Sustainable future


caption Figure 1. Urban and Rural Populations of the World: 1950-2030. Urban populations have now exceeded rural populations. By 2030, over 60% of the global population is expected to reside in urban areas. Think about the many economic, social, and environmental challenges that large populations centered in these large urban areas will face (Source: World Urbanization Prospects: The 2003 Revision. UN Sale No. E.04.XIII.6. UNESA Population Division, New York, 2004.)

Historically humans were able to live within a system of finite resources. Long ago humans had access to a large amount of natural resources and a seemingly unlimited amount of available land. Humans also had a limited population, they consumed very little, and also produced a limited amount of pollutants that the environment was mostly able to assimilate or transform into safe byproducts. Unfortunately, increased population, increased consumption, and advances in technology have increased our individual and collective impact on the environment (i.e., our ecological footprint). Thus, the world now faces serious challenges in terms of long-term economic growth, societal prosperity, and environmental stewardship.

It took the human population hundreds of thousands of years to reach a population of 1 billion. The world's population now exceeds 6 billion and is expected to reach 9 to 10 billion sometime this century before leveling off (see Figure 1). Tied to this increase in population are increases in personal resource consumption in most parts of the world.

Table 1. Ten Existing and Emerging
Environmental Issues
  • Globalization, trade & development
  • Coping w/ climate change & variability
  • The growth of megacities
  • Human vulnerability to climate change
  • Freshwater depletion and degradation
  • Marine and coastal degradation
  • Population growth
  • Rising consumption in developing countries
  • Biodiversity depletion
  • Biosecurity
Source: United Nations Environment Programme

The United Nations Environment Programme (UNEP) lists ten existing or emerging environmental issues the world currently faces (Table 1). Issues such as population growth, climate change & variability, rising consumption, loss of biodiversity, and freshwater depletion (and associated water scarcity) are clearly recognized as major environmental challenges. And importantly, all these issues point to one fundamental aspect of sustainability, that is, the economic and social well being of every citizen and Nation is dependent on the health of the environment.

As an example of how humans are consuming environmental resources in a non-sustainable manner, some scientists estimate that over 25% of the Sun’s energy, that reaches the Earth and is incorporated into ecosystems, is now appropriated by human beings. Think about it, two more doublings of the human impact on the world’s natural resources (from 25% to 50% and then from 50% to 100%) would result in 100% of the Earth’s net primary production being utilized by humans. This scenario can be accomplished through a combination of population increase, economic growth that is based solely on consumption, and advances in technology that allow an even greater proportion of the Earth’s natural resources to be appropriated.

Of course this scenario of human’s capturing 100% of the Earth’s net primary production is an ecological impossibility because it leaves ecosystems with nothing. This scenario would also be dire for humans because of our well established dependency on ecosystems for social and economic prosperity.

The modern movement towards a more sustainable future

The stated mission of UNEP is “to provide leadership and encourage partnership in caring for the environment by inspiring, informing, and enabling nations and peoples to improve their quality of life without compromising that of future generations” (UNEP).

The United Nations Conference on the Human Environment was held in Stockholm (Sweden) in 1972. It is significant because for the first time, the environment was added to the world’s list of problems. The “Stockholm Conference” also resulted in the creation of the U.N. Environment Programme (UNEP).

  •  Principle 1 of the Stockholm Declaration states “Man has the fundamental right to freedom, equality, and adequate conditions of life, environment of quality that permits a life of dignity and well-being, and he bears a solemn responsibility to protect and improve the environment for present and future generations.”
  • Principle 2 of the Stockholm Declaration states “The natural resources of the earth including air, water, land, flora, and fauna and especially representative samples of natural ecosystems must be safeguarded for the benefit of present and future generations through careful planning and management, as appropriate.”

During this time period many individuals began to think carefully about global environmental problems. For example, in 1972 an influential book called the Limits to Growth was published (Meadows, D. H., D. L. Meadows, J. Randers, W. W. Behrens III, Earth Island Limited, London). It warned that if the established unsustainable mode of population growth, industrialization, pollution production, food production, and resource depletion continue unchanged, the most probable result would be a sudden and uncontrollable decline in both population and industrial capacity.

