Sustaining Our Planet
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The authors would like to dedicate this book to Robert (Bob) C. Harriss, a brilliant
scientist, a great mentor to his students, and a wonderful friend to all who are lucky
enough to know him. Bob’s work on greenhouse gas emissions and atmospheric
chemistry paved the way for our understanding today of some of the trade-offs and
challenges associated with the use of natural gas, oil, and coal. Bob has also mentored
and trained a generation of environmental scientists studying energy issues, tropical
deforestation, land-use change, and other critical environmental issues. Bob always has a
smile, a kind word, and a guiding hand for all, and the world could use just a few more
people like him.
Author Terry Bensel with mentor
About the Authors
Terry Bensel is an associate provost and professor of environmental science and
sustainability at Allegheny College in Meadville, Pennsylvania. He teaches courses in
ecological economics, environmental management, sustainable forestry, sustainable
energy, and environmental issues in developing regions. Bensel completed graduate
studies in economics and natural resources (MA and PhD) at the University of New
Hampshire, with his dissertation focusing on the environmental and economic impacts of
biomass energy use in the Philippines.
Ian Carbone serves as an assistant professor of environmental science and sustainability
at Allegheny College in Meadville, Pennsylvania. He received his PhD in physics from the
University of California at Santa Cruz and teaches courses that focus on energy systems,
quantitative research skills, and applied environmental research. Carbone uses his
scholarship to research light concentrating devices for solar power production and works
with Allegheny students to support solar and energy efficiency efforts in northwestern
Sustaining Our Planet is an engaging introduction to the basics of environmental science, with an emphasis on sustainability.
Whether the topic is consumption, agriculture, water, or energy, this text invites you to think critically about humans’ impact on
ecological systems as well as your own environmental footprint. Readers will come away understanding how much we depend on
the natural world and feel inspired and empowered to take action on this planet’s most pressing environmental challenges.
Sustaining Our Planet includes a number of features to help students understand key concepts:
Images and figures illustrate and illuminate the concepts presented.
Multimedia allow readers to explore and interact with the text through videos, photo slide shows, exercises, and timelines.
Apply Your Knowledge feature boxes offer readers the opportunity to practice reading graphs and charts relevant to the topic
Close to Home feature boxes guide readers to opportunities for action in their own communities.
Learn More feature boxes expand on topics of interest and point students to additional web resources.
Pretests and posttests in each chapter give students real-time feedback on their understanding of the content.
Relevant web links at the end of each chapter offer readers the opportunity to explore additional resources, examples, and
applications related to the text.
Key terms are listed at the end of each chapter and at the end of the book. In the e-book, an interactive list allows students to
quiz themselves on definitions.
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The authors would like to thank and acknowledge a number of individuals who made significant contributions to this text. First,
the editorial team at Zovio was incredibly supportive and helpful throughout the project: Anna Lustig, associate vice president,
editorial and media; Rebecca Paynter, senior development editor; Teresa Bdzil, project editor; Kathleen Crampton, assistant editor;
Catherine Morris, production editor; and Jaime LeClair, media editor. Second, we benefited greatly from the feedback and ideas of
the following reviewers: Clifford Blizard, Ashford University; Jeffrey O. French, North Greenville University; Gayle Leith, Ashford
University; Michelle Kozlowski, Ashford University; Kurt M. Leuschner, College of the Desert; Adam Selhorst, Ashford University;
Linda Sigismondi, University of Rio Grande; and Bo Sosnicki, Ashford University.
Terry Bensel would like to thank his coauthor, Ian Carbone, for his timely and engaging contributions to the project. He’d also like
to extend a special thanks to Rebecca Paynter for all the advice and support she provided throughout the project, as well as Clifford
Blizard for his unbridled enthusiasm. Finally, he thanks his wife, Concepcion Angus, and daughters Katherine and Teresa, for their
inspiration and love.
Ian Carbone would like to thank his coauthor, Terry Bensel, and our editor, Rebecca Paynter, for the opportunity to contribute to
this project. He would also like to thank Allegheny College and its Environmental Science and Sustainability Department for
supporting his growth as an educator and allowing him to train future generations of environmental problem solvers.
Understanding Environmental Science and
After reading this chapter, you should be able to
Define environmental science.
Describe the importance of critical thinking, information literacy, and the scientific method.
Analyze the impact of palm oil plantations on biodiversity and the environment in Borneo.
Define the core concepts of natural capital and sustainability.
Define the core concepts of the environmental footprint and the Anthropocene.
Define the core concepts of uncertainty, scale, risk, and cost–benefit analysis.
1.1 Why Study Environmental Science?
Whether we realize it or not, almost every aspect of our daily lives is dependent on and connected to the natural world around us.
We are a part of, and not separate from, that natural world. The food we eat, the air we breathe, and the water we drink all
originate from the natural world. Perhaps less obvious, the items we use every day—such as the fuel for our cars, the clothes we
wear, and our phones and electronic devices—all have their origins in the natural world. At the same time, our everyday actions
and use of these products—be it driving, eating, or throwing out the trash—all have an impact on this natural world on which we
The study of environmental science encompasses all of these relationships. At its most basic, environmental science is the study
of how the natural world works, how we are affected by the natural world, and how we in turn impact the natural world around us.
Our fundamental dependence on the natural world makes the study of environmental science relevant to all of us. Environmental
issues—including deforestation, ozone depletion, water pollution, and climate change—affect us all. These issues are also in the
news now more than ever, and they are often at the center of heated political debates. Acquiring an understanding of the basic
science behind these debates is thus an important part of becoming an educated citizen and forming your own opinion of the
issues. And while you may not go on to make a career in environmental science, you will likely find that this discipline intersects
with your major or field of study in some way.
The goal of this book is to help you understand the basics of environmental science so that you can further explore and research
environmental issues that interest and affect you directly. Because environmental issues can be so complex, developing solutions
requires a solid understanding of policy and scientific concepts. In this book, we will apply natural science and social science
concepts to the study of environmental issues that are in the news every day. The hope is that you—armed with the knowledge,
perspectives, and up-to-date information provided in this book—will begin to form your own, informed opinions on these subjects.
Ideally, you will also develop ideas about how you as an individual or society more broadly can take action to address some of the
most pressing environmental challenges facing the world today. Ultimately, this book aims to empower you as a student both to
grasp the environmental challenges facing the world and to do something about them.
Outline of the Book
Much of the rest of this chapter, and most of Chapter 2, focuses on introducing you to concepts and ways of thinking that are
essential to the study of environmental science and that will appear repeatedly throughout the rest of the book. You can think of
these chapters as laying a foundation for your study of specific environmental issues in subsequent chapters. Just as you would not
expect to be able to cook or repair cars without the right tools and basic knowledge of those activities, it would be difficult to study
environmental issues without the information provided in these first two chapters.
With a strong foundation in place, we’ll move to the study of human
population and material consumption in Chapter 3. Virtually all of the
environmental challenges we face are thanks to the growing number of
people on the planet and high rates of material consumption among some of
those people. In this way, we could say that human population growth and
material consumption are the fundamental drivers of environmental change
in the world today.
Chapters 4 through 9 focus on specific environmental issues and challenges:
management of agricultural and forest resources, freshwater resources,
oceanic resources, energy resources, atmosphere and climate, and waste.
These chapters involve a heavy emphasis on negative news and challenges,
so Chapter 10 aims to end the book on a more upbeat note. While it’s true
that we face enormous and complicated worldwide environmental
problems, it’s also true that governments, nongovernmental organizations
(NGOs), corporations, small companies, schools and universities, and
individual citizens are taking steps to address and reverse those challenges.
We will examine their stories in hopes of inspiring positive change in our
danielvfung/iStock/Getty Images Plus
The biggest driver of environmental change in
today’s world is human population growth and
rates of consumption, which have increased
exponentially in the past 200 years.
Key Definitions in Environmental Science
While we may hear or use the words environment, environmentalism, and environmental science quite often, we might not always
appreciate what they mean and how they are used in the study of environmental issues. At its most basic level, the environment is
everything that surrounds you. This includes all living things (such as animals, plants, and other people), as well as all nonliving
things (such as water, rocks, air, and sunlight). A more scientific definition of the environment would be all physical, chemical, and
biological factors and processes that affect an organism.
Based on that definition, it should be clear that we are all a part of the environment rather than apart from it. In fact, one major
theme of this book is that, despite all the technological gadgets and scientific advances that attract our attention, we are all
fundamentally dependent on the environment for our well-being and survival. The task of sustaining our agricultural resources,
forests, water sources, oceans, atmosphere, and climate is not just about “caring” for this creature or “saving” that endangered
animal. It’s also about saving ourselves and ensuring that we and generations to come can breathe clean air, drink clean water, and
live under relatively stable and benign climate conditions.
