Beyond the Limits-Executive Summary

Confronting Global Collapse, Envisioning a Sustainable Future
by Donella H. Meadows, Dennis L. Meadows, and Jorgen Randers

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Twenty years ago, after working with global data and with a computer model called World3, we came to the following conclusions in a book called The Limits to Growth:

1. If present growth trends in world population, industrialization, pollution, food production, and resource depletion continue unchanged, the limits to growth on this planet will be reached sometime within the next hundred years. The most probable result will be a sudden and uncontrollable decline in both population and industrial capacity.
2. It is possible to alter these growth trends and to establish a condition of ecological and economic stability that is sustainable far into the future. The state of global equilibrium could be designed so that the basic material needs of each person on earth are satisfied and each person has an equal opportunity to realize his or her individual human potential.
3. If the world's people decide to strive for this second outcome rather than the first, the sooner they begin working to attain it, the greater will be their chances of success.

Now with an updated model, with more extensive data, and after twenty years of growth and change in the world, we believe that our original conclusions are still valid, but they need to be strengthened:

1. Human use of many essential resources and generation of many kinds of pollutants have already surpassed rates that are physically sustainable. Without significant reductions in material and energy flows, there will be in the coming decades an uncontrolled decline in per capita food output, energy use, and industrial production.
2. This decline is not inevitable. To avoid it two changes are necessary. The first is a comprehensive revision of policies and practices that perpetuate growth in material consumption and in population. The second is a rapid, drastic increase in the efficiency with which materials and energy are used.
3. A sustainable society is technically and economically possible. It could be much more desirable than a society that tries to solve its problems by constant expansion. The transition to a sustainable society requires a careful balance between long-term and short-term goals and an emphasis on sufficiency, equity, and quality of life rather than on quantity of output. It requires more than productivity and more than technology; it also requires maturity, compassion, and wisdom.

These conclusions constitute a conditional warning, not a dire prediction. They offer a living choice, not a death sentence. The choice isn't a gloomy one. It does not mean that the poor must be frozen in their poverty or that the rich must become poor. It could mean the solution of problems such as poverty and unemployment that humanity has been working at inefficiently or fruitlessly by trying to maintain physical growth.

We hope that the world will make the choice for sustainability. We think that a better world is possible and that the acceptance of physical limits is the first step toward getting there. We see "easing down" not as a sacrifice, but as an opportunity to stop battering against the earth's limits and to start transcending self-imposed and unnecessary limits within human institutions, minds, and hearts.

Overshoot

The following are characteristics of a society that has grown beyond its limits—a society that is drawing upon the earth's resources faster than they can be restored, and that is releasing wastes and pollutants faster than the earth can absorb them or render them harmless.

• Falling stocks of groundwaters, forests, fish, soils.
• Rising accumulations of wastes and pollutants.
• Capital, energy, materials, and labor devoted to exploitation of more distant, deeper, or more dilute resources.
• Capital, energy, materials, and labor compensating for what were once free natural services (sewage treatment, flood control, air purification, pest control, restoring soil nutrients, preserving species).
• Capital, energy, materials, and labor diverted to defend or gain access to resources that are concentrated in a few remaining places (such as oil in the Middle East).
• Deterioration in physical capital, especially in long-lived infrastructure.
• Reduced investment in human resources (education, health care, shelter) in order to meet consumption needs or to pay debts.
• Increasing conflict over resources or pollution emission rights. Less social solidarity, more hoarding, greater gaps between haves and have-nots.

A society like this is in a state of overshoot. To overshoot means to go too far, to grow so large so quickly that limits are exceeded. When an overshoot occurs, it induces stresses—in this case in both natural and social processes—that begin to work to slow and stop growth.

If humanity does not correct its condition of overshoot, problems like the ones listed above will worsen, until human productive capacity, ingenuity, adaptability, and attention are overwhelmed. At that point overshoot will turn into collapse.

However, collapse is not the only possible outcome. The human society can ease down from beyond the limits. That need not mean reducing population or capital or living standards, though it certainly means reducing their growth. What must go down, and quickly, are throughputs—flows of material and energy from the supporting environ-ment, through the economy, and back to the environment.

