What Are Coupled Human-Environment Systems?

What Are Coupled Human-Environment Systems?

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As the concept of the human-environment landscape clearly shows, humans impact the environment, and the environment impacts humans. These impacts happen in many different ways. In other words, there are very many interactions between humans and the environment. In order to help us keep track of all these interactions, and to learn from them, it is very useful to use asystems perspective. This means treating humans and the environment as systems: the human system and the environmental system. We could even treat them as one combined human-environment system.

What is a system? In simple terms, it is a collection of components that interact with each other to form some aggregated whole. For example, this course is a system. It has many components, including the modules, the course project, the instructor, and the students. These components all interact with each other to form the course. The components can also be thought of as systems. For example, this module has several web pages, some supplemental readings, and a learning activity at the end. Each of these module components can be thought of as a system, too.

To help us visualize and understand systems, it is often helpful to use a system diagram.A system diagramdisplays the system’s components and the interactions between them. In a system diagram, we put short descriptive phrases (not sentences) in boxes to represent the components that make up the system. Interactions between the components are often symbolized by arrows pointing in a logical direction. Sometimes we also place single words or short phrases along the arrows to explain the nature of these interactions.

Here is a very simple system diagram showing a human-environment system in which humans and the environment both impact each other:

FIgure 2.2 Human-Environment System Diagram: Both humans and the environment impact each other. Note the arrow from the Environment box to the Humanity box - and the arrow from the Humanity box to the Environment box with the wordaffectsnext to each arrow.

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Here is another system diagram. This one is slightly more complicated. It shows the relationships between different components of GEOG 30.

Figure 2.3Relationships Between Different Components of GEOG 30 System Diagram: Students, Instructor, Project, and Modules are all components of GEOG 30. Therefore, an arrow points from the Students box, from the Instructor box, from the Project box and from the Modules box to the GEOG 30 box. Web Pages, Readings and Learning Activity are all components of Modules. Therefore, an arrow points from the Web Pages box, the Readings box, and the Learning Activity box to the Modules box.

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Note that the arrows in the two system diagrams appear to have different meanings. In the first diagram (Figure 2.2), the arrows represent impacts. Here, A → B means “A impacts B”. In the second diagram (Figure 2.3), arrows represent components. Here, A → B means “A is a component of B”. However, we can also interpret the arrows in the second diagram as representing impacts. It is certainly the case that the web pages, readings, and learning activities impact the modules. Usually the arrows refer to impacts, but we should always pay attention to make sure we’re interpreting a system diagram properly.

Now that we have some a basic familiarity with systems, let’s take a closer look at the concept of human-environment systems. This concept is developed very well in Gerry Marten’s online textbook Human Ecology. This textbook has excellent discussions of other aspects of human-environment systems that could serve as a helpful resource for you if you need it.

Reading Assignment: "What is Human Ecology?"

Here, please read just the first section, “What is Human Ecology?” The second section covers sustainable development, which we’ll return to later.

• Marten, Introduction:What is Human Ecology?(link is external)

As you’re reading this first section, think about how systems are being used to describe humanity, the environment, and interactions between them. Here are some more questions to think about as you read:

• What, according to this reading, is the relationship between humanity and the environment?
• What are some components of the human system and the environment system? How do these components interact?
• What are the specific examples of human-environment systems being presented? What are the components, and how do they interact?
• If you were given a story about a human-environment system, could you draw a system diagram for it? Hopefully you can, since you’ll be asked to do exactly this as part of the course!

Feedback Mechanisms

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What are feedback mechanisms and how do they work?

Let’s revisit that very simple human-environment system diagram from the "What are coupled human-environment systems?" page:

RevisitingFigure 2.2 Human-Environment System Diagram: Both humans and the environment impact each other. Note the arrow from the Environment box to the Humanity box - and the arrow from the Humanity box to the Environment box, with the wordaffectsnext to each arrow.

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The diagram in Figure 2.2 shows that humanity impacts the environment, and that the environment impacts humanity. But if the environment impacts humanity, then that can in turn impact how humanity impacts the environment, which can in turn impact how the environment impacts humanity. So this diagram is perhaps not as “very simple” as it might initially appear!

This phenomenon of system components both impacting each other creates afeedback loop. Feedback is impact to a system component that is a consequence of an action performed by that component. For example, suppose you take the action of writing an email to the instructor, asking a question about the course. The email you get back is a feedback. A loop is a circumstance in which system components impact each other, such that an action by a component affects subsequent performances of that action. This circumstance has a circular, loop-like appearance in a system diagram, as seen in the diagram above.