Because the environment by definition is basically everything, environmental science is a complex and interdisciplinary field of
study. Environmental science draws together knowledge and concepts from many disciplines—ecology, biology, chemistry, geology,
atmospheric science, physics, economics, political science, and other fields—to understand both how we are impacting the
environment and what can be done to lessen that impact.
Note that there is a difference between environmental science and environmentalism. Environmentalism is a social and political
movement committed to protecting the natural world. While many environmental scientists likely consider themselves
environmentalists, as scientists they adopt a more objective approach to the issues they study. This approach is based in large part
on the use of the scientific method, an approach to research based on observation, data collection, hypothesis testing, and
experimentation. As a student, you are not required or expected to become an environmentalist, but as an educated citizen, you
should learn to recognize the critical role played by the scientific method in forming our understanding of the environment and the
environmental challenges we face. Such an understanding of the scientific method will help you develop critical-thinking skills and
enable you to weigh competing claims and arguments about environmental issues.
1.2 Thinking Critically About Environmental Science
Many environmental scientists see their work as largely nonpolitical and
noncontroversial. They are attempting to understand how a particular piece
of the environment or system—a stream, a wetland, a patch of forest—
functions and what might happen to that system in the wake of pollution or
some other environmental disturbance. However, because the findings of
this environmental research are often used in crafting and implementing
environmental policy, environmental science and debates over
environmental issues can become highly contentious and political.
Take, for example, the topic of global climate change (which will be covered
in more detail in Chapter 8). Thousands of environmental scientists are
engaged in research that is in some way related to the subject of climate
change. Some scientists study how combustion of fossil fuels or other
human activities add greenhouse gases to the atmosphere, others how these
gases change the Earth’s energy balance and climate systems, and still
others how changes to the climate are affecting trees, animals, and other
patriziomartorana/iStock/Getty Images Plus
Environmental scientists aim to understand how
different elements of the environment function
and how they change in response to other
factors, such as pollution.
The majority of these scientists would probably not see their work as
contentious or political. They are instead usually motivated by scientific curiosity and a desire to pursue knowledge. However,
because the sum of these thousands of research efforts points with overwhelming confidence to the realities of global climate
change, and because addressing climate change will require changes to all sorts of economic and social behaviors, the efforts of
these environmental scientists can become politicized. Because of this politicization, it’s important to understand the concepts of
critical thinking, information literacy, and the scientific method. Careful application of these approaches to your own study of the
environment will help you develop informed opinions on many issues and help you avoid falling for arguments that are based on
opinion and personal belief rather than grounded in facts and scientific evidence.
Critical Thinking and Information Literacy
Critical thinking is the objective analysis and evaluation of an issue to form a judgment. In this case, the key term is objective
analysis—in other words, analysis that is not based on personal opinion or belief. For example, one of this book’s authors had a
student who, while hiking, saw a number of dead birds on the ground near the base of some wind turbines. The student later
expressed a conviction that wind power was bad for the environment and should not be used. While there are legitimate reasons to
be concerned about the effect of wind turbines on bird (and bat) mortality, this student should also consider what the
environmental impact of other forms of electricity production are. In the authors’ region of the country (Pennsylvania), much of the
electricity is produced by burning coal. A better example of objective analysis would be a comparison of the environmental impacts
of coal mining and coal burning (including the impact on birds and bats) to the impact of wind turbines.
As you engage with the material in this book, and as you do your own research and form your own opinions about environmental
issues, keep the following principles of critical thinking in mind:
Evaluate the basis for a particular conclusion. What evidence is being presented to support a claim or an argument, and
how was that evidence collected?
Keep an open mind. Attempt to gather information from a variety of perspectives before forming a final opinion.
Be skeptical. While keeping an open mind, ask yourself where information is coming from and how it was developed.
Consider possible biases, including your own. Most scientists strive mightily to avoid the introduction of bias into their work,
and the scientific method (described in more detail later) helps them do that.
Distinguish between facts and values or opinions. For example, it is a fact that atmospheric concentrations of the greenhouse
gas carbon dioxide now exceed 400 parts per million (ppm) compared to levels of roughly 280 ppm at the start of the
Industrial Revolution. However, it’s an opinion or value statement to say that the use of all fossil fuels should be halted
immediately to prevent further increases in carbon dioxide concentrations.
A key part of establishing and utilizing critical-thinking skills is to develop what’s often referred to as information literacy.
Information literacy is the ability to know when information is needed and the ability to identify, locate, evaluate, and effectively
use that information to address an issue. For our purposes, the most important of these abilities will be locating and evaluating
information. The past two decades have witnessed an explosion of information and information sources, and our ability to access
that information is becoming easier every day. However, our ability to know where to look for reliable information and to evaluate
that information for reliability and usefulness has not kept pace. For example, there are thousands of sources of information on the
topic of climate change. Who should you believe? Who can you trust? We can see how critical-thinking skills are needed for
information literacy and how information literacy is required for critical thinking. As you read this book and explore on your own
the environmental topics and issues that interest you, ask yourself where information is coming from, how it was gathered, and
how reliable it might be. The Apply Your Knowledge: Is This Information Reliable? feature box presents one quick opportunity to test
your critical-thinking skills.
A less appreciated but nevertheless important skill for environmental analysis and problem solving is creative thinking. As
scientists examine an environmental issue and ponder its possible causes and consequences, it helps if they can think creatively
and with an open mind, as opposed to being locked into one way of looking at the world. Environmental scientists also tap into
creative thinking to design effective field experiments that help them better understand the workings of nature. And as we’ll see
throughout this book, it will take creative thinking and even imagination to develop alternative approaches to meeting our food,
water, energy, and other resource needs in ways that do not destroy the environment.
Apply Your Knowledge: Is This Information Reliable?
Evaluating the quality and reliability of information can be a difficult task, especially when we are considering resources
found on the Internet. We live in a world in which opinions are sometimes presented as the unbiased truth, and pretty much
anyone with a computer can create a convincing website that is accessible to the entire world.
To highlight some of these challenges, let us explore a website called Save the Pacific Northwest Tree Octopus (https://zap
atopi.net/treeoctopus/) . At first, the prospect of a tree-dwelling octopus might seem absurd, but nature often surprises us.
There are birds that can swim and fish that can fly, so why not an octopus that climbs trees? If you read the article, you
might also notice that the information presented is fairly detailed. The author provides a Latin name for this creature, along
with measurements that describe tree octopus physiology. There are even photographs and links to additional resources,
suggesting that others have documented these creatures in the past.
Despite the website’s flashy appearance, it is a total hoax. There is no such thing as a tree octopus, and if we take a closer
look at the website, we can see some warning signs that call its information into question. Take a moment to explore the Sav
e the Pacific Northwest Tree Octopus (https://zapatopi.net/treeoctopus/) website on your own, and see if you can find any
red flags indicating that the article is unreliable.
One characteristic of trustworthy information is that it comes from a reputable author or organization. For example,
information from a government agency, an institution of higher education, or a peer-reviewed journal is often considered to
be more reliable than information from a personal blog. Reliable resources will also provide access to author biographies so
that you can tell if the author is an expert on the subject matter. If you look at the author information at the bottom of the
tree octopus website, you will notice that the author description is downright silly. There is no indication that the person
has any training related to the subject matter.
Reliable resources also need to be fact-checked or backed up with supporting information that is usually identified using
links and citations. This website appears to have active links to other resources, but if you follow these links, you will notice
that they take you to other hoax websites or to sites that have no mention of tree octopuses.
Finally, reliable sources will be clear about whether their goal is to inform you with factual information or to convince you of
a particular argument. A close reading of the material can often tell you if an unreliable resource is trying to convince you of
an opinion while appearing to present objective facts. Consider the following sentence from the tree octopus website:
Tree octopuses became prized by the fashion industry as ornamental decorations for hats, leading greedy trappers
to wipe out whole populations to feed the vanity of the fashionable rich. (Zapato, n.d., para. 8)
Phrases like “greedy trappers” and “vanity of the fashionable rich” suggest that the author is making judgments about
certain actions and groups of people. This is not what we would expect from a well-written article that is intended to
present factual information.
Now, take a moment to explore another web resource titled “Discovery of the First Endemic Tree-Climbing Crab (https://
www.purdue.edu/fnr/extension/discovery-of-the-first-endemic-tree-climbing-crab/) .” Once again, the topic sounds bizarre, but if
we look closely, the information seems much more trustworthy. The article was produced by an academic institution. The
language used in the article appears to be unbiased, and the information can be easily fact-checked using the peer-reviewed
journal articles and academic websites that are referenced at the end. This article appears to be a source of reliable
Save the Pacific Northwest Tree Octopus (https://zapatopi.net/treeoctopus/) is a silly example of “bad” information, but the
critical-thinking skills we used to evaluate this source can be applied to everything that we read, hear, and watch. If we
approach media critically, we’ll be able to recognize the trustworthy information that helps us make better policies and
decisions. In your future studies, look for information that is from a trusted source. Look for information that is backed up
by quality research and journalism. Finally, look for information that is attempting to inform rather than persuade (unless
you are researching opinions, of course).
