Green Planet: How Plants Keep the Earth Alive

Chapter Six: Plants Feed the World

[110] chapter six PLANTS FEED THE WORLD I have often thought that if heaven had given me my choice of position and calling, it should have been on a rich spot of earth, well watered, and near a good market for the productions of the garden. No occupation is so delightful to me as the culture of the earth, and no culture comparable to that of the garden. . . . I am still devoted to the garden. But though an old man, I am but a young gardener. —THOMAS JEFFERSON The rise of fast food chains—spreading late in the twentieth century from the United States to every corner of the world—is one of the defining characteristics of contemporary society. Anywhere in the world you go, you can get exactly the same kind of hamburger and fries, untouched by the finger of any local proprietor’s creativity. And it is, or seems, cheap. As Eric Schlosser has shown in his book Fast Food Nation, the boom in fast foods exacts a tremendous cost on an unskilled and underpaid workforce.1 Morgan Spurlock has explained how a diet of fast food can lead to numerous health problems.2 Given the societal and health-care costs, fast food may not be such a bargain. But our modern food production system has given us food that, at least, seems inexpensive. Although a hamburger may not cost much money, the energy cost of the hamburger is enormous. The energy in the food itself comes from the sun. Most of this biological energy is lost as it moves through the industrial food chain, from corn to cow to human. Even more than this, CH006.qxd 11/12/08 10:49 AM Page 110 Plants Feed the World [111] our food production system relies on the prodigious expenditure of fossil fuels. Modern technology allows American agriculture to be very efficient in terms of the amount of food produced by a small number of farmers (fig. 6.1). Cheap modern food and productive modern farmers require the use of enormous amounts of fossil fuel energy. How Plants Make Food Of all the sunlight energy that shines on the earth, 99 percent just heats the earth’s surface—the rocks, the water, and the plants. Sunlight energy drives the engine of the weather and climate. It not only warms the air but also evaporates water to form clouds and bring rain. When leaves absorb sunlight and become hot, they use transpiration to cool themselves off and figure 6.1. This roadside sign proclaims the efficiency of modern agriculture. (The number has since risen to 129.) But modern agriculture is efficient only in terms of labor; it is very wasteful of energy. Photograph by the author. CH006.qxd 11/12/08 10:49 AM Page 111 green planet [112] thereby create cool shade from which we can benefit (chapter 4). The remaining 1 percent goes into photosynthesis and produces all the food in the world.This is the same process by which plants put oxygen into the air and remove carbon dioxide from it (chapters 2, 3). Photosynthesis uses sunlight energy to synthesize food molecules. More specifically, it brings together energy from the sun and small molecules from the air and soil to create food molecules. Plants use energy from sunlight and electrons from water to bind together carbon dioxide molecules,producing carbohydrates such as sugar.Plants make all of their other molecules from these carbohydrates. Plants and animals need food to provide energy to run their bodily activities and molecules from which to build their tissues. The food molecules created by plants uniquely fulfill both of these needs. As science writer Michael Pollan says, plants create life out of thin air; another science writer, Natalie Angier, says that plants spin the sun into gold and make sweetness from light.3 First, I will outline what happens to food energy as it goes through the food chain. Then I will consider the fossil fuel energy that is consumed by the human food chain. Food Energy:The Tyranny of the Food Chain Some people eat mostly vegetables and grains, while others eat a lot of meat. The calories of energy in food come from photosynthesis either way. So what difference does it make whether you get your food energy from meat, or from vegetables and grains? The answer is, 90 percent. Here’s how I arrive at that number...