This idea of limits to growth evokes the scientific concept of carrying capacity.

Carrying capacity refers to the upper limit to population or community size (e.g., biomass) imposed through environmental resistance. In nature this resistance is related to the availability of renewable (e.g., food) and nonrenewable (e.g., space) resources as they impact biomass through reproduction, growth, and survival.

Defining sustainability

The concept of sustainability has been proposed as a process that will allow the expanding human population to live in better harmony with the environment. Sustainability now has several hundred meanings. Some examples include:

  1. For many indigenous people, the concept of sustainability is very familiar. For example, the Great Law of the North American Iroquois Confederacy required that, “In our every deliberation, we must consider the impact of our decisions of the next seven generations.”
  2. In 1987 Our Common Future (World Commission on Environment and Development, Oxford University Press, Oxford) was released by the United Nations. This book is also referred to as the Brundtland Commission report. Ms. Gro Brundtland, a former prime minister of Norway, chaired the commission. The Brundtland Commission Report defined sustainable development as “development which meets the needs of the present without compromising the ability of the future to meets its needs.”
  3. Sustainability has also been defined as the “design of human and industrial systems to ensure that humankind’s use of natural resources and cycles do not lead to diminished quality of life due either to losses in future economic opportunities or to adverse impacts on social conditions, human health, and the environment”.

Note that all these definitions can be tied back to Principle 1 and Principle 2 of the Stockholm Conference. These definitions also show the need for everyone (individuals, communities, businesses, and governments) to think about the impact their decisions will have on future generations of humans, animals, and plants. Also observe how definitions of sustainability attempt to equally weight issues of the environment, society, and economy, something referred to as “the triple bottom line”.

Equity and fairness

caption Figure 2. Energy consumption per capita (units of million BTU per person) in North America (blue) compared to the rest of the world (red). Note that North America’s energy consumption has been approximately four times higher over a 23-year period.

Sustainable solutions need to be just and equitable. Many have proposed that the world’s economic, social, and environmental problems can be partially addressed by better sharing of global environmental, social, and economic wealth. All the Earth’s citizens would benefit from such a world because we are all tied together via the global environment. This is also a reason why the issue of unsustainable consumption needs to be addressed if the world is to achieve a vision of sustainability.

Figure 2 shows the energy consumption of North America on a per capita basis compared to the rest of the world. In 2003, North America’s per capita energy consumption was approximately four times higher than the rest of the world. Is it fair that one group (or generation) of individuals or one Nation utilize an unfair amount of the Earth’s resources?

Is it fair that certain segments of a population are exposed to elevated levels of mercury and persistent organic pollutants, that bioconcentrate in their bodies, because their subsistence lifestyle results in them eating more fish contaminated by global circulation of pollutants? Is it fair that African American communities situated on the lower Mississippi River are exposed to hazardous chemicals because of economic conditions that cause them to reside near a large number of oil and chemical processing facilities? These individuals at risk could also be the 1 billion people living in the developing world who are exposed to disease-causing pathogens in unsafe drinking water. Even now climate change is believed to be melting Arctic ice. This in turn is adversely impacting the subsistence lifestyles of Inuit who live in Arctic regions while polar bears who reside in the same area are also encountering difficulty in hunting because of less frequent and weaker ice cover.

In a sustainable world, consumption would be more equally distributed around the world and particular segments of human, plant, and animals would not have to assume a greater amount of environmental risk than wealthier individuals. Also important to this discussion, it would be clearly recognized that “adaptation” is not an equitable solution to a fast changing environment. This is because not all humans, plants, and animals have either the financial resources or natural ability to adapt at the same rate.

