The centerpiece of the Feb 2004 issue of Harper's Magazine is a fascinating article titled "The Oil We Eat". Written by Richard Manning and derived from the thesis of his upcoming book Against the Grain: How Agriculture Has Hijacked Civilization, the article blames mankind's move towards agriculture as its primary source of food for a whole host of environmental and social ills.
Who would have thought we'd ever be seeing mug shots of innocuous crops such as wheat, corn, and rice?
Some revealing excerpts:

Agriculture is a recent human experiment. For most of human history, we lived by gathering or killing a broad variety of nature's offerings. Why humans might have traded this approach for the complexities of agriculture is an interesting and long-debated question, especially because the skeletal evidence clearly indicates that early farmers were more poorly nourished, more disease-ridden and deformed, than their hunter-gatherer contemporaries. Farming did not improve most lives. The evidence that best points to the answer, I think, lies in the difference between early agricultural villages and their pre-agricultural counterparts--the presence not just of grain but of granaries and, more tellingly, of just a few houses significantly larger and more ornate than all the others attached to those granaries. Agriculture was not so much about food as it was about the accumulation of wealth. It benefited some humans, and those people have been in charge ever since.

Plato's lament is rooted in wheat agriculture, which depleted his country's soil and subsequently caused the series of declines that pushed centers of civilization to Rome, Turkey, and western Europe. By the fifth century, though, wheat's strategy of depleting and moving on ran up against the Atlantic Ocean. Fenced-in wheat agriculture is like rice agriculture. It balances its equations with famine. In the millennium between 500 and 1500, Britain suffered a major "corrective" famine about every ten years; there were seventy-five in France during the same period. The incidence, however, dropped sharply when colonization brought an influx of new food to Europe.
The new lands had an even greater effect on the colonists themselves. Thomas Jefferson, after enduring a lecture on the rustic nature by his hosts at a dinner party in Paris, pointed out that all of the Americans present were a good head taller than all of the French. Indeed, colonists in all of the neo-Europes enjoyed greater stature and longevity, as well as a lower infant-mortality rate--all indicators of the better nutrition afforded by the onetime spend down of the accumulated capital of virgin soil.
The precolonial famines of Europe raised the question: What would happen when the planet's supply of arable land ran out? We have a clear answer. In about 1960 expansion hit its limits and the supply of unfarmed, arable lands came to an end. There was nothing left to plow. What happened was grain yields tripled.
The accepted term for this strange turn of events is the green revolution, though it would be more properly labeled the amber revolution, because it applied exclusively to grain--wheat, rice, and corn. Plant breeders tinkered with the architecture of these three grains so that they could be hypercharged with irrigation water and chemical fertilizers, especially nitrogen. This innovation meshed nicely with the increased "efficiency" of the industrialized factory-farm system. With the possible exception of the domestication of wheat, the green revolution is the worst thing that has ever happened to the planet.
For openers, it disrupted long-standing patterns of rural life worldwide, moving a lot of no-longer-needed people off the land and into the world's most severe poverty. The experience in population control in the developing world is by now clear: It is not that people make more people so much as it is that they make more poor people. In the forty-year period beginning about 1960, the world's population doubled, adding virtually the entire increase of 3 billion to the world's poorest classes, the most fecund classes. The way in which the green revolution raised that grain contributed hugely to the population boom, and it is the weight of the population that leaves humanity in its present untenable position.

More relevant here are the methods of the green revolution, which added orders of magnitude to the devastation. By mining the iron for tractors, drilling the new oil to fuel them and to make nitrogen fertilizers, and by taking the water that rain and rivers had meant for other lands, farming had extended its boundaries, its dominion, to lands that were not farmable. At the same time, it extended its boundaries across time, tapping fossil energy, stripping past assets.
The common assumption these days is that we muster our weapons to secure oil, not food. There's a little joke in this. Ever since we ran out of arable land, food is oil. Every single calorie we eat is backed by at least a calorie of oil, more like ten. In 1940 the average farm in the United States produced 2.3 calories of food energy for every calorie of fossil energy it used. By 1974 (the last year in which anyone looked closely at this issue), that ratio was 1:1. And this understates the problem, because at the same time that there is more oil in our food there is less oil in our oil. A couple of generations ago we spent a lot less energy drilling, pumping, and distributing than we do now. In the 1940s we got about 100 barrels of oil back for every barrel of oil we spent getting it. Today each barrel invested in the process returns only ten, a calculation that no doubt fails to include the fuel burned by the Hummers and Blackhawks we use to maintain access to the oil in Iraq.
David Pimentel, an expert on food and energy at Cornell University, has estimated that if all of the world ate the way the United States eats, humanity would exhaust all known global fossil-fuel reserves in just over seven years. Pimentel has his detractors. Some have accused him of being off on other calculations by as much as 30 percent. Fine. Make it ten years.

