(21) Environmental Science

Principles of sustainability


What’s the use of a house if you don’t have a decent planet to put it on?

Henry David Thoreau

What Are Four Scientific Principles of Sustainability?

CONCEPT 1-6 Nature has sustained itself for billions of years by using solar energy, biodiversity, population regulation, and nutrient cycling-lessons from nature that we can apply to our lifestyles and economies.

Studying Nature Reveals Four Scientific Principles of Sustainability

How can we live more sustainably? According to environmental scientists, we should study how life on the earth has survived and adapted to major changes in environmental conditions for billions of years. We could make the transition to more sustainable societies by applying these lessons from nature to our lifestyles and economies (Concept 1-6).

• Reliance on Solar Energy: the sun warms the planet and supports photosynthesis used by plants to provide food for themselves and for us and other animals.

• Biodiversity (short for biological diversity): the astounding variety of life forms, the genes they contain, the ecosystems in which they exist, and the natural services they provide have yielded countless ways for life to adapt to changing environmental conditions throughout the earth’s history.

• Population Control: competition for limited resources among different life forms places a limit on how much their populations can grow.

• Nutrient Cycling: natural processes recycle chemicals that plants and animals need to stay alive and reproduce.

Four scientific principles of sustainability: these four interconnected principles of sustainability are derived from learning how nature has sustained a variety of life on the earth for about 3.7 billion years. If we consider an oval we can see the top left oval shows sunlight stimulating the production of vegetation in the Arctic tundra during its brief summer (solar energy) and the top right oval shows some of the diversity of species found there during the summer (biodiversity). The bottom right oval shows Arctic gray wolves stalking a caribou during the long cold winter (population control). The bottom left oval shows Arctic gray wolves feeding on their kill. This, plus huge numbers of tiny decomposers that convert dead matter to soil nutrients, recycle all materials needed to support the plant growth shown in the top left and right ovals (nutrient cycling).

Current Emphasis    -          Sustainable Emphasis

Pollution cleanup – Pollution prevention

Waste disposal – Waste prevention

(bury or burn)

Protecting Species – Protecting habitat

Environmental degradation – Environmental restoration

Increasing resource use – Less resource waste

Population growth – Population stabilization

Depleting and degrading natural capital – Protection natural capital

Using the four scientific principles of sustainability to guide our lifestyles and economies can help us bring about an environmental or sustainability revolution during your lifetime more sustainably.

Scientific evidence indicates that we have perhaps 50 years and no more than 100 years to make such acrucial cultural change. If this is correct, sometime during this century, we could come to a historical fork in the road, at which point we will choose a path toward sustainability or continue on our current unsustainable course. Everything you do, or do not do, will play a role in our collective choice of which path we will take.

One of the goals of this book is to provide a realistic environmental vision of the future that, instead of immobilizing you with fear, gloom, and doom, will energize you by inspiring realistic hope.

Exponential Growth and Sustainability

We face an array of serious environmental problems. Making the transition to more sustainable societies and economies challenges us to devise ways to slow down the harmful effects of exponential growth (Core Case Study) and to use the same power of exponential growth to implement more sustainable lifestyles and economies.

The key is to apply the four scientific principles of sustainability (Concept 1-6) to the design of our economic and social systems and to our individual lifestyles. We can use such information to help slow human population growth, sharply reduce poverty, curb the unsustainable forms of resource use that are eating away at the earth’s natural capital, build social capital, and create a better world for ourselves, our children, our grandchildren, and beyond. Exponential growth is a double-edged sword. It can cause environmental harm. But we can also use it positively to amplify beneficial changes in our lifestyles and economies by applying the four scientific principles of sustainability. Through our individual and collective actions or inactions, we choose which side of that sword to use.

We are rapidly altering the planet that is our only home. If we make the right choices during this century, we can create an extraordinary and sustainable future on our planetary home. If we get it wrong, we face irreversible ecological disruption that could set humanity back for centuries and wipe out as many as half of the world’s species.

You have the good fortune to be a member of the 21st century transition generation that will decide which path humanity takes. What a challenging and exciting time to be alive!


