Food is energy. And it takes energy to get food. These two facts, taken together, have always established the biological limits to the human population and always will.

The same is true for every other species: food must yield more energy to the eater than is needed in order to acquire the food. Woe to the fox who expends more energy chasing rabbits than he can get from eating the rabbits he catches. If this energy balance remains negative for too long, death results; for an entire species, the outcome is a die-off event, perhaps leading even to extinction.

Humans have become champions at developing new strategies for increasing the amount of energy - and food - they capture from the environment. The harnessing of fire, the domestication of plants and animals, the adoption of ards and plows, the deployment of irrigation networks, and the harnessing of traction animals - developments that occurred over tens of thousands of years - all served this end.

The process was gradual and time-consuming. Not only were new tools developed, but, over centuries, small inventions and tiny modifications of existing tools - from scythes to horse-collars - enabled human and animal muscle power to be leveraged more effectively.

This entire exercise took place within a framework of natural limits. The yearly input of solar radiation to the planet was always immense relative to human needs (and still is), but it was finite nevertheless, and while humans directly appropriated only a tiny proportion of this abundance the vast majority of that radiation served functions that indirectly supported human existence - giving rise to air currents by warming the surface of the planet, and maintaining the lives of countless other kinds of creatures in the oceans and on land.

The amount of available human muscle power was limited by the number of humans, who, of course, had to be fed. Draft animals (bred for their muscle-power) also entailed energy costs, as they likewise needed to eat but also had to be cared for in various ways. Therefore, even with clever refinements in tools and techniques, in crops development and animal breeding, it was inevitable that humans would reach a point of diminishing returns in their ability to continue increasing their energy harvest, and therefore the size of their population.

By the nineteenth century these limits were beginning to become apparent. Famine and hunger had long been common throughout even the wealthiest regions of the planet. But, for Europeans, the migration of surplus populations to other nations, crop rotation, and the application of manures and composts were gradually making those events less frequent and severe. European farmers, realizing the need for a new nitrogen source in order to continue feeding burgeoning and increasingly urbanized populations, began employing guano imported from islands off the coasts of Chile and Peru. The results were gratifying. However, after only a few decades, these guano deposits were being depleted. By this time, in the late 1890s, the world's population was nearly twice what it had been at the beginning of the century. A crisis was again in view.

But again crisis was narrowly averted, this time due to fossil fuels. In 1909, two German chemists named Fritz Haber and Carl Bosch invented a process to synthesize ammonia from atmospheric nitrogen and the hydrogen in fossil fuels. The process initially used coal as a feedstock, though later it was adapted to use natural gas. After the end of the Great War, nation after nation began building Haber-Bosch plants; today the process produces 150 million tons of ammonia-based fertilizer per year, equaling the total amount of available nitrogen introduced annually by all natural sources combined.

Fossil fuels went on to offer still other ways of extending natural limits to the human carrying capacity of the planet.

Early steam-driven tractors came into limited use in 19th century; but, after World War I, the size and effectiveness of powered farm machinery expanded dramatically, and the scale of use exploded, especially in North America, Europe, and Australia from the 1920s through the '50s. In the 1890s, roughly one quarter of US cropland had to be set aside for the growing of grain to feed horses - most of which worked on farms. The internal combustion engine provided a new kind of horsepower not dependent on horses at all, and thereby increased the amount of arable land available to feed humans.

Chemists developed synthetic pesticides and herbicides in increasing varieties after WWII, using knowledge pioneered in laboratories that had worked to perfect explosives and other chemical warfare agents. Pesticides not only increased crop yields in North America, Europe, and Australia, but also reduced the prevalence of insect-borne diseases like malaria. The world began to enjoy the benefits of "better living through chemistry," though the environmental costs, in terms of water and soil pollution and damage to vulnerable species, would only later become widely apparent.

In the 1960s, industrial-chemical agricultural practices began to be exported to what by that time was being called the Third World: this was glowingly dubbed the Green Revolution, and it enabled a tripling of food production during the ensuing half-century.

At the same time, the scale and speed of distribution of food increased. This also constituted a means of increasing carrying capacity, though in a more subtle way.

