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Instructions to submit the files for grading.

Dr. Charles E. Ophardt, Elmhurst College, Elmhurst, Illinois. Copyright 1997

Computer Simulation Laboratory




INTRODUCTION: This exercise is based upon the results of a global computer model constructed to model the interaction of five variables - population, food supply, industrial output, pollution, and consumption of nonrenewable natural resources. The results of the computer model scenarios are presented as a series of graphs plotted over a 2 century time frame. The computer program "Limits to Growth" presents the graphs in a variety of ways to enable the use of the scientific method to compare and analyze the results of a variety of changes presented in scenarios. The actual "Limits to Growth" program is not available over the inernet, but the results of the computer model are available as graphs in this exercise.

The Overall Question to be answered at the end of this exercise is:

Which worldview is supported by by the assumptions in this computer model of the world?


World Views
 A. Cornucopian

People in affluent societies usually have cornucopian or throwaway worldview which is based on the ideas that there will always be MORE. The earth has unlimited resources, or if they become scarce, a substitute will be found by advanced technology. The earth has an unlimited capacity to absorb pollution or technological advances will be found to clean up or control pollution. Continued economic growth and technological advances will produce a less crowded, less polluted, and more resource rich world.
 B. Sustainable Earth Views

People with the sustainable-earth view believe that the earth does not have limitless resources. An ever-increasing exponential production and consumption of resources will put a severe stress on the natural processes that renew and maintain air, water, and soil for renewable plant and animal life. If present trends continue, the world will become more crowded, more polluted, and nonrenewable resources will be depleted or severely degraded. Society as we know it may collapse.
Cornucopian viewpoints:

1. We are apart from nature and superior.
2. Conquer and subdue wild nature for our purposes.
3. Resources are unlimited because of our ingenuity to make them available or find substitutes - there is always more.
4. The more we produce and consume, the better off we are. Unlimited material progress can be achieved through economic and technological growth - all growth is good.
5. Population will be naturally limited when an industrial society is reached.
Sustainable-Earth viewpoints:

1. Control population growth.
2. Achieve sustainable use of cropland, forests, grasslands, animals, and fish.
3. Increase use of renewable energy such as solar, wind, geothermal, biomass.
4. Decrease use rate and waste in nonrenewable mineral, fossil fuel, and nuclear resources.
5. Emphasize pollution prevention and more environmentally benign technology.
6. Protect biodiversity and remaining wilderness areas.

Global Computer Model - The Club of Rome

The Club of Rome was formed in 1968 when a group of 30 individuals from 10 countries met in Rome to discuss the present and future predicament of humankind. The group has since expanded to 70 from 25 countries. Its purpose was to foster the understanding of the varied but interdependent components - economic, political, natural, and social - that make up the global system. Phase One of the study was conducted by an international team, under Dr. Dennis Meadows and Dr. J. Forrester at MIT.

A global computer model was constructed to investigate five major trends of global concern:
1. Population - Rapid population growth.
2. Food Supply - Widespread malnutrition.
3. Industrial Output - Accelerating industrialization.
4. Pollution - Deteriorating environment.
5. Supply of Non-Renewable Resources - Depletion of nonrenewable resources.

These trends are all interconnected in many ways, and their development is measured in decades or centuries. The model is used to understand the causes of these trends, their interrelationships, and their implications as much as one hundred years into the future.

All five elements in the model - population, food supply, industrial output, pollution, and supply of nonrenewable natural resources are all increasing or decreasing following a pattern that mathematicians call Exponential Growth . Nearly all of mankind's current activities can be represented by exponential growth curves.

Exponential Growth

A. Paper Doubling:

A simple illustration of exponential growth is to take a piece of paper and fold it in half. You have doubled its thickness. Fold again in half - its thickness is now 4 times the original. How many times can you continue to fold the paper? 10 times?
Assuming you can continue to fold the paper 40 times, how thick do you think it will be? 10 feet? 1 mile?
In fact it would make a pile to reach from the earth to the moon!!!

B. Growth of Savings:

Most people are accustomed to thinking of growth as a linear process.
A linear growth increases by a constant amount in a constant time period. If you save $10 each year and keep it in a piggy bank, at the end of 50 years you would have $500.

A quantity exhibits exponential growth when it increases by a constant percentage of the whole in a constant time period. If you initially invest $100 at 7% interest, you will have $1600 at the end of 50 years.