Fortunately, in a perverse way, the current global economy is so wasteful, inefficient, and inequitable that it has tremendous potential for reducing throughputs while raising the quality of life for everyone. While that is happening, other measures—nontechnical measures, evolutionary human measures—can restructure the social system, so that overshoot never happens again.

Looking into the Future with World3

To understand how the human economy and the environment may unfold in the future, we use a computer model called World3. World3 is, like all models, much, much simpler than the real world. It is, however, more dynamically sophisticated than many computer models. It is a nonlinear feedback model, one that tries to capture the forces behind population and capital growth, the layers of changing, interlinked environmental limits, and the delays in the physical and economic processes through which human society interacts with its environment.


World3 shows, in no uncertain terms, that if the world system continues to evolve with no significant changes, the most likely result is not only overshoot, but collapse, and within another few decades. One possible future, by no means the only one, is shown in Scenario 1.

In this scenario the world society proceeds along its historical path as long as possible without major policy change. Technology advances in agriculture, industry, and social services according to established patterns. The simulated world tries to bring all people into an industrial and then post-industrial economy.

The global population in this scenario rises from 1.6 billion in 1900 to over 5 billion in 1990 and over 6 billion in the year 2000. Total industrial output expands by a factor of 20 between 1900 and 1990, and it does so while using only 20% of the earth's total stock of nonrenewable resources. In 1990 80% of these resources remain. Pollution in that year has just begun to rise significantly. Life expectancy is increasing, services and goods per capita are increasing, food production is increasing. But major changes are just ahead.

Just after the simulated year 2000 pollution rises high enough to begin to affect the fertility of the land. At the same time land erosion increases. Total food production begins to fall after 2015. That causes the economy to shift more investment into the agriculture sector. But agriculture has to compete for investment with a resource sector that is also beginning to sense some limits.

Between 1990 and 2020 in this scenario, population increases by 50% and industrial output by 85%. Therefore the nonrenewable resource use rate doubles. What was a 110-year supply of nonrenewable resources in 1990 is only a 30-year supply in 2020. So many resources have been used that much more capital and energy are required to find, extract, and refine what remains.

As both food and nonrenewable resources become harder to obtain in this simulated world, capital is diverted to producing more of them. That leaves less output to be invested in capital growth. Finally the industrial capital plant begins to decline, taking with it the service and agricultural sectors. For a short time the situation is especially serious, as population keeps rising, because of lags inherent in the age structure and in the process of social adjustment. Finally population too begins to decrease, as the death rate is driven upward by lack of food and health services.

This scenario is not a prediction, but we believe it is a possibility, one among many. Another very different possibility is shown in Scenario 10. To produce it we introduce technical, social, and economic measures quite different from those that are currently being pursued in the world. That is the purpose of a model, not to predict, but to test "what if" possibilities.

In Scenario 10 people in the simulated world decide on an average family size of two starting in 1995, and they have available effective birth control technologies. They also set themselves a consumption limit. When every family attains roughly the material standard of living of present-day Europe, it says "enough" and turns its attention to achieving other, nonmaterial goals. Furthermore, starting in 1995, this world puts a high priority on developing and implementing technologies that increase the efficiency of resource use, decrease pollution emissions, control land erosion, and increase land yields.


We assume in Scenario 10 that these technologies come on only when needed and only after a development delay of 20 years, and that they have a capital cost. The capital is available for them, however, because in this restrained society, capital does not have to support rapid growth or to ameliorate a spiraling set of problems caused by growth. By the end of the twenty-first century in this scenario, the new technologies reduce nonrenewable resource use per unit of industrial out-put by 80% and pollution production per unit of output by 90%. Land yield declines slightly in the early twenty-first century as pollution rises (a delayed effect of pollution emissions around the end of the twentieth century), but by 2040 pollution begins to go down again. Land yield recovers and rises slowly for the rest of the century.

The population in Scenario 10 levels off at just under 8 billion and lives at its desired material standard of living for at least a century. Average life expectancy stays at just over 80 years, services per capita rise 210% above their 1990 levels, and there is sufficient food for everyone. Pollution peaks and falls before it causes irreversible damage. Nonrenewable resources deplete so slowly that half the original endowment is still present in the simulated year 2100.