The Scientific Method
The use of the scientific method is one way that environmental scientists seek to improve the reliability, usefulness, and relevance
of their research. The scientific method is an approach whereby scientists observe, test, and draw conclusions about the world
around us in a systematic manner, rather than simply stating opinion. The scientific method consists of a series of five steps, as
illustrated in Figure 1.1.
Figure 1.1: The scientific method
The scientific method is a five-step model used to observe, test, and draw conclusions scientifically.
Scientists begin with simple observations of the world around us. They then form questions based on those observations. For
example, environmental scientists might observe the death and decline of numerous trees alongside a major highway and naturally
wonder what is causing this to happen. This leads to the third step, the formulation of a hypothesis or hypotheses that might
explain the trees’ death. Hypotheses can be thought of as a first guess or “hunch” about something, and they help scientists
formulate predictions, specific statements that can be tested. In this case, the scientists might form a hypothesis that the trees are
dying because of road salt running off the highway in the winter or because of an herbicide sprayed to control weeds on the side of
the highway. Based on these guesses, they can take the fourth step in the scientific method and develop specific and testable
predictions about how much road salt or herbicide needs to be applied to bring about the same levels of tree death and decline
they have observed in nature.
All of these steps lead up to the final step of testing the predictions. To clearly determine what might be killing the trees, scientists
devise experiments that attempt to hold conditions constant and then change one variable at a time. In this case, scientists might
identify four similar small groves of trees that show no sign of stress or tree death. They might then expose one area to road salt,
another to herbicide, and a third to both road salt and herbicide, while the fourth area is left alone. (Apply Your Knowledge: How
Does Road Salt Affect Trees? shows how scientists might record their data.)
Apply Your Knowledge: How Does Road Salt Affect Trees?
Environmental scientists make use of many different types of graphs to summarize and present the data they gather in their
research. Graphs help in taking enormous amounts of data and information and presenting them in a way that tells a story
or makes an argument. Your ability to understand and interpret graphs will be an important part of reading this book and
learning environmental science.
Consider the following figures, which show possible results from the road salt/herbicide example used in the discussion of
the scientific method. Figures 1.2 and 1.3 report basically the same information on tree death and decline from the
experiment in different ways. Figure 1.2 portrays the number of trees that died in the different plots of the experiment over
time. Figure 1.3 presents overall tree deaths by plot type at the end of the experiment.
Figure 1.2: Line graph showing tree damage
This graph shows tree damage over time.
Figure 1.3: Bar graph showing tree damage
This graph shows tree damage by plot type.
Based on the data presented from this experiment, it appears that road salt might be the biggest contributor to tree
mortality. Imagine then that the scientists conducted a second experiment with four plots of trees in which they applied
different amounts of road salt and measured tree mortality over a 4-week period. Table 1.1 gives information on the amount
of road salt applied to each of the four plots and the corresponding tree mortality. Try plotting these numbers on a piece of
paper. Draw a straight line that comes closest to connecting each of the four points on the graph. What does the shape and
direction of this line tell you about the relationship between road salt application and tree mortality?
Table 1.1: Amount of road salt and tree damage
Road salt application (metric tons/hectare)
Tree damage (dead trees per plot)
Plot 1 (1 metric ton/hectare)
Plot 2 (2 metric tons/hectare)
Plot 3 (3 metric tons/hectare)
Plot 4 (4 metric tons/hectare)
Note that regardless of the outcome of these experiments, scientists will typically still do two additional things. First, if the road
salt or herbicide appeared to have some impact on the trees, the scientists might refine their predictions to gain a better
understanding of why this is happening. This might include adjusting the levels of road salt or herbicide to see if they can better
determine at what levels these applications become toxic. If the trees were not affected by the road salt and herbicide, the
scientists would be forced to revise their hypotheses or form new ones. Second, scientists typically seek to share their results with
others, usually by presenting their research at scientific conferences and publishing articles in professional journals. These
presentations and papers are subject to analysis and scrutiny by other scientists, a process known as peer review. Scientists also
have to explain the methods used in their research so that other scientists can run the same experiments, a process known as
replication. These two aspects of scientific research, peer review and replication, help ensure the accuracy and legitimacy of the
It’s important to recognize just how the scientific method can shield scientists from claims of bias. Scientists don’t really set out to
“prove” anything; instead, they observe, ask questions, hypothesize, predict, test, and usually repeat. Politicians’ demands for
scientific “proof” are therefore problematic. Environmental policy should be informed by the best science available, as well as other
issues such as ethical concerns, economic impacts, and risks involved.
1.3 Case Study: Palm Oil Production and Deforestation in Borneo
Environmental scientists, as well as other natural and social scientists, frequently make use of “case studies” to illustrate important
points or concepts. In some ways, case studies are simply formalized stories about a specific place, person, group, or other thing.
The case study presented here will help illustrate concepts and terms such as environment and environmental science and
demonstrate how environmental scientists make use of critical-thinking skills and the scientific method in their work. This case
study will also be used to explain some of the foundational concepts introduced later in this chapter and in Chapter 2.
The island of Borneo straddles the equator in Southeast Asia and is the third largest island in the world and the largest island in
Asia. The island is divided between Indonesia, Malaysia, and Brunei, with Indonesia controlling roughly 73% of Borneo’s land area,
Malaysia 26%, and tiny Brunei just 1% (see Figure 1.4).
Figure 1.4: Borneo
Located in Southeast Asia, Borneo is known for its high rates of biodiversity, but its rain forests are in
decline due to deforestation
Adapted from PeterHermesFurian/iStock/Getty Images Plus
Until very recently, Borneo was sparsely populated, and much of the island was covered in dense tropical rain forests. Because of
this, Borneo is known for its extremely high rates of biological diversity, or biodiversity—the variety of life and organisms in a
specific ecosystem. That variety can be measured by considering the number of species found in a particular area. Species are
groups of organisms that share certain characteristics, interbreed, and produce fertile offspring. In addition to having an incredibly
high number of species overall, Borneo is also known for having a large number of endemic species—plants and animals that
exist in only one specific geographic region. There are dozens of endemic mammal species (such as the proboscis monkey and
pygmy elephant), hundreds of endemic birds, and thousands of endemic plant species in Borneo. Rates of biodiversity are so high
in Borneo that scientists have identified over 20,000 types of insect species in one small national park alone (Shoumatoff, 2017).
Beginning roughly 50 years ago, Borneo’s rain forests began to decline in dramatic fashion. Actions such as logging trees for timber,
clearing land for small-scale agriculture, and burning large tracts of forest to clear land for palm oil plantations have reduced the
island’s forest cover from 75% in the mid-1980s to less than 50% today. Current rates of deforestation—clearing of forest areas—
in Borneo are estimated to be 1.3 million hectares (over 3 million acres) a year (World Wide Fund for Nature, 2019).
Among the major drivers of deforestation in Borneo, conversion of rain forests to palm oil plantations is currently the most
significant. Palm oil is derived from the nuts of the oil palm tree and is now the second most important oil used in consumer
products after petroleum. Palm oil is a $50-billion-a-year industry (Shoumatoff, 2017), and it is used in a vast array of household
and consumer products, including cooking oil, snack foods, chocolate, cosmetics (such as lipstick), toothpaste, ramen noodles,
shampoo, ice cream, cookies, and soap. It’s estimated that palm oil is an ingredient in roughly half of all packaged products sold in
modern supermarkets. Millions and millions of acres of rain forest have been cut and burned in Borneo to make way for palm oil
plantations, and this deforestation continues today. Because most of us probably consume products made with palm oil, we are all
in some way connected to this problem.
pxhidalgo/iStock/Getty Images Plus
Laszlo Mates/iStock/Getty Images Plus
Much of Borneo’s tropical rain forest has been razed for palm oil plantations.
Conversion of Borneo’s rain forests to palm oil plantations may result in a number of serious environmental and social problems.
Many different types of wildlife depend on forests as their natural habitat—the place or set of conditions an organism depends on
for survival—so deforestation leads to high rates of biodiversity loss and extinction, or the total loss of a species. Cutting up rain
forests also results in habitat loss, driving wildlife species into smaller and smaller areas for survival. Loss of tree cover leads to
increased flooding as heavy tropical rains run off cleared hillsides instead of being absorbed by dense forest soils and vegetation.
This flooding also results in water shortages later on, since rainwater rushes to rivers and the sea instead of replenishing local
groundwater supplies. Lastly, burning of forests worsens climate change in two ways. First, the combustion of trees and other
vegetation pours millions of tons of carbon dioxide, a greenhouse gas, into the atmosphere. We’ll see in Chapter 8 that increased
greenhouse gas concentrations are resulting in global warming and climate change. Second, the ability of those forests to absorb
and store vast amounts of carbon from the atmosphere is lost.
