From Skeptic vol. 5, no. 1, 1997, pp. 46ff.

The following article is copyright ©1997 by the Skeptics Society, P.O. Box 338, Altadena, CA 91001, (626) 794-3119. Permission has been granted for noncommercial electronic circulation of this article in its entirety, including this notice.

Souled out or...souled short?

An Introduction to the Debate Between Ecologists & Economists on How Many People the Earth Can or Should Support & How It Goes Beyond Our Knowledge of Nature & Goes Directly to the Nature of Knowledge & the Nature of Humankind
By Frank Miele

Mother Earth Has Been Souled Out:

"The present population of 5.5 billion is being maintained only through the exhaustion or dispersion of a one-time inheritance of natural capital....[including] high grade agricultural soils, ground water that accumulated during the last ice age, and biodiversity; each is being depleted globally at rates orders of magnitude in excess of regeneration and has no known substitute that could be feasibly supplied at levels close to those required....[I]t is evident that the human enterprise has not only exceeded its current carrying capacity, but is actually reducing future carrying capacity....Our descendants will have fewer of the essential requisites of life-support than we have today."
Paul Ehrlich

Mankind Is Being Souled Short:

"Environmental, resource, and population stresses are diminishing, and with the passage of time will have less influence than now upon the quality of human life on our planet.... Because of the increases in knowledge, the earth's 'carrying capacity' has by now no useful meaning. These trends strongly suggest a progressive improvement and enrichment of the earth's natural resource base, and of mankind's lot on earth. There is only one important resource which has shown a trend of increasing scarcity rather than increasing abundance. That resource is the most important of all--human beings." Julian Simon

Before he became preoccupied making fund-raising phone calls from the Vice President's office, then-Senator Albert Gore (1992) urged us to make the environment "the central organizing principle for civilization"(p. 270). In 1996, two books representing the adversarial positions on the question of human population and the carrying capacity of the Earth were published--Betrayal of Science and Reason: How Anti-Environmental Rhetoric Threatens Our Future by Paul and Anne Ehrlich, and The Ultimate Resource 2 by Julian Simon. The two positions and their advocates differ in their methods, tone, and conclusion. Skeptic contacted both Ehrlich and Simon to ask them to be interviewed the debate on Population and Environment. Julian Simon accepted, and his interview appears in this issue. (Paul Ehrlich declined, though our offer remains open).

Economist Julian Simon's tome is 734 pages long, with 147 figures and 12 tables, and often reads like a prospectus for no-load, emerging-markets mutual fund. Ecologists Paul and Anne Ehrlich's book, which often reads like a combination of J'accuse and the Sixth Chapter of the Book of Relevation (i.e., the starting gate for the Four Horsemen of the Apocalypse), is 335 pages of text. My point is not the literary, analytical, or statistical skills of Simon or the Ehrlichs (which are all considerable), but rather the rhetorical styles in which the respective advocates have chosen to present their case before the jury.

In 1996 the paperback edition of Joel Cohen's How Many People Can the Earth Support? also appeared. While Cohen's perspective is much closer to Ehrlich's than to Simon's, his book provides an invaluable history and a wealth of data to be booked as evidence.

Charting Population Growth

Figure 1 provides demographers' best guesstimates of the growth of human population from the end of the last ice age (about 10,000 years ago) to the present. (All figures, tables, and quotes are taken and adapted from Cohen, unless otherwise noted.) By that time, every continent save Antarctica was inhabited by only one kind of hominid--modern Homo sapiens. Our species had altered the existing ecosystems by introducing a new species (the dog) to Australia and North America and driven the megafauna of the Americas (giant sloths and camelids), and of Madagascar (lemurs the size of small bears) and possibly the Eurasian mammoths over the cliff of extinction, if not necessarily literally.

