Chapter 3 – The Big Picture: Systems of ChangeChapter 3 – The Big Picture: Systems of Change

Chapter OverviewChapter Overview

Environmental science is essentially the study of changes in systems over time. Those changes may occur naturally or may be induced by humans. As you investigate environmental problems you should begin to appreciate the complex and far-reaching interactions that can result.

• Why do solutions to environmental problems involve the study of systems and rates of change?

• How positive and negative feedback operate within environmental systems.

• What are the implications of exponential growth and doubling time?

• What is the role of natural disturbances and changes in systems such as forests, rivers, and coral reefs?

• How human activities influence natural system and can amplify the effects of natural disasters.

Key Topics

• Systems and Feedback (3.1)

• Negative feedback (3.1)

• Positive feedback (3.1)

• Exponential Growth (3.2)

• Environmental Unity (3.3)

• Uniformitarianism (3.4)

• Equilibrium in Systems (3.5)

• Average Residence Time (3.5)

• Introduction to Ecosystems (3.8)

• Difficult Nature of Solving Environmental Problems (3.9)

Correlation to AP Environmental Science Exam

• Multiple Choice 1998 #85 complex interaction #90 positive feedback

2003 #69, 83, 96 complex interactions

• Free Response

1998 #4 solving environmental problems (land use)

1999 #4 solving environmental problems (pesticides)

2000 #2 solving environmental problems (recycling)

2002 #2 solving environmental problems (water diversion)

#4 solving environmental problems (El Nino)

2003 #3 solving environmental problems (wetlands)

Sources of Labs and Activities to Reinforce Key Topics

• Labs/Activities on line at the Environmental Literacy Council website

www.enviroliteracy.org (Go to Environmental Science Teacher Exchange)

With in section “Basic Concepts” consider the “Sustainable Island”

activity. (Note: Some instructors approach this activity as an introduction

to the complex interactions of environmental issues, other prefer to

incorporate this activity within a unit on resource use.)

“Tragedy of the Commons Lab” from Tori Haidinger and Wendy Van Norden

“Thermodynamics” from John Pritchard

• Labs/Activities on line at the College Board website

www.collegeboard.com (Go to AP Central. After login go to APES Lab

and Field Activities.)

“Tragedy of the Commons Lab” from Tori Haidinger and Wendy Van Norden

Case Study: Management of Amboseli National Park in Kenya

● Nature is organized into systems of increasing complexity ranging from atoms to molecules to cells, organs, organisms, populations, communities, ecosystems, landscapes to the biosphere. As the level of complexity increases, the behavior becomes increasingly difficult to predict. The scientific method has been dominated by a reductionist approach in which we attempt to understand a complex system by breaking the problem down into smaller and smaller parts on the assumption that if we can understand the small parts, then we can understand the whole. But the whole is often greater than the sum of its parts. A through understanding of oxygen and hydrogen will not equip you to predict the behavior of a molecule of water. Management of Amboseli National Park in Kenya provides an example of a complex system involving people, their management of the land, changing climate, and the conversion of woodlands into short grass and brush. Natural wet and dry cycles appear to account for the changes in vegetation, though overgrazing and damage to trees by elephants are also factors. There is now a recognition that reductionism must be complemented by a holistic approach.

3.1 SYSTEMS AND FEEDBACK

• A system, generally speaking, may be defined as a set of components or parts that function together to act as a whole. Some systems can be physically isolated (chemicals in a test tube), or isolated in our minds or in a computer. A single organism, a car, a university, and a state are all examples of systems. Systems can be closed, e.g. the earth is a closed system with respect to water, or systems can be open, e.g. the earth is an open system with respect to energy.

• Systems respond to inputs and have outputs. The responses are known as feedback.

• Positive feedback occurs when the output also serves as input that amplifies the output. A forest fire can display positive feedback.

• Negative feedback occurs when the output serves as input that diminishes the output. Negative feedback tends to be stabilizing; it maintains the status quo. Your response to a change in temperature (the input) is a good example of negative feedback. If air temperature increases your body reduces its temperature (the output) by producing sweat, if air temperature decreases you body warms itself by shivering.

3.2 EXPONENTIAL GROWTH

• Exponential growth is a good example of positive feedback. When the growth rate of a population is proportional to the size of the population, then the population size will increase exponentially. You may discuss the technical aspects of exponential growth here (Working It Out 3.1), or defer to the lecture on population growth in Chapter 4.

3.3 ENVIRONMENTAL UNITY

• One feature of systems is that the parts that make up the system are connected. Consequently, when one part of the system changes, another part of the system responds. This is the concept of environmental unity, that is, it is impossible to change one part of a system without affecting the other parts. A food web provides a clear example of this.