We believe that the world could attain a sustainable state similar to that shown in Scenario 10. We think it is a picture not only of a feasible world, but of a desirable one, certainly more desirable than a world that keeps on growing until it is stopped by multiple crises.

Scenario 10 is not the only sustainable outcome the World3 model can produce. There are tradeoffs and choices. There could be more food and less industrial output or vice versa, more people living with a smaller stream of industrial goods or fewer people living with more. The world society could take more time to make the transition to equilibrium—but it cannot delay forever, or even very long. When we postpone for twenty years the policies that brought about the sustainable world of Scenario 10, the population grows too large, pollution builds too high, resources are drained too much, and a collapse is no longer avoidable.

Beyond the Limits and Still Growing

Physical expansion is still the dominant behavior of human society, though the resource base is declining.


In 1991 the human population was 5.4 billion. In that year the population grew by over 90 million people, a one-year addition equivalent to the total populations of Mexico plus Honduras, or to eight Calcuttas. World population is still growing exponentially. Under the most favorable circumstances, the World Bank projects that the population will not level off until late in the next century, at 12.5 billion people.

Industrial production is also growing, more rapidly than the population. It has doubled over the past twenty years. Along with it have doubled, or more than doubled, the number of cars, the consumption of coal and natural gas, the electric generating capacity, the production of grain, the generation of garbage, the emissions of greenhouse gases. If the economy were to support 12.5 billion people, all living the way present North Americans live, it would have to expand at least twenty-fold—twenty more industrial worlds added to the existing one!


The industrial world that already exists is using the earth's resources unsustainably. It is not meeting the basic needs of all the world's people, and yet, given current knowledge and technology, all needs could be met without exceeding the earth's limits.

• Fact: Of the more than 5 billion people on earth, over 1 billion at any time are eating less food than their bodies require. Every day an average of 35,000 people die of hunger-related causes, most of them children.
  Possibility: If the food grown each year on earth were equitably distributed, and if less of it were lost to spoilage and waste, there would easily be enough to give all people an adequate, varied diet.
• Fact: During the past 20 years deserts expanded by 288 million acres, nearly the size of France. Each year 16 to 17 million acres of cultivated land are made unproductive because of erosion, and an-other 3.6 million acres because of salination and waterlogging. Soil erosion exceeds soil formation on a third of U.S. cropland and on 1300 million acres in Asia, Africa, and Latin America. Fertilizers and pesticides acidify and alter soils and run off to contaminate ground and surface waters.
  Possibility: Farming methods that conserve and enhance soils are known and used by some farmers on every continent. In both temperate and tropic zones, some farms are obtaining high yields consistently without high rates of application of fertilizers and pesticides. More food could be grown, and it could be done in ways that are ecologically, economically, and socially sustainable.
• Fact: Before the industrial revolution there were 14 billion acres of forest on the earth. Now there are 10 billion acres, only 3.6 billion of which are undisturbed primary forest. Half of the world's forest loss has occurred between 1950 and 1990. China has lost three-fourths of its forests. Europe has no primary forests left. The United States has lost one-third of its forested cover, and 85% of its primary forest. Half of the tropical forest is gone; half of what remains has been logged and degraded. At current logging rates the rest will be gone within 50 years and with it perhaps half the species of life on earth.
  Possibility: Forest cutting could be greatly reduced while demand for wood products is still fulfilled. Half of U.S. wood consumption could be saved by increasing the efficiency of sawmills and construction, by doubling the rate of paper recycling, and by reducing the use of disposable paper products. Logging could be conducted so as to reduce its negative impact on soils, streams, and unharvested trees. Fast-growing forests could be replanted on already logged lands. High-yield agriculture could reduce the need to clear forests for food, and more efficient stoves could reduce the need for firewood.
• Fact: The average North American uses 40 times as much energy as the average person in a developing country. The energy use of the human economy grew sixtyfold between 1860 and 1985, and it is projected to grow by another 75% by the year 2020. At present 88% of the commercial energy used in the world comes from the fossil fuels—coal, oil, and gas.
• Fact: Fossil fuels are limited both by their sources (the deposits in the earth) and by their sinks (the atmosphere, waters, and soils to which their combustion products and refinery by-products go). The primary product of fossil fuel combustion is carbon dioxide, a greenhouse gas, which is rapidly increasing in the atmosphere. Its atmospheric concentration is now higher than it has been for the past 160,000 years, and it is still growing exponentially.
  Possibility: Through efficiency measures alone the world could maintain its total energy use at or below the current level with no reduction in productivity, comfort, or convenience in the rich countries and with steady economic improvement in the poor countries. Efficiencies of that magnitude would make it possible to supply most or all the world's energy needs from solar-based renewables, whose costs are dropping steadily.
• Fact: As inputs of energy and materials to the human economy increase, so do outputs of waste and pollution. Some forms of pollution, such as lead in gasoline and DDT, have been greatly reduced, primarily by outright bans. In rich countries some widespread pollutants, such as nitrogen oxides in air and phosphates in streams, have been reduced or held constant, at considerable expense. Other kinds of pollutants, particularly nuclear wastes, hazardous wastes, and greenhouse gases, continue to grow unabated.
• Fact: Knowledge about the environment and concern for it has grown enormously all over the world. In 20 years the number of environmental ministries in the world's governments has risen from 10 to over 100. Global monitoring systems now exist, and global conferences, information networks, and agreements have been put into place.
  Possibility: The reorganization of manufacturing and farming practices to reduce pollution outputs has barely begun. Increased efficiencies of fuel and material use and more complete material recycling will reduce both depletion of sources and pollution of sinks. Great reductions in pollution will be a natural result of pricing products to include their environmental costs, and of the adoption of the idea of sufficiency—simply reducing unnecessary, wasteful consumption.

