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Peak Food and Population Overshoot

December 2006

Fossil Fuels at Peak

Peak Food and Population Overshoot

by John Rawlins

John Rawlins has a B.S. in physics and a Ph.D. in nuclear physics. He retired in 1995 from the Westinghouse Hanford Co. at the Hanford site in Eastern Washington. Currently, he teaches physics and astronomy at Whatcom Community College.

Part 3

A wall chart in the Whatcom Community College physics lab shows the historical (and projected future) curve of oil extraction along with other geo-petroleum data. There is also a curve on the chart that, because of its color, is difficult to see and is easy to overlook entirely. When I ask a student in my energy class to notice it and tell everyone else what the label on the curve is, there’s always a moment of realization and the dawning of a major future problem in a world with declining oil availability. The nearly invisible curve shows world population versus time, and the population curve correlates perfectly with the oil extraction rate curve.

Before oil (and natural gas) humans used manual labor to grow food, and the amount of food determines an upper limit on population. The large-scale, increasing use of oil and natural gas in the industrial world’s food-growing enterprise has meant ever-increasing quantities of food — until now. Therefore, population increase over the past 150 years correlates very well with oil extraction.

By far the largest population increase in the history of humans occurred in the 20th century, and the resources making that possible were oil and natural gas. Now that we face a very near-term decline in both of these resources, it is time to start planning how we will continue to feed a population of over 6 billion humans. In about 100 years, when oil and gas are essentially gone, will it even be possible to provide enough food for six to 10 times as many people as populated the planet before oil and gas? This article will summarize what I’ve learned during the past three years on this subject, which still troubles me far more than anything else related to peak oil/gas and climate change. This is a challenging topic to think about, because I continue trying to find reason for hope when the logic seems to provide little justification for it. Still, we can learn from our past, and there are some seeds for food-growing ideas there.

Humans Used Technology Breakthroughs to Increase Food Supply and Population

In my energy class students think about a one-page table showing a summary of the history of human population increases and the technological breakthroughs that enabled those increases. From a few million years B.C. to around 10,000 B.C. world population was likely in the few million range, and the technologies that were important in that period included use of fire, tool-making, spears, and bow-and-arrow. During this period, humans were in hunter-gatherer-scavenger groups. They ate mostly what nature provided: fruits, nuts, berries and meat from other mammals. During this, the longest time period on the list, remember that a few million humans were matched with the available natural food supply.

The next great innovations were cultivation of plants for food and bronze metallurgy. Human diets changed dramatically during the next 6,000 years as a result, and people didn’t have to travel as far to find food since they had planted some of it. The use of grains began during this important period of human history, and population expanded to nearly 100 million humans.

From about 4000 B.C. until around A.D. 1800, humans invented the plow, iron tools and small firearms. Even with those innovations, the population only increased about 10-fold to around a billion people. Even though large population centers developed and persisted, most humans were in some way involved in food production. This 10-fold population increase took only about 6,000 years, comparable with the rate of population growth during the preceding period — a rate of increase of around 1 percent per generation.

Around 1800 the industrial revolution began with the use of fossil-fueled machinery — the beginning of the age of coal. Since it was tough to use coal to grow more food, the population by 1865 was still only about 1.4 billion people — but that represents a 14 percent per generation rate of increase.

With the discovery of the most convenient energy resource humans will ever know — oil — fossil fuels could power farm machinery and greatly expand world food production. In parallel, medical advances extended life expectancy and reduced risks of childbirth, and the rate of population increase blossomed to nearly 30 percent per generation. I have read that, at this point in time, there are more people alive on the planet than have been buried during our entire human history!

This is worrisome to anyone who has thought about the following question: If lilies on a pond increase in number exponentially, say with a 100 percent per day rate of increase, how many days before the pond is entirely covered was the pond only half-covered with lilies? (See answer at the end of the article.)

Are humans near the limits of the planet’s ability to support us? If our numbers depend on oil availability, then how many humans can the planet support 100 years from now when oil and gas availability will be around 10 percent of present values? In a previous article I noted that I see no viable large-scale technology advances to replace oil and gas for transport (hence for food-growing as well).

The idea that humans will migrate throughout the solar system and even to other star systems elsewhere in the galaxy doesn’t pass the snicker test, based on simple energy arguments. We are bound to this planet, and we need to understand the factors that limit our food supply and our numbers. This is just not something most of us ever learned (much less thought about) in our educational system.

In Effect, We Are Eating Petroleum Products

Even if we are currently near the present limit of planet Earth’s human capacity, remember one important fact — the dependence of our food supply on those very fossil fuels that will soon be available in declining amounts: oil and natural gas. So what are the numbers showing this oil/gas dependence in our farm sector?

Today, about 75 percent of direct farm energy use in the U.S. is from diesel (largest), gasoline, LPG (liquid petroleum gas) or natural gas. The remainder is electricity — which in the U.S. is on average mostly generated by fossil fuel — coal and natural gas primarily. The bottom line: the energy responsible for our nation’s food production is about 80 percent oil and natural gas or its derivatives. That just covers food production — but what about the rest of the food chain? Food production accounts for just 21 percent of the energy use in the entire food system.

The average distance that food travels in the U.S. from farm to platter is 1,500 miles. Transporting that food consumes 14 percent of the food system energy, and it’s almost all diesel fuel — an oil derivative. Processing, packaging, food retail, restaurants and home refrigeration and preparation make up the remaining 65 percent — and most of that energy is from electricity with its fossil fuel dependence. Clearly, we have built our food system on energy derived almost entirely from non-renewable sources.