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.
About two thirds of U.S. grain corn is labeled "processed," meaning it is milled and otherwise refined for food or industrial uses. More than 45 percent of that becomes sugar, especially high-fructose corn sweeteners, the keystone ingredient in three quarters of all processed foods, especially soft drinks, the food of America's poor and working classes. It is not a coincidence that the American pandemic of obesity tracks rather nicely with the fivefold increase in corn-syrup production since Archer Daniels Midland developed a high-fructose version of the stuff in the early seventies. Nor is it a coincidence that the plague selects the poor, who eat the most processed food.

There is another energy matter to consider here, though. 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.

You think being a vegetarian gets you out of jail? Think again.

Green eaters, especially vegetarians, advocate eating low on the food chain, a simple matter of energy flow. 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.
This is fine as far as it goes, but the vegetarian's case can break down on some details. On the moral issues, vegetarians claim their habits are kinder to animals, though it is difficult to see how wiping out 99 percent of wildlife's habitat, as farming has done in Iowa, is a kindness. In rural Michigan, for example, the potato farmers have a peculiar tactic for dealing with the predations of whitetail deer. They gut-shoot them with small-bore rifles, in hopes the deer will limp off to the woods and die where they won't stink up the potato fields.
Animal rights aside, vegetarians can lose the edge in the energy argument by eating processed food, with its ten calories of fossil energy for every calorie of food energy produced. The question, then, is: Does eating processed food such as soy burger or soy milk cancel the energy benefits of vegetarianism, which is to say, can I eat my lamb chops in peace? Maybe. If I've done my due diligence, I will have found out that the particular lamb I am eating was both local and grass-fed, two factors that of course greatly reduce the embedded energy in a meal. I know of ranches here in Montana, for instance, where sheep eat native grass under closely controlled circumstances--no farming, no plows, no corn, no nitrogen. Assets have not been stripped. I can't eat the grass directly. This can go on. There are little niches like this in the system. Each person's individual charge is to find such niches.
Chances are, though, any meat eater will come out on the short end of this argument, especially in the United States. Take the case of beef. Cattle are grazers, so in theory could live like the grass-fed lamb. Some cattle cultures--those of South America and Mexico, for example--have perfected wonderful cuisines based on grass-fed beef. This is not our habit in the United States, and it is simply a matter of habit. Eighty percent of the grain the United States produces goes to livestock. Seventy-eight percent of all of our beef comes from feed lots, where the cattle eat grain, mostly corn and wheat. So do most of our hogs and chickens. The cattle spend their adult lives packed shoulder to shoulder in a space not much bigger than their bodies, up to their knees in shit, being stuffed with grain and a constant stream of antibiotics to prevent the disease this sort of confinement invariably engenders. The manure is rich in nitrogen and once provided a farm's fertilizer. The feedlots, however, are now far removed from farm fields, so it is simply not "efficient" to haul it to cornfields. It is waste. It exhales methane, a global-warming gas. It pollutes streams. It takes thirty-five calories of fossil fuel to make a calorie of beef this way; sixty-eight to make one calorie of pork.
Still, these livestock do something we can't. They convert grain's carbohydrates to high-quality protein. All well and good, except that per capita protein production in the United States is about double what an average adult needs per day. Excess cannot be stored as protein in the human body but is simply converted to fat. This is the end result of a factory-farm system that appears as a living, continental-scale monument to Rube Goldberg, a black-mass remake of the loaves-and-fishes miracle. 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.

You'll have to buy the issue to read the entire article, or, for the time being, you can find a transcript online at the blog How to Save the World.