Borneo’s extremely high rates of biodiversity, combined with the widespread deforestation of the past few decades, make this
island one of the world’s most important biodiversity hotspots. A biodiversity hotspot is a region that both has high rates of
biodiversity and is experiencing significant environmental destruction. There are roughly 25 regions of the world that scientists
have labeled as biodiversity hotspots. Scientists hope that by calling attention to these regions and the endangered species—
species at risk of extinction—that live there, they can encourage governments, businesses, and private citizens to take action to
address the problem before it is too late.
A Scientific Approach
Let’s consider how environmental scientists approach the study of an issue like palm oil production and deforestation in Borneo.
First, it’s clear that our own understanding of what’s happening in Borneo is the result of interdisciplinary research by many
different kinds of scientists and experts. Botanists, entomologists, and ornithologists research Borneo’s plants, insects, and bird
species, respectively. Wildlife biologists examine how deforestation is driving endangered species into smaller geographic areas.
Hydrologists seek to understand the impacts of deforestation on flooding and water supplies. Atmospheric scientists and soil
scientists attempt to understand how deforestation impacts carbon storage and greenhouse gas emissions from forest soils.
Remote sensing specialists use satellite imagery to measure rates of deforestation over time. Environmental health specialists
study the impact of pesticide and herbicide spraying of palm oil plantations on local human populations. And social scientists—
economists, anthropologists, policy experts—study what’s driving deforestation, how local human populations are responding, and
what might be done in terms of policies and economic incentives to address this challenge.
All of these scientists and experts apply critical-thinking and information-literacy skills to their work. Most of them also make
regular use of the scientific method in defining and carrying out research in their specific areas. For example, a botanist (plant
expert) or ornithologist (bird expert) might conduct research to measure the number and variety of plant and bird species in intact
forest areas as well as in forest areas that have been fragmented or disturbed. Hydrologists (water experts) might study rates of
water flow and water quality in different river basins that are characterized by different levels of deforestation. These and other
scientists working in a setting such as Borneo might care deeply about wildlife and feel terrible about the environmental
destruction they see, but they still approach their work in an objective and scientific manner.
Borneo is not the only part of the world experiencing extreme rates of deforestation. Explore the
following interactive to learn more.
1.4 Core Theme: Sustaining Our Natural Resources
The remainder of this chapter will focus on introducing you to a series of concepts and terms that will be important as we explore
specific environmental issues in subsequent chapters. This foundation of knowledge will provide you with a vocabulary and way of
thinking that will help frame the rest of the book. As we discuss these concepts and terms, we will return to the example of
deforestation in Borneo to better understand their meaning. We’ll start with the concepts of natural capital and sustainable
development. These concepts lie at the core of environmental scientists’ work, which often focuses on supporting the environment
that we all depend on and are all a part of.
Natural Capital and Ecosystem Services
Most of us have experienced a power outage, an Internet outage, a road
closure, or disruption in some service that we depend on in our day-to-day
lives. Such disruptions often remind us of the basic infrastructure (such as
the power supply, the water supply, and functioning roads) we depend on
but usually take for granted. In much the same way, and to an even greater
degree, we depend on the natural world, the environment, and the natural
systems that make up the environment for our well-being and survival. Yet
we seldom if ever really think about that dependence and what it means to
our quality of life.
Environmental scientists refer to this natural infrastructure as natural
capital. Natural capital can be defined as natural assets such as trees, soils,
streams, oceans, and the atmosphere. Like other forms of infrastructure,
because natural capital is all around us, we seldom give it much thought.
Ecosystems, derived from the Greek word for
Take, for example, the tropical rain forests of Borneo. Managed properly,
home, provide us with areas for recreation,
these forests could yield a steady supply of timber, fruit, and other
spirituality, and joy.
nontimber forest products such as rubber, medicinal plants, and building
materials like bamboo. These forests could also be a destination for ecotourism, tourism that focuses on natural environments in
an effort to help conserve an area and support the local economy.
But understanding natural capital requires us to think more broadly than just in terms of resources. Even as valuable as all of these
things—timber, nontimber products, and tourism—might be, they only scratch the surface of the real value humans derive from
such ecosystems. These stocks of natural capital, through their normal functioning, generate a flow of life-sustaining ecosystem
services that are absolutely essential for human survival (see Figure 1.5). We’ll learn more about what ecosystems are in Chapter
2, but for now think of them as complex systems made up of both living organisms and nonliving components. For example, forests
help purify air and water supplies, help prevent extremes of drought and floods, provide space and conditions for the
decomposition of wastes, provide habitat for pollinating insects and birds that are essential to agriculture, and play a critical role in
storing carbon and maintaining regional and global climate systems. Even this list is incomplete, and this is only describing the
services of one ecosystem. Other systems—grasslands, wetlands, coral reefs, tundra, deserts, coastal systems, and open oceans—all
provide their own ecosystem services that are essential to our survival.
Figure 1.5: Natural capital and ecosystem services
Stocks of natural capital are all around us and generate a flow of ecosystem services and value for
Adapted from “What Is Natural Capital?” by Natural Capital Coalition, n.d. (https://naturalcapitalcoalition.org/natural-capital-2
A simple analogy would be to think of a home. Earth’s natural systems, like a home, take care of climate control, air purification, the
provisioning of food and water, and waste disposal and purification. They provide us spaces for recreation, spiritual growth, and
moments of joy. It’s perhaps no accident that the prefix eco– in ecosystem is derived from the Greek word oikos, or “home.”
In the chapters ahead, try to apply this analogy and the concepts of natural capital and ecosystem services to issues of soil
depletion, deforestation, water and air pollution, overfishing, climate change, ozone depletion, and toxic waste dumping. What are
we doing to our home when we create these problems? How might our actions be destroying natural capital and undermining the
very systems we all depend on? What would alternative approaches, those focused on sustaining natural capital, look like?
Sustainability and Sustainable Development
The concepts of sustainability and sustainable development come up a lot in discussions of the environment. But what do they really
mean? At a basic level, and applied to issues of the environment, sustainability is the maintenance of natural systems and an
ecological balance. Sustainable development brings human and economic needs into the picture and is the achievement of
economic objectives without the depletion or destruction of natural systems. In other words, sustainability and sustainable
development suggest a balancing act between meeting the needs of humans and maintaining the integrity of our natural
Understanding the concepts of natural capital and ecosystem services means understanding that sustainable development is the
only way forward for the human species. Development that is not sustainable, that destroys or depletes natural systems and natural
capital, will only undermine the basic ecological systems that we all depend on. In this sense, it should be clear that viewing
economic progress and environmental protection as competing goals is ultimately foolish and misguided. We cannot sustain
economic progress and human well-being if, at the same time, we are undermining and destroying the natural infrastructure that
makes such progress possible.
Unfortunately, much economic activity and economic development we see around the world today is unsustainable. Think of a
business or a household trying to make ends meet. That business or household might be able to balance its books month to month
by selling off equipment or other assets, but eventually this approach is not sustainable. Likewise, much of the economic progress
in recent decades has been based on liquidating, or using up, natural capital such as oil, coal, soils, forests, fisheries, mineral stocks,
and other resources. This economic progress has also generated massive amounts of pollution and waste products, and this
pollution is overwhelming the natural ability of many ecosystems to provide air and water purification services. In other words,
our current economic progress and economic systems do not meet the definition of sustainability and instead result in natural
capital depletion and destruction.
In Borneo, logging for timber, clearing forests for agriculture, and widespread burning of forests to make way for palm oil
plantations represent one approach to economic development—but in most cases one that is not sustainable. Overexploitation of
timber resources and logging faster than the rate of tree regrowth ultimately reduce the productivity of that forest and make it less
valuable over time. They also increase the risk of flooding, reduce water supply, and diminish water quality, all outcomes that
actually reduce quality of life and impose costs on society. Likewise, conversion of tropical forests in Borneo to palm oil plantations
may result in a short-term boost to the local economy and provide some employment opportunities. However, plantation
establishment also results in flooding, water contamination, loss of forest products, and other problems that might very well offset
any positive economic gains.
In this way we can see how the concepts of natural capital and sustainability are tightly linked. Sustainable economic development
does not depend on the destruction and liquidation of natural systems and natural capital, and therefore it does not undermine
people’s future ability to enjoy the services and benefits of these systems. Instead, sustainability means that we strive to meet our
needs in ways that maintain stocks of natural capital and the ecological integrity of natural systems. Think about this in the
chapters ahead as we examine the environmental and ecological impacts of current approaches to food production, energy use,
waste management, and other activities. Also try to imagine what a sustainable approach to these activities might look like.
