we can eat more readily or, as is more common, to use as raw materials to produce food in other forms. But each of these things carries with it energy costs. As Manning points out:
America's biggest crop, grain corn, is completely unpalatable. It is raw material for an industry that manufactures food substitutes. Likewise, you can't eat unprocessed wheat. You certainly can't eat hay. You can eat unprocessed soybeans, but mostly we don't. These four crops cover 82 percent of American cropland. Agriculture in this country is not about food; it's about commodities that require the outlay of still more energy to become food. (emphasis in original)
It turns out that about eighty percent of the grain the United States produces goes to feed livestock and that it "takes thirty-five calories of fossil fuel to make a calorie of beef this way" and "sixty-eight to make one calorie of pork." Livestock produced this way creates high-quality protein no doubt, but at a cost. In addition, the US produces twice as much per capita protein as the average adult needs each day. This results in over-consumption which leads to fat, resulting in an epidemic of obesity, which now is second only to tobacco in being the cause of health-related problems and fatalities.
The higher you go up the food chain, the more energy that is wasted along the way. All of us know that instinctively but I had not fully appreciated the massive scale of wastage as you ascend each rung of that chain.
Eating a carrot gives the diner all that carrot's energy, but feeding carrots to a chicken, then eating the chicken, reduces the energy by a factor of ten. The chicken wastes some energy, stores some as feathers, bones, and other inedibles, and uses most of it just to live long enough to be eaten. As a rough rule of thumb, that factor of ten applies to each level up the food chain, which is why some fish, such as tuna, can be a horror in all of this. Tuna is a secondary predator, meaning it not only doesn't eat plants but eats other fish that themselves eat other fish, adding a zero to the multiplier each notch up, easily a hundred times, more like a thousand times less efficient than eating a plant.
As Manning sums up: "Prairie's productivity is lost for grain, grain's productivity is lost in livestock, livestock's protein is lost to human fat—all federally subsidized for about $15 billion a year, two thirds of which goes directly to only two crops, corn and wheat."
Even avoiding meat does not quite solve the problem since there are hidden energy costs in non-meat foods as well.
The grinding, milling, wetting, drying, and baking of a breakfast cereal requires about four calories of energy for every calorie of food energy it produces. A two-pound bag of breakfast cereal burns the energy of a half-gallon of gasoline in its making. All together the food-processing industry in the United States uses about ten calories of fossil-fuel energy for every calorie of food energy it produces.
It seems to me that if we are going to learn how to become better custodians of the earth's resources, we need to have a deeper understanding of how those resources are used. It seems like it would be advisable to emphasize the energy aspects of food in our educational system to create a greater awareness of where all the energy goes to and comes from. Right now, I think that students learn about photosynthesis as a purely biological process. Including the energy cycle along with it seems like a good idea, both educationally and in terms of creating increasing awareness of our relationship to nature and the Earth's resources.
POST SCRIPT: Letting Go of God
Julia Sweeney has a CD of her monologue about her drift away from Catholicism to atheism. She was interviewed by late night talk show host Craig Ferguson.