C. Doubling Time:

It is useful to think of exponential growth in terms of doubling time, or the time it takes a growing quantity to double in size. For example, money in a savings account at 7% interest will double in 10 years.

 Growth Rate   Doubling Time
 0.1 % per year  700 years
 1.0  70
 2.0  35
 4.0  18
 5.0  14

D. World Population Growth:

The exponential growth curve of world population is shown in the figure.

1700: The world population was about 0.5 billion and was growing at a rate of approximately 0.3 % per year (corresponds to a doubling time of 250 yr).
1970: The population totaled 3.6 billion and a rate of growth of 2.1 % per year (doubling time is 33 years).
1991: The population was 5.3 billion, rate of growth is 1.7 % (doubling time is 40 years), despite recent drops in birth rates in some countries.

What is the cause of exponential population growth?

Pre-industrial (1700): Both fertility and mortality were comparatively high and irregular. The birth rate exceeded the death rate only sightly, population grew exponentially, but at a very slow rate. The average life expectancy was 30 years. Modern (1970): Modern medicine, public health, and adequate food have led to an average life expectancy of 53 and still rising. Birth rates far exceed mortality rates, which results in a sharp exponential growth of the population.

Population Growth Scenarios

Pre-industrialized: Such as many in Africa, have high mortality and even higher fertility - growth rate = 2-3%/yr. Intermediate Industrialization: Such as Egypt, Mexico, Thailand, have low mortality while fertility is still high but also decreasing - growth rate = 2-4%/yr. Highly Industrialized: North America, Europe, Japan, have low mortality, low fertility, and slow growth rates - less than 1% per year.

Implication: Industrial growth causes transition to lower population growth rate.

Question to be answered by the models - can increased industrialization led to a stable population with enougth resources to support this population????

E. Industrial Output Growth:

A second quantity that has been increasing in the world even faster than population is industrial output. The average growth rate from 1963-1968 was 7 % per year or 5 % per year per person.
The 1970-1990 growth rate in total production has averaged 3.3 % per year or 1.5 % per year per person. If population had held constant, output per person doubles, but because of population growth, output per person grew by only one third.

Industrial Output: Continuous stream of products produced by industrial capital, which are actual factories and machines that produce manufactured products. Industrial capital is itself produced by labor, energy, raw materials, land, water, natural ecosystems, technology, finance, and management.

a. Consumer goods - cars, clothing, houses
b. Resource obtaining - drills, mining equipment, pipelines, tankers, etc.
c. Agricultural capital- tractors, barns, harvesters, which produce agricultural output, mainly food.
d. Service capital - hospitals, banks, stores, which produce health care, education, etc.
e. Industrial investment -more factories, machines to increase the stock of industrial capital.

How to Read World3 Scenarios

This program contains 13 computer runs or "scenarios" generated by the World3 Model. Each run starts with the same basic model structure and changes some of the variables to test different estimates of "real world" parameters.

Some scenarios incorporate more optimistic projections of developing technologies, others project what may happen if the world chooses new policies or goals.

The computer model calculates the interactions among 225 variables for every 6 months in a simulated time starting with the year 1900 to 2100. The model produces 90,000 numbers for every scenario run. Several types of graphs are produced to show correlations among some of the variables. The scales for the variables (constant in all scenarios) have different absolute values, but for comparison simplicity, the numbers are normalized to fit on a single scale.

To make sense of all of this data, the model generates various types of graphs.
For simplicity this program will show the results of only one of them. The State of the World shows global totals for: population, food supply, industrial output, pollution, and remaining nonrenewable resources.

Scenario 1: Standard Run

The world society proceeds along its historical path as long as possible without major policy changes. This is the "reference run ". Technology in agriculture, industry, and social services advances according to current established exponential growth patterns.
 The left hand axis has different values for the units being plotted. The actual numbers are not important, but will be relative for all of the scenarios. The five properties are all scaled to fit on one graph.