3.4 UNIFORMITARIANISM

• The present is a key to the past. The principle that physical and biological processes presently forming and modifying earth can help explain the geological and evolutionary history of earth is known as uniformitarianism. This is an extremely important concept that we use frequently. A great example that has been in the news recently is the search for evidence of water on Mars.

3.5 CHANGES AND EQUILIBRIUM IN SYSTEMS

• When the output of a system is equal to its input, the system is said to be in steady state. If the inputs and outputs are not balanced, then the size of the reservoir will either grow or decline.

• Residence time is a measure of the time it takes for any part of the system to cycle through the system. It is calculated by taking the total pool size and dividing by the rate of transfer through the pool. See Working It Out 3.2.

• Residence time is a concept that gives us important information about how quickly systems can respond to changes in input or output. For example, an increase in the rate of discharge of pollution into the ocean is not likely to change the water quality of the ocean very quickly, but if the quality of water in the ocean water is changed, the recovery will be very slow.

3.6 EARTH AND LIFE

• Life on earth began over 3 billion years ago. The earliest ecosystems were composed entirely of microbes. From those humble beginnings complex life forms have evolved. Probably humans are the most significant organisms to dominate the planet, but in terms of evolutionary time our tenure has been brief.

• The fossil record teaches us that extinction is the ultimate fate of all species. Humans have accelerated the extinction rate and threaten the very life support system upon which people depend. However, the fossil record also teaches us that life on planet Earth will survive, possibly with a very different group of species, with or without us.

3.7 EARTH AS A LIVING SYSTEM

• The earth itself is a system of biological communities interacting with each other and with the earth’s hydrosphere, geosphere, and atmosphere. If you reduced the earth down to the size of an apple, the region that supports life, including the atmosphere would be about the thickness of the peel. This thin film of life, i.e. the space in which life occurs is known as the biosphere. The group of all living things that inhabit a particular area, be it a pond or the entire earth, is known as the biota.

3.8 ECOSYSTEMS

• Ecosystem: a community of different species interacting with one another and with the chemical and physical factors that make up their local nonliving (abiotic) environment (energy and matter). It is a level of biological organization that includes all of the functional groups (primary producers, herbivores, carnivores, detritivores) necessary to sustain life. An ecosystem is a level of biological organization. The size is somewhat arbitrary - except that it needs all of the biotic and abiotic structure (parts) to sustain life.

● The Gaia hypothesis states that the conditions on earth are maintained by the earth’s biota in a state that is optimal for life. This has been an exceedingly controversial idea, advanced originally by James Lovelock and Lynn Margulis, because some scientists object to what they see as a teleology that cannot be explained by natural selection. However, supporters of Gaia cite feedback mechanisms that operate on a global scale and that explain how the biosphere functions as a single system with negative feedback. Maintenance of O2 in our atmosphere, at 20% by volume, is a great example. If the concentration rises, spontaneous fires will reduce the concentration (negative feedback), if the concentration falls then respiration rate will fall and O2 will rise (negative feedback).

3.9 WHY ENVIRONMENTAL PROBLEM SOLVING IS DIFFICULT

• Our environment is a large and very complex system. It displays behaviors that are difficult to predict and even difficult to react to.

• Systems undergoing exponential growth, like the human population, are difficult to control and produce positive feedbacks that have unintended consequences.

• The responses of our environment to human activities, including regulatory activities are often delayed by lag times that make responses difficult to recognize. This can lead to systems overshooting a target followed by collapse, such as a population overshooting its carrying capacity.

• Systems can change in ways that are not always reversible. Desertification provides a good example of an irreversible process that is initiated by people who remove the vegetation from semi arid landscapes.

Critical Thinking Issue. Is the Gaia Hypothesis Science?

• Gaia hypothesis: The earth’s biota manipulates the environment in a way that perpetuates life. Life on this planet has greatly altered the chemistry of the planet. The life on planet earth is capable of physiological self-regulation. The planet has evolved from a primordial state in which there was no oxygen in the atmosphere to its present state that is not in thermodynamic equilibrium. If life on this planet was somehow completely eliminated, the oxygen content of the atmosphere would decline, and the conditions in general would probably be like an interpolation between present day conditions on Venus and Mars, our nearest neighbors. A distortion of the Gaia hypothesis is that life deliberately or consciously controls the global environment. This is not a belief accepted by scientists.

• ORIGINAL ATMOSPHERE

• Methane, nitrogen, hydrogen, ammonia- Stanley Miller passed a spark through this, simulating lightning, and showed that from this mixture organic molecules would form (AMINO ACIDS)