All over the earth soils, forests, surface waters, groundwaters, wetlands, and the diversity of nature are being degraded. Even in places where renewable resources appear to be stable, such as the forests of North America or the soils of Europe, the quality or health of the resource is in question. Deposits of fossil fuels and high-grade ores are being drawn down. There is no plan and no sufficient investment program to power the industrial economy after nonrenewable resources are gone. Pollutants are accumulating; their sinks are overflowing. The chemical composition of the entire atmosphere is being changed.
If only one or a few resource stocks were falling while others were stable or rising, one might argue that growth could continue by the substitution of one resource for another. But when many stocks are eroding and many sinks are filling, there can be no doubt that human withdrawals of material and energy have grown too far. They have overshot their sustainable limits.

The Dynamics of Overshoot and Collapse

A growing population and economy can approach the limits to its physical carrying capacity in one of four ways.

• It can keep growing without interruption, as long as its limits are far away or growing faster than it is.
• It can level off smoothly, slowing and then stopping in a smooth accommodation with its limits, if and only if it receives accurate, prompt signals telling it where it is with respect to its limits, and only if it can respond to those signals quickly and accurately—or if the population and economy limit themselves well below external limits.
  
  It may overshoot its limit for awhile, make a correction, and undershoot, then overshoot again, in a series of oscillations, if the warning signal from the limits to the growing entity is delayed, or if the response is delayed, and if the supporting environment is not erodable when overstressed, or if it is able to recover quickly from erosion.
  
  
  
  
  
  
• If the signal or response from the limit is delayed and if the environment is irreversibly eroded when overstressed, then the growing economy will overshoot its carrying capacity, degrade its resource base, and collapse. The result of this overshoot and collapse is a permanently impoverished environment and a material standard of living much lower than what could have been possible had the environment never been overstressed.

We submit that the human population and economy, drawing resources from a large but finite planet, forms a system that is structured, unless altered by human intelligence and human self-restraint, for overshoot and collapse. The prevailing industrial ethic is one of continuous growth. The resource base is both limited and erodable. The response of biological and geochemical systems to human abuse comes only after long delays. The human population acts only after further delay. And physical processes, from human population growth to forest growth to global climate change, operate with considerable momentum.

A population-economy-environment system that contains feedback delays and slow physical responses, thresholds and erosion is literally unmanageable. No matter how brilliant its technologies, no matter how efficient its economy, no matter how wise its decision makers, it can't steer itself away from hazards, unless it does its best to look far forward and to test its limits very, very slowly. If it keeps its focus only on the short term and if it constantly tries to accelerate, it will overshoot.