1.5 Core Theme: Examining Our Impact
Now that we know what we are trying to sustain—natural capital—how do we know if we are actually doing so? What are some
indicators that can be used to determine if our economic activities have gone too far and are actually undermining our long-term
prospects? This section will introduce two concepts, the environmental footprint and the Anthropocene, that suggest we are
overexploiting natural capital on a worldwide basis and undermining long-term prospects for sustainability.
The Environmental Footprint
Few of us give much thought to the impact we have on the environment. If we do think about our impact, we tend to do so mainly in
terms of our immediate surroundings. In reality, our lifestyle and consumption patterns often have far-reaching effects on many
parts of the environment in ways that are difficult for us even to imagine. For example, how often do you think about where your
water or food comes from? Many of us rely on municipal water systems that might involve pumping water hundreds of miles and
running it through a series of filtration and purification systems before distributing it to thousands of households and businesses.
Almost all of us depend on commercial food systems that distribute food from all over the world using trucks, boats, trains, and
even planes. When you flip a light switch or flush a toilet, do you think about where that electricity comes from or where that waste
is going? All of these services are complex systems that require significant energy and resources, and these systems often have
wide-ranging environmental impacts.
Because so many of our activities and consumption patterns have environmental and
ecological impacts that are invisible to us—out of sight, out of mind—environmental
scientists have developed the concept of an environmental or ecological footprint. An
environmental footprint is a measure of how much land area and water is necessary to
support an individual or a group of people (see Figure 1.6). For example, how much land
and water is needed to grow the food you eat or the timber, paper, and forest products
you use? How big of an area is needed to effectively absorb and convert the liquid, solid,
and gaseous wastes that you produce every day? Because we consume resources in
different ways and live different lifestyles, individuals can have different environmental
footprints. In terms of diet, for example, it takes more land and water to produce meat
than an equivalent amount of grain or vegetables. Therefore, a person with a heavily
meat-based diet is likely to have a larger environmental footprint than someone who eats
less meat or is vegetarian.
Individual environmental footprints can be summed to determine the overall footprint of
a larger group of people, such as a city or an entire country. These cumulative
environmental footprints can be measured against the actual amount of land and water
resources available to that population in order to determine whether current
consumption patterns are sustainable. In other words, the environmental footprint of a
given population is a measure of its natural capital use, and by comparing natural capital
utilization to natural capital availability, a determination can be made as to whether that
population is behaving in a way that meets the definition of sustainability.
Perhaps not surprisingly, the average environmental footprint of a citizen of a country
like the United States, Canada, or France is 5, 10, or even 20 times larger than the
environmental footprint of a citizen of a less developed country like Indonesia, Ethiopia,
or Bangladesh. Furthermore, the overall environmental footprint of developed countries
like the United States exceeds the amount of land and water resources available to
support their populations on a sustainable basis. In other words, the United States is
meeting its current consumption patterns only by drawing down or depleting its own
natural capital resources or by “borrowing” those resources from other countries. You
could say that our environmental footprint shows that we are running a serious
ecological deficit. On a global scale, it’s estimated that the entire human population is
consuming resources and generating waste products at a rate that would require 1.7
planet Earths to be sustainable (Global Footprint Network, 2019). Obviously, we do not
have any other planet Earths available, so we must find ways to reduce the
environmental impacts of our activities and consumption if we are to reach a sustainable
In terms of our Borneo case study, it’s likely that most residents of that island have
relatively small environmental footprints, based on their direct consumption patterns.
However, global demand from countries like the United States for low-cost palm oil is
driving the process of deforestation for palm oil plantations. This example demonstrates
Figure 1.6: Environmental
If we were to illustrate the United States’
environmental footprint, it might look
like this. How much land and water does
your lifestyle require?
how consumption patterns in one place can have serious environmental impacts in
faraway places. As we examine the impact of food production, water management,
fishing, energy use, and waste production on the environment in the chapters ahead, try
to connect these to your own consumption and resource use patterns. What do you think
your own environmental footprint looks like? What steps could you take to reduce it?
Adapted from “WWF Report: Global Wildlife
Populations Could Drop by Almost 70% by 2020,” by
WWF, 2016 (https://www.wwf.org.hk/en/news/
Learn More: Your Environmental Footprint
The Global Footprint Network is the go-to source for information on the idea of environmental or ecological footprints.
The Anthropocene and the Sixth Great Extinction
Geologists and earth scientists use a geologic timescale to measure the history of the Earth. One unit of measure in that timescale is
an epoch, a particular period of time defined by distinctive features or events. For roughly the past 10,000 years, a geologic epoch
known as the Holocene, the Earth has been a fairly stable place. There have been no major shifts in climate, no global extinction
events, and no periods of widespread volcanic activity or changes in ocean chemistry.
These relatively stable conditions have provided the perfect setting for human civilizations to grow and flourish. In that time, the
human population of the entire planet has grown from roughly a few million people, equivalent perhaps to the current population
of Los Angeles, to roughly 7.7 billion people (see Figure 1.7). In just the past 200 years, the human population has increased by a
factor of 8, and the rates of consumption, material and energy use, and waste generation per person have also increased
Figure 1.7: Human population growth
Scientists wonder if Earth can continue to support the current trajectory of human population growth.
Based on data from “Historical Estimates of World Population,” by U.S. Census Bureau, 2018 (https://www.census.gov/data/table
mo/international-programs/historical-est-worldpop.html) ); “World Population Prospects 2019,” by United Nations DESA Population
Division, 2019 (https://population.un.org/wpp (https://population.un.org/wpp) ).
As a result of these dual trends—growing numbers of people and increasing
rates of material and energy use—some scientists now feel that we are
entering a new epoch, one they are calling the Anthropocene. The
Anthropocene, derived from the prefix anthropo–, or “human,” can be
defined as a geologic age or epoch during which human activities are the
dominant influence on the environment, oceans, climate, and other Earth
systems. Humans are literally leaving their mark on the planet, including
fundamentally altering the chemical composition of the atmosphere, oceans,
and soils; converting vast areas of open space to cities, suburbs, farms, and
other forms of development; and driving species to extinction at rates that
are 100 to 1,000 times greater than would otherwise be the case.
naumoid/iStock/Getty Images Plus
These rapid increases in extinction rates are leading environmental
scientists to worry that we are in the early stages of a sixth great extinction.
Scientists believe that since life began on Earth, there have been five great
extinction events—periods in which a significant percentage (70%–95%) of
species were wiped out. The first, known as the Ordovician–Silurian
extinction event, occurred roughly 440 million years ago. The most recent, known as the Cretaceous–Tertiary extinction event,
occurred 65 million years ago. It takes millions of years to bounce back from extinction events and reach comparable levels of
species diversity. But under relatively stable conditions, evolutionary processes create new species faster than others go extinct,
and so species diversity will increase over time. Since the last great extinction, the number of species on Earth has grown into the
tens of millions. Of these, we know the most about numbers of mammals and birds but far less about the status of fish, reptiles,
amphibians, plants, and invertebrates (organisms without a backbone, such as insects). Today, as extinction rates increase and far
surpass the rate at which evolution develops new species, we could be losing hundreds if not thousands of species before we have
had a chance to fully understand and study their place in an ecosystem.
Human activities are changing the planet. Our
choices are affecting the atmosphere, land,
oceans, and other species.
Unlike the first five great extinction events, which were caused by natural forces like mass volcanic eruptions and meteor strikes,
the current crisis is a direct result of human actions. Some of these human actions include pollution, overharvesting and
overhunting of species, the introduction of exotic or invasive species into ecosystems, and the effects of human-caused climate
change. (These and other causes of biodiversity loss and extinction will be reviewed in greater detail in Chapter 2.) However, the
most significant cause of species extinction today is habitat destruction, such as that in Borneo. Widespread conversion of tropical
forests to palm oil plantations, soybean farms, and grazing areas for cattle is wiping out habitat for all kinds of species and
contributing significantly to the rapid increase in extinction rates on the island.
In the chapters ahead, consider how human activities like agriculture, fishing, logging, mining, energy use, and waste generation
might be altering the planet in profound ways. Also consider what these activities might mean for other species and for rates of
biodiversity loss. In doing so, consider an idea proposed by the well-known and highly respected evolutionary biologist E. O.
Wilson. Wilson calls for a plan that would set aside one half of the planet as permanently protected areas for other species, an idea
known as the Half-Earth Project. Wilson and others are convinced that such a bold plan is the only way to avert a sixth mass
extinction event. Is such an idea even possible? Can we find ways to meet the needs of a human population soon to exceed 8 billion
while leaving room for other species?
Learn More: The Half-Earth Project
The Half-Earth Project is an effort designed to conserve half of the world so as to protect biodiversity and the ecosystem
services it provides. You can learn more about this project here.
1.6 Core Theme: Taking Action
Faced with evidence that our global ecological footprint is already exceeding capacity and that we are moving rapidly toward what
could be a sixth mass extinction, how do we change our approach to economic development and meeting our food, water, and
energy needs without making things worse? The chapters ahead will present alternative approaches to meeting our needs side by
side with a discussion of current approaches. But how do we know if those alternatives are worth pursuing, and how much time do
we have to decide whether to pursue them? This section introduces the concepts of uncertainty, scale, risk, and cost–benefit
analysis that help environmental scientists and policy makers grapple with these questions.
