What Are Coupled Human-Environment Systems?

PrintAs 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 a systems 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 diagram displays 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 word affects next to each

arrow.

Credit:

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

Figure 2.3 Relationships 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.

Credit: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 MechanismsPrint

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:

Revisiting 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 word affects next to each arrow.

Credit: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 a feedback 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. A positive feedback loop is 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.A negative feedback loop is 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-checkNow 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 feedbackb. Negative feedbackc. Neither

Click for answer...2. Exponential population growth is an example of:

a. Positive feedbackb. Negative feedbackc. Neither

Click for answer...3. Body temperature control is an example of:

a. Positive feedbackb. Negative feedbackc. Neither

Click for answer...4. Population regulation is an example of:

a. Positive feedbackb. Negative feedbackc. Neither

Click for answer...Carrying CapacityAs 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 words Giving Birth next to the arrow). Also note the arrow from the

Children box to the Parents box (with + and the words Growing Up next to the arrow).

Credit: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...Credit:

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 the carrying 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 called overshoot, 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 ReindeersA 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 SustainabilityCarrying capacity is closed related to sustainability. Sustainability is, 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 the demographic 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 StabilityPrint

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. Resilience is 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:

Figure 2.6 Resilience and State: The metaphor of a ball in a basin.Picture credit: Yooinn Hong

Is Resilience Good?Resilience is often viewed as a good thing. If an ecosystem is resilient, or if human society is resilient, then they will be quite capable of withstanding the disturbances that they face. For any system to sustain any particular state, then the system cannot experience any disturbances that exceed its resilience for that state. Thus resilience, like carrying capacity, is closely related to sustainability. This is why we see efforts to enhance resilience from groups like the Resilience Alliance (link is external) . They would like for our human-environment systems to be sustained.

But whether or not resilience actually is good is an ethical question, and the answer is not automatically yes. We’ll discuss ethics further in Module 3, but for now, consider this. A terrorist network might be resilient if it can withstand many attacks or other efforts to destroy or disrupt it. Likewise, a dangerous pathogenic virus might be resilient if it can withstand many antiviral medicines or other measures that we take to curtail the virus. In these two cases, do you think that resilience is a good thing? At a minimum, we can imagine that in these cases, some people might reasonably consider resilience to be bad. So, while resilience is certainly an important concept and may often be considered a good thing, we should not blindly assume that it always is.

StabilityAn important concept related to resilience is stability. Stability refers to the disturbances a system faces. If there are few disturbances or small disturbances, then the system is relatively stable. If there are many disturbances or large disturbances, then the system is relatively unstable.Stability is a very important concept in agriculture. We would very much like it if our farms would yield (produce) about the same amount of food each year, because in general we eat about the same amount of food each year. If there is an unusually large food yield one year, this can cause complications but is typically not a huge problem. However, if there is an unusually small food yield one year, then this can be a huge problem. A famine can ensue, and people can die. In the agriculture module, we’ll examine yield stability in more detail. There, we’ll consider the Irish Potato Famine, which occurred in the mid-1800s. This was a case of extreme instability in food yield, which had disastrous consequences.

One might think that a resilient system would be one with more stability. However, this is not always the case. Sometimes, some instability can help increase resilience. This occurs when the disturbances increase the system’s ability to respond to further disturbances. For example, think of our bodies as systems. If we don’t exercise a lot, then we can’t do much exercise before we collapse. However, as we get more exercise, then there is an increase in our ability to withstand further exercise without collapsing. Here, the exercise is a disturbance, and collapsing is sending our bodies into a different state. As we exercise more, our bodies get less stability but more resilience. This often happens with other systems, too.

‹ Feedback Mechanisms up

Population, Affluence, and TechnologyPrint

Now that we’ve covered resilience, let’s return to the question of how humans impact ecosystems. These impacts are often very strong – often strong enough to exceed the systems’ resilience. Here, we’re going to explore the relationship between the makeup of a human population and its impact on ecosystems.

The IPAT Equation: I = P x A x TA classic idea about the relationship between a human population and its impact on the environment is the IPAT equation. The equation maintains that impacts on ecosystems (I) are the product of the population size (P), affluence (A), and technology (T) of the human population that is impacting it.

Reading Assignment: "Too Many People, Too Much Consumption"To gain a more detailed understanding of the IPAT equation, please read the article:

“Too Many People, Too Much Consumption(link is external)” by Paul and Anne Ehrlich.The Ehrlichs are among those who initially developed the equation and remain strong supporters of it.

As you read this, consider what the equation means for human impact on the environment.

Which areas of the world will have the largest impact?

Also, note that the equation has been controversial. What parts of it – including how it is being used – do you agree or disagree with? Why?

We can gain a rough understanding of the geographic distribution of the PAT side of the equation by looking at a map of GDP (gross domestic product) density:

Figure 2.7 GDP Density: Map of the world's density of Gross Domestic Production. Europe, North America, China, and several other areas are highlighted as having the highest GDP.

Credit: Econobrowser(link is external)The map shows where economic activity is concentrated. This is a reasonable approximation for population times affluence, though it does not factor in technology. GDP is an important statistic, and it is important to remember that it is a measure of economic production, and not a measure of national wellbeing. One can have a high GDP and still not be well-off, for example, if the population is overworked, or if the environment suffers excessively. Finally, note that this is a (rough) map of the causes of environmental impacts. It is not a map of the impacts themselves. While the environmental impacts may be driven by human activities in these regions, the impacts often occur in different places, due to the globalized nature of both human and environmental systems. For example, economic activity in one place can cause the extraction of resources in other places, or cause pollutions which spread to other places.

Different Perspectives on IPATThe IPAT equation is simple, and it is in part this simplicity that makes it attractive and compelling as a way of understanding the relationship between human activity and environmental impact. But the equation is also controversial. Many people have criticized it, for a variety of reasons. One of the most vocal critics has been the economist Julian Simon.

Reading Assignment: part of "The Doomslayer"Please read part of the article:“The Doomslayer(link is external)” by Ed Regis, which was published in Wired Magazine.Read the text beginning “Still, that was a mere flash in the pan…” and stop at the paragraph beginning “A more perfect resolution of the Ehrlich-Simon debate could not be imagined…”

Consider the following, ... What Simon’s views on the IPAT equation are, and how they compare to Ehrlich’s.Simon is essentially arguing that human impact on the environment is not as large as some people suggest. This is an important aspect of the IPAT equation: if more population, affluence, and technology do not bring more environmental impact, then the equation does not hold. Simon won his bet with Ehrlich (as described in the Wired Magazine reading), so there must be some substance to Simon’s ideas. However, some of Simon’s analysis is questionable, such as his claim that few species are currently going extinct. Thus, when looking at these debates, it is important for us to be able to analyze the evidence and the arguments for ourselves, so that we can avoid making the same mistakes as others may be making.

Reading Assignment: part of "What Are You Optomistic About? Why?"Please read part of the following article by Ray Kurzweil:What Are You Optimistic About? Why?(link is external), by Ray Kurzweil.

Start from the beginning of the article and stop at the paragraph beginning “Almost all the discussions I've seen about energy…”

Consider what Kurzweil’s views on the IPAT equation might be, and how they compare to Ehrlich’s and Simon’s.Kurzweil is a famous inventor and futurist. He argues that future technologies will be able to address our environmental concerns. This argument raises an important point about the “T” in the IPAT equation. While some technology certainly does increase environmental impact, other technology decreases it. For example, coal power technology increase our greenhouse gas emissions, whereas solar power technology decreases emissions. To be more specific, some coal technology can decrease emissions, if it produces energy from coal more efficiently than other coal technology. Also, coal technology can reduce other environmental impacts, such as deforestation, if coal comes to be used for energy instead of wood or charcoal. So, technology impacts the environment in many ways – which is a good reason for us to maintain a systems perspective.

Figure 2.8 Coal Technology System Diagram: In this diagram, two arrows lead from the Coal Technology box, one to the Less Deforestation box and the other to the More

Greenhouse Gas Emissions box.Credit:

Kurzweil is arguing that technology can and will be developed so as to resolve some of our major environmental concerns. Is this true? Right now, it is very difficult to say. Technology is notoriously difficult to predict. While there probably will be at least some technological advances that decrease our environmental impact, we simply don’t know how successful this will be.

Reading Assignment: "Taking Population Out of the Equation"Please read the article:

“Taking Population Out of the Equation(link is external)” by H. Patricia Hynes, published by the Committee on Women, Population, and the Environment.Consider what Hynes’s views on the IPAT equation are, and how they compare to the others we have seen.Hynes is arguing that the IPAT equation has inappropriately focused attention on the world’s poor as causes of environmental problems. Hynes emphasizes a distinction between the environmental impacts of consumption that is necessary for survival and of consumption that is a luxury. Perhaps we should be more critical of luxury consumption. Hynes also

emphasizes the environmental impacts of military activity. It is true that the military has a large environmental impact. For example, the United States military consumes more energy than any other organization in the world(link is external). Finally, Hynes emphasizes the gender issues surrounding population, such as the ability of women to choose when to become pregnant. These are all important to keep in mind when considering both the IPAT equation and, more generally, human impacts on the environment.

‹ Resilience and Stability up We begin our discussion of climate change by considering the concept of planetary boundaries. The planetary boundary concept is a new one, originating in research released in 2009, but it is based on some classic concepts, in particular resilience at the global scale. In short, a planetary boundary is a limit to how much the Earth system can be disturbed without sending Earth into a new, unsafe state.

Video Assignment: Planetary BoundariesThe planetary boundary concept was introduced in 2009 by a group of international researchers lead by Johan Rockström of the Stockholm Resilience Centre.

Johan Rockstrom: Let the environment guide our developmentCredit: TED

As you watch the Johan Rockström video (link is external) , think about the following questions: What is the Holocene, and why does it matter to development/civilization?

Note that the Holocene began about 12,000 years ago. Why is this time significant?

What is the boundary for climate change?

So, humanity is pulling nitrogen from the atmosphere and converting it to other forms. How are we doing this? With what process? Why are we doing this?

Are the boundaries isolated issues or are they interrelated?

Details of the research project can be found at the Stockholm Resilience Centre website (link is external) .As discussed in the video, the Holocene is the most recent epoch of Earth’s history. For the last 12,000 years or so, conditions on Earth have been relatively stable. This can be seen in data from ice cores in Antarctica and Greenland:

Figure 9.1 Isotope Data for Antarctica and Greenland Ice CoresCredit: Work found at Wikimedia Commons (link is external)  / CC BY-SA 3.0 (link is external)

Note that in this graph, time proceeds to the left, meaning that today is at the left edge of the graph and points further to the right are further into the past. The graph shows concentrations of isotopes of hydrogen and oxygen at different times. Ice sheets build gradually over time; the chemical composition of a layer of the ice depends on the chemical composition of Earth’s atmosphere at the time. An ice core is a long cylinder that we remove from the ice sheet, giving us a sample of information about Earth’s atmosphere over long times. Ice cores are valuable sources of information about Earth’s history, which helps us understand how the Earth system works and, in turn, what Earth may be like in the future.The important point to understand from the ice core graph is that the last 12,000 years or so have been relatively stable on Earth. It is during this period of stability that human civilization emerged. No one knows for sure whether civilization would have emerged without this period of stability, but we have strong reason to believe that the stability played an important role. Stable conditions made developing agriculture much easier, since our ancestors could breed plants customized for stable local growing conditions. This may explain why – as we saw in Module 5 – agriculture emerged in several parts of the world within the last 12,000 years, but had not emerged anywhere else prior to then. For those of you interested in religion and its history, you might even ask whether it is a coincidence that in the Judeo-Christian tradition,

the world (and everything else) was created about 6,000 years ago… and that this tradition originated in the Fertile Crescent.

So, what does this all have to do with climate change? Simply put, climate change threatens to cross a planetary boundary, to put the Earth system into a new state, a state different from that in which civilization emerged. Our civilization remains highly customized to Holocene Earth. Climate change may force us to make major adaptations. At this time, it is uncertain whether civilization can survive climate change intact.

Intellectually, we’re going to need a lot of resources to understand climate change and what to do about it. That’s what the rest of this module is about.

The recycling decisions of the Xerox corporation could be either thought of as a common pool resource or as a private property resource. It depends on where and how these decisions are implemented.

While there could be some debate as to the correct order, here is the order we had as to the events that led to the collapse of the North Atlantic Cod industry:

Read more...(link is external)In Module 5, we watched a video by Hans Rosling about global development. Let’s begin our discussion of climate change by watching another Hans Rosling video (4:47) that covers similar ground.

Hans Rosling's 200 Countries, 200 Years, 4 Minutes - The Joy of Stats - BBC FourCredit: BBC

Notice that incomes and life expectancies around the world started increasing about 200 years ago. The United States and Great Britain were among the first countries to experience

increases. Other countries took more time, but, by now, there have been increases almost everywhere. Why is that? What happened 200 years ago that caused health and wealth to start improving?

The answer is the industrial revolution. As societies learned how to develop industrial processes to produce more for us, our health and wealth began improving. By now, industry is so deeply embedded in so many facets of our lives that it’s often difficult to imagine life without it. There are still plenty of people today who produce much of what they use – including food, clothing, and shelter – by hand, but these people are increasingly few. Suffice to say, they are also not the people who tend to find themselves taking online university courses.

Central to the industrial revolution and to contemporary industry is the use of fossil fuels: oil, coal, and natural gas. They are called “fossil” fuels because they are sources of energy that derive from living organisms that were alive a long time ago. Originally, the energy from fossil fuels came from the sun. Ancient plants and other organisms trapped the sun’s energy via photosynthesis. Some of that energy found its way into today’s fossil fuels and is released when we burn the fuels for our industry.

The use of fossil fuels is unsustainable because we are using fossil fuels much faster than they are regenerating. Fossil fuels regenerate on time scales of hundreds of millions of years, but we are burning them up in just a few centuries. We can’t keep using fossil fuels forever as we use them today. Eventually, something must change. Given how central fossil fuels are to our industry, and how deeply embedded industry is within our lives, the depletion of fossil fuel resources represents a major challenge for humanity.

But there is another challenge associated with our use of fossil fuels. These fuels contain more than just energy. They also contain certain matter that, when we burn the fuels, ends up in the atmosphere. Some of this matter is in the form of molecules known as greenhouse gases, for reasons we’ll explain shortly. Greenhouse gases are also released into the atmosphere when we chop down and burn trees and other living matter.

Humanity has burned so much fossil fuel since the industrial revolution that we have significantly changed the concentrations of greenhouse gases in the atmosphere. The most important change is of carbon dioxide (CO2). 400 years ago, before the industrial revolution, there were 280 parts per million (ppm) of CO2 in the atmosphere, meaning that 280 out of every one million molecules in the atmosphere was a CO2molecule. That might not seem like a lot, but it’s enough to make a big impact on the planet. Today, mainly because of burning fossil fuels (and also because of deforestation and a few other activities), there are about 380 ppm of CO2 in the atmosphere. That’s already a fairly large change, and we’re burning more fossil fuels now than ever before. If we burn all of the fossil fuels available on Earth, there could be about 1700 ppm of CO2 in the atmosphere, though we don’t yet know exactly how much fossil fuel exists across the planet. This is a very major change from the pre-

industrial atmosphere, and a frightening thought, given that researchers believe that just 350 ppm may be a planetary boundary.The change in greenhouse gases in the atmosphere is causing changes to the global climate system. These changes are already impacting natural and human systems worldwide. Much larger and more disruptive changes are projected as greenhouse gases continue to accumulate in the atmosphere. Unfortunately, the consequences of these climate changes are the sorts of things that are generally considered to be bad, whether one adopts an anthropocentric ethical view or an ecocentric ethical view.

Climate change is a difficult issue for several reasons. First, avoiding climate change involves reducing greenhouse gas emissions, which is difficult because fossil fuels are so central to our industry and our lives. Second, the global climate system and its interconnections with human and ecological systems are very complicated. We know a lot about these systems, but some important uncertainty remains. Third, the massive scale of climate change makes it a very difficult collective action problem. It involves everyone across the entire planet, from now until many thousands of years into the future. Finally, the severity of climate change is so great that human civilization may not survive it. For these and other reasons, climate change is perhaps the single most important issue for our civilization today.

The Physical BasisPrint

The physical basis of climate change refers to our understanding of the physical properties of the climate and how it is changing. In other words, it is the physical (or natural) science behind climate change. Despite being a physical science, it asks some questions of major political and societal importance. Is the climate changing? In what ways is it changing? Are these changes caused by human activity? Because there is so much at stake with the answers to these questions, the physical science of climate change has been the center of extensive attention and a fair amount of controversy. In order to understand the human aspects of climate change, including the political issues, it is very helpful to have some understanding of the physical basis.Climate vs. WeatherAs a starting point for understanding climate change, we should recognize the difference between climate and weather. The difference is essentially a difference in scale. Climate refers to broad-scale trends in meteorological phenomena such as temperature, precipitation, and wind. Weather refers to local-scale instances of these same phenomena. Whereas climate is often studied in time periods of about 30 years, weather is often studied in time periods of just a few days or even a few hours. Also, whereas weather is very difficult to predict, climate is much more predictable. That is because weather events are driven by highly complex local and regional factors, whereas climate trends are driven by

relatively simple processes. For example, we probably don’t know exactly what the temperature will be just two weeks from now in State College, PA (weather), but we can be quite confident that the average temperature in State College will be warmer next July than it will be next January (climate). The process affecting temperatures in different months of the year is simple: tilt in the Earth’s axis of rotation that causes more sunlight to be received during summer than during winter.The distinction between climate and weather is very important for understanding climate change. A key point is that the existence of unusually hot or cold weather does not prove or disprove the existence of climate change. Even as the climate changes, there will still be hot days and cold days. Furthermore, just because it is hot or cold where you are does not mean that it is hot or cold worldwide. On any given day, it will probably be unusually cold in some places and unusually hot in others. What matter for climate change are the broad-scale trends. This point is important to keep in mind because people have a tendency to base their beliefs about climate change - perhaps subconsciously - at least in part on their immediate weather conditions. This tendency has been observed in survey research about climate change: when weather is warmer, more people tend to believe that climate change is happening, and vice versa for colder weather. By recognizing that this tendency exists, we can make conscious efforts to avoid it in our own thinking.

Climate ChangeLikewise, the primary process driving climate change is also simple: an increase in the concentration of greenhouse gases in the atmosphere. Greenhouse gases cause radiation coming in from the sun to stay near the surface of Earth instead of escaping back into outer space, thereby heating the surface of the planet. As the concentration of several greenhouse gases (in particular carbon dioxide, CO2, and methane, CH4) has increased, more radiation goes towards Earth’s surface, and the planet is heated further. This “global warming,” in turn, causes other changes in climate, such as changes in precipitation. In this module, we use the term “climate change” instead of the term “global warming” because the overall climatic changes occurring involve more than just temperature, and because the temperature changes are not a uniform warming across the planet (though the average global temperature certainly is warming).Despite any controversies you might hear about in the news, we are very, very confident that climate change is happening and is caused primarily by human activities. It is true that some non-human processes do change climates, but these processes are either smaller or operate on much longer time scales than the climate change that we’ve been observing recently. The conclusion that humans are causing climate change is based on three very simple, very well understood points:

1) Certain molecules are greenhouse gases.

2) Atmospheric concentrations of some of these greenhouse gases are rising.

3) Global surface temperatures are rising.

We know (1) from basic physical chemistry and can confirm this in simple laboratory experiments. We know (2) and (3) from both direct observations of the atmosphere and other “proxy” evidence about the atmosphere found in such places as tree rings and ice cores. We further know that (2) is driven mainly by human industrial activity, in particular the burning of fossil fuels, because the change in concentrations coincides with the onset of the Industrial Revolution and because industrial activity is known to emit greenhouse gases into the atmosphere. Finally, we know that (2) is causing (3) due to computer modeling of the global climate system. These models accurately reproduce the observed temperature increases only when the greenhouse gas concentration increases are included. We would literally need to fabricate new physics to explain the observed temperature increases without human-driven increases in atmospheric greenhouse gas concentrations.Is it because of changes in the sun?One of the most common arguments made against the physical basis of climate change is that the temperature increases we are observing are due to an increase in incoming radiation from the sun, not due to greenhouse gases from human activity. If greenhouse gases are not changing temperatures, then we don't have much reason to avoid emitting them. But this argument is incorrect. Changes in the sun are not causing temperature increases. The clearest evidence we have for this comes from temperature trends across the atmosphere.

Earth's atmosphere is composed of several layers. The lowest is the troposphere, followed by the stratosphere, mesosphere, thermosphere, and exosphere. If increasing temperatures were due to the sun sending more radiation, then we would expect all of the layers to be warming. However, only the surface and the troposphere are warming. The higher layers have been cooling!Why would the higher atmosphere layers be cooling? It turns out that greenhouse gases are concentrated in the troposphere. These gases keep more radiation near the surface instead of escaping back towards outer space. With less radiation going from the surface towards outer space, less radiation is passing through the atmosphere layers above the troposphere. So, the temperature increases that we observe on the surface are due to increases in greenhouse gas concentrations, not due to increases in radiation from the sun.

This can be seen from the following figure:

Figure 9.2 Greenhouse Gases: Radiation from the sun passes through several layers including the Stratosphere and the Troposhere to reach the

earth's surface. Greenhouse gases rise and fall within the Troposphere, the layer just above the Earth's surface.

Credit:The following figure shows temperature changes in different parts of the atmosphere:

Figure 9.3 Atmospheric Temperature Changes and Atmospheric Temperature TrendsIf you would like to read more about this topic,

please see the Stanford Solar Center (link is external) Credit: Stanford Solar Center

The Human Dimensions of Climate ChangeThe remainder of this module focuses on the human dimensions of climate change, in particular how humans are impacted by climate change and how humans are responding to climate change. There are two main ways in which humanity is responding to climate change: mitigation and adaptation. Mitigationrefers to efforts to reduce the amount of climate change that will occur via reducing the amount of greenhouse gases in the atmosphere. Adaptation refers to efforts to improve the impacts of whatever climatic changes end up occurring. Exactly what is meant by an “improvement” to the impacts is an ethics question. Similarly, there are ethics questions in what mitigation efforts humanity should make.

The relationship between climate change, mitigation, and adaptation can be seen in a simple system diagram:

Figure 9.4 Climate Change Diagram Diagram shows an arrow from a Mitigation box to a Greenhouse Gas Emissions box (with the

word less next to the arrow) An arrow leads from the Greenhouse Gas Emissions box to a Climate Change box (with the word more next to the arrow). An arrow leads from the Climate Change box to an Adaption box.

Another arrow from Climate Change leads to an Impacts box (with the word more next to the arrow.) An arrow also leads from the Adaption box

to the Impacts box (with the word better next to the arrow).Credit:

As this diagram shows, mitigation causes less greenhouse gas emissions, while greenhouse gas emissions cause more climate change. Thus mitigation causes less climate change. Meanwhile, climate change causes more impacts. Climate change can also cause adaptation, which leads to better impacts.

Impacts & Adaptation

PrintAs the previous page indicates, it is clear that the climate is changing, and that these changes are caused mainly by human emissions of greenhouse gases. But this does not explain why we care so much about climate change, and, in particular, why we think climate change is bad. Why climate change is bad depends on our ethical view of what is “bad.” Here we’ll look at both anthropocentric and ecocentric views. In the case of climate change, disruption to ecosystems often also involves disruption to human systems, so the reasons for believing that climate change is bad are largely the same from both anthropocentric and ecocentric ethical views.

Temperature shiftsThe simplest impacts of climate change are shifts in temperatures around the world. Overall, temperatures are increasing. Zones within a certain temperature range are shifting towards the north and south poles and towards higher elevations. Some species, in particular plant species, are adapted to certain temperature ranges. These species are often shifting to different locations along with the temperature zones. But this shifting is imperfect. First, species may also be adapted to certain elevations or to certain latitudes. Latitude is important for plants because latitude defines how long days and nights are at a given time of year. Second, there may be obstacles impeding the species’ shift. For example, if a species lives on a mountain, it may not be able to cross a valley to get to the next mountain over. Thus some species will not successfully adapt to the temperature shifts caused by climate change. This includes both species in natural ecosystems and species used in human agriculture. (As we will have seen in previous modules, agriculture is always part of an ecosystem, so natural ecosystems and human agriculture are not completely separate from each other.)

Shifts in waterWater patterns are closely connected to temperature patterns. When temperatures are warmer, more water melts and evaporates. This affects precipitation patterns. Shifts in precipitation patterns complicate the process of species adapting to temperature shifts, since species are generally also adapted to certain precipitation. For example, a plant might shift towards the north pole to stay within the same temperature zone, but if the precipitation zone does not also shift north, then the plant will have to struggle with different precipitation.

One of the most important shifts in water from climate change is the melting of ice at several places around the world.

In the Arctic Ocean, ice melting is leading to the opening of the Northwest Passage, a sea route between the north Atlantic and north Pacific oceans. The Passage is becoming increasingly navigable, making shipping (especially freight shipping) much less expensive between the wealthy and populous northern nations of Europe, North America, and east

Asia. Other countries will be hurt by this, in particular Panama, whose Canal will diminish in importance.

In central Asia, ice melting in the Himalayas is disrupting water supplies of crucial importance to very large human populations in India, China, and surrounding areas. There is concern about whether these populations will have access to enough fresh water in the future.

In Antarctica and Greenland, large amounts of ice are melting, increasing the amount of water in the oceans. This, in turn, raises sea level. Sea level rise is further increased by thermal expansion: as ocean temperatures increase, the water expands, pushing sea level higher. Ice melt and thermal expansion are causing enough sea level rise that some low-lying coastal areas could become uninhabitable. This is a particularly serious concern because a large portion of the human population lives in such areas. Many major world cities are threatened, including New York, Los Angeles, Mumbai, Tokyo, Hong Kong, and even London, which is near sea level despite being inland along the River Thames. Already, London has movable barriers to protect against high tide storm surges. Sea level rise threatens to make the surges more severe.

Figure 9.4: River Thames Barrier in LondonCredit: File found at Wikimedia Commons (link is external)  /(CC BY-SA 3.0) (link is external)

Extreme weather eventsAs we saw in Module 8, extreme weather events can cause major disruptions. Climate change is affecting extreme weather events, often by making them more extreme and disruptive. One example of this is hurricanes. Hurricanes get their energy from the warm waters they pass over. This is why the strongest hurricanes occur in warmer regions. As waters warm, they gain more energy, thereby making hurricanes more powerful. For this reason, climate change is expected to increase the intensity of hurricanes and, unfortunately, more intense hurricanes often cause much more damage.

AdaptationHuman and non-human systems alike are adapting and will continue to adapt to climate change. These adaptations are not always successful; the impacts of climate change will inevitably cause harm. But adaptation can reduce the amount of harm caused.

Adaptation raises some large ethical questions. Who should pay for the costs of adaptation: the people who are adapting or the people who emit the greenhouse gases that made the adaptations necessary? It might seem unfair for some people to force other people to adapt, but it is difficult to get emitters to pay when the emitters are everyone across the planet! Another question is: How should we prioritize among adaptation projects? Should we support the projects that a few wealthy people are able to pay for or the projects that many poor people really need? There are distributive justice issues here. Also, how should we prioritize adaptations for humans vs. adaptations for ecosystems? Finally, what process should be used to make adaptation decisions? These questions and others are heavily debated among those involved in adaptation across all scales from local to global.

One final point to remember about impacts and adaptation is that they are occurring in the context of other changes to natural and social systems. In other words, climate change is not the only aspect of our world that is changing. There are also political, economic, technological, ecological, and other changes going on. As we prepare for the future impacts of climate change, it is important to remember that it will be the future world doing the adapting, not the present world. When we treat climate change as only one aspect of our world, we are more likely to be successful at adapting to future conditions in general, including conditions affected by climate change.

Plan where you liveWhere you choose to live is probably the single biggest factor in how much greenhouse gases you emit. This includes what city you live in, what neighborhood you live in within the city, and even what building you live in within the neighborhood. Where you live is important for several reasons.

First, as we saw in Module 7, the type of urban area you live in has a large influence on your transportation. This includes what modes of transportation you use (cars, transit, walking, etc.). In general, cars cause the most greenhouse gas emissions, followed by transit. Walking and bicycling cause almost no greenhouse gas emissions. This also includes how much transportation you’ll be using. In general, the farther you travel to go from place to place, the more greenhouse gas emissions you’ll cause.

Second, as we also saw in Module 7, buildings vary tremendously in how much energy they require per person. Much of this energy is in heating and air conditioning. Buildings in more moderate climates (such as the west coast of the United States) need less energy for heating and air conditioning than buildings in more extreme climates (such as the east coast of the United States). Apartment buildings need less energy per person than stand-alone houses because apartments share walls with each other and don’t lose heating and cooling to the outside as much. Finally, buildings can vary in the efficiency of their design. Buildings with better insulation and other ‘green’ design features require less energy for heating and air conditioning. Buildings with energy efficient technologies also require less energy.

Where you live also influences what social interactions you’ll have. This includes who you’ll meet and be friends with and what opportunities you’ll have to get involved in a democracy. These factors are also important to greenhouse gas emissions, though this relates to social norms and collective action as much as it does to individual action. Wherever you choose to live, it’s also important to maintain your residence effectively. This includes using insulation and choosing efficient appliances. It also includes using less heating and air conditioning by setting the temperature lower in the winter and higher in the summer. Finally, it means turning off lights and other devices when they’re not needed. In general, the biggest electricity savings come from the biggest devices: washing machines, driers, refrigerators, and other big appliances that get used frequently. Lightbulbs are also important because they are used so often and there’s such a big efficiency difference between incandescent (less efficient) and fluorescent (more efficient) lights.

Choose low-impact foodsIn Module 6, we saw that livestock has a large shadow, i.e., a large environmental impact, including a large amount of greenhouse gas emissions. This is because we need to grow a lot of plants to feed livestock animals, and because the animals produce pollution, including greenhouse gases, on their own. Eating less of an animal-based diet and more of a plant-based diet will in general have much lower greenhouse gas emissions. This is among the biggest actions that individuals can take to reduce emissions.

There are other actions we can take with food as we also saw in Module 6. We can eat locally-grown foods that do not use as much energy for shipping. Eating fresh foods instead of refrigerated or frozen foods also helps, because the refrigeration and freezing processes use a lot of energy. Food processing in general requires energy, so processed foods will usually require more energy. This includes processing we do in our homes: cooking, refrigerating leftovers, etc. But there can be tradeoffs. For example, some processed foods last longer than fresh foods and are thus less likely to go to waste. It can often be difficult to identify exactly which foods cause the least emissions.

Buy carbon offsetsA carbon offset is a way to pay other people to reduce their emissions. It’s called an offset because you can use it to ‘offset’ the emissions that you cause. It’s an appealing scheme because you get to do what you wanted that causes emissions and the climate won’t be affected. This depends on the offset working as it's supposed to. This scheme follows from ends ethics and not means ethics: the means of causing emissions are OK as long as the ends of climate change is unaffected.

Consider This: The Idea Behind Carbon OffsetsYouTube link for How Does Carbon Offsetting Work (link is

external)Credit: BP London 2012

As you watch the video, think about these questions: Are there some issues surrounding carbon offsets? Is carbon offsets an effective way for climate change mitigation?Carbon offsets are somewhat controversial. Some people are concerned that offsets make it easier for the rich to keep polluting while placing the mitigation burden on the others, instead of having all members of society carry their share of the burden. Others respond that with offsets, everyone benefits, since the people who are reducing their emissions in an offsets scheme are agreeing to make the reductions in exchange for being paid. Another concern is that sometimes the offset doesn't actually happen. If the money isn't spent properly, then the climate benefits won't be realized. For example, the money could go to an emissions reductions project that would have happened anyway, in which case the offsets bring no additional climate benefits. This 'additionality' issue is a major concern with offsets. All things considered, offsets cannot, on their own, solve all of our mitigation problems, but they can be a useful component to a broader set of mitigation efforts.

Collective Action on MitigationPrint

Climate change mitigation can often be treated as a collective action problem. This happens when individuals don’t want to reduce their own emissions. Sometimes we do want to reduce emissions. For example, low-emission food, transportation, and buildings are often healthier, more convenient, and less expensive. But, often, we don’t want to reduce emissions. Instead, we would rather continue doing whatever we had been doing before. In the language of Unit 2, we don’t want to transition to sustainability. When this happens, we face a collective action problem. It is in our individual interest to keep emitting, but it is in our group interest to reduce emissions.

This has its challenges. With climate change, we are trying to foster collective action among all of humanity, now more than 7 billion people. This has many more challenges. There are language barriers. There are differences in values. There are differences in awareness about climate change. And there is the monumental logistical challenge of reaching some sort of agreement across so many people.

Since 1992, global collective action on climate change has been promoted via the United Nations Framework Convention on Climate Change (UNFCCC). Note that it is the United Nations. This means that the world’s population is grouped by nationality, instead of by religion, wealth, ethnicity, ethics views, or anything else. Each nation sends representatives to treaty negotiations that occur once or twice per year. The biggest meeting happens each December in a different city. In 1997, the meeting was in Kyoto. This meeting resulted in the Kyoto Protocol, a treaty signed by most countries (but not the United States) that was aimed at reducing emissions between 2008 and 2012, but was largely unsuccessful. In 2009, the meeting was in Copenhagen. Hopes were high that a more successful Kyoto Protocol replacement would be achieved at Copenhagen. Instead, the much weaker Copenhagen

Accord was reached, a non-binding document negotiated by US and other countries. In 2012, at the meeting in Doha, Qatar, the Doha Amendment was adopted, which extended the Kyoto Protocol until 2020. Ongoing efforts continue to seek an international treaty, though it is unclear if such a treaty will ever be reached.

There are several reasons why it is so difficult to reach a strong international treaty to reduce greenhouse gas emissions. First, reaching any international treaty is difficult, given the large number of nations around the world. The UNFCCC has 194 member nations. Even North Korea participates, despite being absent from many other international processes. Second, reducing emissions is very difficult. Emissions are closely tied to fossil fuel use, which is, in turn, closely tied to industrial activity. For a nation to reduce its emissions, it might have to reduce its standard of living or even its geopolitical strength. Third, there are major differences between the positions and views of different countries. Poor countries often feel that it is unfair for rich countries to ask them to reduce emissions when the rich countries cause most of the emissions and when the poor are just trying to develop a decent standard of living. Countries that own a lot of fossil fuels often want the opportunity to extract and use the fossil fuels, either for their own activities or to sell to other countries. Countries that are especially vulnerable to the impacts of climate change (e.g., small island developing states in the Caribbean and Pacific) are especially eager for emissions to be reduced. All of these factors (and others) combine to make it very difficult to achieve international collective action on mitigation.