1 = Green = Population: increases to 6 billion by 2000. The simulated world tries to bring all people into the industrial and post-industrial economy. Reaches a maximum about 2030 and begins to decline - probably because the food supply started to decrease 10-20 years earlier.
2 = Blue = Food Supply: The agricultural sector grows and begins to increase food per person, but begins to decrease sharply at 2015.
3 = Black = Industrial output: Grows until a combination of environmental (pollution = 4= red) and natural resource (5 = purple) constraints eliminate the capacity of the capital sector to sustain investment.
4 = Red = Pollution: Steadily increases as industrial output increases (3 = black) and...
5 = Purple = Nonrenewable resources: begins to decline more sharply after 2000. Eventually the lack of resources causes the industrial output (3 = black) to decrease.

In this Scenario 1, no extraordinary efforts are made to abate pollution or conserve resources. Both begin to increase rapidly.

when the graphs reach a peak or a maximum.
The world society will will collapse as the graph lines decrease. A stable sustinable society is reached if the graph lines become and remain more or less horizontal.

The objective of this exercise is to find a scenario where the graph lines become and remain horizontal.

Further explanation about Scenario 1:

Industrial capital begins to depreciate faster than new investment can rebuild it.
As it falls, food and health services also fall, decreasing life expectancy and raising the death rate.

In this scenario, shortly after 2010 the growth of the economy stops and reverses because of a combination of LIMITS.
1. Pollution rises high enough to effect land fertility.
2. Land erosion increases.
3. Economy shifts to more investment in agriculture.
4. Resource sector also beginning to sense limits and requires more investment.
5. Capital is diverted to producing more food and resources.
6. Less capital for other growth, cannot keep up with depreciation.
7. Capital plant begins to decline taking with it the food and service sectors.
8. For a short time population continues to rise.
9. Finally, increasing death rate, caused by lack of food and health services, causes population decline.

End Introduction and Start of Simulated Laboratory:

 This is finally, the start of the laboratory exercise. It would be most helpful for you to download the brief text file version of the questions and print a hard copy. You can write in the answers as you go along with the computer.  Brief Text report version
Then later open the text file in a word processor to type in the answers, and then finally email the anwers to the instructor.  Instructions to submit the files for grading.
 This exercise is not designed to be very hard. We are just looking for general trends in the graphs and changes in the graphs from one scenario to the next. To complete this exercise you will be applying elements of the scientific method. One scenario will serve as a "control", while the second scenario will have a change of one or more variables. By comparing the two or more scenarios, you will be able to draw conclusions about the cause and effect relationships of the variable changes.
 NOTE: The first several questions are mostly answered for you, just fill in the blanks. We are looking for things like increase, decrease, rise rapidly, stay constant, give an approximate year, etc. Eventually you will need to make your own intrepreations of the graphs in future questions.


Scenario 2: Doubled Resources - The number of estimated natural resources is doubled from the current "best" estimate.

Since the amount of nonrenewable resources still to be discovered are simply unknown, the model can be used to test this range of uncertainty. In this scenario it is assumed that there are twice as many resources waiting to be discovered than were assumed in Scenario 1.
QUES. 1: What if more resources are actually available than current estimates predict? (Fill in the blanks below for answer)
 Compare Scenarios 1 and 2. Scenario 1 Graph
Scenario 2 Graph
Compare Scenarios 1 and 2 all on one graph.

a. When comparing Scenarios 1 and 2, the resources (purple) last considerably longer, but the general behavior of the model is still overshoot and collapse, just delayed by 30-40 years.
Additional resources allow industry (black) to grow _____ years longer in Scn 2 than Scn 1, which in turn causes pollution (red) to be ____ times higher and peak ____ years later.
b. In Scn 2, population (green) rises to more than 9 billion in 2040, which in turn increases the pollution to _______ levels than in Scn 1. The greater pollution has a greater impact on the food supply (blue), causing it and population (green) to _____ more sharply than in Scn 1. The higher pollution reduces land yield and forces much greater investment in agriculture. Eventually declining food raises the death rate to decrease the population.

Scenario 3: Doubled Resources and Pollution Control Technology
Allocate capital to bring pollution to 1975 levels. 20 year lag time.

In scenario 2, growth was ended by a pollution crisis. What if the simulated world responded by making a determined investment in pollution control technology?

In scenario 3, and all further runs, we assume double resources and apply one variable change at a time.

In scenario 3, we have assumed that in 1995, long before pollution rises high enough to cause measurable damage, the world decides to bring pollution down to 1975 levels and systematically allocates capital to achieve that goal.