Uncertainty and Scale
The concepts of uncertainty and scale play an important role in how we define and address different environmental challenges.
Uncertainty is a defining characteristic of much of the work done by environmental scientists. The natural systems that these
scientists study are often so complex that there are always things they can’t be certain about. The scientific method is one
important way in which scientists reduce uncertainty. However, some uncertainty and even ignorance will still be present, and it’s
important to understand this when we examine evidence of environmental problems and the need to address them. Waiting for
“scientific certainty” before addressing an environmental challenge, a call often made by politicians in cases like climate change, is
simply an argument for doing nothing. Instead of waiting on a certainty that will almost never be achievable, policies and other
approaches for addressing environmental problems should be based on the best possible science available at that moment, even if
it still includes elements of uncertainty.
The concept of scale is also important to consider as you undertake the
study of environmental science. Environmental issues occur at many
different scales—local, regional, national, and global—and the larger the
scale, the more complex and difficult it tends to become to deal with these
issues. For example, small-scale deforestation in Borneo may be mainly a
local scale issue that might be understood and addressed in a fairly direct
fashion. If the scale of that deforestation increases, either because of larger
clearings or a larger number of small clearings that have begun to connect,
then we might move to a regional scale issue with broader impacts.
Understanding those impacts and developing ways to address them also
grow in complexity.
At this point, deforestation in Borneo has actually reached the level of a
national and global scale issue. National governments and international
Action needs to happen early. If we wait for
environmental groups are involved in defining and attempting to reduce the
scientific certainty before addressing issues,
problem. Global demand for palm oil and other products is driving
then we might face irreparable damage to our
deforestation not only in Borneo but also in the Brazilian Amazon and
environment and its creatures.
regions of central Africa. Meanwhile, land use practices in Borneo are
resulting in biodiversity loss, air pollution, and greenhouse gas emissions that are felt on a global scale.
zanskar/iStock/Getty Images Plus
As we study a variety of environmental issues in the chapters ahead, consider how issues of uncertainty and scale might affect
debates about the scope of the problem and possible solutions. Understand that scientists readily acknowledge elements of
uncertainty in their work and in what they study, but this does not mean they don’t know what they are talking about, nor is it an
excuse for inaction. Also consider how environmental issues operate at different scales and whether you can see this in your own
actions and their impacts on the environment.
Risk and Cost–Benefit Analysis
We make decisions about risk in our lives every day. Every time you fly on an airplane, drive a car, walk to work, fall in love, decide
to have a family, or enter a business relationship, you incur a risk that something will go wrong. Therefore, whether you are
conscious and deliberate in your choices or reckless and haphazard, you are making a personal form of risk analysis, or risk
In a similar manner, society must make risk analyses in setting environmental policy. You can see this type of decision making in
the news almost every day, along with the political and economic arguments on a local, state, or national level. For any issue, there
are a series of simple questions that must be addressed before choosing a path of action.
First, one must ask, “What is the probability that a given activity will cause harm?” Because systems are so complex, it is seldom
possible to say action A definitely will cause consequence B. Scientists build models based on experiments and observation and
test their models to the best of their ability. Rational nonscientists must then develop a course of action based on the probabilities
expressed by the majority of scientists working in the field.
Second, given that outcomes are usually uncertain, one must ask, “What are the consequences if we do nothing?” In our normal
lives, we spread a bigger safety net when the consequences are serious than we do when they are minor. If the brakes were likely to
fail on your car, you would act more aggressively to get them fixed than you would if the interior dome light were not working.
Because outcomes are never certain, we must balance risk and consequence in setting environmental policy.
Finally, one must ask, “What are the costs and risks of choosing other options?” In the case of Borneo, we know with a lot of
certainty that current land use practices are not sustainable. We also know that things will only get worse if we do nothing. The
real question comes when we consider what other options might exist. Environmental scientists, economists, and other
development experts can point to many alternative land use practices and economic models that could help better protect Borneo’s
environment while still providing livelihood opportunities to its residents. However, these alternative approaches may do less to
enrich certain members of society who hold a disproportionate amount of political power. Alternative approaches might make
sense from an overall societal perspective, but they might not be implemented due to local, regional, national, and even global
One commonly used tool in environmental risk assessment is cost–benefit analysis. It costs money to install pollution control in
factories, mining operations, automobiles, power plants, and other human-operated systems. These pollution control costs are
called internal costs because they are borne by the industries that produce specific goods and services. Consumers pay internal
costs whenever they turn on electricity, pump gasoline into a car, or buy anything at the store. But if pollution control is
nonexistent or inadequate, then everyone has to pay the cost of a dirty and unhealthy environment. Environmental disasters can
result in sickness, death, destroyed property, loss of work, reduction of home values, and so on. These societal costs of unregulated
pollution are called external costs, or externalities, because they are outside the activity itself and are not reflected in direct costs.
External costs are paid by everyone in society, regardless of what he or she purchases. Thus, if electric generation creates pollution
that causes negative health effects, a poor person who uses little electricity pays the same price as a rich person who uses a lot of
electricity. In fact, a poor person is likely to pay an even higher price, since many electric power plants and other polluting
industrial facilities (such as oil refineries) tend to be located in low-income areas.
Cost–benefit analyses can be used to compare the cost of pollution control with the cost of externalities. For example, as the cost of
pollution control increases, the cost of externalities decreases. The total cost to society can be found by combining costs of
pollution control and externalities. This total cost typically reaches a minimum when some, but not all, of the pollution is
controlled. Many suggest that we should strive to achieve this minimum cost even though this approach accepts some pollution,
with its possible discomfort, sickness, and even death. They argue that the alternative, more expensive pollution control, will slow
economic growth and lead to unemployment, with its own forms of human misery. Others argue that that cost–benefit analysis is
flawed because it ignores both the quality and the value of human life. How, they ask, can you place a dollar value on the spiritual
quality of a walk in the woods or a swim in a crystal clear mountain stream? How can you measure the economic value of even one
life cut short by cancer? If noneconomic costs of pollution are considered, then more pollution control becomes desirable.
No one knows the future. But the outcome will affect every person on the planet. We study environmental science because the
issues facing society are complex. There are no absolute answers. But certainly we—as individuals, municipalities, states,
countries, and citizens of the world—need to develop scientific, economic, and political policy based on an accurate evaluation of
the problems we face today and the future we envision for tomorrow. Certainly, an informed awareness is essential to making the
decisions that will affect all of us. As we study specific environmental issues in the chapters ahead, think about how issues of
uncertainty, scale, and risk might combine to shape perceptions and attitudes about how best to address that environmental
challenge. Also consider whether making use of risk analysis and cost–benefit analysis might help in guiding policy makers to a
better resolution of that challenge.
Bringing It All Together
This opening chapter introduced you to a lot of new terminology, concepts, and ways of seeing the world. The goal is not to just
have you memorize what these terms and concepts mean but to provide you with the tools you need to further explore a range of
environmental issues presented in the chapters to come. This chapter also provided you with the opportunity to begin to think
about your own connection to the environment, in terms of both your dependence and your impact on it. The next chapter will
continue to introduce you to concepts and terms important to the study of environmental science. The focus of Chapter 2, however,
will be on the field of ecology and establishing a natural science foundation. As we move to Chapter 3 and its focus on human
population growth and material consumption, and then to Chapters 4–9 with their focus on specific environmental issues and
challenges, see if you can connect and apply the terms and concepts introduced in this chapter to your own understanding of the
Our Connection to the Natural World
We seldom think about the important question of whether we view ourselves as apart from nature or as a part of nature. In this
interesting essay, leadership consultant Kathleen Allen asks that question and what the answer might mean for each person’s
This TED Talk argues that nature is not just some pristine wilderness thousands of miles away from where we live, but rather any
open space right outside our door. By going out into that space, we can develop a relationship with nature that’s good for us and for
Educator and speaker Michael Stevens has developed something of a cult following around his TED Talks on YouTube videos that
deal with how we ask and answer questions. His insights shine a light on how scientists approach their work and use a
combination of creative and critical thinking to ask and answer questions about the world around them.
Deforestation in Borneo
There has been a lot of good coverage of the deforestation issue in Borneo in recent years, including analysis of its causes, history,
future trends, and how our own consumption decisions might be implicated in that destruction. This well-written and insightful
piece examines the issue and what part you might play in reversing it.
Natural Capital and Ecosystem Services
Natural capital and ecosystem services can sometimes be difficult concepts to understand. These resources help explain what
natural capital and ecosystem services are and why they are so important for human well-being and survival.