Role of technology

Sustainable solutions can not be totally based on a quick-fix technological solution. For example, creating automobiles that have increased gas mileage is a positive step forward. However, this measure alone will not solve the environmental and societal problems associated with a car-dependent society if more cars are simply added to roads. In brief,

{more vehicles} x {less pollution per vehicle} = {greater & unsustainable amount of pollution}

In this example, a sustainable solution not only needs to incorporate technological advances to develop greener vehicles, but also address issues of society having access to goods and services. That is, perhaps:

  • trains can be used more frequently to move goods and people
  • communities can be better planned to facilitate personal use of mass transit, bicycles, and walking
  • individuals could work part of the time at home where they would have an added benefit of being closer to their family.

This in term could lead to a healthier society because less air pollution would be created and health of individuals would improve through walking and riding bicycles. This would then reduce societal health care costs and get community members out in streets where they could interact with their neighbors. Think of all the health advantages to our children if they spent more time walking and riding a bike, and less time sitting in an automobile. These societal changes would also spur economic innovation through creation of new ideas, jobs, and services. And of course these changes would better protect the environment for future generations.

Similarly, technological and societal solutions need to be applied to other consumer products and buildings. For example, buildings are now responsible for:

  • 2/5 of the world’s material and energy flows;
  • 1/6 of freshwater withdrawals; and,
  • 1/4 of wood harvest.

In addition, buildings are responsible for a large amount of energy consumption. For example, in the United States, 54% of energy consumption is directly or indirectly related to building construction and operations.

But building “greener” homes and commercial buildings that use less energy but are larger and larger in size is not sustainable. And if these green buildings serve an ever expanding population the total impact on the environment would still be great as can be seen from the following Equation which is adapted from the earlier one.

{more and/or bigger buildings} x {less resources consumed per building} = {greater and unsustainable amount of pollution}

These examples show why sustainable solutions need to combine advances in technology with societal changes in personal and collective behavior. They also provide a basis for how sustainable solutions can lead to economic innovation.

Life cycle thinking and household decisions

It is quite common for a consumer to think of the environmental impact associated with manufacturing a product. For example, some consumers are concerned whether the factory at which their product was produced is meeting environmental standards in terms of safely controlling emissions.

Life cycle thinking is a process where an individual (and companies and governments) can think of the environmental impact throughout the whole life of the product. Life cycle thinking can also be used to assess the environmental sustainability of choices, for example, paper versus plastic bag, travel by air versus travel by car, purchasing food made locally versus importing food from far away distances.

caption Figure 3. Five life cycle stages of an individual product showing a “cradle to grave” methodology when thinking about the environmental burden of an individual choice.

A life cycle assessment (termed an LCA) is a method to determine the environmental burden in terms of natural resource usage, energy requirements, and pollution generation associated with the total life of a product (termed a “cradle-to-grave” approach). In this assessment, the total life of a product not only includes the manufacturing stage that occurs within an industrial factory, but it also includes those life stages of a product when the materials and components of a product are mined or assembled, as well as the environmental impact associated with getting the product to a store, the customer use of the product, and finally the environmental stress associated with what happens to the product at the end of its useful life.

The LCA approach typically includes five life stages (as shown in Figure 3):

  1. a pre-manufacturing stage (i.e., mining, other raw material acquisition)
  2. the manufacturing stage (what goes on inside the factory)
  3. the packaging associated with a product and then the energy to transport the product to a store or directly to the consumer
  4. the customer use stage (especially important, for example, in the driving and maintenance of one’s vehicle)
  5. a final life stage when the product has outlived its usefulness and is either recycled, refurbished, or most likely disposed of.

This “cradle-to-grave” approach looks at the environmental burden (raw material and energy use, and pollutant emissions) associated with all the life stages of a product, not simply just what goes on inside the factory. For example, life cycle thinking informs us that manufacturing an aluminum can is very energy intensive during the “pre-manufacturing” life stage where the ore is smelted. Thus, a consumer can reduce global energy consumption (and resulting greenhouse gas emissions) by ensuring they recycle aluminum products at the “end-of-life” stage so virgin ore does not need to be smelted.