1. What is exponential growth? Why is living in an exponential age a cause for concern for everyone living on the planet?

2. Discuss the environmental factors that keep us alive. Explain the term natural capital. Describe the ultimate goal of an environmentally sustainable society.

3. What is the difference between economic growth and economic development? Discuss the key economic characteristics of developed versus developing countries.

4. What are the earth’s main types of resources and how are they being degraded? What is an ecological footprint?

What is a per capita ecological footprint? How do these compare and contrast on a global scale?

5. Describe the cultural changes that have occurred since humans arrived on the earth which have led to more environmental degradation as our ecological footprints have increased.

6. Define pollution. What are the two main sources of pollution? Describe two different ways that we can deal with pollution.

7. Identify the five basic causes of the environmental problems that we face today. In what ways do poverty and affluence affect the environment?

8. Discuss the lessons we can learn from the environmental transformation of Chattanooga, Tennessee.

9. List the four scientific principles of environmental sustainability. Explain how each is affected by exponential growth.

10. Describe the different types of environmental worldviews that are held by people on the planet. How are these linked to environmental ethics? What is social capital?


1. List three ways in which you could apply Concepts 1-5A and 1-6 to making your lifestyle more environmentally sustainable.

2. Describe two environmentally beneficial forms of exponential growth (Core Case Study).

3. Explain why you agree or disagree with the following propositions: a. stabilizing population is not desirable, because without more consumers, economic growth would stop. b. The world will never run out of resources because we can use technology to find substitutes and to help us reduce resource waste.

4. Suppose the world’s population stopped growing today. What environmental problems might this help solve? What environmental problems would remain? What economic problems might population stabilization make worse?

5. When you read that at least 19,200 people die prematurely each day (13 per minute) from preventable malnutrition and infectious disease, do you (a) doubt that it is true, (b) not want to think about it, (c) feel hopeless, (d) feel sad, (e) feel guilty, or (f) want to do something about this problem?

6. What do you think when you read that (a) the average American consumes 30 times more resources than the average citizen of India, and (b) human activities are projected to make the earth’s climate warmer? Are you skeptical, indifferent, sad, helpless, guilty, concerned, or outraged? Which of these feelings help perpetuate such problems, and which can help solve them?

7. Which one or more of the four scientific principles of sustainability are involved in each of the following actions: (a) recycling soda cans; (b) using a rake instead of leaf blower; (c) choosing to have no more than one child; (d) walking to class instead of driving; (e) taking your own reusable bags to the grocery store to carry things home in; (f) volunteering in a prairie restoration project; and (g) lobbying elected officials to require that 20% of your country’s electricity be produced by renewable wind power by 2020?

8. Explain why you agree or disagree with each of the following statements: (a) humans are superior to other forms of life, (b) humans are in charge of the earth, (c) all economic growth is good, (d) the value of other forms of life depends only on whether they are useful to us, (e) because all forms of life eventually become extinct, we should not worry about whether our activities cause their premature extinction, (f) all forms of life have an inherent right to exist, (g) nature has an almost unlimited storehouse of resources for human use, (h) technology can solve our environmental problems, (i) I do not believe I have any obligation to future generations, and (j) I do not believe I have any obligation to other forms of life.

9. What are the basic beliefs of your environmental worldview? Record your answer. Then at the end return to your answer to see if your environmental worldview has changed. Are the beliefs of your environmental worldview consistent with your answers to question? Are your daily choices consistent with your environmental worldview?

10. List two questions that you would like to have answered. 

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(20) Environmental Science

 Food Chains ,Food Webs,Energy Pyramid in Ecosystems- Video for Kids


What Happens to Energy in an Ecosystem?

CONCEPT 3-5 As energy flows through ecosystems in food chains and webs, the amount of chemical energy available to organisms at each succeeding feeding level decreases.

Energy Flows through Ecosystems in Food Chains and Food Webs

All organisms, whether dead or alive, are potential sources of food for other organisms. A caterpillar eats a leaf, a robin eats the caterpillar, and a hawk eats the robin. Decomposers consume the leaf, caterpillar robin, and hawk after they die and return their nutrients to the soil for reuse by producers.