The advent of new technologies and the flexibility of the market system are no antidotes to overshoot, and they cannot by themselves prevent collapse. In fact they themselves operate with delays that enhance the economy's tendency to overshoot. Technology and markets serve the values of society. If the primary goal is growth, they will produce growth, overshoot, and collapse. If the primary goals are equity and sustainability, then technology and markets can also help bring about those goals.

Overshoot is a condition in which the delayed signals from the environment aren't yet strong enough to force an end to growth. That means that a society in overshoot still has a chance, if it acts quickly, to bring itself below its limits and avoid collapse.

There even may be a recent example of the human world doing just that in its response to the destruction of the ozone layer.

The Ozone Layer: Back from Beyond the Limits?

The ozone story illustrates all the ingredients of an overshoot and collapse system: exponential growth, an erodable environmental limit, and long response delays, both physical and political.

• The growth: Chlorofluorocarbons, or CFCs, are some of the most useful compounds ever invented by human beings. They were originally sold as refrigerants under the trade name Freon. Then they were found to be useful in insulation, as propellants in aerosol cans, as solvents for cleaning metals. By the early 1970s, the world was making a million tons of CFCs per year and discarding them safely into the atmosphere, or so everyone thought.
• The limit: High in the atmosphere, twice as high as Mount Everest, is the gossamer ozone layer that screens out a particularly harmful wavelength from the sun's incoming light—UV-B, a stream of energy of just the right frequency to destroy the organic molecules that make up all life. If the ozone layer thins and more UV-B light reaches the earth's surface, the results will include human skin cancers, blindness in many kinds of animals, decreased growth of green plants, and disruption of oceanic food chains. Each 1% decrease in the ozone layer is expected to produce a 1% decrease in soybean yield and a 3% to 6% increase in human skin cancer.
• Signals: The first scientific papers postulating that CFCs could destroy the ozone layer were published in 1974. The first measurements of a precipitous drop in ozone concentration over Antarctica were taken in the late 1970s and finally published in 1985. Since then, scientists have come up with an explanation of the "ozone hole" and have uncovered the disquieting fact that each atom of chlorine released into the stratosphere from the decay of a CFC molecule can destroy about 100,000 ozone molecules.
• Delays: After its manufacture, a CFC molecule may be released quickly into the atmosphere from an aerosol can, or it may remain for years in a refrigerator or air conditioner. Upon its release, it takes about 15 years to rise up to the stratosphere. Its residence time there may vary, depending on type of CFC, from 65 to 500 years.
• The human response: The first official international meeting to discuss the ozone layer was convened by the United Nations Environment Program in 1985. It produced no agreement. But by 1987 the "Montreal Protocol" was signed by 36 nations, agreeing to cut their production of CFCs in half by 1998. Continuing ozone deterioration then spurred the world to toughen that agreement: 92 nations agreed in London in 1990 to phase out all CFC production by 2000. In 1991, in response to further ozone depletion, several nations unilaterally moved up their deadlines for eliminating CFCs.

It took thirteen years from the first scientific papers to the signing of the Montreal Protocol. It will take thirteen more years until the Protocol, as strengthened in London, is fully implemented. The chlorine already in the stratosphere will remain there for more than a century. In fall 1991 the Antarctic ozone hole was the deepest ever measured, and in winter 1992 chlorine concentrations in the stratosphere over the Northern Hemisphere were the highest ever measured.

This is a story of overshoot and of a remarkable, worldwide human response. Whether or not it will be a story of collapse depends on how erodable or self-repairable the ozone layer is, on whether future atmospheric surprises appear, and on whether humanity has acted, and will continue to act, in time.

Six Steps to Avoid Collapse

Six broad measures lead to the avoidance of collapse in the World3 model and, we believe, in the world. Each of them is described here in general terms. Each can be worked out in hundreds of specific ways at all levels, from households to communities to nations to the world as a whole. Any step in any of these directions is a step toward sustainability.