There are two basic types of feedback: positive and negative. Apositive feedback loopis a circumstance in which performing an action causes more performances of the action. For example, suppose that every time you e-mailed the instructor with a question about the course, the instructor wrote back with an e-mail so confusing that you had even more questions about the course, which cause you to write two e-mails back for more clarification. This would be a positive feedback loop.

Anegative feedback loopis a circumstance in which performing an action causes fewer performances of the action. For example, suppose that every time you e-mailed the instructor with a question about the course, the instructor wrote back with an e-mail that clarified the course for you, so that you had fewer questions about the course and thus wrote fewer e-mails for clarification. This would be a negative feedback loop.

It is important to understand that for feedback loops, the terms positive and negative do not mean good and bad. A positive feedback loop can be a bad thing, and a negative feedback loop can be a good thing, or vice versa. Whether or not any given feedback loop is positive or negative is ultimately an ethical question. We’ll cover ethics in Module 3.

Self-check

Now that you have read a bit about what feedback loops entail, here are a few multiple choice questions that will test your understanding of the differences between what a feedback loop is, and whether it is positive or negative feedback. These should be very simple questions and the purpose here is to give you some confidence in understanding this material so far.

Think About It!

Come up with an answer to these questions by yourself and then click below to reveal the answer.

1. An arms race is an example of:

a. Positive feedback
b. Negative feedback
c. Neither

Click for answer...

2. Exponential population growth is an example of:

a. Positive feedback
b. Negative feedback
c. Neither

Click for answer...

3. Body temperature control is an example of:

a. Positive feedback
b. Negative feedback
c. Neither

Click for answer...

4. Population regulation is an example of:

a. Positive feedback
b. Negative feedback
c. Neither

Click for answer...

Carrying Capacity

As the Self-check indicates, population change can involve either positive or negative feedback loops. When population is growing exponentially, there is a positive feedback loop: more children bring more parents, which in turn bring even more children, and so on:

Figure 2.4 Parents and Children System Diagram: Parents give birth to children who grow up to be parents who give birth to children...Note the arrow from the Parents box to the Children box (with+and the wordsGiving Birthnext to the arrow). Also note the arrow from the Children box to the Parents box (with+and the wordsGrowing Upnext to the arrow).

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The plusses here signify that each set of parents brings more children, and each group of children brings more parents. If the birthrate is constant over time, and if each generation is larger than the previous, then there will be exponential population growth, as shown in Figure 2.10 in the Marten reading“What is Human Ecology?”But population can’t maintain exponential growth forever. To do so would require an infinite amount of resources, but we live in a finite world. Here’s where the negative feedback loop comes in. The resources provide sustenance to the population: food, water, energy, or whatever other resources are being used. As the population runs out of resources, it can’t have as many children – or, the children can’t grow up to become parents.

Figure 2.5 Individuals and Resources System Diagram: Individuals consume resources which are needed to provide sustenance for more individuals who then consume more resources...

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Note that the 'Individuals' box has an arrow pointing to the 'Resources' box. The word 'Consumption' is next to the arrow. There is also a minus sign next to the arrow. The 'Resources' box has an arrow pointing to the 'Individuals' box. The word 'Sustenance' is next to the arrow. There is also a plus sign next to the arrow.

The + here signifies that more resources bring more individuals, since individuals need resources to survive. The - here signifies that more individuals bring fewer resources, since a larger population will consume more, leaving fewer resources available for anyone else. If a population continues to grow exponentially for long enough, eventually it will hit a point where there aren’t enough resources for it to continue growing. At this point, the population has reached the largest size that the resources permit. This size is called thecarrying capacity.

It is important to understand that the carrying capacity refers to the largest population that can be sustained over the long-term. Carry capacity is not constant and varies over time in response to changes in the environment. For example, disturbances from extreme natural events (e.g., volcanic eruptions) and human activities (e.g., pollution) can alter the environment to a great extent and consequently influence carrying capacity.

A population can temporarily exceed the carrying capacity. For example, imagine a population of rabbits that lives off of carrots. The rabbits have to leave enough carrots in the ground each year so that they will have enough carrots to eat the following year. The carrying capacity is thus the largest number of rabbits that can live one year while still leaving enough carrots left over for the same number of rabbits to live the following year. The rabbits could exceed the carrying capacity one year, but then there wouldn’t be enough carrots the following year. To exceed the carrying capacity is calledovershoot, as seen in Figure 2.11 of the Marten reading“What is human ecology?”Overshoot is followed by a major decline in population.