A sequence of organisms, each of which serves as a source of food for the next, is called a food chain. It determines how chemical energy and nutrients move from one organism to another and return their nutrients to the soil for reuse by producers through thetrophic levels in an ecosystem along the same pathways-primarily through photosynthesis, feeding, and decomposition.

In natural ecosystems, most consumers feed on more than one type of organism, and most organisms are eaten by more than one type of consumer. Because of this, organisms in most ecosystems form a complex network of interconnected food chains called a food web. Trophic levels can be assigned in food webs just as in food chains. Food chains and webs show how producers, consumers, and decomposers are connected to one another as energy flows through trophic levels in an ecosystem.

Usable Energy Decreases with Each Link in a Food Chain or Web

Each trophic level in a food chain or web contains a certain amount of biomass, the dry weight of all organic matter contained in its organisms. In a food chain or web, chemicalenergy stored in biomass is transferred from one trophic level to another.

Energy transfer through food chains and food webs is not very efficient because, with each transfer, some usable chemical energy is degraded and lost to the environment as low-quality heat, as a result of the second law of thermodynamics. In other words, as energy flows through ecosystems in food chains and webs, there is a decrease in the amount of chemical energy available to organisms at each succeeding feeding level (Concept 3-5).

The percentage of usable chemical energy transferred as biomass from one trophic level to the next is called ecological efficiency. It ranges from 2% to 40% (that is, a loss of 60–98%) depending on what types of species and ecosystems are involved, but 10% is typical.

Assuming 10% ecological efficiency (90% loss of usable energy) at each trophic transfer, if green plants in an area manage to capture 10,000 units of energy from the sun, then only about 1,000 units of chemical energy will be available to support herbivores, and only about 100 units will be available to support carnivores.

The more trophic levels there are in a food chain or web, the greater is the cumulative loss of usable chemical energy as it flows through the trophic levels. The pyramid of energy flow illustrates this energy loss for a simple food chain, assuming a 90% energy loss with each transfer.


Energy Flow and the Second Law of Thermodynamics

Explain the relationship between the second law of thermodynamics and the flow of energy through a food chain or web.

Energy flow pyramids explain why the earth can support more people if they eat at lower trophic levels by consuming grains, vegetables, and fruits directly rather than passing such crops through another trophic level and eating grain eaters or herbivores such as cattle. About two-thirds of the world’s people survive primarily by eating wheat, rice, and corn at the first trophic level, mostly because they cannot afford meat.

The large loss in chemical energy between successive trophic levels also explains why food chains and webs rarely have more than four or five trophic levels. In most cases, too little chemical energy is left after four or five transfers to support organisms feeding at these high trophic levels.


Food Webs, Tigers, and Insects

(a) Why there are not many tigers in the world and (b) why there are so many insects (Core Case Study) in the world.

Some Ecosystems Produce Plant Matter Faster Than Others Do

The amount of life (biomass) that a particular ecosystem can support is determined by the amount of energy captured and stored as chemical energy by the producers of that ecosystem and how rapidly they can produce and store such chemical energy. Gross primary productivity (GPP) is the rate at which an ecosystem’s producers convert solar energy into chemical energy as biomass. It is usually measured in terms of energy production per unit area over a given time span, such as kilocalories per square meter per year (kcal/m2/yr).

To stay alive, grow, and reproduce, producers must use some of the chemical energy stored in the biomass they make for their own respiration. Net primary productivity (NPP) is the rate at which producers use photosynthesis to produce and store chemical energy minus the rate at which they use some of this stored chemical energy through aerobic respiration. In other words, NPP = GPP - R, where R is energy used in respiration.

NPP measures how fast producers can provide the nutrients or chemical energy stored in their tissue that is potentially available to other organisms (consumers) in an ecosystem.

Primary productivity is similar to the rate at which you make money, or the number of dollars you earn per year. Net primary productivity is like the amount of money earned per year that you can spend after subtracting your work expenses such as transportation, clothes, food, and supplies.