The graph shows the tremendous increase not only in the estimated absolute numbers of humans, but also the increase in the rate of increase. How accurate are such estimates? Cohen suggests within a factor of 10 at the start to a factor 1.05 at 1750 CE (Common Era). How can demographers estimate the population before the dawn of history? Primarily by multiplying the population density of known hunter-gatherer cultures in comparable climatic zones by the area known or believed to have been inhabited by ancestral populations. But the further back in time, the less certain the figures. One study contends that the relative lack of diversity in mitochondrial DNA implies that all living humans are survivors from a drop of the ancestral population from about 100,000 to only 10,000 people that took place around 80,000 to 100,000 years ago (Rogers and Harpending, 1993).

Figure 2 charts the historical increase in population from 1 CE to the present in greater detail. Note that these figures depict the estimates of total human population. The best estimates of different demographers vary, the rate of increase was not constant in all parts of the world, and even the overall graph does not describe perfect exponential growth.

Baron Rothschild is credited with having said, "I do not know the Seven Wonders of the World, but I have no doubt Compound Interest is the Eighth!" Table 1 at the bottom of the page shows the compounding of human numbers. What explains these increases in rate of growth and the concomitant increases in the absolute number of humans alive at any point in history? Obviously, the rate of birth and the rate of death. And what explains the differences in these rates for different societies and different periods in history?

Cohen explains the trajectory of human population (Figure 2) in terms of stages (Table 1), which he terms "evolutions," rather than "revolutions" to emphasize their gradual and haphazard, as opposed to abrupt and intentional, nature. The first three all produced increases in global population, the fourth produces declining growth because of reduced fertility. They are:

(1) The Local Agricultural Evolution, which took place at varying times from the end of the last ice age until 3000 BCE in Africa, Asia, Europe, Meso-America, and the Middle East;
(2) The Global Agricultural Evolution, which coincided with the Industrial Revolution and took place from 1650 to 1850 CE;
(3) The Public Health Evolution, which started around 1945 and is still taking place in some parts of the world;
(4) The Fertility Evolution, which began around 1785 in France and the United States and has yet to begin in some parts of the world.

Figure 3 highlights the expected pattern in which the fall in birth rates lags behind the fall in death rates, and thereby generates an initial increase in population, followed by a later decline, as societies make the transition from Stage 1 to Stage 4. But this is by no means always the case.

Figure 4 shows how growth in world population reached its maximum rate of 2.1% per year between 1965 and 1970 and then began to fall, as more counties made the transition from Cohen's Stage 3 to Stage 4. This was primarily because of the drop of the growth rate in highly populated nations such as China, India, Indonesia, and Brazil. The absolute number of people, however, continued to increase, rising from 3.7 billion in 1970 to 5.3 billion in 1990. And even with the drop in the rate of growth, given the high absolute number of people, the number of souls added to the Earth each year rose from 72 million in 1970 to 92 million in 1990.

Estimating Carrying Capacity

Demographers use the term "carrying capacity" to designate how many people the Earth can support. If numeric population estimates are subject to error and disagreement, "guesstimating" how many people there ought to be reflects a serious conflict of visions. Cohen is again an invaluable source, summarizing the estimates, the methods used to derive them, and the limitations of the concept.

The concept of carrying capacity assumes that each additional person consumes an additional part of the Earth's resources and depletes (or at least alters) the environment, but also contributes through their productivity to the total resources available to others. Any reckoning of how many people the Earth can support depends upon how you estimate each term and the level of affluence at which you think the population can (or should) live.

