The Limits to Growth was the first widely distributed, nontechnical text that described how the computer could be used to model the global future of humankind.

During the ecological awakening of the 1960’s, the public was swamped with books dealing with various aspects of the emerging environmental crisis. The authors of these books appealed to their readers’ emotions to bring about change. Each book dealt with an individual environmental problem, and the reading public was left to synthesize this material on its own. Club of Rome
World3[World three]
Computing, applied;environmental modeling
Environmental modeling
Club of Rome
World3[World three]
Computing, applied;environmental modeling
Environmental modeling
Forrester, Jay Wright
Meadows, Dennis L.
Meadows, Donella H.
Peccei, Aurelio

Because computers were not widely available, a traditional, one-topic-at-a-time approach to environmental problems made sense. Following rapid development of computer technology during the 1960’s, the need to synthesize data from many sources was met in the early 1970’s. The result was the publication of The Limits to Growth, the first nontechnical book providing a computer-based analysis of the global future of humankind. Knowing that growth could not go on forever, the authors asked two questions: How will the global population-capital system that has existed for the last one hundred years behave as the end of growth approaches? What will the world be like after growth ceases? The answers to both questions were frightening, even though the most optimistic assumptions were made about the functioning of the system. Wars and epidemics, variables that could hasten global collapse, were not included in the model. No military sector draining off industrial capital was simulated.

The Limits to Growth was an outgrowth of the Club of Rome, an informal organization of scientists, government officials, industrialists, educators, and others interested in the future of humankind. The club’s original 1968 meeting in Rome led to the production of The Limits to Growth, which was based on a computer model called World3 prepared by Jay Wright Forrester of the Massachusetts Institute of Technology (MIT). World3 integrated five variables, or feedback systems, of global concern—industrialization, population growth, agricultural production, resource consumption, and pollution—into a single system. Although evaluating how a single variable, such as population size, varies with time is comparatively easy, evaluating changes of many interrelated variables over time requires a computer. Using the model, researchers and policy makers could look many decades into the future to see the potential impacts of their decisions.

World3 had two basic characteristics. First, the model was global in nature, treating the world as a uniform entity. Therefore, the depletion of an average nonrenewable resource was simulated rather than the depletion of every specific resource. Second, the model did not take social change into account. Once the starting parameters of the simulation were set, no changes could be introduced, and development proceeded to its mathematical conclusion. By running the simulation several times and changing the variables to reflect different social options, the effect of specific decisions on future growth could be studied. Exact predictions about the future were never the goal. Only the behavior of the system mattered.

Each of the five feedback systems was growing exponentially, increasing by a constant percentage each year. As a result, the larger the variable, the greater its increase will be. Because the growth rate of most variables is also growing exponentially, the variables increase even faster.

A variable that is growing exponentially can suddenly exceed a fixed limit on its growth. One such limit is the amount of arable land on the earth. Other limits are harder to assess. The upper limits for the exposure to many kinds of pollution, for example, are not known. There is delay between the time a pollutant is first released and the time when its harmful effects are first noted. By then, irreversible damage may already have occurred.

The upper limit for the size of the human population is called the “carrying capacity”—that is, the maximum number of people the earth can support. A variable may exceed a limit for a short time, but the ultimate result is the collapse of the system. For the human population, the collapse is called dieback, because people will continue to die until equilibrium with the carrying capacity of the environment is reached. The equilibrium value does not have to be the same as the original carrying capacity. If the environment is sufficiently degraded, the carrying capacity will be significantly lowered.

World3 showed that, if no changes occurred in global physical, economic, and social relationships, the world system would overshoot an upper limit (resource availability) sometime in the twenty-first century, after which a rapid and uncontrollable collapse (a crash) in industry, agricultural production, and population would occur. Long-term planning is necessary if future generations are to exist at more than a subsistence level. Pollution never became a factor before collapse occurred.