Ecosystems and life zones differ in their NPP. Despite its low NPP, the open ocean produces more of the earth’s biomass per yearthan any other ecosystem or life zone, simply because there is so much open ocean.

As we have seen, producers are the source of all nutrients or food in an ecosystem for themselves and for consumer organisms. Only the biomass represented by NPP is available as nutrients for consumers, and they use only a portion of this amount. Thus, the planet’s NPP ultimately limits the number of consumers (including humans) that can survive on the earth. This is an important lesson from nature.

Peter Vitousek, Stuart Rojstaczer, and other ecologists estimate that humans now use, waste, or destroy about 20–32% of the earth’s total potential NPP. This is a remarkably high value, considering that the human population makes up less than 1% of the total biomass of all of the earth’s consumers that depend on producers for their nutrients. These scientists contend that this is the main reason why we are crowding out or eliminating the habitats and nutrient supplies of so many other species and degrading or destroying some of the ecosystem services they provide.

Generalized pyramid of energy flow showing the decrease in usable chemical energy available at each succeeding trophic level in a food chain or web. In nature, ecological efficiency varies from 2% to 40%, with 10% efficiency being common. This model assumes a 10% ecological efficiency (90% loss in usable energy to the environment, in the form of low quality heat) with each transfer from one trophic level to another. Question: Why is a vegetarian diet more energy efficient than a meat-based diet?

Estimated annual average net primary productivity in major life zones and ecosystems, expressed as kilocalories of energy produced per square meter per year (kcal/m2/yr). Question: What are nature’s three most productive and three least productive systems?


Resource Consumption

What might happen to us and to other consumer species as the human population grows over the next 40-50 years and per capita consumption of resources such as food, timber, and grassland rises sharply? What are three ways to prevent this from happening?


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(19) Environmental Science



What Is Biodiversity and Why Is It Important?

CONCEPT 3-4A The biodiversity found in the earth’s genes, species, ecosystems, and ecosystem processes is vital to sustaining life on the earth.

CONCEPT 3-4B Soil is an important component of biodiversity that supplies most of the nutrients needed for plant growth and helps purify and store water and control levels of carbon dioxide in the atmosphere.

Biodiversity Is a Crucial Part of the Earth’s Natural Capital

Biological diversity, or biodiversity, is the diversity of the earth’s species, the genes they contain, the ecosystems in which they live, and the ecosystem processes of energy flow and nutrient cycling that sustain all life. Biodiversity is a vital renewable resource (Concept 3-4A) shows just two of the great variety of species found in tropical forests. Populations of these and countless other species in other ecosystems contain the variety of genes that make the genetic component of biodiversity. Genetic diversity provides a variety of genes that enable life on the earth to adapt to and survive dramatic environmental changes.

Ecosystem diversity-the earth’s variety of deserts, grasslands, forests, and mountains, oceans, lakes, rivers, and wetlands is another major component of biodiversity.

Each of these ecosystems is a storehouse of genetic and species diversity. In terrestrial ecosystems, soil is an essential component of biodiversity. Another important component of biodiversity is functional diversity-the variety of processes of matter cycling and energy flow within ecosystems and the biosphere.

Functional Diversity - The biological and chemical processes such as energy flow and matter recycling needed for the survival of species, communities, and ecosystems.

Ecological Diversity - The variety of terrestrial and aquatic ecosystems found in an area or on the earth.

Genetic Diversity - The variety of genetic material within a species or a population.

Species Diversity - The number and abundance of species present in different communities

Natural capital: the major components of the earth’s biodiversity-one of the earth’s most important renewable resources

Soil Is the Base of Life on Land

Most land is covered thinly by soil - a complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, and billions of living organisms, most of them microscopic decomposers.

Soil formation begins when bedrock is slowly broken down into fragments and particles by physical, chemical, and biological processes.

Soil, the base of life on land, is a key component of the earth’s natural capital and biodiversity. It supplies most of the nutrients needed for plant growth, purifies, and stores water, and helps control the earth’s climate by removing carbon dioxide from the atmosphere and storing it as carbon compounds (Concept 3-4B).