Figure 5 shows the highest estimated carrying capacity presented by various scholars since Leeuwenhoek looked up from his microscope long enough to hazard a guess in 1679. Multiplying the surface area of the world by the population density of his native Holland at the time, he arrived at 13.4 billion. The subsequent numerical estimates range from Ehrlich's 1971 low ball figure of 0.5 to 1.2 billion, ("There are 3.6 billion human beings on the face of the Earth....between three and seven times more people than this planet can possibly maintain over a long period of time" [p. 410]) to Fremlin's intentionally-off-the-graph augmentio ad absurdum of 1018 (p. 408), where the only limitation is the ability of future technology to cool the heat generated by packing people as tightly as possible on the surface of the planet. >h4>Is Carrying Capacity a Meaningful Concept? According to Julian Simon and Herman Kahn the benefits of increasing human knowledge render the term "carrying capacity" devoid of "useful meaning"(p. 420). Garrett Hardin, who agrees with Simon on little else (Miele, 1996 ) also rejects the concept, arguing that "No thoughtful person is willing to assume that mere animal survival is acceptable when the animal is Homo sapiens." In its place, he offers the term "cultural carrying capacity," which includes supporting "The artifacts of human existence" and is therefore "Inversely related to the quality of life"(p. 421). Lester Thurow amusingly draws attention to the degree to which carrying capacity is a function of human behavior and social organization:

If the world's population had the productivity of the Swiss, the consumption habits of the Chinese, the egalitarian instincts of the Swedes, and the social discipline of the Japanese, then the planet could support many times its current population without privation for anyone. On the other hand, if the world's population had the productivity of Chad, the consumption habits of the United States, the inegalitarian instincts of India, and the social discipline of Argentina, then the planet could not support anywhere near its current numbers (p. 420).

Julian Simon and many economists look at the growth of human population and the accompanying overall increase in the standard of living and foresee the rise of humanity to an ever brighter future. For ecologists such as Paul Ehrlich and E.O. Wilson, and climate scientists like Steven Schneider, on the other hand, the future isn?? what it used to be. They see an increasing population that is depleting the Earth's resources, irrevocably decreasing biodiversity, and driving, figuratively and literally, toward disastrous global warming.

What can account for the conflict between the economists' vision of the world as half-developed and the ecologists' vision of the world as half-destroyed? The answer lies less in the data we have reviewed than in what the disputing parties bring to the discussion table--he methodologies they employ, and the paradigms in which they work. We can see this more clearly by looking briefly at two counts in the ecologists' indictment--global warming and biodiversity.

Global Warming

Steven Schneider is one of the leading climate scientists in the world. (He and Paul Ehrlich lost the famous wager to Julian Simon--see Simon interview for the details and fallout.) Schneider's book, Laboratory Earth, provides an excellent summary of the evidence that supports the theory of industrially-induced climate change. Figure 6 (adapted from Schneider) shows the annual temperature (dots) over the last 150 years, shown as deviations using the 1951-1980 average as a baseline. There is a century-long warming trend (line) of about .5 degrees C (.9 degrees F), with the period 1981-1995 containing most of the warmest years on record.

Carbon dioxide (CO2) absorbs infrared radiation, thereby trapping some of the Earth's radiant heat and raising temperatures (the greenhouse effect). How much of the century-long warming trend is due to ongoing temperature variation and how much is the result of the increased atmospheric CO2 caused by the combustion of fossil fuels? Analysis of air bubbles trapped in ice cores from Antarctica shows that temperature and CO2 levels have been highly correlated over the last 160,000 years, implying that the warming trend is not caused by human activity (see Figure 7, adapted from Schneider). But we also see the upward spike in temperature over the last 150 years, during which CO2 has increased by 25%.

Schneider has developed a model to explain such climate change in terms of a positive feedback loop between CO2 and temperature. This implies that a small human-induced change could jolt the system into a more severe warming cycle. In 2050, when emissions have doubled the concentration of CO2 (or equivalent amounts of other greenhouse gases), the model predicts temperature change will occur at 10 to 50 times the ongoing rate, with potentially disastrous ecological and economic consequences.


The word biodiversity was coined by ecologists and biologists. They wanted to focus attention on the evidence that increasing human population and development, especially the clearing of the world's rain forests, were dangerously increasing the rate at which species were becoming extinct.

How many species are there in the world? What is the background rate at which they become extinct? How many have become extinct in the last 25 years? Nobody knows. Zoologist Robert May notes that science has a better estimate of how many atoms there are in the universe than of how many species exist on earth (May, 1992).

Biologist E.O. Wilson, the originator of sociobiology, has been the most eloquent advocate for the cause of preserving biodiversity. Wilson and Robert MacArthur developed the theory of island biogeography. They found that there was a consistent relationship between the size of an island and the number of species it contained, S = CAZ, where S is the number of species, A is the area of the island, C is a constant, and Z is a parameter whose value depends on the type of organism (bird, insect, plant, etc.) and the distance of the island from other islands (Figure 8, adapted from Wilson, 1992).

Wilson then tested these estimates by literally crawling over every square foot of some tiny islets of varying size, from the mud to the tree tops, and counting the number of species. He then had the island fumigated and studied recolonization. Other estimates come from comparing areas of Amazonian forest that have been converted into pasture against adjacent pristine areas of equal size. They show that when an area is reduced by 90%, the number of species drops by 50%. A greater number of extinctions probably takes place in rain forests, which are inhabited by a greater number of species than other areas.

Multiplying the amount of rain forest cleared as measured by satellite photographs and using modest values for the parameters, Wilson estimates that "human activity has increased extinction between 1,000 and 10,000 times" the background rate. He concludes that species are now going extinct at the rate of 27,000 species each year, or 74 per day, three per hour, and that we are "in the midst of one of the great extinction spasms of geological history"(p. 280).

"Show Me the Money"

To arguments such as these, Julian Simon replies, "Show me the money!" i.e., the shortages in commodities (as measured by an increase in the market price), the roster of species proven to be extinct, the famines brought on by global warming, or any of the disasters predicted by ecologists. His book is filled with graphs like Figure 9, which shows the fall in the price of copper (measured either against prices in general or hours of labor). Pick just about any commodity you want, Simon has a similarly shaped graph. If things are becoming scarcer, why aren't they becoming more expensive? Looking back on intellectual history since Malthus, economists sarcastically note that the end of the world has been coming for a long, long time.

The reason we get such diametrically opposite closing arguments is that the opposing parties are asking different questions, using different methods to answer them, and basing their case on different underlying assumptions. Economists and ecologists differ not only in how they estimate impact, but in how they believe we adjust to it.

William Nordhaus is an economist (co-author with Paul Samuelson of the widely-used text Economics) and a member of the National Academy of Sciences Carbon Dioxide Committee. He surveyed a group of experts (10 economists, four social scientists, five natural scientists, and two engineers) drawn from the NAS greenhouse-warming panels and asked them to estimate the likelihood of varying degrees of global warming and their economic consequences. He found that the natural scientists considered global warming much more likely, and that the adverse economic impact would be as much as 30 times greater than did the economists. One economist thought that the impact of global warming would be "small potatoes," while one of the natural scientists thought it would exceed the effects of the Great Depression.

When asked to explain such large differences, one of the respondents answered, "Economists know little about the intricate web of natural ecosystems, whereas scientists know equally little about the incredible adaptability of human economies"(p.48). The ability of people, especially with modern technology, to find substitutes when the need arises lies at the heart of the economists' argument. While the price of copper has indeed gone down, the World Wide Web is increasingly being connected by even less expensive fiber optic cable, which also provides greater bandwidth and throughput. Perhaps the ultimate extension of the concept of adaptability is Simon's advice that even if thinning of the ozone layer were to increase UV radiation "people can intervene in many ways--even with as simple a device as wearing hats more frequently"(Myers and Simon, p. 63).

Steven Schneider tells his readers that the two most important questions to ask are simply: "What can happen? and What are the odds of it happening?" Julian Simon, on the other hand, told Skeptic, "We can never deal with the number of 'what ifs' or 'how abouts'." Schneider's climate forecasts and Wilson's extinction forecasts are based on extrapolation from the underlying theories of their respective sciences. To Simon and the economists, such underlying theories are irrelevant to forecasting human consequences, which are better estimated by past performance measured in terms of the market price.

Expert Opinion and Public Policy

Should we base our policies then on the demonstrated past history of market prices or on the risk avoidance models derived from scientific theory? Each has a problem.