Pollution control technology is applied at the "end of the pipe" approach to control emissions, rather than reducing throughput at the source. It reduces pollution emitted by up to 3% per year until brought down to 1975 level. It is also assumed that it takes 20 years for any new pollution abatement technology to be developed and installed worldwide.

 QUES. 2: What is the effect of applying all pollution control technologies? Fill in the blanks below.
 Compare Scenarios 2 and 3 Scenario 2 Graph
Scenario 3 Graph
Compare Scenarios 2 and 3 all on one graph.

a. In this scenario, pollution continues to rise in spite of the abatement programs, because of the delays in implementation and continued growth in agricultural and industrial production. Scenario 3 has pollution control technology, pollution (red) stays ______ than in Scenario 2, but it does reduce land fertility after about 2015.

b. In Scn 3, population (green) continues to grow to about the same level at 2050, but does not ____ as drastically. In Scn 3, food (blue) stays at ______ levels as in scenario 2.

c. In Scn 3, total industrial output (black) peaks by 2035 at a _____ level than in scenario 2, because so much capital has been pulled into agricultural, resource, and pollution sectors.

Scenario 6: Double Resources, Pollution Control Technologies, Land Yield and Erosion Control Technologies, and Resource Efficiency Technology.

In this scenario, double resources are assumed, as well as a variety of advanced technologies including pollution control already described.
Land yield technologies are applied in 1995, well in advance of a global food crisis, new technologies such as genetics, more fertilizer, and pesticides are applied. Capital inputs are needed to achieve a 2%/year increase in land yields. This implies a 7 times increase in 100 years!! The model tries to reduce land erosion by a factor of 3.
A final program of resource efficiency technology is instituted to reduce the amount of nonrenewable resources needed per unit of industrial output by 3 % per year until total resource consumption decreases to the approximate 1975 level.

 QUES. 3: What is the effect of applying all advanced technologies possible? Fill in blanks below for the answer.

Compare Scenarios 2 and 6. Scenario 2 Graph
Scenario 6 Graph
Compare Scenarios 2 and 6 all on one graph.

a. In Scn 6, this combination of technologies permits the simulated world economy to go on growing smoothly until ______ years.
b. In Scn 6, nonrenewable resources (purple) are depleted more ________ than in Scn 2; their cost remains low. Industrial output (black) peaks at _____ year and then begins to ______ more slowly.
c. Food production (blue)_____ steadily, but pollution gets high enough to depress land fertility, but its effect can be overcome by additional agricultural inputs.
d. Population (green) appears to become almost ______ by the year 2100. Eventually death rates rise to equal birth rates.
Although right at the edge of the graph at 2100, more gradually but still inevitably, the world over shoots its limits. It cannot maintain living standards, population and food will begin to fall following the decrease in industrial output.

Scenario 8: Stabilize World Population at 2 children per family in 1995.

Suppose that, starting in 1995, all couples in the world understood the implication of further population growth for the welfare of their own children. All couples decide to limit their family size to two children on the average. All available fertility control technologies are readily available to achieve the desired family size.
If just this change in population growth were made and no others for this scenario 8 compared to Scenario 2.

QUES. 4: What happens if the population is controlled and no other things are changed? (Fill in the blank below)

 Compare Scenario 2 and 8 Scenario 2 Graph
Scenario 8 Graph
Compare Scenarios 2 and 8 all on one graph.

As a result the world population continues to grow moderately to 7.4 billion in 2040.

a. In Scn 8, surprisingly, industrial output (black), pollution (red), and food supply (blue) all peak at the ________ time and collapses (graph lines go down) at roughly the_____ time as in Scenario 2 for the same reasons. The larger industrial plant emits more pollution and use more resources.
b. Given the present limits and technologies as seen in Scn 8, the world _______ sustain 7.4 billion people with an ever increasingly per person industrial output.

Scenario 10: Stabilize Population; All Technologies from Scenario 6 and Moderate Industry and Lower Standard of Living; apply controls in 1995 with 20 year lag time.

In Scenario 10, population growth and all of the control technologies: pollution, land yield, erosion control, and conservation of resources - all developed in Scn 6 are applied together. In addition a new goal is for a more simple but adequate material standard of living. The mind set is changed from pursuing an ever-accumulating material wealth. The world has decided to aim for an average consumer goods per person of the 1968 level of $350 per year. This is equivalent to South Korea or twice the level of Brazil in 1990.