The trading of food goes back to Paleolithic times; but, with advances in transport, the quantities and distances involved gradually increased. Here again, fossil fuels were responsible for a dramatic discontinuity in the previously slow pace of growth. First by rail and steamship, then by truck and airplane, immense amounts of grain and ever-larger quantities of meat, vegetables, and specialty foods began to flow from countryside to city, from region to region, and from continent to continent.

William Catton, in his classic book Overshoot, terms the trade of essential life-support commodities "scope expansion."1 Carrying capacity is always limited by whatever necessity is in least supply, as Justus von Liebig realized nearly a century-and-a-half ago. If one region can grow food but has no exploitable metal deposits, its carrying capacity is limited by the lack of metals for the production of farm tools. Another region may have metals but insufficient topsoil or rain; there, carrying capacity is limited by the lack of food. If a way can be found to make up for local scarcity by taking advantage of distant abundance (as by exporting metal ores or finished tools from region A to help with food production in region B, and then exporting food from B to A), the total carrying capacity of the two regions combined can be increased substantially. We can put this into a crude formula:

CC of A+B > (CC of A) + (CC of B)

From an ecological as well as an economic point of view, this is why people trade. But trade has historically been limited by the amount of energy that could be applied to the transport of materials. Fossil fuels temporarily but enormously expanded that limit.

The end result of chemical fertilizers, plus powered farm machinery, plus increased scope of transportation and trade, was not just a three-fold leap in crop yields, but a similar explosion of human population, which has grown five-fold since dawn of industrial revolution.

Agriculture at a Crossroads

All of this would be well and good if it were sustainable, but, if it proves not to be, then a temporary exuberance of the human species will have been purchased by an eventual, unprecedented human die-off. So how long can the present regime be sustained? Let us briefly survey some of the current trends in global food production and how they are related to the increased use of inexpensive fossil fuels.

Arable cropland: For millennia, the total amount of arable cropland gradually increased due to the clearing of forests and brush, and the irrigation of land that would otherwise be too arid for cultivation. That amount reached a maximum within the past two decades and is now decreasing because of the salinization of irrigated soils and the relentless growth of cities, with their buildings, roads, and parking lots. Irrigation has become more widespread because of the availability of cheap energy to operate pumps, while urbanization is largely a result of cheap fuel-fed transportation and the flushing of the peasantry from the countryside as a consequence of their inability to buy or to compete with fuel-fed agricultural machinery. Roads that cover former cropland are built from oil, and the erection of buildings has been facilitated by the mechanization of construction processes and the easy transport of materials.

Topsoil: The world's existing soils were generated over thousands and millions of years at a rate averaging an inch per 500 years. The amount of soil available to farmers is now decreasing at an alarming rate, due mostly to wind and water erosion. In the US Great Plains, roughly half the quantity in place at the beginning of the last century is now gone. In Australia, after two centuries of European land-use, more than 70 percent of land has become seriously degraded.2 Erosion is largely a function of tillage, which fractures and loosens soil; thus, as the introduction of fuel-fed tractors has increased the ease of tillage, the rate of soil loss has increased dramatically.

The number of farmers as a percentage of the population: In the US at the turn of the last century, 70 percent of the population lived in rural areas and farmed. Today less than two percent of Americans farm for a living. This change came primarily because fuel-fed farm machinery replaced labor, which meant that fewer farmers were needed. Hundreds of thousands - perhaps millions - of families that desperately wanted to farm could not continue to do so because they could not afford the new machines, or could not compete with their neighbors who had them. Another way of saying this is that economies of scale (driven by mechanization) gave an advantage to ever-larger farms. But the loss of farmers also meant a gradual loss of knowledge of how to farm and a loss of rural farming culture. Many farmers today merely follow the directions on bags of fertilizer or pesticide, and live so far from their neighbors that their children have no desire to continue the agricultural way of life.

The genetic diversity of domesticated crop varieties: This is decreasing dramatically due to the consolidation of the seed industry. Farmers on the island of Bali in Indonesia once planted 200 varieties of rice, each adapted to a different microclimate; now only four varieties are grown. In 2000, Semenis, the world's largest vegetable seed corporation, eliminated 25 percent of its product line as a cost-cutting measure. This ongoing, massive genetic consolidation is also being driven by the centralization of the seed industry (the largest three field seed companies - DuPont, Monsanto, and Novartis - now account for 20 percent of the global seed trade), which is in turn consequent upon fuel-fed globalization.