U.S. food production (farm only) requires about 400 gallons of oil equivalent for each resident each year. Of this amount, the breakdown by function is as follows:

•31 percent to manufacture inorganic fertilizer from natural gas

•19 percent for operation of field machinery (diesel)

•16 percent for transportation to processing plants

•13 percent for irrigation (electricity)

• 8 percent for raising livestock (not including feed)

• 5 percent for crop drying

• 5 percent for pesticide production (from oil)

• 3 percent miscellaneous

This tally does not include any post-processing energy requirements. A specific concern is that natural gas on the North American continent is already in decline, and already much fertilizer manufacturing has moved out of the U.S. and closer to more reliable sources of natural gas (Middle East, for example) — and therefore requires shipping back to the U.S. for use (another oil consuming function). Without that fertilizer input, present-day crop yields in our massive agri-businesses would simply be impossible.

An interesting result of the U.S. food production business is that only about 1 percent of U.S. residents work at farm-related jobs — down from around 50 percent in the pre-industrial age. So we live in a country in which very few have food-growing knowledge, and much of that is not even applicable to the post-carbon era that is rapidly approaching. Likewise, the knowledge required for food preservation is greatly diminished from pre-industrial times.

Since current industrialized nation food production is completely unsustainable, and is already experiencing oil/gas cost increases as peak oil/gas production approaches, it is time to begin planning for a very different world — one in which conventionally produced food will cost more, one in which total food supply will decrease, and one in which many more people must learn to produce and preserve food without the prodigious oil/gas requirements. Finally, we cannot learn from our present food production practices the answer to the original question posed: How many people can planet Earth support in year 2100?

Estimates for the Earth’s Sustainable Human Carrying Capacity Vary Significantly

Various analysts have used widely different lines of reasoning to estimate the Earth’s post-carbon sustainable carrying capacity for humans and have arrived at widely different conclusions. Some of the references at the end of this article are well worth reading for those with interest in this subject — particularly the book by William Catton called “Overshoot: The Ecological Basis for Revolutionary Change.” I discovered and read this book based on very high recommendations from Richard Heinberg (author of “The Party’s Over” and “Powerdown”).

Catton argues that we have not just built our modern society on an unsustainable basis, but that in addition we have done huge harm to our food growing environments with the modern food-growing methods (climate change, soil erosion, water over-use, soil fertility decreases …). We are able to support the present world population only because of the fossil fuel input, and he makes a good case for the conclusion that we have overshot the planet’s sustainable human carrying capacity by a factor of from three to six — i.e., the carrying capacity will likely turn out to be between 1 and 2 billion humans because of the combined effects of less food production and a poorer environment for that food production. Several other authors arrive at similar conclusions. If these estimates are valid humanity faces a very difficult 21st century and a large die-off seems entirely possible. To reach a population of three billion humans by 2100 would imply an average percentage annual decrease of close to 1 percent per year!

The only more optimistic estimate of which I am aware is that of Lester Brown, who is well known for monitoring of world environmental trends over several decades. Brown wrote the book “Plan B 2.0; Rescuing a Planet Under Stress and a Civilization in Trouble.” The reason for his optimism is based on his assumption that humans will be smart enough to make a large number of major changes throughout society, and his conclusion is that the Earth carrying capacity is even more than the present 6.5 billion humans — around 8 billion or so — but of course with far less per capita energy use than U.S. citizens are accustomed to. I am highly skeptical of Brown’s estimate based on the totality of my reading to date — largely because I am convinced that efforts to replace declining oil and natural gas will prove largely futile and today’s production of food depends almost totally on huge non-human energy inputs.

Whatever the answer to Earth’s carrying capacity turns out to be, we must learn very, very soon about lower-energy methods for food production and start implementing them as rapidly as possible. One interesting case study comes from Cuba, which lost much of its oil supply (from Russia) when the former Soviet Union collapsed. Following some scary years amidst fear of wide-spread starvation, most Cubans are now involved in food production in fields and yards, and the practice of food growing advocated by permaculture activists has taken root in Cuba. One of the fundamental ideas of permaculture is to plant food species that require less human energy than the conventional intensively managed vegetable garden. The concept of forest gardens — involving fruit and nut trees, combined with perennial understory plants such as berries and food-producing groundcover — evolved from permaculture ideas. In essence, such forest gardens are a dense source of food for the future’s hunters and gatherers. Even today’s urban and suburban dwellers can participate by replacing their grassy lawns with perennial food crops. A future article will describe in more detail the business of forest gardening and permaculture.

Answer to Lilly Pond Question: One Day §

Next Month: Other Impacts: Banking, Computer/Electronic Culture, Clothing, Medicine


•“The Tightening Conflict: Population, Energy Use, and the Ecology of Agriculture,” by Mario Giampietro and David Pimentel — online at

•“How Long Can the World Feed Itself?” by Gwynne Dyer — online at

•“Oil and Food: A Rising Security Challenge,” by Danielle Murray — online at (note the data link at

•William R. Catton, Jr. (1982), “Overshoot: The Ecological Basis of Revolutionary Change.”

•Lester R. Brown (2006), “Plan B 2.0; Rescuing a Planet Under Stress and a Civilization in Trouble.”

•Dale Allen Pfeiffer (2006), “Eating Fossil Fuels.”

•See numerous articles about food and agriculture at the following online reference:

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