 QUES. 5: What happens if all advanced technologies are applied, as well as, population control, and moderate standard of living? (Fill in the blanks below.)

 Compare Scenarios 2 and 10. Scenario 2 Graph
Scenario 10 Graph
Compare Scenarios 2 and 10 all on one graph.

a. The result of scenario 10 is what might happen in a sustainable world society. Population (green), food (blue), industrial output (black) graph lines are _______________ after about 2030. For the first time we see that a more restrained society is at a rough state of equilibrium. Capital does not have to go either toward further growth or to offset a spiraling set of problems. A population of just under 8 billion lives at a reasonable standard of living.
b. In Scn 10, nonrenewable resources deplete _________ so that more than half are still present at 2100 conmpared to Scn 2.
This is a picture of a SUSTAINABLE SOCIETY. The graph lines show _______ trends. Society is expending considerable effort to protect the land, reduce pollution, and use nonrenewable resources highly efficiently.

Scenario 7: All advanced technologies from Scenario 6 with lag time of only 5 years instead of 20.

The normal time lag for complete implementation of a new technology is about 20 years. Each of the previous technologies: pollution control, land yield, erosion control, and resource use reduction are implemented world wide in 1995. Each new device is installed around the world in only 5 years instead of 20 years.
The simulated world is foresighted, highly technical, and frugal.

 QUES. 6: What if technologies are brought on faster with delay reduced from 20 years to five years?
Compare Scenario 6 and 7.

 Compare Scenario 6 and 7.  Scenario 6 Graph
Scenario 7 Graph
Compare Scenarios 6 and 7 all on one graph.

Discuss the results following the model answers from previous questions.

What if technologies are brought on faster with delay reduced from 20 years to five years?

Scenario 11: Stabilize Population; All Technologies from Scenario 6 and Moderate Industry and Lower Standard of Living; apply controls in 1975 with 20 year lag time.

What is the difference in applying sustainability policies 20 years sooner?
Scenario 11 is exactly the the same as in Scenario 10, except that the policy changes were all applied in 1975 rather than 1995. This is 20 years backwards in time, a future that might have been, but is no longer available.

Scenario 12 Stabilize Population; All Technologies from Scenario 6 and Moderate Industry and Lower Standard of Living; apply controls in 2015 with 20 year lag time.

What happens if further delays occur before sustainable policies are adopted and put into effect? Twenty years forward to 2015 will make a big difference if you remember the mathematics of exponential growth. By that time it may be too late to avoid some very serious problems.

Compare: Scenario 11 - all controls in 1975

Scenario 10 - all controls in 1995

Scenario 12 - all controls in 2015

 QUES. 7: a. Discuss and compare the results of these three scenarios.

b. What is the effect of the starting time on the implementation of all policies with a 20 year lag time?

c. What happens if we wait too long to apply controls?

 Compare Scenarios 10, 1l, and 12: Scenario 11 - all controls in 1975
Scenario 10 - all controls in 1995
Scenario 12 - all controls in 2015
Compare Scenarios 10, 11, 12 all on one graph.

Scenario 13: Stabilize Population; All Technologies from Scenario 6, but with Higher Goals (Standard of Living) for Food and Industry Output; apply controls in 1995 with 20 year lag time.

What happens if the model society aims too high in the goals for standard of living? This scenario is directly comparable to scenario 10. The difference is the goal for food per person is set 50 % higher and the goal for consumer goods per person is set at about 3.5 times the 1990 world average.

 QUES. 8: a. What happens if the standard of living is too high and requires excessive industrial output?
b. Will the world be able to sustain a higher standard of living as in Scn 13? Explain.

 Compare Scenarios 6, 10, and 13. Scenario 10 Graph
Scenario 13 Graph
Compare Scenarios 6, 10, and 13 all on one graph.

Discuss the results.


QUES. 9: Which worldview is supported by by the assumptions in this computer model of the world? Explain.

 QUES. 10: Which worldview most closely corresponds to your own view point? Explain how you view some of the issues such as the use of resources, population control, and the use of the nature.

Brief Text report version

1. Meadows, D.H. & Meadows, D.L., et al, "The Limits to Growth", New American Library, 1972.

2. Meadows, D.H. & Meadows, D.L., Randers, J., "Beyond the Limits", Chelsea Green Publishing Co., 1992.

3. Graphs from STELLA II software, World3 Model.