If we take the market price as the measure of all things, at some point we must "internalize the externalities" so that the price paid reflects not just the costs of production and distribution, but also the cost of correcting any adverse environmental impact. The simplest mechanism is a tax. But at what rate? And who pays?

On the other hand, Ehrlich and Schneider both admit that their risk avoidance models do not produce the 5% level of confidence that is standard in statistical tests of scientific hypothesis. How do we weigh the obvious economic impact of regulation aimed at protecting the environment against potential downside risk predicted by the various models?

Since we have no idea how many species actually exist, any estimate of human impact beyond "a lot" is difficult to support. If no one knows how many species there really are, how can you know if one has gone extinct? How do you prove a negative? How do you know someone won't fish up a coelacanth? Increasingly ecologists have focused on variation within species and on ecosystems rather than species. How do you quantify those in a way that will satisfy critics?

What is certain is that the debate on whether the Earth has been souled out or humanity souled short is no isolated esoteric dispute. One way or another, it encompasses all of the following sub-debates: Abortion, Animal Rights, Endangered Species, Energy Alternatives, Environmental Justice, Euthanasia, Family Planning, Global Resources, Global Warming, Hunger, Immigration, Male/Female Sex Roles, Pollution, Poverty, Science and Religion, Third World Debt, and Trade.

Al Gore was half-right--the environment will become the central debating principle for the post-Cold War world. For most of history, traditional religion defined the relationship between humanity and nature. It remains to be seen whether the ecologists' vision or the economists' vision or some yet-to-be-worked out synthesis will become the central organizing principle for civilization in the next millennium.

This introduction is followed by the "Statement by the Union of Concerned Scientists" that alerts humanity to what its signers see as the clear and present danger to the survival of humanity and life on Earth. Economist Julian Simon then tells Skeptic why he finds the Statement clearly wrong and why Skeptic should not present it. Elie Shneour argues for applying the methodology of risk assessment to the question of population and environment. Paul Lindholt critically examines the sources and methods of the wise use movement, a vocal and active group opposing government intervention on behalf of the environment. Michael Shermer concludes the debate by debunking the tempting Beautiful People Myth, when humankind supposedly lived in perfect harmony with nature before technology, phallocentrism, the Aryan invaders, the division of labor, capitalism, the Judaeo-Christian ethic, or Christopher Columbus appeared on the scene.

We realize population and the environment are extremely controversial subjects requiring, if one is to aim for balance, a diversity of viewpoints. We look forward to those of our readers in what should be a lively Forum in the next issue. Bibiography Cohen, J. 1996. How Many People Can the Earth Support? NY: Norton.
Ehrlich, P. and Ehrlich, A. 1996. Betrayal of Science and Reason--How Anti-Environmental Rhetoric Threatens Our Future. Washington, D.C.: Island Press.
Gore, A.1992. Earth in the Balance--Ecology and the Human Spirit. Boston: Houghton Mifflin.
May, R. 1992. "How Many Species Inhabit the Earth?" Scientific American. Vol. 267. No.4. pp. 42-49.
Miele, F. 1996. "Living Within Limits and Limits On Our Living. Garrett Hardin on Ecology, Economy, and Ethics." Skeptic V.4. No. 2 pp.42-46.
Myers, N. and Simon, J. 1994. Scarcity or Abundance? A Debate on the Environment. New York: Norton.
Nordhaus, W. 1994. "Expert Opinion on Climatic Change," American Scientist.Vol. 82, pp. 45-51.
Rogers, A. and Harpending, H. 1993. "Population Growth Makes Waves in the Distribution of Pairwise Genetic Distribution." Molecular Biology and Evolution. Vol. 9, No. 1, May.
Schneider, S. 1997. Laboratory Earth--The Planetary Gamble We Can't Afford to Lose. NY: Basic Books.
Simon, J. 1996. The Ultimate Resource 2. Princeton, NJ: Princeton University Press.
Wilson, E.O., 1992. The Diversity of Life. Cambridge, MA: Harvard University Press.