A number of alternatives, called scenarios, were investigated to see if there was any hope for humankind. In each case only one variable was altered, so that its effect on the model could be evaluated. The first change was to double the amount of nonrenewable resources available for growth. This was followed by adding nuclear power as the chief source of energy. Then pollution control was added. In every case, first one and then another natural limit was met and exceeded, resulting in global collapse. Equilibrium was reached only when humankind intervened in the functioning of the world system to prevent it from reaching a natural limit.

A state of dynamic global equilibrium could be achieved through the lowering of population growth rates, conservation of resources, emphasis on investment in agriculture and service industries, and de-emphasis on the manufacture of consumer goods. These changes prevented sudden, uncontrollable collapse. Because the final equilibrium was dynamic, population levels and the types of goods and services fluctuated within set limits. Every person satisfied his or her material needs and was free to reach full potential. World3 asserted that the changes needed for equilibrium would have to be implemented almost immediately and on a global scale. The probability of success decreased with each passing year.

Many people rejected the conclusions of The Limits to Growth because the model was too simplistic to account for the development of crises in different parts of the world at different times and too inflexible to allow individual and societal changes to immediately influence the model when crises became apparent during processing. The developers quickly countered these arguments by making the model more complex and flexible.

Two years after the publication of The Limits to Growth, Mihajlo Mesarović Mesarović, Mihajlo and Eduard Pestel Pestel, Eduard published Mankind at the Turning Point: The Second Report to the Club of Rome (1974). Mankind at the Turning Point (Mesarović and Pestel) Four significant changes had been made in the computer model, now called the World Integrated Model. World Integrated Model First, the number of variables studied had increased from approximately 100 to more than 100,000. Second, the model had been divided into ten regions to account for the political, cultural, and economic diversity of the world. Third, each region’s development was simulated at levels, or strata, starting with the individual and ending with the environmental level. Finally, individual, societal, and technological change could be injected into the operation of the model through interactive processing when an approaching disaster became apparent.

Although the operation of the model changed considerably, the conclusions did not: If the personal and societal convictions of the world’s people did not change, catastrophe in the form of famine and perhaps global war would result in the collapse of the world system. Growth must change from undifferentiated (exponential) to organic (dynamic equilibrium). Because the regions are so interdependent, each region’s people must be willing to lose some independence. A new global economic order based on interdependence and transcendence of national interest must be developed, according to the model, to avoid eventual systemic collapse.

In 1977, President Jimmy Carter Carter, Jimmy
[p]Carter, Jimmy;environmental policy focused the attention of the federal government on these problems. The result was the publication in 1980 of The Global 2000 Report to the President: Entering the Twenty-First Century. Global 2000 Report to the President, The (Council on Environmental Quality)[Global Two Thousand Report] That report concluded that rapid population growth would continue and that 92 percent of the growth would occur in the less industrialized countries. The gap in the gross national product of the industrialized and less industrialized countries would widen. Food production would increase, but the increases would not filter down to the most destitute countries or layers of society. Natural resources such as petroleum, topsoil, water, and wood would be consumed at an alarming rate. Pollution would increase. Up to 20 percent of the world’s plants and animals would be extinct by 2000. In contrast to other reports, The Global 2000 Report indicated that adequate amounts of minerals remain, but it concluded that an era of unprecedented global cooperation and commitment would be necessary to save humankind. Unfortunately, because the report projected trends only to the year 2000, it was not an instrument for long-term planning. After its appearance in 1980, it was largely ignored in policy-making decisions. Its language was too technical to be accessible to the general public.

In 1992, Beyond the Limits
Beyond the Limits (Meadows, Meadows, and Randers) was published as the twentieth-anniversary successor to The Limits to Growth. The computer simulation used in Beyond the Limits returned to a one-world simulation. A thirty-year update was published in 2004. Beyond the Limits concludes that in many areas, such as materials and energy usage, humankind will pass “beyond the limits” of the natural environment if behavioral changes are not initiated. During the 1970’s and 1980’s, industrial output grew faster than population, but most of the economic growth occurred in the industrialized nations, where populations were approaching stability and the economic base was already large. In the less industrialized countries, rapidly growing populations consumed any economic gain so that poverty was perpetuated, fueling even greater population increases.