Sustainability and Sustainable Development
The United Nations is attempting to make the concepts of sustainability and sustainable development a reality through its
Sustainable Development Goals. You can learn more about these efforts and the idea of sustainability in general at these sites.
The Anthropocene and the Sixth Great Extinction
The idea of the Anthropocene and the question of whether we are now entering this new epoch are being hotly debated among
environmental scientists and geologists. Learn more about this concept, and the scientific debate surrounding it, here.
A geologic age or epoch during which human activities are the dominant influence on the environment, oceans, climate, and
other Earth systems.
The variety of life and organisms in a specific ecosystem.
A region that has high rates of biodiversity and is also experiencing significant environmental destruction.
A systematic approach to calculating and comparing the costs and benefits of different policies.
The ability to analyze and address situations and challenges in new and creative ways.
The objective analysis and evaluation of an issue in order to form a judgment.
The act of clearing of forest areas.
The beneficial resources and processes that ecosystems supply to humans.
Tourism that is focused on natural environments in an effort to help conserve an area and support the local economy.
Species at risk of extinction.
Plants and animals that exist in only one specific geographic region.
Everything that surrounds us, including living and nonliving things; all physical, chemical, and biological factors and processes
that affect an organism.
A measure of how much land area and water is necessary to support an individual or a group of people.
A social and political movement committed to protecting the natural world.
The study of how the natural world works, how we are affected by the natural world, and how we in turn impact the natural
world around us.
The total loss of a species.
The place or set of conditions an organism depends on for survival.
The destruction of specific habitats.
The current epoch or geologic time period, roughly the past 10,000 years.
The ability to know when information is needed and the ability to identify, locate, evaluate, and effectively use that information
to address an issue.
Pertaining to multiple disciplines, or areas of study.
Natural assets such as trees, soils, streams, oceans, and the atmosphere.
An evaluation that considers the probability that a given action will cause harm, the consequences of inaction, and the costs and
risks of other options. Also known as risk assessment.
An approach to research based on observation, data collection, hypothesis testing, and experimentation.
Groups of organisms that share certain characteristics, interbreed, and produce fertile offspring.
The maintenance of natural systems and an ecological balance.
The achievement of economic development without the depletion or destruction of natural systems.
Understanding Ecology and Biodiversity
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After reading this chapter, you should be able to
Describe the components of the ecological hierarchy.
Identify characteristics of all ecosystems.
Explain how energy flows through ecosystems.
Describe how matter cycles in ecosystems.
Explain how and why eutrophication occurs.
Describe the importance of biodiversity and the major threats to it.
Discuss what is being done to address threats to biodiversity.
Define the term planetary boundaries.
The environment and the study of the environment encompass everything that surrounds us, including all living and nonliving
things. Ecology is the study of the relationships and interactions between living organisms and their surrounding environment.
The term ecology derives from the Greek word for “house” or “dwelling,” oikos, and “study,” or logy. In other words, ecology is the
“study of our house,” and it is at the core of what environmental science is about.
The goal of this chapter is to give you a foundation in some key ecological concepts that will be important to studying
environmental issues in subsequent chapters. The chapter starts by introducing the idea of the Earth as a system and how
ecologists and environmental scientists use a “systems view” or “systems thinking” in the work they do. We will then focus on the
study of the environment at the ecosystem scale, considering what ecosystems are, how they are defined, and what some of their
key characteristics are. We will review two fundamental ecosystem processes—energy flow and matter cycling—that play a central
role in understanding environmental issues.
We then shift to the concept of biodiversity: what it means, why it matters, and what are the major threats to it. The chapter
concludes with a brief discussion of an interesting concept known as planetary boundaries. These boundaries were developed as a
way to help us think of the planet’s overall health and to warn us when our actions might be jeopardizing the environment we all
depend on. If we think of ecology as the study of our “house,” planetary boundaries are a way for us to monitor and stay aware of
threats or dangers to the planet we all call home.
2.1 The Earth as a System
Throughout this book, and in the study of environmental science, you will frequently hear the environment described as a system
or as being composed of numerous, interconnected systems. What does this mean, and why does it help to think about the
environment in terms of systems?
A system can be defined as a set of connected or interdependent things that together form a more complex whole. For example, the
car you drive is made up of multiple, interacting systems that work together to provide you with mobility. These include the
ignition, electrical, braking, steering, cooling, and suspension systems. Likewise, a rain forest in Borneo, a wetland along the Gulf
Coast, a mountain stream in the Rockies, or a grassland in the upper Midwest can all be thought of as systems (in this case,
ecosystems). Forests, wetlands, streams, grasslands, and other ecosystems all consist of organisms and elements that are
interdependent and that together make up a more complex whole.
Given the sheer complexity of the Earth as a system, ecologists and environmental scientists find it helpful to view and study the
world at different scales. They do this through an approach known as the ecological hierarchy theory. The ecological hierarchy
illustrates the relationships between different organisms and organizes those relationships into different levels.
At the first level of the ecological hierarchy are individual organisms, such as a single elephant or bird. Multiple individuals of the
same species living in a particular location, such as a herd of elephants or a flock of birds, are considered a population, the second
level of the ecological hierarchy. A group of populations of different species that interact and live in the same place—such as a
forest, stream, or wetland—is known as a community, the third level of the ecological hierarchy. This community and its physical
environment make up the next level, an ecosystem. In other words, ecosystems include the living, or biotic, communities that
occupy them, as well as the nonliving, or abiotic, characteristics that often shape the abundance and diversity of life in that location.
Different ecosystems connect and interact with one another—for example, a forest ecosystem connects with the stream ecosystem
that runs through it—and make up a landscape. At an even larger scale, or higher level, ecosystems and landscapes that have
similar climate and vegetation can be grouped into biomes (see Figure 2.1). Generally speaking, tropical regions characterized by
warm temperatures, an abundance of moisture, and relatively constant levels of daylight contain the biomes with the highest
number and diversity of organisms.
Figure 2.1: Biomes
Earth’s major biomes result primarily from differences in climate. Each biome contains many
ecosystems made up of species adapted for life in their specific biome.
Adapted from “Global Soil Regions Map,” by U.S. Department of Agriculture Natural Resources Conservation Service, 2005 (http://ww
Explore the following interactive to learn more about specific biomes.
Let’s use an example to illustrate the ecological hierarchy at work (see Figure 2.2). We’ll start with a single bird common to our
state of Pennsylvania, the wood thrush. A certain population of wood thrushes breeds and reproduces in a specific forested region
near the home of one of the authors. That population of wood thrushes interacts with other populations of birds, mammals, insects,
and plants at the community or biotic community scale. The biotic community, combined with the abiotic or nonliving components,
make up an ecosystem—in this case a forested ecosystem that the wood thrush favors as habitat. That forest is embedded in a
larger landscape of rivers, streams, wetlands, and human-dominated land uses. The forests of Pennsylvania are similar to
temperate forests in other regions of the United States and the world and make up part of the temperate forest biome.
Figure 2.2: The ecological hierarchy
The ecological hierarchy enables ecologists and environmental scientists to study the Earth at different
At the highest scale, or level, the entire planet is made up of four separate but interacting realms or spheres (see Figure 2.3). These
four spheres include the lithosphere (or geosphere), the hydrosphere, the atmosphere, and the biosphere. The lithosphere is the
solid Earth, specifically the upper crust (extending up to 100 kilometers, or 62 miles, below the surface) and the uppermost mantle
(extending as far as 2,500 kilometers, or 1,550 miles, below the surface). The hydrosphere is the watery parts of our planet: the
oceans, rivers, lakes, clouds, groundwater reservoirs, and glaciers that cover three quarters of the Earth’s surface. The atmosphere
is a mixture of gases, mostly nitrogen and oxygen, with smaller amounts of argon, carbon dioxide, and other trace gases. The
atmosphere is held to the Earth’s surface by gravity and thins rapidly with altitude. Ninety-nine percent of the Earth’s atmosphere
is concentrated in the first 30 kilometers (19 miles), but a few traces of atmospheric gases remain even in frigid, near-space
conditions thousands of kilometers above the Earth’s surface. The biosphere is the zone where life exists on Earth. Most life
concentrates at or near the surface of the land and ocean, but some bacteria thrive in rocks 4 kilometers (2.5 miles) beneath the
surface, some organisms live in deep ocean trenches, and a few windblown microorganisms drift in thin, cold, inhospitable air
waves 10 kilometers (6 miles) above the surface. Most of this book will focus on issues and conditions that occur in the biosphere,
but we will also examine the lithosphere (energy resources), the hydrosphere (freshwater and ocean resources), and the
atmosphere (climate change, air pollution, and ozone depletion).
Figure 2.3: The four spheres
The highest scale, or level, of the ecological hierarchy is made up of four spheres. Environmental
scientists study interactions among the atmosphere, lithosphere, and hydrosphere. The biosphere is the
zone of all three spheres that contains life.