Grain production per capita: A total of 2,029 million tons of grain were produced globally in 2004; this was a record in absolute numbers. But for the past two decades population has grown faster than grain production, so there is actually less available on a per-head basis. In addition, grain stocks are being drawn down: According to Lester Brown of the Earth Policy Institute, "in each of the last four . . . years production fell short of consumption. The shortfalls of nearly 100 million tons in 2002 and again in 2003 were the largest on record."3 This trend suggests that the strategy of boosting food production by the use of fossil fuels is already yielding diminishing returns.

Global climate: This is being increasingly destabilized as a result of the famous greenhouse effect, resulting in problems for farmers that are relatively minor now but that are likely to grow to catastrophic proportions within the next decade or two. Global warming is now almost universally acknowledged as resulting from CO2 emissions from the burning of fossil fuels.

Available fresh water: In the US, 85 percent of fresh water use goes toward agricultural production, requiring the drawing down of ancient aquifers at far above their recharge rates. Globally, as water tables fall, ever more powerful pumps must be used to lift irrigation water, requiring ever more energy usage. By 2020, according to the Worldwatch Institute and the UN, virtually every country will face shortages of fresh water.

The effectiveness of pesticides and herbicides: In the US, over the past two decades pesticide use has increased 33-fold, yet, each year a greater amount of crops is lost to pests, which are evolving immunities faster than chemists can invent new poisons. Like falling grain production per capita, this trend suggests a declining return from injecting the process of agricultural production with still more fossil fuels.

Now, let us add to this picture the imminent peak in world oil production. This will make machinery more expensive to operate, fertilizers more expensive to produce, and transportation more expensive. While the adoption of fossil fuels created a range of problems for global food production, as we have just seen, the decline in the availability of cheap oil will not immediately solve those problems; in fact, over the short term they will exacerbate them, bringing simmering crises to a boil.

That is because the scale of our dependency on fossil fuels has grown to enormous proportions.

In the US, agriculture is directly responsible for well over 10 percent of all national energy consumption. Over 400 gallons of oil equivalent are expended to feed each American each year. About a third of that amount goes toward fertilizer production, 20 percent to operate machinery, 16 percent for transportation, 13 percent for irrigation, 8 percent for livestock raising, (not including the feed), and 5 percent for pesticide production. This does not include energy costs for packaging, refrigeration, transportation to retailers, or cooking.

Trucks move most of the world's food, even though trucking is ten times more energy-intensive than moving food by train or barge. Refrigerated jets move a small but growing proportion of food, almost entirely to wealthy industrial nations, at 60 times the energy cost of sea transport.

Processed foods make up three-quarters of global food sales by price (though not by quantity). This adds dramatically to energy costs: for example, a one-pound box of breakfast cereal may require over 7,000 kilocalories of energy for processing, while the cereal itself provides only 1,100 kilocalories of food energy.

Over all - including energy costs for farm machinery, transportation, and processing, and oil and natural gas used as feedstocks for agricultural chemicals - the modern food system consumes roughly ten calories of fossil fuel energy for every calorie of food energy produced.4

But the single most telling gauge of our dependency is the size of the global population. Without fossil fuels, the stupendous growth in human numbers that has occurred over the past century would have been impossible. Can we continue to support so many people as the availability of cheap oil declines?

Feeding a Growing Multitude

The problems associated with the modern global food system are widely apparent, there is widespread concern over the sustainability of the enterprise, and there is growing debate over the question of how to avoid an agricultural Armageddon. Within this debate two viewpoints have clearly emerged.

The first advises further intensification of industrial food production, primarily via the genetic engineering of new crop and animal varieties. The second advocates ecological agriculture in its various forms - including organic, biodynamic, Permaculture, and Biointensive methods.

Critics of the latter contend that traditional, chemical-free forms of agriculture are incapable of feeding the burgeoning human population. Here is a passage by John John Emsley of University of Cambridge, from his review of Vaclav Smil's Enriching the Earth : Fritz Haber, Carl Bosch, and the Transformation of World Food:

If crops are rotated and the soil is fertilized with compost, animal manure and sewage, thereby returning as much fixed nitrogen as possible to the soil, it is just possible for a hectare of land to feed 10 people - provided they accept a mainly vegetarian diet. Although such farming is almost sustainable, it falls short of the productivity of land that is fertilized with "artificial" nitrogen; this can easily support 40 people, and on a varied diet.5

This seems unarguable on its face. However, given the fact that fossil fuels are non-renewable, it will be increasingly difficult to continue to supply chemical fertilizers in present quantities. Nitrogen can be synthesized using hydrogen produced from the electrolysis of water, with solar or wind power as a source of electricity. But currently no ammonia is being commercially produced this way because of the uncompetitive cost of doing so. To introduce and scale up the process will require many years and considerable investment capital.

The bioengineering of crop and animal varieties does little or nothing to solve this problem. One can fantasize about modifying maize or rice to fix nitrogen in the way that legumes do, but so far efforts in that direction have failed. Meanwhile, the genetic engineering of complex life forms on a commercial scale appears to pose unprecedented environmental hazards, as has been amply documented by Dr. Mae Wan-Ho among many others.6 And the bio-engineering industry itself consumes fossil fuels, and assumes the continued availability of oil for tractors, transportation, chemicals production, and so on.

Those arguing in favor of small-scale, ecological agriculture tend to be optimistic about its ability to support large populations. For example, the 2002 Greenpeace report, "The Real Green Revolution: Organic and Agroecological Farming in the South," while acknowledging the lack of comparative research on the subject, nevertheless notes:

In general . . . it is thought that [organic and agroecological farming] can bring significant increases in yields in comparison to conventional farming practices. Compared to "Green Revolution'"farming systems, OAA is thought to be neutral in terms of yields, although it brings other benefits, such as reducing the need for external inputs.7

Eco-agricultural advocates often contend that there is plenty of food in the world; existing instances of hunger are due to bad policy and poor distribution. With better policy and distribution, all could easily be fed. Thus, given the universally admitted harmful environmental consequences of conventional chemical farming, the choice should be simple.

Some eco-ag proponents are even more sanguine, and suggest that their methods can produce far higher yields than can mechanized, chemical-based agriculture. Experiments have indeed shown that small-scale, biodiverse gardening or farming can be considerably more productive on a per-hectare basis than monocropped megafarms.8 However, some of these studies have ignored the energy and land-productivity costs of manures and composts imported onto the study plots. In any case, and there is no controversy on this point, Permaculture and Biointensive forms of horticulture are dramatically more labor- and knowledge-intensive than industrial agriculture. Thus the adoption of these methods will require an economic transformation of societies.

Therefore even if the nitrogen problem can be solved in principle by agro-ecological methods and/or hydrogen production from renewable energy sources, there may be a carrying-capacity bottleneck ahead in any case, simply because of the inability of societies to adapt to these very different energy and economic needs quickly enough, and also because of the burgeoning problems mentioned above (loss of fresh water resources, unstable climate, etc.). According to widely-accepted calculations, humans are presently appropriating at least 40 percent of Earth's primary biological productivity.9 It seems unlikely that we, a single species after all, can do much more than that. Even though it may not be politically correct in many circles to discuss the population problem, we must recognize that we are nearing or past fundamental natural limits, no matter which course we pursue.

Given the fact that fossil fuels are limited in quantity and we are already in view of the global oil production peak, the debate over the potential productivity of chemical-gene engineered agriculture versus that of organic and agroecological farming may be relatively pointless. We must turn to a food system that is less fuel-reliant, even if it does prove to be less productive.

The Example of Cuba

How we might do that is suggested by perhaps the best recent historical example of a society experiencing a fossil-fuel famine. In the late 1980s, farmers in Cuba were highly reliant on cheap fuels and petrochemicals imported from the Soviet Union, using more agrochemicals per acre than their American counterparts. In 1990, as the Soviet empire collapsed, Cuba lost those imports and faced an agricultural crisis. The population lost 20 pounds on average and malnutrition was nearly universal, especially among young children. The Cuban GDP fell by 85 percent and inhabitants of the island nation experienced a substantial decline in their material standard of living.