In contrast, the major environmental impact of the automobile, in terms of air emissions and energy use, comes during the “product use” life stage. Here there are many more air pollutants (such as smog-forming chemicals and carbon monoxide) and greenhouse gases (carbon dioxide) emitted and also more energy is consumed. In addition, during the “product use” life stage, there is toxic water runoff from roads that adversely impairs the water quality of our streams, rivers, lakes, and wetlands. Thus, a consumer can lessen the overall environmental burden of an automobile by not only purchasing a highly fuel efficient automobile, but also using it more wisely (the book Divorce your Car, New Society Publishers, 2000, provides many examples of how to use your car less).

An automobile company could use the life cycle assessment to design cars that are not only more fuel efficient, but more easily disassembled at the “end-of-life” life stage so the components of the car can be easily reused or recycled. A company might also set up a program to “take back” your consumer product at the end-of-life stage. From a business standpoint, this is innovative because it is method for the company to re-establish a connection with the consumer and perhaps even get you back into their store.

In terms of the washing machine, the life cycle assessment shows us that the “product use” stage is the life stage where most energy and water are consumed. One reason for this is because heating water is a very inefficient process, thus, using any amount of hot water will always consume a lot of energy.

Choices made at the household level thus have a large influence on the total environmental burden, in terms of selecting a particular washing machine model and also in how the washing machine is operated. In particular,

  • Consumers should always purchase the most energy- and water-efficient appliances. Any higher initial cost is easily recouped after several years of operation. They may also consider installing a solar hot water heater on their roof to take advantage of the free energy the Sun provides to heat water.
  • Clothes can still be cleaned by washing on cold/cold cycles that require no energy to heat water. At worst, warm/cold should be the preferred choice.
  • Pollution to lakes and rivers can be controlled by making the choice to not use phosphorus-containing soaps and detergents and not purchasing those that contain chemical additives such as fragrances that do nothing to make the clothes cleaner.
  • Individuals also determine how frequently they wash their clothes. For example, studies show that people now wash clothes, not because the clothes need to be cleaned, but so their clothes “smell clean.” Interestingly, this increase in the frequency of clothes washing is occurring at a time when humans are performing less labor-intensive work and spending more and more time inside the home or office.

In terms of selecting a dishwasher, again, the life cycle assessment shows us that the “product use” stage is the life stage where most energy and water are consumed. Again, consumers should always purchase the most energy- and water-efficient appliance. Dishwashers that use less water also use less energy to heat that water. Dishwashers should always be operated when there is a full load. And consumers should not waste large volumes of water by pre-rinsing dishes by hand before placing them in a dishwasher (which is usually against the manufacturer’s advice). And again, a consumer can make the choice to not purchase dishwashing detergents that contain phosphorus and other unnatural chemical additives such as fragrances.

Finally, in terms of housing, studies show that each generation keeps building bigger and bigger homes, even though the size of families is decreasing in many countries. Life cycle thinking shows that conventional new building construction, built to code, that even considers required improvements in energy efficiency, consumes non-sustainable amounts of wood, water, energy, and other raw materials, when compared to less efficient, but smaller homes that were constructed several generations ago.

Life cycle thinking shows that architects and homeowners can make more sustainable choices in terms of not only “right sizing” the home, but also in the selection of appliances and lighting, use of renewable energy, use of passive solar heating in the winter and natural shading and overhangs in the summer, greater use of insulation, and creative use and placement of porches, windows, and fans to eliminate and minimize the need for air conditioning.

Measuring sustainability

Our path towards sustainability also needs to be measured. For this “sustainability indicators” have been developed that allow communities, governments, and corporations to track their progress towards a more sustainable future.

As the International Institute for Sustainable Development describes, “Societies measure what they care about. Measurement helps decision-makers and the public define social goals, link them to clear objectives and targets, and assess progress toward meeting those targets. It provides an empirical and numerical basis for evaluating performance, for calculating the impact of our activities on the environment and society, and for connecting past and present activities to attain future goals. Measuring sustainable development, just as we currently measure economic production, makes it possible for social and environmental goals to become part of mainstream political and economic discourse.”

A sustainability indicator measures the progress toward achieving a goal of sustainability. The best sustainability indicators are multidimensional, considering environmental, social, and economic facets. Examples of methods to measure sustainability include: the Index of Sustainable Economic Welfare, the Environmental Sustainability Index, and the Genuine Progress Indicator.