Large population increases coupled with production, storage, and distribution problems in the less industrialized countries kept per-capita food production low and largely unchanged. In Africa, the amount of food per capita decreased. Finally, throughout human history, land has been abundant. Since 1960, however, exponential population growth has led to a land shortage. Ultimately, according to the model, if conditions do not change, overshoot and collapse will occur because events become unmanageable.

Beyond the Limits concludes that there is hope. A sustainable, dynamic equilibrium is possible, if humankind will scale back its expectations. The required changes seem obvious. First, the consumption of material goods and energy must be scaled back. Second, the efficiency of material and energy usage must be increased. Growth could still occur, but it would be cultural rather than material. The ultimate limit is time. Beyond the Limits maintains that, if change is delayed until 2015 or beyond, some dieback and, eventually, total collapse is inevitable.

The history of the Limits to Growth approach to environmental modeling suggests that the models are little better than the assumptions and data projections built into them. None of the dire predictions made in the initial studies has transpired, and in the area of population growth, one of the key variables to such models, substantial decline in growth rates and fertility rates has already been realized in many parts of the world. Moreover, the substantial depopulation taking place in many parts of the world is not a factor of catastrophic collapse in carrying capacity but rather of economic and social factors. Club of Rome
World3[World three]
Computing, applied;environmental modeling
Environmental modeling

• Cole, H. S. D., Christopher Freeman, Marie Jahoda, and K. L. R. Pavitt. Models of Doom: A Critique of “The Limits to Growth.” New York: Universe Books, 1973. Fourteen articles discussing the accuracy of The Limits to Growth as well as a response by its authors.
• Forrester, Jay Wright. World Dynamics. Cambridge, Mass.: Wright-Allen Press, 1971. The prototype of the computer model used in The Limits to Growth is discussed in detail. Some of the variables in this version, such as the effect of crowding on population growth, are not emphasized in other works. Presents solutions that would be extremely unpopular: reducing food production, health services, and industrialization to curb population growth.
• Meadows, Donella H., Dennis L. Meadows, and Jørgen Randers. Beyond the Limits: Confronting Global Collapse, Envisioning a Sustainable Future. Post Mills, Vt.: Chelsea Green, 1992. An updated version by three of the original authors of the Club of Rome’s 1972 report The Limits to Growth.
• Meadows, Donella H., Dennis L. Meadows, Jørgen Randers, and William W. Behrens III. The Limits to Growth. New York: Universe Books, 1972. The book that set the stage for all further discussions of global modeling.
• Meadows, Donella H., Jørgen Randers, and Dennis L. Meadows. Limits to Growth: The Thirty-Year Update. White River Junction, Vt.: Chelsea Green, 2004. Authors assess the availability of natural resources for the world’s population and demonstrate why the world may face catastrophe. Includes helpful charts illustrating findings.
• Mesarović, Mihajlo, and Eduard Pestel. Mankind at the Turning Point: The Second Report to the Club of Rome. New York: E. P. Dutton, 1974. Complex but readable analysis of the world’s potential future. The sections dealing with oil production detail the clash for scarce oil resources and the attempt to pretend that limits do not exist.
• U.S. Department of State. Council on Environmental Quality. The Global 2000 Report to the President: Entering the Twenty-First Century. 3 vols. Washington, D.C.: U.S. Government Printing Office, 1980. Highly technical report of a study of probable changes in world population, natural resources, and the environment commissioned by President Jimmy Carter in 1977. Calls for changes on an international scale, including radical measures to promote birth control.

Commoner Publishes The Closing Circle

Heilbroner Predicts Growth Limits

The Global 2000 Report Is Issued

The Ultimate Resource Argues in Favor of Population Growth

Our Common Future Is Published