Cuban authorities responded by breaking up large state-owned farms, offering land to farming families, and encouraging the formation of small agricultural co-ops. Cuban farmers began employing oxen as a replacement for the tractors they could no longer afford to fuel. Cuban scientists began investigating biological methods of pest control and soil fertility enhancement. The government sponsored widespread education in organic food production, and the Cuban people adopted a mostly vegetarian diet out of necessity. Salaries for agricultural workers were raised, in many cases to above the levels of urban office workers. Urban gardens were encouraged in parking lots and on public lands, and thousands of rooftop gardens appeared. Small food animals such as chickens and rabbits began to be raised on rooftops as well.

As a result of these efforts, Cuba was able to avoid what might otherwise have been a severe famine. Today the nation is changing from an industrial to an agrarian society. While energy use in Cuba is now one-twentieth of that in the US, the economy is growing at a slow but steady rate. Food production has returned to 90 percent of its pre-crisis levels.10

The Way Ahead

The transition to a non-fossil-fuel food system will take time. And it must be emphasized that we are discussing a systemic transformation - we cannot just remove oil in the forms of agrochemicals from the current food system and assume that it will go on more or less as it is. Every aspect of the process by which we feed ourselves must be redesigned. And, given the likelihood that global oil peak will occur soon, this transition must occur at a rapid pace, backed by the full resources of national governments.

Without cheap transportation fuels we will have to reduce the amount of food transportation that occurs, and make necessary transportation more efficient. This implies increased local food self-sufficiency. It also implies problems for large cities that have been built in arid regions capable of supporting only small populations on their regional resource base. One has only to contemplate the local productivity of a place like Nevada, to appreciate the enormous challenge of continuing to feed people in such a city such as Las Vegas without easy transportation.

We will need to grow more food in and around cities. Currently, Oakland California is debating a food policy initiative that would mandate by 2015 the growing within a fifty-mile radius of city center of 40 percent of the vegetables consumed in the city.11 If the example of Cuba were followed, rooftop gardens would result, as well as rooftop raising of food animals like chickens, rabbits and guinea pigs.

Localization of the food process means moving producers and consumers of food closer together, but it also means relying on the local manufacture and regeneration of all of the elements of the production process - from seeds to tools and machinery. This would appear to rule out agricultural bioengineering, which favors the centralized production of patented seed varieties, and discourages the free saving of seeds from year to year by farmers.

Clearly, we must minimize chemical inputs to agriculture (direct and indirect - such as those introduced in packaging and processing).

We will need to re-introduce draft animals in agricultural production. Oxen may be preferable to horses in many instances, because the former can eat straw and stubble, while the latter would compete with humans for grains.

Governments must also provide incentives for people to return to an agricultural life. It would be a mistake simply to think of this simply in terms of the need for a larger agricultural work force. Successful traditional agriculture requires social networks, and intergenerational sharing of skills and knowledge. We need not just more agricultural workers, but a rural culture that makes agricultural work rewarding.

Farming requires knowledge and experience, and so we will need education for a new generation of farmers; but only some of this education can be generic - much of it must of necessity be locally appropriate.

It will be necessary as well to break up the corporate mega-farms that produce so much of today's cheap grain. Industrial agriculture implies an economy of scale that will be utterly inappropriate and unworkable for post-industrial food systems. Thus land reform will be required in order to enable smallholders and farming co-ops to work their own plots.

In order for all of this to happen, governments must end subsidies to industrial agriculture and begin subsidizing post-industrial agricultural efforts. There are many ways in which this could be done. The present regime of subsidies is so harmful that merely stopping it in its tracks might in itself be advantageous; but, given the fact that a rapid transition is essential, offering subsidies for education, no-interest loans for land purchase, and technical support during the transition from chemical to organic production would be essential.

Finally, given carrying-capacity limits, food policy must include population policy. We must encourage smaller families by means of economic incentives and improve the economic and educational status of women in poorer countries.

All of this constitutes a gargantuan task, but the alternatives - doing nothing or attempting to solve our food-production problems simply by applying more technological intensification - will almost certainly result in dire consequences. In that case, existing farmers would fail because of fuel and chemical prices. All of the worrisome existing trends mentioned earlier would intensify to the point that the human carrying capacity of Earth would be degraded significantly, and perhaps to a large degree permanently.

In sum, the transition to a fossil-fuel-free food system does not constitute a utopian proposal. It is an immense challenge and will call for unprecedented levels of creativity at all levels of society. But in the end it is the only rational option for averting human calamity on a scale never before seen.