An example of a one-dimensional indicator of economic progress is gross national product (GNP). GNP tracks the total economic activity of an individual Nation. Besides being one dimensional, another reason GNP is a poor indicator of sustainability is because it includes attributes of our economy that would never be a large part of a vision of a more sustainable future. For example, GNP now includes the economic activity associated with bad things that a sustainable society would not want to be a large part of their society: pollution control, cancer treatment, and health costs associated with sick indoor environments, and operating of prison systems.

The vocabulary of a sustainable future

A sustainable future is possible if individuals, communities, governments, and corporation could collectively envision this sustainable future. In this sustainable future our daily vocabulary would be different. Words like “renewable energy” would replace “fossil fuels”. “Resource equity” would replace “consumption” and “accessibility” would replace “transportation.” Words like toxic chemical, pollution, smog, and bioaccumulation would simply disappear from our daily vocabulary and words like biodiversity, ecological restoration, and equity would became part of everyday vocabulary. This is what sustainability is about.

Local economies and our health systems would not be centered on expensive cancer treatment, instead local economies (and government sponsored research) would be constructed around cancer prevention. Our children would go to school in a “green” building that had healthy indoor air, instead of spending 1/3 of their day in a building that had air that made them ill, lowered their ability to learn, and caused society to absorb enormous health care costs, In fact, in the U.S, it is estimated that properly designed indoor environments would provide society with the following health savings: $6-14 billion in respiratory disease, $10-30 billion from sick-building syndrome, and $20-160 billion from work productivity gains unrelated to health.

Lastly, in a sustainable future, the word “waste” would not be a large part of our vocabulary. In the natural world, wastes simply serve as food inputs for other plants and animals. Waste products would not be discharged into our air, water, soil, and bodies or entombed in a landfill. Instead, in a sustainable future, wastes would be viewed as a resource that could be used in another process that would benefit the economy, society, and environment. This sustainable future would mimic nature so that through the disciplines of green chemistry and green engineering we would create economic prosperity without the production of hazardous and toxic wastes.

Further Reading

  • Alvord, Katharine T., 2000. Divorce your Car. New Society Publishers. ISBN: 0865714088
  • Daly, H.E., Beyond Growth: The Economics of Sustainable Development, Beacon Press, Boston, MA, 1996.
  • Meadows, D. H., D. L. Meadows, J. Randers, W. W. Behrens III, 1972. Limits to Growth. Earth Island Limited, London. ISBN: 1844071448
  • Meadows, D., J. Randers, D. Meadows, Limits to Growth. The 30-Year Update, Chelsea Green Publishing Company, White River Junction, VT, 2004.
  • Mihelcic, J.R., 1999. Fundamentals of Environmental Engineering. John Wiley & Sons, New York, NY. ISBN: 0471243132
  • Mihelcic, J.R. et al., 2003. Sustainability Science and Engineering: Emergence of a New Metadiscipline. Environmental Science & Technology, 37(23):5314-5324.
  • Mihelcic, J.R. J.B. Zimmerman, A. Ramaswami,Integrating Developed and Developing World Knowledge into Global Discussions and Strategies for Sustainability Part 1: Science and Technology,” Environmental Science & Technology, 41(10); 3415 - 3421, 2007.
  • Ramaswami, R., J.B. Zimmerman, J.R. Mihelcic, “Integrating Developed and Developing World Knowledge into Global Discussions and Strategies for Sustainability Part 2: Economics and Governance,” Environmental Science & Technology, 41(10): 3422 - 3430, 2007.
  • <> World Resources Institute (WRI) in collaboration with United Nations Development Programme, United Nations Environment Program, and World Bank (2005) World Resources 2005: The Wealth of the Poor – Managing Ecosystems to Fight Poverty. Washington, DC: WRI.<>
  • <>World Commission on Environment and Development, 1987. Our Common Future. Oxford University Press, Oxford. ISBN: 019282080X


Mihelcic, J. (2008). Sustainable future. Retrieved from


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