The concepts of the ecological hierarchy and the four spheres allow us to take something as vast and complex as the entire planet
and view it at many different scales. A systems view or systems thinking helps us see how the pieces within each level connect and
interact. Systems thinking is an approach to science that considers not just the individual parts of a system but also how they
interact and interrelate over time. When we think of the environment as a system, we become more aware of how our actions in
one place might have consequences in another. The late ecologist Barry Commoner (1971) summed this up in his first law of
ecology: Everything is connected to everything else.
Section 2.2 will home in on one level of the ecological hierarchy—the ecosystem. Much of the work done by ecologists and
environmental scientists is at the ecosystem scale, and so it is important to better define and understand what ecosystems are and
how they operate.
2.2 Ecosystems as a Concept
Section 2.1 described ecosystems as a collection of living (biotic) and nonliving (abiotic) entities that exist and interact in a
particular location and time. For example, the forest ecosystem that is home to the wood thrush is made up of birds, insects,
mammals, amphibians, fungi, trees and plants, soils, rocks, and nutrients. Forests and other ecosystems are characterized by a
number of factors that are the focus of this section.
Ecosystems Are Open
Virtually all of the Earth’s ecosystems are open systems, meaning that they receive inputs from surrounding systems and produce
outputs. Some of ecosystems’ most important inputs and outputs come in the form of energy and matter, which will be described in
much greater detail in Section 2.3. For now, it’s enough to visualize an ecosystem in much the same way you might view your home,
as an open system that relies on inputs of food, energy, and water while producing outputs like solid waste, wastewater, and
emissions of air pollutants. Ecologists refer to the energy and matter that flow into, through, and out of an ecosystem as
Ecosystems Are Subject to Feedback Loops
As energy and matter flow into and out of ecosystems, and as ecosystems
are subject to various kinds of disturbance and change, we often see what
are known as feedback loops. A positive feedback loop causes the system
to keep changing further in the same direction. A negative feedback loop
causes the system to change in the opposite direction.
In nature, a positive feedback loop might occur when a section of a forest is
clear-cut, creating light and temperature conditions along the new forest
edge that lead to even further loss of trees and worsening deforestation. A
negative feedback loop might occur if there were a sudden increase in the
population of a certain insect species. This might lead to an equivalent
increase in the population of birds and other organisms that prey on or eat
that insect, returning the insect population to what it was originally. Positive
feedback loops tend to be destabilizing, resulting in continual change, while
negative feedback loops tend to be self-correcting or stabilizing.
Clear-cutting forest can create conditions that
In other words, don’t think of positive feedback loops as “good” or negative lead to further deforestation—an example of a
feedback loops as “bad.” In fact, the opposite is generally the case. Most positive feedback loop.
systems in nature are characterized by negative feedback loops, which
result in a dynamic equilibrium or homeostasis—the tendency of a system to maintain relatively stable conditions over time.
When a system is experiencing a series of positive feedback loops, changing further and further in the same direction, it’s possible
that it could reach a threshold or tipping point. When this happens, the system collapses or shifts to a new, different state. For
example, when water is boiled to a tipping point of 100 °C (212 °F), it turns to vapor. When water is cooled to 0 °C (32 °F), it turns
A potential tipping point that worries many environmental and climate scientists involves a positive feedback loop from melting
permafrost areas in the Arctic. This will be explained in more detail in Chapter 8, but basically, permafrost soils hold large
quantities of methane and carbon, which can become carbon dioxide as these soils thaw. Human activities like burning fossil fuels
are already raising methane and carbon dioxide levels in the atmosphere. Methane and carbon dioxide are greenhouse gases that
trap heat in the atmosphere, and this is increasing temperatures in the Arctic. As temperatures increase, permafrost soils begin to
thaw and release more methane and carbon dioxide into the atmosphere. This methane and carbon dioxide leads to further
warming and more thawing of permafrost soils, which results in even greater releases of methane and carbon dioxide, and so on.
Such a situation could lead to rapid and runaway global warming and climate change, pushing our planet beyond a threshold and
over a tipping point.
Ecosystems Provide a Range of Conditions
For a wood thrush to survive in the forested ecosystem in Pennsylvania, it requires certain resources and conditions such as food,
water, and reasonable temperatures. When these environmental factors and conditions are present in a way that is most favorable
for the wood thrush, they are said to be in the optimal range. The entire range over which the wood thrush could survive, even if it
did not thrive in an optimal sense, is known as the range of tolerance, with the extreme ends of that range known as the limits of
tolerance. Conditions that fall between the optimal range and the limits of tolerance are known as zones of stress because organisms
experience increasing stress the further they are from their optimal range.
All living organisms have an optimal range, zones of stress, and limits of tolerance for every abiotic factor they depend on, and
these are different for different species. Some species have a very broad optimal range and can tolerate a wide variety of
conditions, while other species are more sensitive and have optimal ranges that are narrow. Ecologists refer to a factor that limits
growth as a limiting factor, meaning that even if other factors and conditions are present in optimal amounts, the absence or
shortage of a limiting factor will stress organisms that depend on it. For example, you can give a plant all the water and nutrients
you want, but if there is not enough light, the plant will be limited in its growth. Lastly, we generally find that certain species, like
the wood thrush, are present in specific habitats, like a temperate forest. Within that forest, the wood thrush occupies a specific
ecological niche, the combination of conditions and resources needed for it to live. Different species can occupy the same habitat
but have very different niches. Different bird species in the same forest habitat can nest in different places, eat different foods, eat
at different times of day, and have other differences in their ecological niche that limits competition between them.
2.3 Fundamental Ecosystem Processes: Energy Flow and Matter Cycling
Despite the range of conditions that characterize the ecosystems found in different biomes around the world, all these ecosystems
have something in common. With few exceptions, Earth’s ecosystems are powered by solar energy, and the organisms within those
ecosystems depend on matter in the form of nutrients, water, oxygen, and other gases to survive. This section reviews two
fundamental ecosystem processes that will help you better understand life on Earth: energy flow through ecosystems and matter
cycling in ecosystems.
Energy Flow Through Ecosystems
The most basic definition of energy is the capacity or ability to do work. In
ecology, the term energy is usually used to define the ability of organisms to
do biological work, such as moving, growing, eating, or reproducing.
Scientists further divide energy into two basic forms: kinetic and potential.
Kinetic energy is energy in motion, while potential energy is stored
energy. The image of a dam is often used to illustrate the difference between
these two types of energy. By holding moving water back, a dam is creating
a reservoir, which represents accumulated or potential energy. When the
gates of the dam are opened and the water starts to move again, that
potential energy is converted to kinetic energy. Likewise, gasoline
represents a type of potential energy, stored in the chemical bonds among
the atoms that compose it. When that gasoline is ignited in the engine of a
car, the potential energy held in those chemical bonds is released and
converted to the kinetic energy of motion.
Laws of Thermodynamics
A dam represents the difference between kinetic
and potential energy. Water held by the dam in a
reservoir is potential (stored) energy. When the
water is released by opening the gates of the
dam, it turns into kinetic energy.
There are two fundamental laws or principles that apply to energy. The first
law of thermodynamics (also known as the law of conservation of energy)
states that energy can change from one form to another but cannot be created or destroyed. When we burn gasoline in a car engine,
we are converting that chemical energy to the energy of motion and heat, but we end up with the same amount of energy. The
second law of thermodynamics states that even though the overall amount of energy is conserved, energy conversion will always
change that energy from a more useful to a less useful state. Gasoline is a highly useful form of energy because small quantities of it
contain great potential to do work, but once combusted it changes to mostly heat energy that is too diffuse to be useful. This
tendency for energy to move from a more useful state to a less useful state is known as entropy. An important implication of the
laws of thermodynamics is that energy conversions tend to be inefficient. Only a small portion of the chemical energy stored in
gasoline (typically 15%–25%) is actually converted to mechanical energy.
If every energy conversion moves us from a more useful state to a less useful state, we would appear to be doomed to a world of
increasing disorder. Yet in the world around us, we see many signs of increasing order—for example, humans, animals, plants, and
other organisms being born and growing. So how can this be? The answer lies in the fact that the Earth is an open system subject to
inputs of solar energy. That incoming solar (light) energy drives processes that create new stores of potential energy that fuel
virtually all the Earth’s ecosystems.
Fuel for Life
Most living systems and organisms on the planet are ultimately powered by energy from the sun. The starting point is a group of
organisms known as autotrophs or primary producers: mostly plants, algae, and some types of bacteria. Primary producers take
the building blocks of carbon dioxide and water and produce sugar (glucose) molecules with high potential energy content.
Primary producers do this through a process known as photosynthesis. Photosynthesis is driven by light energy from the sun, as
illustrated in Figure 2.4.
Figure 2.4: Photosynthesis
Producers use photosynthesis to convert the basic building blocks of sunlight, carbon dioxide, and water
into energy other organisms can use.
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