Most mature soils-ones that have developed over a long period of time-contain at least three horizontal layers, or horizons, each with a distinct texture and composition that varies with different types of soils. Think of them as floors in the building of life underneath your feet.

The roots of most plants and the majority of a soil’s organic matter are concentrated in a soil’s two upper layers, the O horizon of leaf litter and the A horizon of topsoil.

In most mature soils, these two layers teem with bacteria, fungi, earthworms, and small insects all interacting in complex ways. Bacteria and other decomposer microorganisms found by the billions in every handful of topsoil break down some of its complex organic compounds into simpler inorganic compounds soluble in water. Soil moisture carrying these dissolved nutrients is drawn up by the roots of plants and transported through stems and into leaves as part of the earth’s chemical cycling processes.

The B horizon (subsoil) and the C horizon (parent material) contain most of a soil’s inorganic matter, mostly broken-down rock consisting of varying mixtures of sand, silt, clay, and gravel, much of it transported by water from the A horizon. The C horizon lies on a base of parent material, which is often bedrock.

The spaces, or pores, between the solid organic and inorganic particles in the upper and lower soil layers contain varying amounts of air (mostly nitrogen and oxygen gas) and water. Plant roots use the oxygen for cellular respiration. As long as the O and A horizons are anchored by vegetation, the soil layers as a whole act as a sponge, storing water and releasing it in a nourishing trickle.

Although topsoil is a renewable resource, it is renewed very slowly and thus can be depleted. Just 1 centimeter (0.4 inch) of topsoil can take hundreds of years to form, but it can be washed or blown away in a matter of weeks or months when we plow grassland or clear a forest and leave its topsoil unprotected.

Since the beginning of agriculture, human activities have accelerated natural soil erosion.

Critical Thinking

How does soil contribute to each of the four components of biodiversity?

The earth’s biodiversity is a vital part of the natural capital that helps keep us alive. It supplies us with food, wood, fibers, energy, and medicines-all of which represent hundreds of billions of dollars in the world economy each year. Biodiversity also helps preserve the quality of the air and water, maintain the fertility of soils, dispose of wastes, and control populations of pests.

In carrying out these ecological services that are part of the earth’s natural capital, biodiversity helps sustain life on the earth.


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(18) Environmental Science

Components of the Ecosystem


What Are the Major Components of an Ecosystem?

CONCEPT 3-3 Some organisms produce the nutrients they need, others get the nutrients they need by consuming other organisms, and some recycle nutrients back to producers by decomposing the wastes and remains of organisms.

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(17) Environmental Science

What If The Sun Disappeared?


What Keeps Us and Other Organisms Alive?

CONCEPT 3-2 Life is sustained by the flow of energy from the sun through the biosphere, the cycling of nutrients within the biosphere, and gravity.

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(16) Environmental Science

What is ecology?


What Is Ecology?

CONCEPT 3-1 Ecology is a study of how organisms interact with one another and with their physical environment of matter and energy.

Cells Are the Basic Units of Life

All organisms are composed of cells: the smallest and most fundamental structural and functional units of life.

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(15) Environmental Science

What is an Ecosystem



Ecosystems: What Are They and How Do They Work?

Have You Thanked the Insects Today?

Insects have a bad reputation. We classify many insect species as pests because they compete with us for food, spread human diseases such as malaria, and invade our lawns, gardens, and houses. Some people fear insects and think the only good bug is a dead bug. They fail to recognize the vital roles insects play in helping to sustain life on earth.

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(14) Environmental Science


Sustainable Energy Choices for the 21st Century

Sustainable Consumption

How Can We Use Matter and Energy More Sustainably?

The second law of thermodynamics holds, I think, the supreme position among laws of nature. . . If your theory is found to be against the second law of thermodynamics, I can give you no hope.

Arthur S. Eddington

CONCEPT 2-5A The processes of life must conform to the law of conservation of matter and the two laws of thermodynamics.

CONCEPT 2-5B We can live more sustainably by using and wasting less matter and energy, recycling and reusing most matter resources, and controlling human population growth.

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