• Improve the signals. Learn more about and monitor both the welfare of the human population and the conditions of local and planetary sources and sinks. Inform governments and the public as continuously and promptly about environmental conditions as about economic conditions. Include real environmental costs in economic prices; recast economic indicators like the GNP so that they do not confuse costs with benefits, or throughput with welfare, or the depreciation of natural capital with income.
• Speed up response times. Look actively for signals that indicate when the environment is stressed. Decide in advance what to do if problems appear (if possible, forecast them before they appear) and have in place the institutional and technical arrangements necessary to act effectively. Educate for flexibility and creativity, for critical thinking and for systems understanding.
• Minimize the use of nonrenewable resources. Fossil fuels, fossil groundwaters, and minerals should be used only with the greatest possible efficiency, recycled when possible (fuels can't be recycled, but minerals and water can), and consumed only as part of a deliberate transition to renewable resources.
• Prevent the erosion of renewable resources. The productivity of soils, surface waters, rechargeable groundwaters, and all living things, including forests, fish, game, should be protected and, as far as possible, restored and enhanced. These resources should only be harvested at the rate they can regenerate themselves. That requires information about their regeneration rates, and strong social sanctions or economic inducements against their overuse.
• Use all resources with maximum efficiency. The more human welfare can be obtained with the less throughput, the better the quality of life can be while remaining below the limits. Great efficiency gains are both technically possible and economically favorable. Higher efficiency will be essential if current and future world populations are to be supported without inducing a collapse.
• Slow and eventually stop exponential growth of population and physical capital. There are real limits to the extent that the first five items on this list can be pursued. Therefore this last step is the most essential. It involves institutional and philosophical change and social innovation. It requires defining desirable, sustainable levels of population and industrial output. It calls for goals defined around the idea of "enough" rather than "more." It asks, simply but profoundly, for a vision of the purpose of human existence that does not entail constant physical expansion.

This last and most daunting step toward sustainability requires solutions to the pressing problems that underlie much of the psychological and cultural commitment to growth: the problems of poverty, unemployment, and unmet nonmaterial needs. Growth as presently structured is in fact not solving those problems, or is solving them only slowly and inefficiently. But until better solutions are in sight, society will never let go of its addiction to growth. Therefore there are three problems for which completely new thinking is urgently needed.

• Poverty. "Sharing" is a forbidden word in political discourse, probably because of the deep fear that real equity would mean not enough for anyone. "Sufficiency" and "solidarity" are concepts that can help structure new approaches to ending poverty. Everyone needs assurance that sufficiency is possible for everyone and that there is a high social commitment to ensure it. And everyone needs to understand that the world is tied together both ecologically and economically. There is enough to go around, if we manage well. If we don't manage well, no one will escape the consequences.
• Employment. Human beings need to work, to have the satisfaction of personal productivity, and to be accepted as responsible members of their society. That need should be not be left unfulfilled, and it should not be filled by degrading or harmful work. At the same time, employment should not be a requirement for the ability to subsist. An economic system is needed that uses and supports the contributions that all people are able and willing to make, that shares work and leisure equitably, and that does not abandon people who for reasons temporary or permanent cannot work.

• Nonmaterial needs. People don't need enormous cars; they need respect. They don't need closetsful of clothes; they need to feel attractive and they need excitement, variety, and beauty. People need identity, community, challenge, acknowledgement, love, joy. To try to fill these needs with material things is to set up an unquenchable appetite for false solutions to real and never-satisfied problems. The resulting psychological emptiness is one of the major forces behind the desire for material growth. A society that can admit and articulate its nonmaterial needs and find nonmaterial ways to satisfy them would require much lower material and energy throughputs and would provide much higher levels of human fulfillment.

The Sustainable Society

A sustainable society is one that can persist over generations, one that is far-seeing enough, flexible enough, and wise enough not to undermine either its physical or its social systems of support. It is, in the words of the World Commission on Environment and Development, a society that "meets the needs of the present without compromising the ability of future generations to meet their own needs."

In a sustainable society population, capital, and technology would be balanced so that the per capita material living standard is adequate and so that the society's material and energy throughputs meet three conditions:

• Its rates of use of renewable resources do not exceed their rates of regeneration;
• Its rates of use of nonrenewable resources do not exceed the rate at which sustainable renewable substitutes are developed;
• Its rates of pollution emission do not exceed the assimilative capacity of the environment.

A sustainable society is not necessarily a "zero growth" society. That concept is as primitive as is the concept of "perpetual growth." Rather a sustainable society would discriminate among kinds of growth and purposes for growth. It would ask what growth is for, who would benefit, what it would cost, how long it would last, and whether it could be accommodated by the sources and sinks of the earth.

That is to say, a sustainable society would be less interested in growth than in development. As a recent World Bank report says: "Following the dictionary distinction... TO GROW means to increase in size by the assimilation or accretion of materials. TO DEVELOP means to expand or realize the potentialities of; to bring to a fuller, greater, or better state. When something grows it gets quantitatively bigger; when it develops it gets qualitatively better."

A sustainable society would not paralyze the poor in their poverty. To do so would not be sustainable for two reasons. First, the poor would not and should not stand for it. Second, keeping any part of the population in poverty would not, except under dire coercive measures, allow the population to be stabilized. For both practical and moral reasons any sustainable society would have to be just, fair, and equitable.

A sustainable society would not experience the despondency and stagnancy, high unemployment and bankruptcy that current market systems undergo when their growth is interrupted. The difference between the transition to a sustainable society and a present-day economic recession is like the difference between stopping an automobile with the brakes and stopping it by crashing into a brick wall. A deliberate transition to sustainability would take place slowly enough so that people and businesses could find their proper places in the new society.

There is no reason why a sustainable society need be technically or culturally primitive. Freed from both material anxiety and material greed, human society could have enormous possibilities for the expansion of creativity.

A sustainable world need not be a rigid one, or a centrally controlled one. It would need rules, laws, standards, boundaries, and social agreements, of course, as does every human culture. Rules for sustainability, like every workable social rule, would be put into place not to remove freedoms but to create them or to protect them against those who would destroy them. They could permit many more freedoms than would ever be possible in a world that continues to crowd against its limits.

Diversity is both a cause of and a result of sustainability in nature, and therefore a sustainable human society would be diverse in both nature and culture.

A sustainable society could and should be democratic, evolving, technically advanced, and challenging. It would have plenty of problems to solve and plenty of ways for people to prove themselves, to serve each other, to realize their abilities, and to live good lives—perhaps more satisfying lives than any available today.

The Next Revolution

We don't underestimate the gravity of the changes that will take the present world down from overshoot and into sustainability. We think a transition to a sustainable world is technically and economically possible, but we know it is psychologically and politically daunting. The necessary changes would constitute a revolution, not in the sense of the American or French political revolutions, but in the much more profound sense of the Agricultural and Industrial Revolutions.

Like those revolutions, a sustainability revolution would change the face of the land and the foundations of human self-definitions, institutions, and cultures. It is not a revolution that can be planned or dictated. It won't follow a list of fiats from a government or from computer modelers. The sustainability revolution, if it happens, will be organic and evolutionary. It will arise from the visions, insights, experiments, and actions of billions of people. It will require every human quality and skill, from technical ingenuity, economic entrepreneurism, and political leadership to honesty, compassion, and love.

Are any of the necessary changes, from resource efficiency to human compassion, really possible? Can the world actually ease down below the limits and avoid collapse? Is there time? Is there enough money, technology, freedom, vision, community, responsibility, foresight, discipline, and love on a global scale?

The general cynicism of the day would say there's not a chance. That cynicism, of course, is a mental model. The truth is that no one knows.

The world faces not a preordained future, but a choice. The choice is between models. One model says that this finite world for all practical purposes has no limits. Choosing that model will take us even further beyond the limits, and, we believe, to collapse within the next half century.

Another model says that the limits are real and close, and that there is not enough time and that people cannot be moderate or responsible or compassionate. That model is self-fulfilling. If we choose to believe it, we will get to be right.

A third model says that the limits are real and close, and there is just exactly enough time, with no time to waste. There is just exactly enough energy, enough material, enough money, enough environmental resilience, and enough human virtue to bring about a revolution to a better world.

That model might be wrong. All the evidence we have seen, from the world data to the global computer models, suggests that it might be right. There is no way of knowing for sure, other than to try it.