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We started this book with the views expressed in The Limit to Growth, which painted a pessimistic picture of the world if population and energy consumption were to continue their exponential growth. We would like to conclude the book by giving a sharply contrasting, optimistic view of how the future could be if we take the necessary actions to preserve the environment and our natural resources. This does not necessarily have to be a painful process, but can be accomplished utilizing small steps that enrich our lives as well as the lives of our children and grandchildren.

We will start this section by discussing what sustainability is, then offer recommendations on how to achieve it on personal, national, and global levels. All it takes to achieve these goals is an open mind, a little sacrifice, and a well thought-out pathway.

The technological advances of the last few decades have provided unprecedented opportunities for greater material wealth, better health care, and a more comfortable life for the great majority of people, but have also resulted in the accumulation of a tremendous amount of waste, depletion of a large fraction of our natural resources, and the acceleration of environmental degradation. This naturally leads to the question of how to continue with economic progress while keeping environmental damage to a minimum. Two approaches to sustainability are proposed by economists.

Neoclassical economists consider a sustainable environment to be that which provides an average person a future with a living standard that is better, or at least as good, as that of an average person today (a). They maintain that our children will be collectively better off if the economy expands at a faster rate than resources are depleted. After all there are no guarantees that we will ever run out of natural resources. Neoclassical economists are technological optimists; they believe that a free-market economy has the built-in mechanisms that would prevent ecological collapse, by promoting technologies that will help overcome resource scarcity and environmental damage. They cite increases in food production, discoveries of new energy reserves, and better and more efficient manufacturing technologies of the last century as proof that the overall standard of living around the globe has improved. They also claim that the living standard will continue to improve in the future and conclude that we are living in a sustainable environment.

Ecological economists (or ecologists), on the other hand, consider an environment sustainable only if future generations can enjoy essentially the same resources and a similar environment as we do today (b). Although technological advances can help prevent resource scarcity and environmental damages in the short term, they will ultimately be used to accelerate the ecological abuses. Unlike the neoclassical economists, ecologists see material goods as only useful in serving people to a point; therefore, economic well-being alone cannot compensate for a loss of natural resources or environmental degradation.

Question: Can we maintain a sustainable environment and still use fossil fuels and pollute the air?

Answer: Neoclassical economists do not see continued use of fossil fuels as necessarily bad, as increases in the rate of energy consumption increase economic output and help improve living standards. By allocating sufficient resources we can develop technologies that combat environmental damage and maintain a reasonable degree of sustainability. Ecological economists believe that sustainability is possible if benefits of fossil consumption outweighs the damages it causes to the environment. To be sustainable, the noted economist, Herman Daly, set three citerias (1):

1. For renewable resources, the sustainable rate of use can be no greater than the rate of regeneration. For example, geothermal hot water and steam resources are used at a rate that is being regenerated by nature.

2. For nonrenewable resources, the sustainable rate of use can be no greater than the rate at which a renewable resource can be substituted for it. For example, photovoltaic and wind technologies allow equivalent amount of energy and at comparable prices to become available, once the nonrenewable resources are exhausted.

3. For environmental pollution, the sustainable rate of emissions can be no greater than the rate at which that pollution can be rendered harmless. For example, the volume of carbon dioxide emission balances the removal of other substances that there is no net contribution of green house gases to the environment.

Question: According to a study, from 1930 to 2000, the money value of the world industrial output grew by a factor of 14 (2). During the same period -- because of the population growth -- the average per capita output increased by a factor of 5. Has society’s progress been sustainable?

Answer: Neoclassical economists see this data as an indication of an improved standard of living during that period and thus conclude that the progress was sustainable. The ecological economist, argues however, that if the population had been stable, the material standard of living would have grown by a factor of 14 also. Furthermore, although the cumulative wealth has been greater, the gap between the rich and poor nations has increased, and therefore we experienced an unsustained growth.

Among the first to quantify the impact of increasing consumption on the environment were Ehrlich and Holdren, who proposed a simple model commonly known as the IPAT equation (3). According to this model, total environmental damage (ecological footprint) is determined by three factors: the number of people, consumption per capita, and the state of technology (damage done per unit of consumption). This is represented as:

I = P . A . T (1)

Impact = Population x Affluence x Technology


I is the impact on the environment resulting from consumption,

P is the population,

A is the degree of affluence measured as consumption per capita, and

T is the technological factor that accounts for both the positive and negative impacts of technology on the environment.

Example: Using the IPAT model estimate what impact automobiles have on global warming.

Solution: Assuming 6.3 billion people live on earth, that there is roughly one car for every 7 persons, and that with the current state of technology, each car produces 5.4 tons of CO2 per year, we can evaluate automobiles’ impact as:

I = P . A . T

This accounts for roughly 22% of total carbon dioxide emission (and thus global warming) (c).



(1) Daly, H., “Toward Some Operational Principles of Sustainable Development,” Ecological Economics 2, 1990.

(2) Meadows, D., et al., Limit to Growth: 30-Year Update, Chelsea Green Publishing, 2004.

(3) Ehrlich, P. R., and Holdren, J., “Impact of Population Growth,” Science 171, no. 3977, pp. 1212-1219, 1971.

Additional Comments

(a) Neoclassical economics is a school of thought in which maximizing profit is the ultimate goal of any organization.

(b) Ecological economics is a branch of economists who see a direct link between the health of the ecosystem and that of human beings. Ecological economics is sometimes referred to as “Green Economics.”

(c) It is assumed that the world’s total carbon dioxide emissions will remain constant at their 2002 level of 24.5 billion tons (

Further Reading

Hawkens, P., Lovins, A, and Lovins, L. H., Natural Capitalism: Creating the Next Industrial Revolution, Rocky Mountain Institute, 1999.

Meadows, D., Randers, J., and Meadows, D., Limit to Growth: 30-year Update, Chelsea Green Publishing, 2004.

Diamond, J., Collapse: How Societies Choose to Fail or Succeed, Penguin Group, USA, 2004.

Journal of Political Ecology: Case Studies in History and Society, JPE is produced at the Bureau of Applied Research in Anthropology, the University of Arizona Library, Tucson, Arizona. The journal covers research articles into the linkages between political economy and human environmental impact.

World Watch Magazine (

External Links

World Bank (

United Nations Environment Program (

Rocky Mountain Institute (

Greenpeace (

Green Seal (

Nature Conservancy (

The Sierra Club (

Friends of the Earth (

Women’s Environment and Development Organization (

World Wide Fund (