Reading Assignment: The St. Matthew Island Reindeers

A vivid example of population overshoot is found in the story of the reindeer that briefly lived on St. Matthew Island off the coast of Alaska. Please read the story in the following article:

When Reindeer Paradise Turned to Purgatory(link is external), Article #1672,Alaska Science Forum, November 13, 2003, by Ned Rozell

As you read this, consider the following questions. When and why did the population crash occur? How could it have been prevented? Is the human population destined for the same fate? Why or why not?

A graph showing the reindeer’s exponential population growth and dramatic decline can be found here at the top of David Klein's article on the same incident. Please examine this graph.

“The Introduction, Increase, and Crash of Reindeer on St. Matthew Island(link is external)” at greatchange.org

As you examine the graph, consider how the graph relates to the story and to the concept of feedback mechanisms within a system.

Note that the greatchange.org link is an html version of a published journal article. Here is the reference:

David R. Klein, “The Introduction, Increase, and Crash of Reindeer on St. Matthew Island,” Journal of Wildlife Management, Vol. 32, No. 2 (Apr., 1968), pp. 350-367.

[The original version of this article is available via Penn State e-journals via JSTOR.] You don’t have to read the journal article, but it may be worthwhile to glance through it to see a classic academic article on population ecology.

Carrying Capacity and Sustainability

Carrying capacity is closed related to sustainability.Sustainabilityis, in the simplest terms, the ability for something to be sustained. If that something is a population, then for it to be sustained, it cannot exceed the carrying capacity of the system it’s living in. This is just a brief introduction to the idea of sustainability. There is a lot more to it. We’ll cover sustainability in more detail in the ethics module.

A key question in GEOG 030 – perhaps the key question – is whether today’s human population is sustainable. Answering this question requires comparing the human population to Earth’s carrying capacity for humans. But this is not an easy answer to provide! One reason is that the global human-environment system is very complex. Another reason is that human activity is changing the carrying capacity, in both positive and negative ways. Many of the new technologies that we develop enable us to support larger populations, thereby increasing the carrying capacity. Some things we do such as unchecked timber harvesting deteriorate our resource base, lowering the carrying capacity. Given all this, no one is sure just how many people can be sustained on Earth over the long term. But we can get some important insights by studying human-environment systems, as we do in this course.

It is worth noting that the global human population has not been exactly following an exponential growth curve. Across the planet, population growth rates have been declining. In some countries such as Italy, Russia, and Japan, population growth rates are negative, meaning that the populations are declining. This phenomenon of declining population growth rates is known as thedemographic transition, in which populations transition from:

1. high birth rates and high death rates to
2. high birth rates and low death rates, as health conditions improve, to
3. low birth rates and low death rates.

Resilience and Stability

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On the previous page, we saw that the idea of carrying capacity is closely related to the idea of sustainability. Here we’re going to explore another closely related idea: resilience.Resilienceis a property of systems related to how a system responds to a disturbance or stressor. In rough terms, the more resilient a system is, the larger a disturbance it can handle.

To understand resilience with more precision, we need to first understand the concept of system state. A system’s state is the general configuration that it is in. For example, if we think of a glass jar as being a system, then smashing the jar into little pieces would be a change to the system’s state. Or, if we think of a farm as being a system, then neglecting the farm for so long that it grows into a forest would be a change to the system’s state.

What qualifies as a state change depends on how we define the system. There are often many ways of defining a system, so there will also be many ways of defining its states and changes to them. We should have the mental flexibility to imagine systems and states being defined in different ways, so that we can define them in ways that are helpful for our purposes, and so that we can understand how other people are defining them.

Given this understanding of system state, we can now define resilience with more precision.

Resilience is the ability of a system to return to its initial state after a disturbance.

This means that if a disturbance is so large that it exceeds the system’s resilience, then the system will enter into a new state. For example, if a glass jar is thrown at a wall with enough force, it will smash into little pieces. The jar’s resilience is thus the size of the impact it can withstand without smashing.

This definition of resilience is often represented using the metaphor of a ball in a basin. If the ball is pushed a little bit, it will return to the bottom of the basin, i.e., to its initial state. If the ball is pushed hard enough, it will leave the basin and eventually settle somewhere else, i.e., in an additional state. The height of the basin thus corresponds with resilience: the higher the basin, the harder of a push the ball can withstand and still return to its initial state: