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Prior to beginning this discussion, read Chapters 7 and 8 in your course textbook.
Imagine that you are a resident of Arzaville, a community whose characteristics are described below. You have come together with your neighbors for a special meeting to devise a plan for helping the community become carbon-neutral by 2050, meaning that by that time, no net carbon dioxide emissions will be produced by residents as a whole.
Fortunately, you have all attended the meeting with knowledge that you have gained from your readings in this course. Now it is time to put your thinking cap on and get to work! Your plan should consist of the following elements:

Energy conservation measures (e.g., promoting carpooling by adding special lanes to local highways).
Steps to move toward sustainable energy production (e.g., installing solar panels on town government buildings).

Reducing energy consumption will help, but some actions will have to involve switching to other power sources for buildings and vehicles as well.

This week’s discussion will take place in an online app called Tricider. There, you will be able to post your ideas for plan components and share pros and cons of different proposals during the week. Finally, you will be able to vote on the three components that you think the plan should include.
For directions on how to use the Tricider app, please review the Tricider Help Guide Download Tricider Help Guide. In Tricider. You will be expected to do the following:

Post at least two separate and entirely original ideas. Do not duplicate ideas already posted by your peers.

Include your full name for each one.

Post at least six different pros and six different cons for your classmates’ proposed ideas (12 in all).
Vote on what you feel are the top three ideas in the list.

Do not vote before Friday, so that you can vote from the full collection of student ideas.

You must complete the three tasks above to receive full credit for this discussion.
Please note: You are welcome to post questions and comments to this board for your instructor; however, this discussion board does not have any posting requirements of its own, and no additional credit will be given for posts made here.
In the discussion area, the instructor will post the following:

The Arzaville description you will be using for this activity
The link you will be using to access Tricider for this activity.

8 Sustaining Our Atmosphere and Climate

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Learning Outcomes

After reading this chapter, you should be able to

• Differentiate between the troposphere and the stratosphere and between weather and climate.
• Describe different sources of air pollution and their environmental and health impacts.
• Identify different ways to reduce air pollution.
• Describe causes and impacts of stratospheric ozone depletion.
• Explain the relationship between the Earth’s energy balance and the greenhouse effect.
• List evidence for the warming of the Earth and humanity’s role in global climate change.
• Describe the impacts of global climate change on the environment, economy, and human

health.
• Identify different ways to address global climate change.

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Section 8.1 Earth’s Atmosphere

Beijing, a city of 17 million people, has some of the worst air pollution of any major city in
the world. When the 2008 Summer Olympic Games were held in the Chinese capital, there
was widespread concern over the effect air pollution might have on the athletes as well as
spectators attending the games. Some athletes with preexisting health conditions refused to
participate, while others caused a stir by arriving at the games wearing protective face masks.

Chinese government leaders took action to address concerns and avoid the possible embarrass-
ment of hosting a major global event shrouded in smog. Two months before the Summer Games
were set to begin, heavily polluting factories were shut down, large-scale construction projects
were halted or scaled back, and measures were taken to drastically limit the number of cars and
trucks on the road. Overall, close to $20 billion was spent to clean up the city’s air, and the efforts
did appear to have some positive impact. Reduced emissions from cars and factories combined
with favorable weather conditions to avert terrible smog conditions, even though most major
air pollutants continued to exceed safe levels throughout most of the games.

Aware that China was going to implement these pollution restrictions, scientists and pub-
lic health experts saw an opportunity to study the effects of air pollution on human health.
One such study recruited 125 healthy premedical students in Beijing and began monitoring
their heart and lung conditions before the pollution restrictions were put in place, during the
restrictions and the period of the Summer Games, and for months afterward. The results of
this research were published in the Journal of the American Medical Association in 2012 and
showed clearly that during the period of the pollution restrictions, the heart and lung condi-
tions of the research subjects improved dramatically (Rich et al., 2012). A different study
examined birth weights of babies born in Beijing hospitals before, during, and after the pollu-
tion restrictions. It found that women who were 8 months pregnant during the period of the
2008 Summer Olympic Games gave birth to heavier and healthier babies, compared to the
other two groups (Rich et al., 2015).

The story of the 2008 Summer Olympic Games is a dramatic example of how pollution can
affect human health. And yet it is just one example of how our quality of life worsens when
we use the air around us as a dumping ground. This chapter will examine three different envi-
ronmental challenges that result from our disregard for the air and atmosphere: air pollu-
tion, stratospheric ozone depletion, and global climate change. Each challenge has a different
cause and operates on a different timescale, geographic scale, and location.

The bulk of this chapter will focus on what is perhaps the most serious of the three challenges
and arguably the greatest environmental challenge facing the world today: global climate
change. As its name suggests, global climate change is a global problem with no easy, quick fix.
In fact, many environmental scientists are worried that our current inaction in the face of global
climate change is locking in catastrophic levels of change for the planet for centuries to come.

8.1 Earth’s Atmosphere

A recurring theme in this book is the degree to which we tend to take for granted and over-
look the natural systems that surround us. That’s certainly also the case for our atmosphere.
When human populations were small and geographically spread out, pollutant emissions

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Section 8.1 Earth’s Atmosphere

could mix and disperse and not pose much
of a problem. However, as our population
approaches 8 billion, and as our activi-
ties involve ever greater consumption of
energy and other material, our impacts on
the atmosphere are becoming more severe.
To fully understand how human activities
lead to air pollution, ozone depletion, and
runaway climate change, we need a basic
understanding of the atmosphere itself.
What is the atmosphere? How does this crit-
ical form of natural capital help make life on
Earth possible in the first place?

Because our atmosphere cannot really be seen or touched, we often use interesting ways to
describe it. Our atmosphere has been called a “thin envelope” or a “thin blanket” of gases sur-
rounding the Earth and held in place by gravity. Despite the atmosphere extending miles into
the sky, it’s been pointed out that if the Earth were an apple or a peach, the thickness of the
atmosphere would be equivalent to the thickness of the skin on those fruits. Our atmosphere
provides us with the air we breathe, helps regulate climate in ways that make the planet hab-
itable, and contains gases that filter out dangerous forms of solar radiation that could other-
wise make life on the surface of the Earth impossible.

The Earth’s atmosphere is divided, from lowest to highest, into four layers—the troposphere,
the stratosphere, the mesosphere, and the thermosphere. For the purposes of this chapter,
we will focus on the two lowest layers, the troposphere and the stratosphere (see Figure 8.1).

Johnson Space Center/NASA
When viewed from the International Space
Station, Earth’s atmosphere is a thin blue layer
over the surface of the planet.

Figure 8.1: Earth’s atmosphere

The troposphere and the stratosphere are the layers of the atmosphere that most directly affect our
daily lives.

Troposphere

Stratosphere

Ozone layer

Earth

Mt. Everest

9 km

10 km

50 km
Ozone layer

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Section 8.1 Earth’s Atmosphere

Troposphere
The troposphere ranges in height from 8 kilometers (5 miles) in polar regions where air is
cold and dense to 18 kilometers (11 miles) over tropical regions where warm air causes ris-
ing air currents. The troposphere is the region of the atmosphere that most directly impacts
our day-to-day lives. It’s where we live and breathe and is where virtually all the water vapor,
clouds, and weather on the planet exist. Air in the troposphere is 78% nitrogen (N2), 21%
oxygen (O2), and 0.9% argon (Ar). The remaining one tenth of 1% is made up of “trace” gases
like carbon dioxide (CO2), neon (Ne), methane (CH4), and nitrous oxide (N2O), as well as water
vapor. As we’ll discuss, some of these gases, though present in very small quantities, exert an
important influence on the Earth’s climate system. The top of the troposphere is known as the
tropopause, something of a boundary between the troposphere and the stratosphere above.

Stratosphere
The stratosphere ranges in height from 18 to 50 kilometers (11 to 31 miles) above the Earth’s
surface. The chemical composition of air in the stratosphere is similar to that of air in the tro-
posphere, with a couple of key exceptions—air in the stratosphere contains almost no water
vapor, and it has about 1,000 times more ozone (O3). While ozone is a dangerous air pollutant
near the Earth’s surface, it plays a critical role in the stratosphere. Most of the ozone in the
stratosphere is concentrated in an area 18 to 26 kilometers (11 to 16 miles) above the Earth
in a region known as the ozone layer. Ozone molecules in the ozone layer effectively absorb
certain wavelengths of incoming ultraviolet (UV) solar radiation that can seriously damage
living tissues. For this reason, the stratosphere and the stratospheric ozone layer have been
referred to as “Earth’s sunscreen.” You’ll learn more about the ozone layer, and threats to it,
in Section 8.3.

Weather Versus Climate
Energy from the sun is constantly striking the atmosphere. About one fourth of this energy is
reflected by clouds and the atmosphere back to space, about one fourth is absorbed by clouds
and atmospheric gases, and about half reaches the Earth’s surface. The solar energy that is
absorbed by clouds, atmospheric gases, and surfaces on Earth is reemitted as longer wave
infrared or heat energy, warming the air and causing evaporation. This warms the air near the
surface and causes it to rise, before that air cools again and sinks. This rising and falling of air
creates what is known as convective circulation.

Convective circulation patterns help drive the planet’s weather, since heat and moisture get
moved around the globe in the process. Weather consists of the day-to-day changes in tem-
perature, atmospheric pressure, precipitation, humidity, and wind. In contrast, climate refers
to average temperature and precipitation patterns in a given area over a longer period, such
as a year. As you’ll see, confusion over the difference between weather and climate is one of
the reasons why global climate change is misunderstood.

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Section 8.2 Air Pollution

8.2 Air Pollution

Air pollution is the presence of substances (air pollutants) in the atmosphere in high enough
concentrations to harm humans, other organisms, and inanimate structures such as buildings.
Air pollutants can come from natural sources like volcanoes, forest fires, and dust storms, as
well as from a variety of human activities. Once in the atmosphere, air pollutants can create
problems based on their concentration; how they react with sunlight, water vapor, and other
chemicals in the atmosphere; how they are transported from one place to another; and how
and where they eventually wash out of the atmosphere (atmospheric deposition). The chapter
will first examine major sources and types of air pollution and then consider their impacts
and possible ways to control and address the air pollution challenge.

Sources and Types of Air Pollution
Environmental scientists typically start by breaking air pollution down into two major cat-
egories. Primary air pollutants are those that are emitted directly into the atmosphere, such
as particulate matter and sulfur dioxide emitted from burning coal in a power plant. Sec-
ondary air pollutants are formed through chemical reactions in the atmosphere between
primary air pollutants and other substances. Environmental scientists also find it helpful to
distinguish between air pollutants that come from a stationary source like a coal-fired power
plant versus those that are emitted by a mobile source like a car or truck.

Primary Pollutants
Carbon monoxide (CO) is an invisible, odorless, tasteless gas that results from the incom-
plete combustion of carbon-based fuels, primarily from motor vehicle exhaust. A second major
source of CO is firewood burning and forest fires. Carbon monoxide is dangerous because of
its ability to bind to hemoglobin and impair the delivery of oxygen to tissues. Overexposure
to carbon monoxide can result in headaches, nausea, fatigue, and ultimately heart damage
and death.

Nitrogen oxides (NOX) include nitric oxide
(NO) and nitrogen dioxide (NO2). Most NOX
emissions come from internal combustion
engines in vehicles, as well as from wood
burning and forest fires. NO2 is a reddish-
brown gas that can cause lung irritation
and respiratory disease; it can also react
with water vapor to form a secondary pol-
lutant known as nitric acid (HNO3). Nitric
acid is one of the causes of acid deposi-
tion, or acid rain, which is precipitation—
including dust, gas, and fog—that contains
acid and falls to the ground. Acid deposition
can damage plants, harm aquatic life, and
even eat away at statues and the exterior of
buildings.

Sebastian Kunigkeit/picture-alliance/dpa/AP Images
Michel Picaud, president of the charity Friends
of Notre-Dame de Paris, points out damage
caused by acid deposition at the famous Notre
Dame Cathedral in Paris, France.

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Section 8.2 Air Pollution

Sulfur dioxide (SO2) results from the combustion of fuels that contain sulfur, primarily from
burning coal in power plants. SO2 can react in the atmosphere to form a secondary pollutant
known as sulfuric acid (H2SO4), which also contributes to acid deposition. Sulfur dioxide and
sulfuric acid aerosols or droplets reduce visibility, damage crops and trees, corrode metals,
damage exterior surfaces, and cause respiratory problems.

Suspended particulate matter (PM) refers to a range of solid and liquid particles that are
small enough and light enough to remain suspended in the air. Particulate matter can come
from natural sources (pollen, spores) as well as from human activities (soot and smoke from
fuel combustion, dust from construction projects). Scientists and environmental regulators
classify particulate matter into two categories based on their size. Fine particulate matter,
or PM-10, are particles with a diameter of 2.5 to 10 micrometers. (For comparison, a typical
human hair is roughly 70 micrometers in diameter.) Ultrafine particulate matter, or PM-2.5,
are particles smaller than 2.5 micrometers in diameter. Public health experts are particularly
concerned about PM 2.5 pollution because smaller particles are more likely to enter deep into
the lungs, where they can damage tissue and impair lung, heart, and brain function.

Volatile organic compounds (VOCs) are a range of chemical compounds that originate from
both natural sources (e.g., plants) and human activities. VOCs are labeled as “volatile” because
they are compounds that can easily become vapors or gases. Major anthropogenic, or human
sources, of VOCs include gases that escape from dry-cleaning solvents, gasoline fumes, paint
fumes, and plastics manufacturing. VOCs are a major contributor to the formation of ozone
pollution, described in more detail later.

Lead (Pb) is a metal, particulate air pollutant that can enter the atmosphere from combustion
of leaded fuels as well as from waste incinerators, lead smelters, coal burning, mining, and
battery manufacturing facilities. Lead is toxic to the human nervous system and can impede
brain functioning and development. Prior to 1986 the main source of atmospheric lead pol-
lution in the United States was leaded gasoline combustion. The phaseout and banning of
leaded gasoline in the United States during the 1980s is a regulatory success story, and public
health research has confirmed that in the years following the ban, average IQs of children
actually increased. Globally, most countries now ban leaded gasoline, although a handful still
allow the use of this product.

Ozone
We briefly touched on some secondary pol-
lutants such as nitric acid and sulfuric acid,
but one secondary pollutant that needs
greater attention is ozone. Ozone (O3) is
formed in the troposphere as a result of reac-
tions between VOCs and NOX. These chemi-
cal reactions need energy from sunlight to
occur, so ozone pollution is also referred to
as a photochemical oxidant. Ozone mixes
with other pollutants in the troposphere to
form photochemical smog.

John Partipilo/The Tennessean/Associated Press
Some cities issue warnings about air quality
when the smog is bad enough to affect
public health.

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Section 8.2 Air Pollution

Recall that ozone in the stratosphere is “good ozone” and necessary for the survival of life on
the planet as we know it. However, ozone near the Earth’s surface, in the troposphere where
we live and breathe, is a different story. One easy way to remember this distinction is to use
the phrase “ozone, good up high, but bad nearby.” Down here ozone is “bad.” It can cause
breathing problems, throat and eye irritation, and coughing and can aggravate heart and lung
conditions. Ozone is also damaging to plant tissues as well as human-made materials like
fabric, paints, and rubber. It’s for these reasons that “ozone alerts” are issued in many met-
ropolitan areas during periods when oz one pollution is bad enough to significantly impact
public health. In particular, ozone alert days are especially dangerous to vulnerable popula-
tion groups like small children, the elderly, and people suffering from respiratory and heart
conditions.

Impacts of Air Pollution
It’s evident from the review of primary and secondary air pollutants that there are a wide
range of known health impacts associated with exposure to air pollution. These include heart
and lung damage, respiratory conditions like asthma, brain impairment, and cancer. Some
of these conditions are chronic or long term, while others—like an asthma attack or a heart
attack—are acute and can occur suddenly.

Because changes to human health are caused by so many interacting factors (environment,
diet, genetic traits), it’s sometimes difficult to pinpoint the specific impact of any one factor
like air pollution. However, by analyzing large population data sets and controlling for other
factors, scientists and public health experts are developing a much better understanding of
just how significant a role air pollution plays in human health. For example, a 2019 report
in the journal Lancet Planetary Health estimates that 4 million children worldwide develop
asthma every year as a result of air pollution (Achakulwisut, Brauer, Hystad, & Anenberg,
2019). While conditions are worse in countries like India and China, air pollution is still a
major contributor to new childhood asthma cases in many parts of the United States as well.
A 2019 report by the Health Effects Institute estimated that air pollution will shorten the
average expected life span of a child born today by almost 2 years. Likewise, research by the
University of Chicago’s Energy Policy Institute indicates that the average person alive today
would live 2.6 years longer if that person were not exposed to the worst levels of primary
and secondary air pollutants described previously (University of Chicago, n.d.). Finally, WHO
(2014) estimates that as many as 7 million premature deaths occur worldwide each year as a
combined result of outdoor and indoor air pollution.

Air pollution is bad not only for humans but also for other animals and organisms. Plants are
particularly sensitive to certain forms of air pollution. It’s estimated that tropospheric ozone
pollution leads to crop losses of 5% to 15% for major crops like corn, soybeans, and wheat
(United Nations Economic Commission for Europe, n.d.). Ozone pollution and acid deposition
can also impact forest health and productivity. Trees that are weakened by exposure to air
pollution are also less able to withstand pest and disease outbreaks. Finally, air pollution can
even impact life underwater in aquatic ecosystems. For example, acid deposition can change
the chemistry and pH of lakes and streams. Because many fish and other aquatic organisms
are adapted to living in a narrow range of chemical conditions, these changes can stress and
even kill them.

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Section 8.2 Air Pollution

Lastly, air pollution can damage exterior surfaces, statues, and buildings. Some of the most
obvious effects are aesthetic, since dust, soot, and other particles darken and discolor exte-
rior surfaces. Acid deposition can eat away at limestone and marble statues and building
facades and cause them to crumble and erode. Ozone pollution can weaken and deteriorate
rubber products like tires and can degrade fabrics and other materials. Acid deposition and
other air pollutants can even corrode metal and weaken highways and bridges. A 2014 study
in the American Journal of Engineering Research estimated that structural corrosion linked
to air pollution was costing the Indian economy $45 billion each year (Rao, Rajasekhar, &
Rao, 2014).

Addressing Air Pollution
Over the long term, one of the most effective ways to address many air pollution problems is
to drastically reduce combustion of fossil fuels and transition to a greater reliance on renew-
able energy sources. As we saw in Chapter 7, however, that transition is still underway and
could take decades to complete. As a result, we still need to take steps to limit air pollution for
the immediate future.

One way to reduce air pollution and limit the negative impacts of this environmental chal-
lenge is through regulation. The first real federal regulation of air pollution in the United
States came in 1955 with the Air Pollution Control Act. This act was spurred in part by “killer
smog” events in Donora, Pennsylvania, in 1948 and London, England, in 1952. Both of these
events occurred when weather conditions worked to trap heavy air pollution from industries,
coal-burning stoves, cars, and trucks in the lower atmosphere. By the time the air cleared,
it had killed dozens of people in the small town of Donora and thousands in London, while
sickening many more. However, the 1955 Air Pollution Control Act had a very limited impact,

and growing public disgust with worsening
air pollution prompted the passage of the
Clean Air Act (CAA) in 1970. The CAA sets
air-quality standards for six specific pollut-
ants (carbon monoxide, lead, nitrogen diox-
ide, ozone, particulate matter, and sulfur
dioxide), known as criteria air pollutants,
and then imposes fines and penalizes viola-
tors of those standards. Additional amend-
ments in 1977 and 1990 further strength-
ened the CAA.

Another regulatory approach that has
proved effective in limiting sulfur dioxide
pollution is known as cap and trade. Under
cap and trade, the EPA sets maximum allow-
able levels (“caps”) for SO2 emissions and

then issues (or sells) permits to large-scale stationary facilities like coal-fired power plants
that emit large amounts of SO2. These facilities then have to find a way to lower their SO2
emissions to match the number of permits they have or purchase (“trade”) additional permits
from facilities that have extra permits as a result of reducing their own SO2 emissions beyond

Ina Fassbender/picture-alliance/dpa/AP Images
The Clean Air Act prompted the development
of the catalytic converter, which reduces
pollutant emissions from cars and trucks.

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Section 8.3 Stratospheric Ozone Depletion

what they were required to do. The SO2 cap-and-trade program has proved very effective at
reducing sulfur pollution and provides an economic incentive for companies to move “beyond
compliance” so that they can be in a position to profit from the sale of extra permits.

As with most forms of regulation, many industries furiously resisted the enactment of the
CAA and subsequent amendments. These industries lobbied Congress and launched pub-
lic relations campaigns arguing that the CAA would harm the economy without necessar-
ily delivering any measurable public health or other benefits. However, one research study
after another has shown this position to be wrong. Research conducted by Harvard Univer-
sity scientists in 1993 and 2006 attempted to quantify the public health benefits achieved
through CAA regulations (Dockery et al., 1993; Laden, Schwartz, Speizer, & Dockery, 2006).
This research showed a clear and unmistakable connection between cleaner air and lower
rates of premature death, although it estimated that there are still as many as 75,000 prema-
ture deaths each year in the United States as a result of air pollution. A 2011 study by the EPA
estimated that from 1990 to 2020 the CAA would impose direct costs on the economy of $65
billion. However, over that same period the CAA regulations would yield $2 trillion in benefits
in the form of reduced illnesses, death, and lost work time. The 30-to-1 benefit–cost ratio in
this analysis demonstrates that while environmental regulations might impose some neces-
sary costs on specific industries and economic sectors, they can yield significantly greater
benefits to the broader society as a whole.

Regulations like the CAA can also spur innovation and the development of new technolo-
gies to help control pollution. For example, most particulate matter from stationary sources
like power plants can be controlled by using a device known as an electrostatic precipitator.
Likewise, wet scrubbers can be used to remove PM and SO2 pollution from stationary sources.
In terms of mobile sources like cars and trucks, the CAA prompted the development of a key
piece of technology known as the catalytic converter. Catalytic converters reduce pollutant
emissions from cars and trucks by 90%. As a result, and even though vehicle miles driven
have more than tripled since 1970, air pollution from mobile sources is actually significantly
lower today than it was decades ago.

Overall, while dramatic progress has been made in reducing the impacts of air pollution in
countries like the United States over the past 50 years, this is not the case everywhere. Rapidly
growing emerging economies like China and India are grappling with far more serious air pol-
lution levels. And even in the United States and other developed countries, air pollution still
takes a toll on public health, the environment, and infrastructure. As we’ll discuss, addressing
the air pollution challenge by reducing levels of fossil fuel use will also help address the chal-
lenge of global climate change—another of those win–win scenarios.

8.3 Stratospheric Ozone Depletion

The gradual formation of the ozone layer over 1 billion years ago represents one of the single
most important preconditions for the evolution of life on land. Prior to that, Earth’s surface
was constantly being bombarded with UVB and UVC radiation. This UV radiation is carcino-
genic and mutagenic, so the surface of the planet was mostly devoid of life.

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Section 8.3 Stratospheric Ozone Depletion

The only protection from this radioactive bombardment was underwater, and it’s there that
single-celled marine bacteria and algae first emerged. Recall that marine bacteria and algae
are capable of photosynthesis and that one by-product of photosynthesis is oxygen. As the
numbers of these organisms increased, there was a gradual buildup of oxygen in the atmo-
sphere. When an oxygen (O2) molecule is struck by UVB or UVC radiation, it splits into two
free oxygen atoms (O + O). These free oxygen atoms are then available to combine with an
oxygen molecule to form ozone (O + O2 = O3). Over hundreds of millions of years, as oxygen
levels increased in the atmosphere, so did levels of ozone, resulting in the formation of the
ozone layer.

Ozone in the stratosphere shields us from harmful UV radiation by undergoing a constant
process of destruction and re-creation. Incoming UV radiation strikes an ozone molecule and
breaks it apart into O and O2, but in the process the energy in that UV radiation is used up
and dissipated as heat. After that, the free O can recombine with O2 to once again form O3.
It’s believed that this constant cycle of ozone creation and destruction has been going on in
the stratosphere for over 1 billion years. Much like aquifer recharge (Chapter 5), this ozone
creation–destruction process can be likened to a bathtub filled with water, with the faucet on
but the drain also open. As long as the water is flowing into the bathtub (ozone creation) at
the same rate it is being drained out (ozone destruction), the level of water in the bathtub (or
ozone in the stratosphere) will remain in a dynamic equilibrium.

Causes of Ozone Depletion
It’s only in the past 100 years that human activities have thrown off that dynamic equilibrium.
Stratospheric ozone depletion is often confused with climate change, with some thinking
that the resulting “hole” in the ozone layer was responsible for letting in more heat. In fact,
stratospheric ozone depletion is fundamentally a separate issue from climate change: Recall
that less ozone means more UV radiation, not more heat. The two problems are related only
because they are both the result of human-generated chemicals in the atmosphere.

In the case of stratospheric ozone depletion, the issue stems from the development, mass
production, and pervasive use of a class of chemicals known as ozone-depleting substances.
Chief among these substances is a product known as chlorofluorocarbons (CFCs). CFCs
were first invented in the 1920s as a refrigerant and a propellant for spray cans, but they did
not come into widespread production until the 1950s. CFCs offered a number of advantages
over other chemicals being used for these applications at the time—namely that they were
nontoxic, inexpensive to produce, light, and extremely stable and chemically nonreactive.
The latter two characteristics are what led to CFCs becoming a culprit in stratospheric ozone
depletion. Because CFCs are so light, they tend to float upward once released to the atmo-
sphere. And because CFCs are stable and nonreactive, they do not chemically react or wash
out of the atmosphere once put there. As CFCs came into greater and greater use, more of
these chemicals were being released into the atmosphere, where they slowly floated toward
the stratosphere.

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Section 8.3 Stratospheric Ozone Depletion

In some ways the fact that CFCs seemed to float away made them an ideal chemical com-
pound. However, recall that in nature “there is no away” and that “everything must go some-
where” (Commoner, 1971, p. 39). It was this basic understanding of nature that led scientists
to begin to ask questions about the fate of increasing levels of CFCs being released to the
atmosphere. In 1973 atmospheric scientists Mario Molina and F. Sherry Rowland began to
speculate that CFC molecules could be reaching the stratosphere, where extremely intense
UV radiation would be strong enough to break them apart. A single chlorine atom broken free
from a CFC molecule would then be available to react with and “destroy” an ozone molecule in
a cycle that could repeat itself thousands of times over. To return to the bathtub analogy, the
introduction of CFCs and chlorine to the stratosphere was the same as widening the drain—
resulting in declining levels of ozone in the stratosphere. Rowland and Molina’s theory that
chlorine from CFCs could be destroying the protective ozone layer got a lot of media atten-
tion, but industries dependent on CFCs pushed back strongly and argued that there was no
evidence that such a situation was occurring.

It wasn’t until 10 years later that scientific teams using weather balloons to measure atmo-
spheric chemistry over Antarctica first reported substantial declines in levels of stratospheric
ozone. Soon after, a satellite-based ozone mapping instrument confirmed large losses of ozone
over the poles, and the idea of an “ozone hole” and increased risk for skin cancer grabbed the
public’s attention. In the late 1980s and early 1990s, further satellite measurements revealed
stratospheric ozone losses of as much as 15% over heavily populated regions of the Northern
Hemisphere.

Addressing Ozone Depletion
Because even a 1% decline in stratospheric ozone can result in a 2%–4% increase in cases
of skin cancer as well as other health problems like cataracts, there was tremendous public
pressure on governments to act. In 1987, 45 of the world’s largest economies agreed to what
became known as the Montreal Protocol. The Montreal Protocol originally called for a 50%
reduction in CFC use by 1998, but after further research showed ozone loss accelerating, this
was changed to a complete phaseout of CFCs by 1996. Eventually, more than 180 nations
signed the Montreal Protocol, and this agreement is still the basis for global efforts to protect
the ozone layer today.

The stratospheric ozone depletion issue is one of the rare “good news” stories in the envi-
ronmental field. Over the past 2 decades, stratospheric ozone concentrations have begun to
stabilize and are now even beginning to return to previous levels in some locations. While the
ozone loss remains significant (see Figure 8.2), scientists estimate that if current trends hold,
the entire ozone layer could completely “heal” by 2060 (Reiny, 2018).

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Section 8.4 Earth’s Climate System

The ozone depletion issue offers us a number of important lessons about how to deal with
potentially catastrophic and global environmental challenges. First, we should always remem-
ber the basic environmental rules of “there is no away” and “everything must go somewhere”
(Commoner, 1971, p. 39). Second, scientific uncertainty and the complexity of global-scale
environmental issues should be no excuse for inaction when the stakes are so high. Third, we
should expect that private businesses and some of the politicians they lobby will use scientific
uncertainty and the media to cast doubt on the seriousness of a given issue. Finally, global
environmental challenges require global solutions. These lessons will be important to keep in
mind as we examine an even greater threat to the planet in the next section—global climate
change.

8.4 Earth’s Climate System

One way to think about the Earth’s climate is to use the analogy of a house in the middle of the
winter. All houses lose heat through walls, windows, doors, and the roof in winter months, so
how do these houses stay warm? A source of heat (a furnace or space heater) applies enough
warmth at the right rate to offset the heat being lost. In other words, the house is in an energy
balance, and a constant temperature can be maintained.

Figure 8.2: Ozone hole

NASA has been monitoring the ozone layer for decades. Blue and purple represent areas where there is
the least ozone. Red and yellow show where there is the most ozone. While the ozone hole has begun to
repair itself, it still has a ways to go.

Source: “NASA Ozone Watch,” by National Aeronautics and Space Administration, n.d. (https://ozonewatch.gsfc.nasa.gov/monthly
/SH.html).

September 17, 1979

September 17, 2014

October 7, 1989 October 9, 2006

November 4, 2018October 2, 2015

October 1, 2010

August 21, 2019

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https://ozonewatch.gsfc.nasa.gov/monthly/SH.html

https://ozonewatch.gsfc.nasa.gov/monthly/SH.html

Section 8.4 Earth’s Climate System

The same principle is at work for Earth and other planets. In this case energy, in the form of
solar radiation or sunlight, strikes the Earth and warms it. Eventually, that energy escapes
back to space as longwave radiation or heat following fundamental laws of physics, and the
Earth is in an energy balance. Based solely on this process of incoming solar radiation and
outgoing longwave radiation, scientists can predict that the average surface temperature on
Earth over the entire year should be !18 °C (0 °F). In reality, the Earth’s average surface tem-
perature over the entire year is closer to 15 °C (59 °F). What could explain this difference?

The reason for the 33 °C difference between predicted and actual temperatures on Earth
is because of our atmosphere and what is known as the greenhouse effect, best explained
through Figure 8.3. Scientists estimate that, on average, the amount of solar energy reaching
the Earth’s atmosphere every second is 340 watts per square meter. For the sake of simplic-
ity, we will use a generic figure of 100 solar energy units reaching the atmosphere. Of those
100 units, about 30 are reflected back into space by clouds, airborne aerosol particles, and
ice, snow, and light-colored land on the Earth’s surface. About 70 units are absorbed by the
atmosphere or by land and water on the surface of the Earth and then reradiated as infrared
or heat energy. Some of this heat energy passes back through the atmosphere and is lost
to space, but much of it is absorbed by greenhouse gases—the term for gases that absorb
infrared radiation—and then reemitted as heat back toward the surface. This helps warm the
Earth’s atmosphere. The layer of greenhouse gases in the atmosphere acts like the windows
in a car or a greenhouse on a sunny day—hence the term greenhouse effect. The greenhouse
gases allow incoming solar radiation to pass through, but they trap outgoing heat energy and
warm the surface of the planet.

Figure 8.3: Greenhouse effect

While some incoming solar radiation is reflected back into space, much is absorbed by Earth’s
atmosphere, land, and water and reradiated as infrared radiation, or heat energy. Some of that heat
is lost to space, but much of its absorbed by greenhouse gases and reemitted back to the surface. The
greenhouse effect is a naturally occurring phenomenon that has intensified due to humans adding more
greenhouse gases to the atmosphere.

Source: Adapted from “Human Influence on the Greenhouse Effect,” by GlobalChange.gov, n.d. (https://www.globalchange.gov/browse
/multimedia/human-inf luence-greenhouse-effect).

Greenhouse
gases

Infrared radiation
absorbed by
greenhouse

gases

Outgoing
infrared
radiation

Incoming
solar

radiation

Outgoing (reflected)
solar radiation

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https://www.globalchange.gov/browse/multimedia/human-influence-greenhouse-effect

https://www.globalchange.gov/browse/multimedia/human-influence-greenhouse-effect

Section 8.5 Global Climate Change

Returning to the analogy of the home and energy balance, greenhouse gases and water vapor
in the atmosphere are akin to walls in that they help retain some of the heat in the home
before it is eventually lost. In the case of our planet, it does not get hotter and hotter with each
passing day, because energy is always escaping. As the sun goes down, heat energy built up
near the Earth’s surface gradually dissipates back into space. This is why the coldest time of
day is usually just before dawn and why cloudy nights (when water vapor is present) are less
cold than clear nights. In other words, the Earth is in energy balance between incoming solar
radiation and outgoing infrared or heat energy. Greenhouse gases and water vapor naturally
retain some of that outgoing heat energy long enough to keep the lower atmosphere about
33 °C warmer than it would otherwise be.

Given the beneficial role that greenhouse gases and the greenhouse effect play in moderating
climate and making our planet habitable, why are we so concerned about greenhouse gas
emissions from fossil fuel combustion and other human activities? As we’ll discuss, rising
concentrations of greenhouse gases in the atmosphere are resulting in an enhanced green-
house effect and global warming. Returning once again to our house analogy, rising green-
house gas concentrations are like adding insulation to the walls while still supplying the same
amount of heat from a furnace. The result is that Earth is warming in ways that may not be
beneficial for us or other organisms that make this planet home.

8.5 Global Climate Change

The reality and importance of the natural greenhouse effect cannot be called into question.
Without it, Earth would have an average surface temperature that would result in most of the
planet being permanently covered in snow and ice. Our real concern, from an environmental
standpoint, is that human activities are enhancing that greenhouse effect and resulting in
“global warming” as the atmosphere and oceans rise in temperature. This warming is driv-
ing changes in climate—in average precipitation patterns, air currents, humidity, and other
factors—and so scientists prefer to use the term global climate change to describe these
worldwide trends.

However, humanity’s role in global climate change is frequently called into question in politi-
cal debates. This section, therefore, will focus on two critical questions. First, is the Earth
actually warming? Second, and most critical, are human actions responsible for any warming,
or is this just part of natural climate variability?

Is the Earth Warming?
The Intergovernmental Panel on Climate Change (IPCC, 2014), the world body charged with
providing an objective and scientific review of climate change, states that recent warming of
the planet is beyond a doubt:

Human influence on the climate system is clear, and recent anthropogenic
[human] emissions of greenhouse gases are the highest in history. . . . Warming
of the climate system is unequivocal, and since the 1950s, many of the observed
changes are unprecedented over decades to millennia. The atmosphere and

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Section 8.5 Global Climate Change

ocean have warmed, the amounts of snow and ice have diminished, and sea level
has risen. (p. 2)

The IPCC goes on to confirm that each of the past 3 decades have been successively warmer
than any preceding decade and that the period from 1983 to 2012 was likely the warmest
30-year period in the past 1,400 years. Things have only gotten worse since then—the four
warmest years on record, in order, are now 2016, 2017, 2015, and 2018. In addition, July
2019 is now the warmest month in recorded history.

The IPCC bases its conclusion on a wide range of evidence. First, scientists, meteorologists,
and regular citizens have been measuring and recording local temperatures all over the world
for centuries. Regular and consistent measurements of surface temperatures over wide areas
of the globe did not begin, however, until roughly 150 years ago. Those temperature measure-
ments have been plotted against an average temperature to show temperature anomalies
or deviations over time. Figure 8.4 displays temperature trends over land and ocean since
1880 relative to the 1901–2000 average and illustrates that the planet has warmed about 1 °C
(1.8 °F) over that time period. The global network of thermometers used to record this tem-
perature data has come under criticism for a variety of reasons having to do with consistency
of measurement and other possible biases. However, climate scientists regularly review and
modify the data provided by these thermometers to factor in those biases, and this surface
temperature record is considered highly reliable as a result.

Figure 8.4: Global mean temperature over land and ocean, 1880–2017

This graph showing deviations from the average global temperature over time indicate that the Earth
today is about 1 °C warmer than the 1901–2000 average.

Source: Adapted from “Climate Change: Global Temperature,” by R. Lindsey and L. Dahlman, 2018 (https://www.climate.gov/news
-features/understanding-climate/climate-change-global-temperature).

1870

1.0

0.8

0.6

0.4

0.2

0.0

-0.2

-0.4

-0.6

1880

G
lo

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)

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20
0

0

1890 1900 19201910 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Year

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https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature

Section 8.5 Global Climate Change

We know from the scientific method, however, that scientists prefer to have data from mul-
tiple sources before making conclusions, and the issue of climate change is no different. Start-
ing in 1978 climate scientists began to use satellite-based instruments to measure average
temperature for the bottom 8 kilometers (5 miles) of the atmosphere, confirming the warm-
ing trend detected by surface thermometer readings. More importantly, National Aeronau-
tics and Space Administration (NASA) climate scientists published a report in Environmental
Research Letters in April 2019 that showed that satellite-based temperature measurements
were “highly consistent” with information collected by surface-based thermometers (Suss-
kind, Schmidt, Lee, & Iredell, 2019). The close consistency of the satellite temperature mea-
surements with surface temperature records significantly increases the certainty of climate
scientists that our planet is actually warming.

In addition to surface thermometer and satellite-based temperature measurements, scientists
point to a number of other pieces of evidence to confirm that the Earth is, in fact, warming.
First, scientists have been monitoring close to 200 glaciers around the world since as early as
1860. In that time period, only three of the glaciers studied actually advanced or increased in
size, while 177 retreated and became smaller (Lindsey, 2018b; Zemp et al., 2019). Second, sci-
entists have been using satellite imagery to monitor the extent of sea ice since the mid-1970s.
In that time sea ice coverage has declined, especially over the Arctic region (NASA, 2019a;
National Snow & Ice Data Center, 2018).

Third, scientists have also been monitoring the two largest ice sheets on the planet, one cover-
ing most of Greenland and the other on Antarctica. These two ice sheets are massive (almost
3.2 kilometers, or 2 miles, thick in some locations) and contain most of the world’s freshwater
supply. Satellite measurements begun in 2002 show that these ice sheets have lost 200 billion
metric tons or more of ice every year and over 1 trillion metric tons of ice since measure-
ments began (National Snow & Ice Data Center, n.d., NASA, 2019c, Mouginot et al., 2019).

NASA Earth Observatory
The area covered by Arctic sea ice at least 4 years old has decreased from 1.9 million square
kilometers (718,000 square miles) in September 1984 (left) to 110,000 square kilometers
(42,000 square miles) in September 2016 (right). The oldest ice—represented by white—is
the least vulnerable to melting away.

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Section 8.5 Global Climate Change

Fourth, as discussed in Chapter 6, ocean temperatures are increasing dramatically worldwide
as oceans absorb much of the extra heat being trapped by higher concentrations of green-
house gases. Finally, sea levels are rising as a result of global warming for two reasons—ocean
water expands as it warms, and melting ice from glaciers and ice sheets adds water to the
oceans. Sea level measurements date back over 100 years and confirm that sea level has been
rising steadily during that time and that the rate of sea level rise has increased sharply in the
past couple of decades (NASA, 2019d; Lindsey, 2018c).

Taken together—surface thermometer records, satellite temperature readings, and observa-
tions of glaciers, sea ice, ice sheets, ocean temperatures, and sea levels—all evidence points
clearly and unequivocally to the observation that the world is, in fact, in the process of warming.

Are Humans Responsible?
The next question to consider is to what extent the observed warming of the planet is due
to human activities rather than some sort of natural cause. Scientists refer to this question
as one of attribution: In other words, to what factor(s) can the observed warming be attrib-
uted? One of the best ways to determine whether human actions are mainly responsible for
global warming is to consider and review other factors that have been known to change cli-
mate in the past. For example, movement of the Earth’s continents over geologic timescales
has changed the climate in the past. Likewise, changes in Earth’s orbit affect how sunlight
is distributed around the planet and are known to have caused ice ages in the past. How-
ever, both continental movements and orbital variations occur on timescales of thousands to
millions of years, and so neither of these can explain the observed warming of the past 150
years. Another possible nonhuman cause of climate change could be changes in the amount
of energy reaching our planet from the sun. Scientists have been using satellite-based instru-
ments to measure solar output (known as the solar constant) since 1970, and that research
shows that solar energy reaching Earth does vary on an 11-year cycle. However, there has
been no long-term increase in the solar constant since 1970, and so this explanation for a
warming planet also does not hold up.

The one scientific explanation for recent global warming trends that is highly consistent with
the observed warming of the past 150 years is the increase in atmospheric concentrations of
greenhouse gases. Recall from the discussion of the greenhouse effect and the atmosphere
that small quantities of greenhouse gases in our atmosphere exert a strong influence over
climate. The basic physics of how greenhouse gases warm the planet was established close
to 200 years ago, and our understanding of their role has only strengthened since then. In
addition, scientific research that uses ice cores, mineral deposits, and radiocarbon dating of
ancient pollen levels demonstrates an extremely strong correlation between the tempera-
ture of the Earth and levels of the greenhouse gas carbon dioxide (see Figure 8.5). The Earth
has experienced a number of “greenhouse periods” over the past 800,000 years, with these
episodes being caused by increased volcanic activity, changes in solar output, and other natu-
ral causes that occurred over tens of thousands of years. What’s different about the current
period of warming is that human activities are the cause, and it’s happening faster than it ever
has in the past.

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Section 8.5 Global Climate Change

Human activities are leading to increased atmospheric concentrations of four important
greenhouse gases. Carbon dioxide (CO2) comes mainly from combustion of fossil fuels as
well as from deforestation and other land-use changes. Methane (CH4) comes mainly from
agricultural activities like rice farming and cattle production, as well as from leaks from natu-
ral gas pipelines and drilling facilities. Nitrous oxide (N2O) comes from fertilizer use and
fossil fuel combustion. Halocarbon gases, including the CFCs implicated in ozone depletion,
also act as a greenhouse gas in the troposphere.

For now, let’s zero in on carbon dioxide because it is the most abundant greenhouse gas emit-
ted by human activities. (For more on the other greenhouse gases, see the Apply Your Knowl-
edge feature.) We know from Chapter 7 that the carbon contained in fossil fuels like coal, oil,
and natural gas comes from organic material that lived and died hundreds of millions of years
ago. When we mine and burn these fuels, we are moving carbon from one place (deep geologic
storage) to another (the atmosphere).

Human emissions of CO2 are relatively small compared to natural sources of this gas. As part
of the carbon cycle, plant respiration and decomposing vegetation release close to 100 billion
metric tons of carbon each year, and oceans release another 90 billion metric tons. By com-
parison, human activities are responsible for the release of only about 7 billion to 8 billion
metric tons of carbon (equivalent to about 30 billion metric tons of CO2) each year.

Figure 8.5: Temperatures and carbon dioxide

Atmospheric carbon dioxide concentrations in parts per million (ppm) for the past 800,000 years, based
on EPICA (ice core) data. The peaks and valleys in carbon dioxide levels track the coming and going
of ice ages (low carbon dioxide) and warmer interglacials (higher levels). Throughout these cycles,
atmospheric carbon dioxide was never higher than 300 ppm; in 2017 it reached 405 ppm.

Source: Adapted from “Climate Change: How Do We Know?” by Global Climate Change: Vital Signs of the Planet, n.d. (https://climate.nasa
.gov/evidence/).

420
400
380
360
340
320
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240
220
200
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ar
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ve
l (

p
ar

ts
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ill
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n
)

800,000 700,000 600,000 500,000

Years before 1950 (0 = 1950)

400,000 300,000 200,000 100,000 0

Current
level

1950
level

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https://climate.nasa.gov/evidence/

https://climate.nasa.gov/evidence/

Section 8.5 Global Climate Change

However, natural sources of carbon are balanced out by natural sinks—natural processes
that absorb and store carbon. Just as much CO2 is absorbed by plants through photosynthesis
as is released through respiration and decomposition. In contrast, human sources of CO2 are
not balanced by sinks, and that is why they result in gradual increases in atmospheric CO2
levels. Preindustrial concentrations of CO2 were 280 ppm but are now well over 400 ppm.
Likewise, atmospheric concentrations of methane and nitrous oxide have followed a similar
trend. In terms of attribution, then, there is little question that the observed warming of the
past 150 years is due primarily to human activities in the form of increased greenhouse gas
emissions.

As increased greenhouse gas concentrations lead to more warming of the oceans and Earth
surfaces, scientists worry about the possibility of secondary impacts or feedback effects. It’s
true that some feedback effects could counteract global warming. Consider the formation and
distribution of clouds. As the Earth warms, we expect there to be more evaporation and more
water vapor in the atmosphere as a result. That increased water vapor could result in more
cloud cover, which would reflect more incoming sunlight back to space and possibly cool the
planet. On the other hand, water vapor itself is a powerful greenhouse gas, and more of it in
the atmosphere could lead to greater warming.

It’s not clear to what extent these two cloud-based feedback effects will cancel each other
out, but what is clear is that most of the possible feedback effects that scientists are aware
of will make things worse. For example, recall from Chapter 2 that large areas of the Arctic
are made up of what is known as permafrost. These areas are essentially frozen swampland,
and they contain a massive amount of carbon dioxide and methane that’s frozen in place. As
permafrost regions have become warmer and begun to thaw, they are releasing that CO2 and
CH4 to the atmosphere, worsening global warming and thawing even more permafrost in a
“feedback” cycle that’s become known as a “carbon bomb” or “methane bomb.” Likewise, we
know that light-colored surfaces like ice and snow reflect incoming solar radiation back to
space, rather than absorbing it. In scientific terms, ice and snow have a high albedo, or degree
of reflection. As global warming causes more ice and snow to melt, it reveals surfaces that are
darker in color and that absorb more incoming solar radiation; that is, surfaces that have low
albedo. This causes even more warming and even more ice and snow melting in a feedback
cycle known as the ice-albedo feedback loop.

Apply Your Knowledge: What About the Other
Greenhouse Gases?

When we discuss climate change, our conversations often focus on CO2 emissions, but what
about the other greenhouse gases mentioned in this chapter? Should we be concerned about
releasing materials like methane and nitrous oxide too? We will explore these greenhouse
gases in greater detail so that we can identify the ones that pose the greatest threat to the
environment.

(continued)

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Section 8.5 Global Climate Change

Apply Your Knowledge: What About the Other
Greenhouse Gases? (continued)

To begin our analysis, try to imagine how the Earth’s temperature might respond to
releasing a large pulse of greenhouse gas emissions all at once. At first, we would see
significant warming, but over time, we might expect the quantity of greenhouse gases in our
atmosphere to change. Methane molecules, for example, react with other materials in the
Earth’s atmosphere, and if no further emissions were produced, excess levels of methane
would decrease over time. Similarly, nitrous oxide molecules would eventually break down
from UV radiation, and even though it takes a really long time, excess levels of CO2 can be
sequestered by oceans and geologic formations in the absence of new emissions. If we take
all this into consideration, we might expect temperatures to eventually recover from an
isolated period of emissions.

We can see this process in action in Figure 8.6. In this chart, simulated temperature changes
are plotted against time for large releases of methane and CO2. In both cases we expect
temperatures to rise immediately after the gases are emitted, and in both cases temperatures
begin to recover as excess levels dissipate.

Figure 8.6: Temperature changes of isolated greenhouse
gas emissions

Notice the difference in potency and longevity between carbon dioxide and methane.

Source: Data from “The Jury Is Still Out on Global Warming Potentials,” by B. C. O’Neill, Climatic Change, 44.

0.006

0.004

0.002

0

2000

Year

Te
m

p
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h
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C

)

2050 2100 2150 2200

Methane

CO2

(continued)

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Section 8.5 Global Climate Change

Apply Your Knowledge: What About the Other
Greenhouse Gases? (continued)

If you study the curves more closely, you might also notice two important differences
between the two gases. First, the methane emissions result in a larger temperature spike
than the CO2 emissions. This is because the chemical structure of methane is much better
at trapping energy than that of CO2. This leads to more warming in the short term. Second,
the temperature recovers more quickly from the methane emissions. This happens because
methane is more easily removed from the atmosphere than CO2. While most excess methane
will be gone after a couple of decades, excess levels of CO2 can hang around for hundreds or
even thousands of years. From our analysis, we can begin to understand how the potency and
the longevity of greenhouse gases are both important characteristics to consider when trying
to understand their environmental impacts.

To help us consider both strength and endurance when comparing greenhouse gases,
scientist developed a metric called Global Warming Potential (GWP). GWP is the total
amount of energy trapped by a greenhouse gas over a specified time horizon. Given the data
in Figure 8.6, we might expect methane to have a larger GWP than CO2 over a shorter time
period because it causes much more short-term warming. However, if we were to consider a
really long time horizon, CO2 might end up trapping more heat than the short-lived methane.

To make GWP values easier to interpret, they are always calculated relative to CO2. In
other words, CO2 will always have a GWP equal to 1 regardless of the time horizon being
considered. If another gas has a GWP of 10, then that gas will trap 10 times more energy than
CO2 over that period.

Take a look at the GWP values in Table 8.1 that describe CO2, methane, and nitrous oxide
emissions over several different time horizons. Based on these values, how does CO2 compare
to methane and nitrous oxide?

(continued)

Table 8.1: GWP and lifetimes of CO2, methane, and nitrous oxide

Greenhouse gas Lifetime in years

GWP

20 years 100 years 500 years

CO2 Variable 1 1 1

Methane 12 72 25 7.6

Nitrous oxide 114 289 298 153

Source: Data are from “2007: Changes in Atmospheric Constituents and in Radiative Forcing,” by P. Forster, V.
Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D. W. Fahey . . . and R. Van Dorland, in S. Solomon, D. Qin, M. Manning,
Z. Chen, M. Marquis, K.B. Averyt . . . and H. L. Miller (Eds.), Climate Change 2007: The Physical Science Basis.
Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate
Change (p. 212), 2007, Cambridge, United Kingdom: Cambridge University Press (https://www.ipcc.ch/site/assets
/uploads/2018/02/ar4-wg1-chapter2-1.pdf ).

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Section 8.5 Global Climate Change

Why the Debate?
A number of global surveys of public opinion have shown that Americans are generally less
well informed and less worried about global climate change compared to residents of other
countries. One possible source for this situation is the way in which climate change science
is presented in the American media. Because journalistic standards call for balance in cover-
age of an issue, media outlets will frequently try to give both sides to any story about climate
change or its impacts. And because there are powerful financial interests, such as fossil fuel
companies, opposed to policies to address climate change, media outlets are able to find indi-
viduals who will question whether climate change is happening and whether it is a serious
threat.

A helpful way to approach the scientific, economic, political, and ethical debates over climate
change is to consider the difference between arguments that are based on positive claims
versus those based on normative claims. A positive claim is a statement about what we know,
while a normative claim is a statement about what we value.

When a climate scientist makes a claim that atmospheric concentrations of greenhouse gases
are increasing or that ocean temperatures are rising, these are positive claims, statements
about the way things actually are. When a politician makes a claim that we need to tax fossil
fuels to help address climate change, that is a normative claim, a statement about the way
things should be, at least in the view of that politician. While the results of scientific research
have political implications, the scientific process itself is not political. (Recall the discussion
of the scientific method in Chapter 1.) Instead, scientists are guided by a set of principles that
keep them focused on trying to understand the way the world works.

Apply Your Knowledge: What About the Other
Greenhouse Gases? (continued)

You might be wondering why we talk so much about CO2 when methane and nitrous oxide
appear to be stronger greenhouse gases for all time horizons. One important reason is that
we emit a lot more CO2 than we do methane or nitrous oxide. In fact, we emit hundreds of
times more CO2 than we do methane and thousands of times more CO2 than nitrous oxide. In
total, CO2 emissions are responsible for about 80% of the warming caused by humans.

That being said, other greenhouse gases like methane and nitrous oxide are still responsible for
20% of climate warming, and this is because of their high GWPs. CO2 is public enemy number
one, but we should probably be concerned about all three greenhouse gases if we want to
address climate change. Luckily, we can reduce the emissions of all three greenhouse gases at
the same time by transitioning away from fossil fuels and improving farming practices.

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Section 8.5 Global Climate Change

There is now broad scientific consensus and an overwhelming body of evidence that the planet
is warming and that human activities are responsible for this warming. There is also strong and
growing evidence that some of the impacts of this warming could be catastrophic to human
and natural systems. These are positive claims, statements about the way things actually are.
As a result, the real debate at this point should be about how and when we should respond to
climate change, who will pay for that response, and whether we should focus mainly on pre-
venting further warming or trying to adapt to an already changing climate. These are norma-
tive debates, arguments about the way the world should be.

The remainder of this chapter focuses on the impacts and possible solutions to what is argu-
ably the single most critical issue in environmental science today. We can say this for a couple
of reasons. First, global climate change is just that, global. The impacts of climate change on
food, water, human health, weather, and other aspects of our lives are already impacting every-
body on the planet. Likewise, the necessary responses and solutions to climate change—in
terms of energy use, transportation, and diet—will also touch everyone’s lives. Second, global
climate change is potentially irreversible, and many scientists worry that we are on the brink
of (or already past) a tipping point. Human society has evolved and adapted to our current cli-
mate state, and so a sudden shift to a new climate state could be catastrophic at many levels.

Mick Stevens/Cartoon Collections

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Section 8.6 Impacts of Global Climate Change

8.6 Impacts of Global Climate Change

In November 2018 the USGCRP (2018), made up of scientists from 13 federal government
agencies, issued its Fourth National Climate Assessment (Reidmiller et al., 2018). Despite its
release on the Friday after Thanksgiving, the report received widespread media coverage and
generated dramatic headlines. Some of the most alarming forecasts in the report had to do
with massive economic losses and thousands of additional premature deaths caused by cli-
mate change each year. But more importantly, the USGCRP firmly established the reality of
global climate change and the fact that it is already impacting the United States and other
nations around the world. David Easterling, a National Oceanic and Atmospheric Administra-
tion (NOAA) scientist and one of the authors of the report, stated:

Learn More: Climate Change Myths

Katharine Hayhoe is an atmospheric scientist, director of the Climate Science Center at Texas
Tech University, and one of the lead authors of the U.S. Global Change Research Program’s
(USGCRP) Fourth National Climate Assessment. In late 2018 Hayhoe wrote a short opinion
column that was published in a number of major newspapers around the country titled
“Five Myths About Climate Change” (Hayhoe, 2018a, 2018b). In that piece, Hayhoe describes
the myths and addresses why they are wrong. A simple summary of those five myths and
Hayhoe’s refutation of them looks like this:

• Myth 1: Climate scientists are “in it for the money.” In reality, climate scientists like
Hayhoe could be making far more money working in the private sector, such as for
an oil company. The relatively small amount of money that climate scientists collect
for their work is used to support their laboratories, graduate students, and other
aspects of their work.

• Myth 2: The climate has changed before; it’s just a natural cycle. As we just saw,
while the climate has changed before and does go through natural cycles, none of the
factors that have caused earlier changes can explain what we are experiencing now.

• Myth 3: Climate scientists are split on whether warming is real. In reality, more than
97% of climate scientists agree that global warming is happening and that humans
are causing it (NASA, 2019b).

• Myth 4: Climate change won’t affect me. While only 40% of Americans think climate
change will harm them personally, the wide range of impacts described in the next
section will likely affect everyone.

• Myth 5: It’s cold outside, so global warming can’t be real. This confuses weather
and climate. As Hayhoe points out, weather is like your mood, while climate is your
personality. Occasional bouts of very cold weather in some regions of the world do
nothing to refute the larger trend of increasing temperatures worldwide.

You can read Hayhoe’s full column at either of the following publications. Hayhoe is also an
evangelical Christian and the coauthor of A Climate for Change: Global Warming Facts for
Faith-Based Decisions.

• https://www.chicagotribune.com/opinion/commentary/ct-perspec-climate
-change-five-myths-hayhoe-1209-20181206-story.html

• https://www.washingtonpost.com/outlook/five-myths/five-myths-about-climate
-change/2018/11/30/9f ba233a-f428-11e8-bc79-68604ed88993_story.html

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

https://www.chicagotribune.com/opinion/commentary/ct-perspec-climate-change-five-myths-hayhoe-1209-20181206-story.html

https://www.chicagotribune.com/opinion/commentary/ct-perspec-climate-change-five-myths-hayhoe-1209-20181206-story.html

https://www.washingtonpost.com/outlook/five-myths/five-myths-about-climate-change/2018/11/30/9fba233a-f428-11e8-bc79-68604ed88993_story.html

https://www.washingtonpost.com/outlook/five-myths/five-myths-about-climate-change/2018/11/30/9fba233a-f428-11e8-bc79-68604ed88993_story.html

Section 8.6 Impacts of Global Climate Change

The global average temperature is much higher and is rising more rapidly than
anything modern civilization has experienced, and this warming trend can only
be explained by human activities. (as cited in Yang, 2018, para. 7)

The USGCRP report carefully documents the ways in which global climate change is and will
be impacting our health, weather, water and food supply, wildlife and biodiversity, oceans,
and overall economy.

Human Health
One of the first human health impacts of global climate change comes as a result of rising tem-
peratures. While a 1 °C (1.8 °F) increase in temperature may seem small, and while politicians
may joke about welcoming global warming during cold spells, this figure represents an aver-
age global increase over the whole planet over an entire year. This means that localized heat
waves and extreme heat events are already happening with increased frequency and deadly
results. Global average temperatures are expected to continue to increase, further exacerbat-
ing the dangers of heat stress and other heat-related health conditions. The increased fre-
quency and intensity of heat waves will also worsen air pollution conditions, including the
formation of ground-level ozone and photochemical smog. In addition, as temperature and
climate zones shift further away from the equator, tropical diseases like malaria and den-
gue fever will also reach into new regions and affect larger numbers of people. Overall, WHO
(2018) estimates that rising global temperatures could result in as many as 250,000 pre-
mature deaths each year. In 2019 a report published in the New England Journal of Medicine
called the WHO estimate too conservative and adjusted that figure to over 500,000 premature
deaths every year (Haines & Ebi, 2019).

Severe and Extreme Weather
As the surface of the planet, the oceans, and
the atmosphere warm, we can expect to
see changes in rates of evaporation, cloud
formation, and weather patterns. While no
single weather event can be directly attrib-
uted to global climate change, scientists
are now convinced that global warming
has already begun to influence precipita-
tion patterns and the frequency and inten-
sity of severe storms. Some regions of the
world are becoming wetter as a result of
these changes, while others, like the west-
ern United States, are becoming drier. The
regions becoming wetter are having to
grapple with “too much of a good thing” as
more frequent, sudden, and intense down-
pours create flooding conditions. In contrast, the drier regions are having to grapple with
drought, reduced water supplies, and outbreaks of severe forest fires. It’s no exaggeration to
state that extreme weather has become the “new normal,” and this has drawn the attention

Carsten Schertzer/iStock/Getty Images Plus
The Thomas Fire in Santa Barbara, California,
in 2017 was one of the largest and most
destructive in the state’s history. Catastrophic
forest fires are one outcome of climate change
in drier regions.

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Section 8.6 Impacts of Global Climate Change

and concern of major global insurance companies. Forbes magazine recently reported that
the cost of climate-related disasters has increased over 150% in the 21st century (McCar-
thy, 2018).

Water and Food Supply
As the weather changes, so will the reliability of water supply and our ability to grow food
in certain locations. The USGCRP report mentioned at the start of this section estimates that
higher temperatures in the U.S. Midwest will reduce corn and soybean yields by over 25% in
the next few decades. Other research has established that global “wheat belts”—regions ideal
for wheat production—are moving toward the poles (Jones, 2018). In Australia and South
America, this means that the wheat belt is moving farther south, while in North America and
Russia, it’s shifting northward.

While this may sound relatively harmless, consider the fact that there is an entire infrastruc-
ture that has been developed around specific regions to support crop production in that
location. Rail lines, roads, grain elevators, irrigation infrastructure, and warehouses would
all have to be moved to keep up with shifting crop production zones. While such a move is
conceivable in relatively wealthy countries like the United States and Australia, that’s not the
case in poorer regions of the world. Farmers in Africa, Latin America, and southern Asia are
already suffering from climate-related crop losses and outright crop failure. Worsening agri-
cultural conditions in these regions are contributing to poverty and an increase in the number
of migrants and refugees fleeing these conditions. This has given rise to the notion of climate
refugees. The World Bank (2018) estimates that climate change could soon cause over 140
million people to become climate refugees. Water shortages caused by shifting precipitation
patterns and increased heat waves will only make this situation worse.

Wildlife and Biodiversity
A 2019 report by the Intergovernmental Science-Policy Platform on Biodiversity and Eco-
system Services warns that climate change could soon become the leading cause of species
extinction and biodiversity loss (Díaz et al., 2019). This is because climate change—espe-
cially when combined with habitat destruction, pollution, and overexploitation—can rapidly
modify the habitats and conditions that species have adapted to over long periods. A 2018
study published in the journal Science concluded that within a century climate change could
result in many of the Earth’s major ecosystems being “unrecognizable” (Nolan et al., 2018).
For example, large areas of the Amazon rain forest could convert to savanna and grassland
because of warmer temperatures and shifts in precipitation, no longer supporting the species
that are adapted to living there.

The IPCC forecasts that approximately 30% of all land-based plant and animal species could
be driven to extinction as a result of the most likely predicted increase in temperature. If
actual warming is worse than that, this figure could increase to 70%. Biodiversity loss in the
oceans could be as bad or even worse, as warming ocean waters and acidification make con-
ditions uninhabitable for marine species. Climate change has already been implicated in the
extinction of a number of amphibians, plants, insects, birds, and mammals, but the most sig-
nificant impacts will begin to be felt over the next few decades. Unless global climate change

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Section 8.6 Impacts of Global Climate Change

and global warming are brought under control, they will be key drivers of the sixth great
extinction.

Economy and Infrastructure
Nearly all the climate change impacts just discussed have direct and indirect impacts on our
economy. More frequent and severe heat waves lower productivity and increase health care
costs. Increased frequency and damage from severe weather and storms will raise insur-
ance rates and require increased spending by governments on disaster relief and rebuilding.
Lower crop productivity and water shortages increase food prices and require increased pub-
lic investment in water management and distribution systems. In addition, we know that sea
levels are rising worldwide as a result of the expansion of warmer ocean waters and the melt-
ing of glaciers and ice sheets. This has resulted in increased coastal flooding in cities around
the world and will make the problem of climate refugees even worse.

When sea level rise is combined with more
severe hurricanes and storms, it becomes
even more of a concern. This was demon-
strated in New York City during Hurricane
Sandy in 2012 and in the Carolinas during
Hurricane Florence in 2018. Given the mas-
sive cleanup costs associated with coastal
flooding, many cities are investing in coastal
barriers and other flood control structures.
However, these structures are expensive to
build and are not always effective at pre-
venting flooding. In addition, scientists are
increasingly concerned that global warming
could lead to the complete collapse of the
Antarctic ice sheets and unleash as much as
4 meters (13 feet) of sea level rise. Such an
outcome would overwhelm any flood control structures, displace tens of millions of people,
and wipe some cities and coastal regions off the map. A 2017 report in the journal Land Use
Policy estimates that rising sea levels could result in as many as 2 billion people being dis-
placed by the year 2100 (Geisler & Currens, 2017).

A somewhat unexpected economic consequence of global climate change is that it is opening
up the Arctic region at “the top of the world” to increased shipping, mineral exploration, and
other development activities. Mariners have long dreamed of a “Northwest Passage” from
Europe through the Arctic to Asia, but thick sea ice for much of the year has made this almost
impossible for most ships. As Arctic sea ice becomes thinner and less widespread, there is
growing interest in this possibility (Struzik, 2016). Likewise, a reduction in sea ice is making
more of the Arctic region accessible for mineral exploration and development (Rosenthal,
2012). While both of these developments could have some positive economic benefits in the
short term, they also open up environmentally sensitive Arctic regions to increased ship traf-
fic, oil spills, and other forms of pollution. In addition, because parts of this region are not
clearly the territory of one country, it increases the probability of international disputes over
valuable minerals and shipping lanes.

View Pictures Ltd/SuperStock
A number of major cities are investing in flood
control technology, such as these large barriers
on the Thames River in London.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

Section 8.7 Addressing Global Climate Change

This section has only reviewed some of the possible consequences and impacts of global cli-
mate change. Yet it reveals how climate change is already affecting many aspects of our lives
and how these impacts are forecast to get much worse in the next few decades. Given the
direct and indirect costs of climate change to our health, food and water supply, homes and
cities, and livelihoods, as well as to other organisms and species that share the Earth with us,
what can be done to address this issue? We turn to that question in the next section.

8.7 Addressing Global Climate Change

Before we get into the specifics of how we might address the challenge of global climate
change, we should first acknowledge that there are a growing number of individuals asking
if we are already too late. For example, environmental author and journalist Bill McKibben
(2012) has written about what he calls “global warming’s terrifying new math.” By this McK-
ibben is referring to the fact that over the period from 1800 to the present, human activities
have resulted in the release of roughly 1,400 gigatons (1,400 billion metric tons) of carbon
dioxide to the atmosphere. Those emissions are largely responsible for the already observed
1 °C global warming experienced over the past century. Climate scientists and world leaders
are now focused on keeping any future warming below 2 °C (in other words, we are already
halfway there). In order to do that, they estimate that we should release no more than an
additional 500 billion metric tons of carbon dioxide over the remainder of this century.

The problem, according to McKibben, is that there are at least another 2,800 billion metric
tons of carbon dioxide locked up in known remaining coal, oil, and natural gas deposits. Given
that fossil fuel companies have a record of funding “climate science denial” organizations and
lobbying politicians against any action on climate change, McKibben and others worry that
we are likely on a path to realizing those levels of emissions. If that were to happen, the planet
would be in for global warming of at least 6 °C (11 °F) with absolutely catastrophic conse-
quences for human and natural systems worldwide. These worst-case scenarios are being
talked about more frequently in the scientific and policy communities, and they have resulted
in what some are calling “a kind of dark realism” (Mufson, 2018). This has led to greater
emphasis on finding ways to adapt to what is increasingly perceived to be inevitable climate
change.

Climate change adaptation can take many different forms. In the agricultural sector, adap-
tation means helping farmers shift to drought-resistant crops or crops better suited to new
climate conditions. In terms of cities and infrastructure, adaptation means planning and
building in ways that are more “climate-proof ” than is currently the case. For example, when
Hurricane Michael struck the Florida Panhandle in 2018, it destroyed all the homes along
Mexico Beach except for one that was built to withstand hurricanes. Other adaptation strate-
gies center on water management, fire prevention, and disease control, but all of them start
with accepting the reality and severity of global climate change and preparing for the worst.
(For information on your area, see the Close to Home feature.)

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

Section 8.7 Addressing Global Climate Change

Close to Home: Adapting to Shifting Climates

Climate change adaptation is all about anticipating the shifts that accompany climate change.
To help us visualize climate-related changes in the United States, researchers from the
University of Maryland created a climate analogy map that predicts how specific locations
might change by the year 2080 if we do not curb emissions. You can select a location, and
the app will identify an analog city that best represents the future climate. Take a moment
to explore the changes happening around the country and see if you can identify any major
trends.

You might notice that several locations in the
Northeast could begin to resemble locations
in the southern and central United States. The
western United States could start to resemble
the Southwest, and the southern United
States might start to look a lot like Mexico. On
average, climates would shift by more than 965
kilometers (600 miles) with just a few degrees
of warming, and many places could have a hard
time adjusting.

Locations in the Northeast, for example, will
likely experience some of the most dramatic
temperature changes in the continental United
States. Winters are expected to warm 3 times
faster than summers, and ecosystems could be
radically altered as a result. Many locations in
the Southwest will need to cope with less rain and more frequent forest fires. Meanwhile,
locations in the Northwest will grapple with irregular rainfall and flooding. Coastal locations
will experience higher sea levels, more frequent hurricanes, and saltwater intrusion into
freshwater sources. Most places are going to experience more extreme periods of hot
weather. This will be a public health issue in places that are not used to the heat, and it will
decrease economic productivity in southern locations that are already very hot.

With changes like these on the horizon, some cities are taking precautionary measures
to become more climate resilient. New York created a task force to identify areas that are
prone to flooding with sea level rise. Los Angeles is adding new infrastructure to capture
rainwater. Cities like Oakland and St. Paul are rebuilding wetlands to provide flood control,
and locations like Minneapolis and Chicago are adding green spaces to help manage the heat
island effect.

With some of these challenges and solutions in mind, take a closer look at your hometown
using the climate analogy map. If you would like to learn more about trends in your region,
you can also explore the NOAA’s Climate at a Glance tool. This online resource allows users
to visualize several decades of temperature and precipitation data that is organized by state,
county, and city. Based on what you can learn from these two sources, how will temperature
and precipitation change in your area, and what specific concerns do you have for your
community? Most importantly, what are some ways that your community might prepare so
that it is ready for these changes? As you go forward, take time to appreciate the things that
make your hometown special and start the conversation about climate resilience in your
community.

robertharding/SuperStock
Beachside houses, such as these in
Galveston, Texas, are at high risk
during hurricanes, with only careful
structural engineering giving homes a
chance at survival.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

https://fitzlab.shinyapps.io/cityapp/

https://fitzlab.shinyapps.io/cityapp/

https://www.ncdc.noaa.gov/cag/national/time-series

Section 8.7 Addressing Global Climate Change

While climate change adaptation will be important, there is still a need to focus on practices
that can reduce or prevent greenhouse gas emissions in the first place. Those practices repre-
sent an approach known as climate change mitigation, and there are a number of ways that
we can accomplish this.

Using Policy
Politically, many (but not all) world governments are now attempting to tackle the climate
change challenge through the Paris Agreement. The Paris Agreement was signed in 2016
and commits participating countries to reduce greenhouse gas emissions according to formu-
las that take into consideration a country’s historical emissions. The goal is to reduce green-
house gas emissions enough to keep any global warming below 2 °C. At this point, however,
countries participating in the Paris Agreement have only actually pledged to cut emissions by
about one third of what is needed to limit warming to 2 °C, and these pledges are voluntary.
To make matters worse, in June 2017 President Trump announced that the United States
would withdraw from the agreement. Seeing that the United States is the number two emit-
ter of greenhouse gases (after China), this decision has further called into question whether a
global climate agreement can have enough of an impact in a short enough time period.

While the Trump administration has decided to turn its back on the challenge of global cli-
mate change, the same cannot be said for many state and local governments. For example, 10
states in the northeastern United States have formed the Regional Greenhouse Gas Initiative
as a market-based program to reduce greenhouse gas emissions. California adopted a green-
house gas cap-and-trade program in 2013 that allows polluting industries to buy and sell
greenhouse gas emission permits from each other while gradually reducing overall emission
levels. Other states are developing climate action plans, setting renewable energy targets, and
promoting energy efficiency in homes and businesses to help reduce greenhouse gas emis-
sions. Private companies and institutions such as colleges and universities are also taking
steps to lower their greenhouse gas emissions. These companies and institutions are moti-
vated both by a desire to do what they can to avoid climate change and by the financial savings
that come from reducing energy use. This “no-regrets” or “win–win” approach to reducing
greenhouse gas emissions could also apply at the national level, but it’s more difficult to gain
traction there due to opposition from fossil fuel industries.

Using Technology
Given the dangers associated with some of the worst predictions around global climate
change, some scientists are not waiting for political action or economic incentives to have an
impact on reducing emissions. These scientists are focused on technological approaches that
either would pull or remove greenhouse gases from the atmosphere or would create condi-
tions to offset or counter the warming caused by increased greenhouse gas concentrations.
The first set of approaches are known broadly as negative emissions technologies, while the
second set of approaches has been labeled geoengineering.

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Section 8.7 Addressing Global Climate Change

Negative Emissions Technologies
The most common negative emissions technologies (NET) approaches focus on remov-
ing carbon dioxide from the atmosphere in large enough quantities to impact greenhouse
warming. This can be done by simply growing more trees (reforestation), since trees use CO2
during photosynthesis and store that carbon in their tissue. Likewise, bioenergy with carbon
capture and sequestration (BECCS) involves growing plants that suck up carbon dioxide and
then burning those plants for energy in a way that captures CO2 emissions.

IGphotography/iStock/Getty Images Plus
One NET approach involves walls of giant fans that suck in air to remove the CO2 and store it
underground.

The problem with both reforestation and BECCS is that in order to remove just one fourth
of our annual CO2 emissions, we would have to make use of approximately 40% of all global
farmland, impacting food supply and prices. A different NET approach involves walls of giant
fans that suck in air and remove the CO2, although prototypes of this technology in Switzer-
land and Iceland have proved expensive. Despite these challenges, NET approaches are draw-
ing increased attention, such as a 2019 National Academy of Sciences report that details the
potential and limitations of these technologies (National Academies of Sciences, Engineering,
and Medicine, 2019).

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

Section 8.7 Addressing Global Climate Change

Geoengineering
Geoengineering involves deliberately trying to alter Earth’s energy balance. For example, the
1991 eruption of Mount Pinatubo in the Philippines resulted in a massive injection of sulfur
particles into the atmosphere. Sulfur particles reflect incoming sunlight, and in the months
that followed the eruption, temperatures in the Northern Hemisphere actually dropped
by about 0.6 °C (1 °F). One approach to geoengineering would therefore involve artificially
injecting massive amounts of sulfur particles into the upper atmosphere. Another approach
involves “fertilizing” regions of the ocean with iron in order to promote algae blooms. The
algae would absorb carbon dioxide through photosynthesis and then sink to the bottom,
where that carbon could be stored. Geoengineering, however, is risky and highly controver-
sial. It involves actions on a global scale that could have serious unintended consequences.
Nevertheless, given the seriousness of global climate change, some scientists argue that we
need to keep researching it as a possibility.

Taking It One Step (or Wedge) at a Time
Because addressing global climate change can seem overwhelming, some scientists are
using a concept known as stabilization wedges. The stabilization wedge approach basically
involves taking our current greenhouse gas emissions and identifying ways to reduce those
emissions one small piece, or wedge, at a time. These wedges include energy efficiency, a shift
to more renewable energy, making vehicles more fuel efficient, and capturing and storing car-
bon using negative emissions technologies. When looked at this way, tackling greenhouse gas
emissions and global warming seems a little less daunting. The key will be to move beyond
the backward-looking and potentially paralyzing debates over whether climate change is
happening (it is) and whether we are causing it (we are) and speed up the adoption of these
wedge approaches.

Learn More: NET Approaches

Download a free PDF of the 2019 National Academy of Sciences report on NET approaches at
the following link:

• https://www.nap.edu/catalog/25259/negative-emissions-technologies-and
-reliable-sequestration-a-research-agenda

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

https://www.nap.edu/catalog/25259/negative-emissions-technologies-and-reliable-sequestration-a-research-agenda

https://www.nap.edu/catalog/25259/negative-emissions-technologies-and-reliable-sequestration-a-research-agenda

It’s instructive to consider the question of why the world was able to so effectively respond
to address the global challenge of stratospheric ozone depletion but has not been able to
reach much consensus on the more pressing issue of global climate change. There appear to
be at least three key answers to this question.

First, in the case of ozone depletion, there was only one class of chemicals (CFCs) respon-
sible for the problem, and by the time the Montreal Protocol was being negotiated, effec-
tive substitutes were being developed to replace them. In contrast, global climate change is
being caused by a wide variety of human actions, and the number of industries potentially
impacted by climate change regulations is also far greater than was the case for ozone
depletion. The fossil fuel industry, in particular, has waged a low-profile but highly effec-
tive campaign for decades to cast doubt on the scientific consensus surrounding climate
change (Banerjee, Song, & Hasemyer, 2015; Frumhoff & Oreskes, 2015; Jerving, Jennings,
Hirsch, & Rust, 2015; Union of Concerned Scientists, n.d.). As a result, public opinion has
been split over the urgency of dealing with climate change, and the issue has become highly
politicized.

A second reason for the different response to ozone depletion versus climate change has to
do with the sense of immediacy and urgency of the problem. Media reports of ozone deple-
tion and an ozone hole in the 1980s and 1990s focused on the risk of skin cancer and death.
In contrast, while global climate change poses an even greater overall risk to humanity than
ozone depletion, it is sometimes difficult for the average person to pinpoint how climate
change might already be impacting him or her.

Finally, a scientific understanding and explanation for ozone depletion was easier to achieve
because of the relatively limited scope of the problem and its causes. In contrast, the global
climate system is far more complex, and predicting precisely how the climate will respond
to increasing greenhouse gas concentrations in any one location is challenging.

In order to move beyond the political gridlock that is currently limiting our ability to
respond effectively to global climate change, we need to go back to the concept of positive
and normative claims. Climate scientists are growing increasingly frustrated with bogus
arguments about climate change being some kind of “hoax” or “fake news.” Scientific obser-
vations and reporting of rising greenhouse gas concentrations, increasing temperatures,
rising sea levels, shrinking ice caps and ice sheets, retreating glaciers, and more severe
weather are not fake news. Attributing those changes to human actions, in particular the
burning of fossil fuels, is not part of some elaborate hoax designed to bring about the end
of the free world and capitalism. Instead, the reality of a changing climate and the role of
humans in that process are grounded in the positive and scientific approach that’s focused
on how the world actually is.

Once we acknowledge that reality, we can then shift to normative debates about what to do
about the problem, when to take action, and who should pay for addressing this challenge.
In order to do that, we need a scientifically literate (indeed, a “climate literate”) public, and
so we hope that this chapter has helped explain some of the major threats to sustaining our
atmosphere and climate, as well as what we might do to respond to those threats.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

The National Weather Service has on online Air Quality Index map that show what air-
quality conditions are in your area.

• https://www.weather.gov/safety/airquality-aqindex

Smog City 2 is an online, interactive pollution simulator that allows you to manage air pollu-
tion conditions in a fictional city.

• http://www.smogcity2.org

Stratospheric Ozone Depletion

NASA has a couple of web pages that allow you to visualize how conditions in the ozone
layer have changed over time.

• https://ozonewatch.gsfc.nasa.gov
• https://climate.nasa.gov/climate_resources/186/video-ozonewatch-2018

A recent NASA research study demonstrated that the phaseout of many ozone-depleting
substances through the Montreal Protocol has definitely helped restore the ozone layer.
However, soon after this report was released, evidence emerged that the use of these same
ozone-depleting substances was on the increase again in parts of China. You can learn more
about these good news/bad news stories at these sites.

• https://www.nasa.gov/feature/goddard/2018/nasa-study-first-direct-proof-of
-ozone-hole-recovery-due-to-chemicals-ban

• https://e360.yale.edu/features/how-an-illicit-chemical-is-jeopardizing-recovery
-of-the-ozone-layer-china

The Science of Global Climate Change

NASA has a number of great online resources that help explain the science of climate change,
how climate has changed over time, what the impacts of climate change might be, and what
some possible solutions are.

• https://climate.nasa.gov
• https://climate.nasa.gov/interactives/climate-time-machine
• https://earthobservatory.nasa.gov/world-of-change

Likewise, the NOAA also has excellent resources devoted to the science of climate change.

• https://www.climate.gov
• https://www.noaa.gov/education/resource-collections/climate-education

-resources
• https://www.ncdc.noaa.gov/cag/national/time-series

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

https://www.weather.gov/safety/airquality-aqindex

http://www.smogcity2.org

https://ozonewatch.gsfc.nasa.gov

https://climate.nasa.gov/climate_resources/186/video-ozonewatch-2018

https://www.nasa.gov/feature/goddard/2018/nasa-study-first-direct-proof-of-ozone-hole-recovery-due-to-chemicals-ban

https://www.nasa.gov/feature/goddard/2018/nasa-study-first-direct-proof-of-ozone-hole-recovery-due-to-chemicals-ban

https://e360.yale.edu/features/how-an-illicit-chemical-is-jeopardizing-recovery-of-the-ozone-layer-china

https://e360.yale.edu/features/how-an-illicit-chemical-is-jeopardizing-recovery-of-the-ozone-layer-china

https://climate.nasa.gov

https://climate.nasa.gov/interactives/climate-time-machine

https://earthobservatory.nasa.gov/world-of-change

https://www.climate.gov

https://www.noaa.gov/education/resource-collections/climate-education-resources

https://www.noaa.gov/education/resource-collections/climate-education-resources

https://www.ncdc.noaa.gov/cag/national/time-series

The website Skeptical Science is “skeptical about global warming skepticism” and has a
wealth of information on the basic science behind climate change.

• https://skepticalscience.com

Impacts of Global Climate Change

Few regions of the planet are being impacted as much by climate change as the Arctic. This
fascinating photo essay by The Washington Post shows how lakes across the Arctic region
are bubbling and changing in other ways as thawing permafrost releases carbon dioxide,
methane, and other gases that have been trapped below them for thousands of years.

• https://www.washingtonpost.com/graphics/2018/national/arctic-lakes
-are-bubbling-and-hissing-with-dangerous-greenhouse-gases

An interesting interactive feature in The New York Times allows you to examine how much
hotter your hometown is today compared to when you were born.

• https://www.nytimes.com/interactive/2018/08/30/climate/how-much-hotter-is-
your-hometown.html

A Washington Post photo essay documents how climate change is already disrupting lives
across America.

• https://www.washingtonpost.com/graphics/2019/national/gone-in-a-generation

These two essays from Yale Environment 360 show how climate change is already pro-
foundly impacting Greenland and Antarctica.

• https://e360.yale.edu/features/in-greenlands-melting-ice-a-warning-on-hard
-climate-choices

• https://e360.yale.edu/features/polar-warning-even-antarctica-coldest-region
-is-starting-to-melt

Action on Global Climate Change

These two TED Talks by 16-year-old climate activist Greta Thunberg and climate scientist
Katharine Hayhoe deliver a simple but powerful message on how and why to act on climate
change.

• https://www.youtube.com/watch?v=H2QxFM9y0tY
• https://www.youtube.com/watch?v=-BvcToPZCLI

This New York Times interactive feature shows how the United States could do more to
reduce greenhouse gas emissions if we did more of what some other countries are already
doing.

• https://www.nytimes.com/interactive/2019/02/13/climate/cut-us-emissions
-with-policies-from-other-countries.html

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https://skepticalscience.com

https://www.washingtonpost.com/graphics/2018/national/arctic-lakes-are-bubbling-and-hissing-with-dangerous-greenhouse-gases

https://www.washingtonpost.com/graphics/2018/national/arctic-lakes-are-bubbling-and-hissing-with-dangerous-greenhouse-gases

https://www.nytimes.com/interactive/2018/08/30/climate/how-much-hotter-is-your-hometown.html

https://www.nytimes.com/interactive/2018/08/30/climate/how-much-hotter-is-your-hometown.html

https://www.washingtonpost.com/graphics/2019/national/gone-in-a-generation

https://e360.yale.edu/features/in-greenlands-melting-ice-a-warning-on-hard-climate-choices

https://e360.yale.edu/features/in-greenlands-melting-ice-a-warning-on-hard-climate-choices

https://e360.yale.edu/features/polar-warning-even-antarctica-coldest-region-is-starting-to-melt

https://e360.yale.edu/features/polar-warning-even-antarctica-coldest-region-is-starting-to-melt

https://www.nytimes.com/interactive/2019/02/13/climate/cut-us-emissions-with-policies-from-other-countries.html

https://www.nytimes.com/interactive/2019/02/13/climate/cut-us-emissions-with-policies-from-other-countries.html

Geoengineering and negative emissions technologies are now being more openly discussed
as a “last chance” strategy for dealing with the worst impacts of climate change. You can
learn more about these approaches here.

• https://e360.yale.edu/features/geoengineer-the-planet-more-scientists-now-say
-it-must-be-an-option

• https://e360.yale.edu/features/negative-emissions-is-it-feasible-to-remove
-co2-from-the-air

• https://www.nap.edu/resource/25259/Negative%20Emissions%20
Technologies.pdf

Key Terms
acid deposition Precipitation containing
acid. Also known as acid rain.

acid rain See acid deposition.

albedo Degree of reflection.

cap and trade A regulatory approach
that establishes a maximum level (“cap”)
for pollutant emissions and allows
facilities to purchase (“trade”) additional
permits for emissions beyond the cap.

carbon dioxide (CO2) A greenhouse gas
that comes mainly from combustion of
fossil fuels as well as from deforestation
and other land-use changes.

carbon monoxide (CO) A primary
pollutant. An invisible, odorless, tasteless gas
that results from the incomplete combustion
of carbon-based fuels, primarily from motor
vehicle exhaust. A second major source of
CO is firewood burning and forest fires.

chlorofluorocarbons (CFCs) An
ozone-depleting substance
typically used as a coolant.

Clean Air Act (CAA) A law passed in 1970
(and strengthened in 1977 and 1990)
that sets air-quality standards for specific
pollutants like carbon monoxide and
nitrogen oxides and then imposes fines and
penalizes violators of those standards.

climate Average temperature and
precipitation patterns in a given
area over a longer period.

climate change adaptation A response
to global climate change that involves
making changes and strategizing in
preparation for a different climate.

climate change mitigation A response
to global climate change that tries to
limit or halt the effects of global climate
change and often involves trying to reduce
or prevent greenhouse gas emissions.

climate refugees People displaced
due to global climate change.

convective circulation The circular motion
of air that results as air warms and rises,
cools and sinks, then warms and rises again.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

https://e360.yale.edu/features/geoengineer-the-planet-more-scientists-now-say-it-must-be-an-option

https://e360.yale.edu/features/geoengineer-the-planet-more-scientists-now-say-it-must-be-an-option

https://e360.yale.edu/features/negative-emissions-is-it-feasible-to-remove-co2-from-the-air

https://e360.yale.edu/features/negative-emissions-is-it-feasible-to-remove-co2-from-the-air

https://www.nap.edu/resource/25259/Negative%20Emissions%20Technologies.pdf

https://www.nap.edu/resource/25259/Negative%20Emissions%20Technologies.pdf

criteria air pollutants The six air
pollutants limited by the Clean Air Act:
carbon monoxide, lead, nitrogen dioxide,
ozone, particulate matter, and sulfur dioxide.

energy balance When referring to
the Earth, the equilibrium between
incoming energy from the sun
and outgoing energy as heat.

geoengineering An approach to climate
change mitigation that involves trying
to alter the Earth’s energy balance.

global climate change A worldwide shift in
climate (precipitation patterns, air currents,
humidity, and other factors) due to the
warming of the atmosphere and oceans.

greenhouse effect The process by which
the Earth’s atmosphere retains outgoing
infrared (heat) energy and warms the planet.

greenhouse gas Any atmospheric gas
that absorbs infrared radiation and
contributes to the greenhouse effect.

halocarbon gas A greenhouse gas and
ozone-depleting substance, including
chlorofluorocarbons (CFCs).

lead (Pb) A primary pollutant. A metal,
particulate air pollutant that can enter the
atmosphere from combustion of leaded
fuels as well as from waste incinerators,
lead smelters, coal burning, mining,
and battery manufacturing facilities.

methane (CH4) A greenhouse gas that
comes mainly from agricultural activities
like rice farming and cattle production,
as well as from leaks from natural gas
pipelines and drilling facilities.

Montreal Protocol An agreement
among 180 countries to address
the issue of ozone depletion by
phasing out chlorofluorocarbons.

negative emissions technologies
(NET) Approaches to climate change
mitigation that usually focus on removing
carbon dioxide from the atmosphere.

nitrogen oxide (NOX) A primary pollutant.
Includes nitric oxide (NO) and nitrogen
dioxide (NO2). Most NOX emissions come
from internal combustion engines in
vehicles, as well as from wood burning
and forest fires. NO2 is a reddish-brown
gas that can cause lung irritation and
respiratory disease; it can also react
with water vapor to form a secondary
pollutant known as nitric acid (HNO3).

nitrous oxide (N2O) A greenhouse
gas that comes from fertilizer use
and fossil fuel combustion.

ozone (O3) A molecule made up
of three oxygen atoms that is an air
pollutant in the troposphere but absorbs
UV radiation in the stratosphere.

ozone-depleting substances A class of
chemicals that are known to destroy ozone.

ozone layer A region 18 to 26
kilometers (11 to 16 miles) above
the Earth that contains most of the
ozone in the stratosphere and that
helps filter out harmful UV radiation
before it strikes the Earth’s surface.

Paris Agreement An international
climate change agreement signed
in 2016 that commits countries to
reduce greenhouse gas emissions.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

particulate matter (PM) A primary
pollutant. Solid and liquid particles
that are small and light enough to
remain suspended in the air.

photochemical oxidant Ozone pollution.

photochemical smog A form of air
pollution that contains photochemical
oxidants such as ozone.

primary air pollutants Pollutants that
are emitted directly into the atmosphere.

secondary air pollutants Pollutants that
are formed through chemical reactions
in the atmosphere between primary
pollutants and other substances.

sinks Natural processes that absorb
and store a chemical such as carbon.

stabilization wedges An approach
to climate change mitigation that
identifies ways to reduce greenhouse gas
emissions one step (wedge) at a time.

stratosphere The region of the
atmosphere above the troposphere that
ranges from 18 to 50 kilometers (11 to 31
miles) above the surface of the Earth.

stratospheric ozone depletion The
reduction of ozone in the stratosphere.

sulfur dioxide (SO2) A primary pollutant.
Results from the combustion of fuels that
contain sulfur, primarily from burning
coal in power plants. SO2 can react in
the atmosphere to form a secondary
pollutant known as sulfuric acid (H2SO4).

troposphere The lowest region
of the atmosphere; it extends from
the surface to 8 to 18 kilometers (5
to 11 miles) above the Earth.

volatile organic compounds (VOCs) 
A range of chemical compounds that
originate from both natural sources
and human activities and that can
easily become a vapor or gas.

weather Day-to-day changes in
temperature, atmospheric pressure,
precipitation, humidity, and wind.

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Bookmarks

7 Sustaining Our Energy Resources

Mimadeo/iStock/Getty Images Plus

Learning Outcomes

After reading this chapter, you should be able to

• Define basic energy concepts.
• Describe current energy sources and uses and how that might change in the future.
• Explain how fossil fuels are formed.
• Analyze the impact and future of coal.
• Analyze the impact and future of oil.
• Analyze the impact and future of natural gas.
• Analyze the impact and future of nuclear energy.
• Describe the opportunities and challenges of the energy transition.
• Identify examples of energy efficiency and conservation.
• Analyze the impact and future of solar energy.
• Analyze the impact and future of wind energy.
• Analyze the impact and future of bioenergy.
• Analyze the impact and future of hydroelectric energy, geothermal energy, and ocean energy.
• Describe what goes into the true cost of energy and what policies might be enacted to

encourage renewable energy.
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Section 7.1 Our Current Energy System

Much like water, energy is a resource we use every day without ever really giving much
thought to where it comes from or what the consequences of its use are for the planet. Take
a casual inventory of your home or apartment and consider all the devices and consumer
products that are currently plugged into a wall outlet. Televisions, computers, refrigerators,
microwave ovens, toasters, cell phone chargers, and other consumer products are constant
users of energy, day in and day out.

Now consider that your household is only 1 of about 130 million households in the United
States, and only 1 of about 1.6 billion households worldwide. Now add to this all the energy
that you and others use outside of your home—for transportation, while at work, and in other
settings like schools and hospitals. Finally, add to that all the energy used worldwide by com-
mercial businesses and industries to produce, package, transport, and deliver all the items
you consume every day—your food, water, clothing, and other consumer products.

The sheer scale of global energy use would seem to make its measurement almost impossible,
and yet every year experts at the U.S. Energy Information Administration (EIA) do just that.
The EIA estimates that global energy consumption in 2018 was almost 600 quadrillion Brit-
ish thermal units (Btu). This compares with global energy use of about 360 quadrillion Btu
(quads) in 1990, 400 quads in 2000, and 500 quads in 2010. Furthermore, the EIA (2018)
projects global energy use to increase to 739 quads by 2040.

It’s difficult to attach a human scale to these numbers. What is a Btu, and what does it mean
to use 600 quadrillion (600 with 15 zeros added) of them? Technically, a Btu is the amount
of heat energy required to raise the temperature of 1 pound of water by 1 degree Fahrenheit.
Six hundred quadrillion Btu is roughly equivalent to the amount of energy in 27 billion metric
tons of coal or 102 billion barrels of oil. In reality, even these measures are difficult to com-
prehend in the abstract. What we can say, however, is that global energy use is massive and
growing.

Our global energy use is also highly destructive to the environment. We currently depend
to a great extent on coal, oil, and natural gas to meet our energy needs. These resources are
finite, and the extraction and use of these fuels contributes to water pollution, air pollution,
ecosystem destruction, and global climate change, among other environmental impacts. Envi-
ronmental scientists are more convinced than ever that we need to move away from what are
known as nonrenewable sources of energy to renewable sources, including solar and wind.
Such an energy transition is already under way. The question is whether it can happen fast
enough to avoid the worst of the environmental impacts described.

7.1 Our Current Energy System

While we may hear the term energy used frequently in the news, in political debates, and in
discussions of environmental issues, we seldom take the time to ask what that term means.
Recall from Chapter 2 that energy is the capacity to do work. Sunlight (solar energy) enables
plants to photosynthesize and grow. Humans and other animals eat plants to obtain the
energy stored there in order to build our bodies, move, and do other forms of work. And we
use energy stored in coal, oil, and other fuels to heat our homes, power our devices, and move
our vehicles.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

Section 7.1 Our Current Energy System

This section is designed to provide you with an overview of how our energy system works.
Understanding the forms energy takes in our everyday lives is important as you consider how
we might transition to a new energy economy.

Key Concepts
We can classify energy a number of different ways. Primary energy is the energy stored in
natural resources such as coal and wind. Primary energy typically must be converted into a
form more useful to us—a process known as energy conversion. For example, the primary
energy contained in a ton of coal is used in an electric power plant to boil water and produce
steam, which spins a turbine that produces electricity. In this case, the electricity produced is
known as secondary energy—a form of energy that is more convenient for us to use. Like-
wise, the energy contained in a gallon of gasoline can be converted to kinetic energy in an
automobile. We ultimately use energy to achieve an “end use” such as lighting for our homes
or movement of our cars.

Recall from Chapter 2 that the second law of thermodynamics holds that no energy conver-
sion is 100% efficient and that in every energy transformation, some energy is lost as heat.
For example, when coal is burned in a power plant to produce electricity, roughly 70% of
the chemical energy available in that coal is lost to heat, while only 30% is converted into an
electric current. Likewise, when that electricity reaches your home or apartment and is trans-
formed into light energy in an incandescent lightbulb, as much as 95% of the electric current
is converted to heat, while only 5% or less is used to produce visible light. The term energy
conversion efficiency describes the percentage of primary energy converted to secondary
form—30% in the case of coal in an electric power plant. The term energy end-use effi-
ciency describes the percentage of primary energy used in its final destination. In the case of
burning coal to produce electricity to power an incandescent lightbulb, the energy end-use
efficiency can be as low as 1% to 2% overall (see Figure 7.1).

Figure 7.1: Energy conversion

Only 2% of the energy available in coal is used to power an incandescent lightbulb because so much
energy is lost in the process.

100 energy units
in coal at start

62 units lost
at power plant

2 units lost
in transmission

34 units lost
in heat

2 energy units used
for illumination

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Section 7.1 Our Current Energy System

Primary energy sources can be further broken down into categories of nonrenewable or
renewable. Nonrenewable energy sources are just what they sound like; energy sources
that, once consumed, are no longer available for future use. Nonrenewable energy sources
include the three main types of fossil fuels—coal, oil, and natural gas—as well as nuclear. As
we’ll discuss, fossil fuels were formed by geological processes that took millions of years, so
once we use them, they are essentially gone forever. Nuclear energy is produced using ura-
nium, another resource that exists in limited supply. Compare that with renewable energy
sources like solar and wind. Using sunlight to generate electricity through a solar panel, or
wind to generate electricity through a spinning turbine, does not deplete those resources.
However, we can only make use of these renewable energy sources when they are available.
For this reason, energy experts often refer to nonrenewable energy sources as being “stock
limited” and renewable energy sources like solar and wind as being “flow limited.”

Global Energy Consumption
For most of human history, the primary sources of energy were sunlight, muscle power,
and firewood. The ability to do work was limited by the number of hands available. With
the agricultural revolution and the domestication of animals, activities like plowing and pull-
ing wagons could be accomplished with animal power. Technological innovations gradually
introduced ways to use energy from moving water (waterwheels) or wind (windmills) to mill
grain or pump water. And throughout most of human history, we have burned firewood, crop
residues, and dried animal dung for cooking, heating, and lighting.

The ways in which we use energy, as well as the types and quantities of energy used, began
to change dramatically in the second half of the 18th century. The single most important rea-
son for this change was the development of the steam engine. Steam engines could be used
to move ships, trains, farm equipment, and factory machinery. Initially, steam engines were
powered by firewood, but in major areas of demand this resulted in overcutting of forests and
eventually wood shortages. In response, coal began to be exploited as an energy source, and
by the late 19th century it became the dominant form of energy worldwide.

Coal remained the number one source of energy in the world until around 1950, when oil
took over the number one spot. Oil was easier to extract and was much easier and cleaner to
use, so many homes and businesses began to prefer oil to coal. Nevertheless, coal remains to
this day the second most important global source of energy, and it is particularly important
for industrial uses and electric power production. Since the late 20th century, natural gas has
grown in importance and is projected to surpass coal in the near future to become the second
most important energy source. Natural gas is a cleaner burning fuel than coal and is relatively
easier to extract, transport, and utilize. As a result, many electric power companies have been
shifting from coal to natural gas for electricity production. Renewable energy sources like
hydropower, geothermal energy, solar energy, wind power, and biomass energy are currently
the fourth most important form of energy worldwide, although these energy sources are also
witnessing the fastest growth. Finally, nuclear energy—used almost exclusively for electric
power production—is the fifth most important form of energy worldwide.

In addition to the EIA’s report, BP (2019) also publishes an annual Statistical Review of World
Energy. BP reports global energy production and consumption in millions of tonnes of oil
equivalent (Mtoe), rather than in quads. BP estimates global energy consumption in 2017

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

Section 7.1 Our Current Energy System

was 13,511 Mtoe, up from 11,588 Mtoe 10 years earlier. Of that 13,511 Mtoe of consumption,
nonrenewable fossil fuels are currently meeting about 85% of global energy demand. At the
same time, the nonrenewable share of global energy supply is slowly declining over time.
Oil, coal, and natural gas combined for 95% of global commercial energy demand in the late
1960s, 90% in the late 1980s, and 88% in 2008. Recent declines in the share of global energy
from nonrenewable sources, while small, can be entirely accounted for by increases in the use
of renewable energy sources like wind and solar.

If we look at global energy use on an individual, or per capita, basis, we can observe large
differences in both the amounts and types of energy used in different countries around the
world. The World Bank reports per capita energy use by country in kilograms of oil equiva-
lent (kgoe). For 2013, the last year the World Bank published estimates, per capita energy
consumption varied from as low as 215 kgoe per person per year in Bangladesh to as much as
7,202 kgoe per capita in Canada. Developing countries like Ghana, Haiti, and the Philippines
had per capita energy consumption rates from 343 to 457 kgoe, while energy use in more
developed countries like France, Germany, and Japan averaged around 3,700 kgoe per person
per year. And whereas China is now the world’s largest consumer of energy, with the United
States second, per capita rates of energy use in China (2,226 kgoe) are only one third of those
in the United States (6,916 kgoe; World Bank, 2014).

Energy Sources and Uses
Unlike our use of drinking water, seafood, fruits, vegetables, or meat discussed in recent chap-
ters, we don’t really “demand” energy resources directly. We do not wake up in the morning
and decide that we really need a ton of coal or pick up a barrel of oil on the way home from
work. Instead, what we want from energy resources are the services they provide—heat,
mobility, and electricity for lighting and powering our devices. These are known as energy
end uses. Broadly speaking, we can break our nation’s energy consumption into four major
end-use categories: transportation, industrial uses, residential uses, and commercial uses. We
can also consider electric power generation as a major end use for energy resources, although
in this case it actually represents a transformation of energy from one form to another.

It turns out that certain types of energy resources are better adapted or better matched to
specific energy end uses than others. For example, coal may be the second most important
energy resource worldwide, but it makes essentially no contribution to meeting our trans-
portation needs. Likewise, oil or petroleum may be the single most important energy source
globally, but—at least, in the United States—it makes almost no contribution to electric power
generation. Understanding the connection between energy sources and uses is important if
we are to avoid misunderstandings about appropriate energy policy. During the oil crises of
the 1970s, when a global oil embargo severely reduced the supply of oil to the United States,
the nuclear power industry launched an advertising campaign arguing for increased nuclear
power production as a way to reduce dependence on imported oil. However, since our trans-
portation system at the time, and even today, depended almost entirely on oil rather than
electricity, increased nuclear power production would have had essentially no impact on oil
import levels.

Perhaps one of the best ways to understand energy sources and uses, as well as levels of
overall energy use in our economy, is to examine what’s known as an energy flow chart. In

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Section 7.1 Our Current Energy System

the United States the Lawrence Livermore National Laboratory (LLNL) produces the most
detailed and informative energy flow charts. For our purposes, we will discuss the chart the
LLNL published in 2018, which you can view at the following link: https://f lowcharts.llnl
.gov/content/assets/docs/2018_United-States_Energy.pdf. A more recent energy flow chart
may be available at https://f lowcharts.llnl.gov.

The left side of the LLNL energy flow chart shows the major energy sources used in the United
States in 2018, such as petroleum, natural gas, and hydroelectric power. The number below
each listed energy source represents the total amount consumed, measured in quads, and
corresponds to the width of the line flowing out from each box to the right. For example, the
light blue natural gas line is more than twice as wide as the black coal line because natural
gas was used more than twice as much as coal was. Added together, all these energy sources
totaled 101.2 quads of energy consumption in the United States, or about one sixth (17%) of
global energy consumption for that year.

The boxes those lines flow toward indicate how certain energy sources are matched with
specific energy end uses. For example, in the United States petroleum is predominantly used
for industry and transportation, and the width of the dark green lines tell us that petroleum
is first and foremost a source of energy for transportation. Likewise, coal, nuclear, hydro, and
wind are almost entirely utilized to produce electricity. That electricity is then utilized in the
residential, commercial, and industrial sectors, with virtually no electricity going to the trans-
portation sector. Natural gas appears to be a more versatile energy source, with significant
uses in electric power production, industrial purposes, residential home heating, and com-
mercial applications.

The LLNL energy flow chart shows us that not all energy sources are created equal. As we
consider our energy future, we must recognize that we cannot simply stop using petroleum
overnight and power our trucks and cars with coal, wind, or nuclear power. We could do this
over time if we changed the way we build cars and trucks and shift to electric engines, but
such a transition takes time.

The LLNL energy flow chart also clarifies just how much energy is lost during energy conver-
sions, which is referred to as rejected energy (light gray lines and boxes). For example, of the
38.2 quads of energy that are utilized to generate electricity, fully 25.3 quads (66.2%) are
lost as rejected energy, mainly in the form of heat. Likewise, of the 28.3 quads of energy from
petroleum and small amounts of ethanol and natural gas used in the transportation sector,
22.4 quads (79%) are lost as rejected energy. Overall, 68.5 of the 101.2 quads (67.7%) of
energy used in the United States in 2018 were lost as rejected energy, with only 32.7 quads
delivering actual energy services of mobility, heat, lighting and other applications.

There is growing consensus that the United States and the rest of the world need to undergo a
rapid energy transition, moving away from an overwhelming reliance on nonrenewable fos-
sil fuels to a world powered primarily by cleaner renewable energy resources. Such an energy
transition is already under way, and we will discuss the opportunities and challenges later in
the chapter. At this point, simply remember that planning this energy transition involves care-
ful consideration of available energy sources and uses. For example, 95% of the 28.3 quads
of energy currently used in the U.S. transportation sector comes from either petroleum or
natural gas. To successfully and quickly transition away from these nonrenewable fossil fuels,
what are our options?

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https://flowcharts.llnl.gov/content/assets/docs/2018_United-States_Energy.pdf

https://flowcharts.llnl.gov/content/assets/docs/2018_United-States_Energy.pdf

https://flowcharts.llnl.gov

Section 7.1 Our Current Energy System

One possible approach is to shift to liquid fuels derived from biomass, such as ethanol from
corn. Biofuels like ethanol currently meet about 10% of transportation energy needs in the
United States, so this is something of a proven technology. However, as we’ll discuss, increas-
ing corn production to produce more biofuels generates a different set of environmental
impacts that may actually be worse than continuing to rely on petroleum.

A second option for transitioning away from fossil fuels in the transportation sector is to move
toward electric cars and trucks. When in use, electric vehicles (EVs) emit no air pollution or
greenhouse gas emissions, and so they would seem to be an ideal way to transition from non-
renewable fossil fuels to a clean energy future. However, the actual impact of a transition to an
EV fleet will depend to a large extent on how we generate the electricity used to charge these
vehicles. Considering that we currently depend on coal for 34% of electric power production
in the United States and natural gas for another 26% of our electricity, transitioning to EVs
would have only a limited impact on efforts to reduce our dependence on nonrenewable fossil
fuels and reduce greenhouse gas emissions. Furthermore, shifting from an oil-based trans-
portation system to one that is powered by electricity would require significant investments
in new infrastructure that would take time to put in place.

Achieving a clean energy transition in the
transportation sector thus depends on
accomplishing two large-scale changes in
terms of energy sources and uses. First, we
need to continue to increase the percent-
age of electric power produced by clean
energy sources like solar and wind. Second,
we need to undertake a fundamental shift
away from a vehicle fleet built on the inter-
nal combustion engine to one powered by
electric motors. The first of these changes
appears to be well under way. The per-
centage of U.S. electric power production
coming from solar, wind, hydro and other
renewable energy sources doubled from
9% in 2008 to 18% in 2018 (EIA, n.d.). In
terms of the second change—a large-scale shift from internal combustion to EVs—there is
disagreement among energy experts as to how or when this will happen. Some experts pre-
dict that we are on the verge of a large-scale changeover and that rapid growth in demand
for EVs in places like China will prompt U.S. automakers to speed up their production and
distribution of these vehicles in the United States as well. However, other experts are more
skeptical and point to infrastructure challenges such as a lack of charging facilities as a key
barrier to rapid adoption of EVs.

The important point to make at this stage is to reemphasize that energy sources and uses are
not easily interchangeable. Earlier energy transitions—from wood to coal in the 18th and
19th centuries and from coal to oil in the 20th century—involved numerous changes in the
ways we produced and utilized energy. Likewise, transitioning away from nonrenewable coal,
oil, and natural gas to renewable energy sources will also require changes in the ways we
convert, store, and utilize that energy. An important factor in determining how fast such an
energy transition can occur will be energy policy and how energy prices are determined and

Sven Loeffler/iStock/Getty Images Plus
Transitioning fully to electric cars would take
time, since infrastructure is still a challenge.
The overall environmental impact would
ultimately depend on how we generate the
electricity used to charge these vehicles.

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Section 7.2 The Cost of Fossil Fuels

set. We’ll consider those factors in more detail in section 7.13. The next section takes a closer
look at the fossil fuels that currently dominate our energy economy, including an examination
of their origin, extraction, end use, environmental impacts, and future potential.

7.2 The Cost of Fossil Fuels

Coal, oil, and natural gas are known as fossil fuels because they were formed from the remains
of organisms that lived 100 million to 500 million years ago. During that period, large areas of
the planet were covered in freshwater swamps and shallow oceans that supported an abun-
dance of plant life and phytoplankton. This plant life and phytoplankton utilized solar energy
through photosynthesis to convert carbon dioxide and water into organic carbons.

Because these environments were so productive, organic material from dead plants, phyto-
plankton, and other dead organisms accumulated more quickly than they could be broken
down by decomposers. Thick layers of organic material accumulated at the bottom of these
bodies of water and built up over time. Gradually, this organic material was covered by layers
of sediment, further impeding any decomposition. Over millions of years, as sediment layers
covering this organic material became thicker and thicker, a tremendous amount of weight,
pressure, and heat were applied, producing coal, oil, or natural gas, depending on conditions
and the organic source material. In a somewhat ironic twist, you could say that fossil fuels are
an ancient form of solar energy, since they originated from plant material and living organ-
isms formed through photosynthesis.

Even though there are many different terms and categories used to classify fossil fuel depos-
its, geologists focus on two primary breakdowns. The first has to do with how concentrated
and accessible a fossil fuel deposit is. Geologists use the concept of a resource pyramid to
express this. Highly concentrated and easily accessible fossil fuels make up the top of the
pyramid. These are the fuels that energy companies exploit first because they have the lowest
production costs, such as oil deposits that gush from the ground or high-quality coal deposits
close to the surface. When these deposits have been exhausted—as most have been—energy
companies have to move down the resource pyramid to deposits that are more numerous
but also more difficult to develop. These deposits are less concentrated, are more remote and
harder to access, and require more effort to develop, such as offshore oil or deep coal depos-
its. Further yet down the resource pyramid are fossil fuel deposits that are of such low con-
centrations and/or in such difficult-to-reach locations that it would not make any economic
sense to extract them unless energy prices were to go much higher.

This is also why geologists and energy experts point to the fact that we won’t really run out
of fossil fuels, since there will always be some deposits that are simply not worth the effort to
extract. It also highlights a concept known as energy return on investment (EROI), or the
amount of useful energy extracted from a resource divided by the amount of energy it took
to produce that energy. Energy deposits at the top of the resource pyramid have a high EROI
since they produce a lot more energy than the energy needed to extract them. Further down
the resource pyramid, the EROI number declines, until we reach an EROI of 1:1, where the
amount of energy extracted is equal to the amount of energy used to extract it. Such a situ-
ation makes little sense, and so energy companies would probably abandon a deposit long

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Section 7.3 Coal

before that point. In the United States the EROI for oil and gas production has declined from
30:1 in the 1960s to about 10:1 today (Guilford, Hall, O’Connor, & Cleveland, 2011).

The second category of difference for classifying fossil fuels (especially oil and gas) involves
whether a particular deposit is conventional or unconventional. Historically, we have
exploited conventional deposits of oil and gas found in porous rock formations. Traditional
drilling techniques are used to bring oil and gas from these deposits to the surface. However,
geologists have long been aware of oil and gas found in unconventional deposits, such as
oil-soaked sands or shale formations that have trapped gas. As we’ll discuss, these uncon-
ventional deposits are more difficult to exploit, and extraction typically results in more seri-
ous environmental impacts. But because most of the productive conventional deposits have
already been heavily exploited, unconventional deposits are now the focus of much more
attention than they were in the past. The move from conventional to unconventional deposits
also helps explain the declining EROI figure for oil and gas production, since the latter require
more energy and effort to exploit.

Another concept common to the use of fossil
fuels is that of external costs or externalities.
An external cost is a cost associated with the
use of a product that is not reflected in the
price we actually pay for that product. For
example, when coal is mined and burned
to produce electricity, it can have a number
of environmental impacts. Coal mining can
harm water quality, and coal burning can
create air pollution. If poor water quality or
air pollution make someone sick, the cost of
treating that illness is usually not factored
into the price for that coal or the electricity
it was used to produce. Those health care
costs are external costs, and they represent
a hidden cost to the use of fossil fuel energy
resources because they mask or hide the
true costs associated with actually using
that resource.

The next sections will take a closer look at each of the three main fossil fuels and consider
issues related to their production, use, environmental impacts, and future.

7.3 Coal

Most of the coal we use today originates from swampy forests of 300 million to 400 million
years ago. Over millions of years vegetation in these swamps fell to the ground and accumu-
lated in layers faster than it could decompose. Swampy conditions limited oxygen supply and
resulted in partial, anaerobic decomposition, producing a material known as peat. As peat
was buried under more and more layers of sediment, it pressed out most of the water and

ping han/iStock/Thinkstock
Conventional deposits can be more easily
accessed and brought to the surface using
conventional drilling techniques, like those
pictured. Unconventional deposits require
more energy to extract and have lower EROI.

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Section 7.3 Coal

squeezed the organic material more tightly
together. This pressure combined with heat
from the Earth’s interior to produce layers
of coal, or coal seams.

Coal production in the United States has an
estimated EROI of roughly 60:1, whereas
in China this figure is closer to 25:1. This
means that from 25 to 60 useful units of
coal energy are extracted for every 1 unit of
energy used in its extraction. This relatively

high EROI (compared to oil and gas) reflects coal’s abundance and ease of extraction. Coal is
the most abundant of the fossil fuels, with global proven reserves estimated at about 1.1 tril-
lion metric tons. Proven reserves of a fossil fuel are defined as the quantities of that energy
source that can be extracted from known deposits, using current technology, at current prices.

When thinking about the future of fossil fuels, it’s useful to consider the reserves-to-
production (R/P) ratio (the proven reserves divided by annual consumption), which indi-
cates how long a resource will last. With 1.1 trillion metric tons of proven coal reserves and
global coal consumption at 7.8 billion metric tons a year, the R/P ratio is about 140, mean-
ing that at current rates of consumption, we have at least 140 years of coal remaining. The
R/P ratio in the United States is even better: With about 240 billion metric tons of proven
reserves and annual consumption of about 1 billion metric tons, the United States has at least
240 years of coal remaining. However, burning all this coal using current technology would
certainly doom the planet to catastrophic climate change. So unless another way can be found
to utilize coal, this relatively high R/P ratio doesn’t actually mean much.

Extraction
Coal is removed from the ground or mined in one of two ways. Underground mining, or
subsurface mining, involves digging tunnels or shafts into the ground to reach coal seams
that are deeper than 60 meters (200 feet). Surface mining, or strip mining, involves using
giant earth-moving machines to scrape away
vegetation, topsoil, and rock to reveal a shal-
lower coal seam.

One form of strip mining, known as moun-
taintop removal mining, is used widely in
the Appalachian region of Kentucky and West
Virginia. In this approach, the entire top por-
tion of a mountain is removed to expose the
coal underneath, and the material (referred
to as overburden) is dumped into surround-
ing valleys. Mountaintop removal mining is
highly destructive to surrounding ecosys-
tems, and the practice has been blamed for
severely contaminating groundwater and
causing downstream flooding.

kodachrome25/iStock/Getty Images Plus
Coal seams like this one are the result of
swampy vegetation that was buried under
sediment and then transformed by pressure
and the Earth’s heat.

edb3_16/iStock/Getty Images Plus
During the process of mountaintop removal
mining, large overburden machines are used
to transfer and dump excess material.

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Section 7.3 Coal

Once coal is mined it is used primarily for electric power production. Globally, around 40%
of all electric power production comes from burning coal, whereas in China and India (the
world’s number one and number three top coal consumers), that figure is 65% and 62%,
respectively. In the United States (the number two coal consumer), about one third of our
electric power production comes from burning coal. In addition, well over 90% of the coal
consumed in the United States is used to produce electricity, with small amounts used in steel
production and for other industrial purposes.

Impact and Future
Beyond the negative environmental impacts associated with coal mining, especially moun-
taintop removal mining, burning coal also results in a number of other serious environmental
problems. Coal combustion is a major contributor to smog formation and increased particu-
late levels in the atmosphere, both of which have negative health impacts and are associ-
ated with respiratory diseases and reduced life spans. Coal burning releases mercury, arsenic,
lead, and other toxins that can impact human health and wildlife. Finally, as a major source of
CO2 emissions, coal burning can be linked with the impacts of global climate change, including
changing weather patterns, increases in natural disasters, acidification of the oceans, and a
variety of other effects associated with a warming world. Overall, we can say that coal extrac-
tion and use impose significant external costs—in terms of health impacts, water and air pol-
lution, ecosystem destruction, and climate change—on society; costs that are not always fac-
tored into the price we pay for the electricity produced by coal.

Coal consumption peaked in the United States around 2007 and has been in sharp decline
since. U.S. coal consumption in 2018 fell to its lowest level since 1979. While some politicians
and coal industry executives have blamed this decline on a regulatory “war on coal,” the actual
reason for declining coal use lies with the energy market. Specifically, the past 10 to 15 years
have seen sharp increases in the production and supply of natural gas and declining prices
for this fuel. Cheaper and cleaner natural gas has been displacing coal in many parts of the
electric power sector.

Given the significant environmental impacts associated with coal extraction and use, as well
as declining demand in the United States since 2007, it’s fair to ask whether coal has much
of a future. Proponents of coal energy point to two types of technology change that might
possibly prolong our utilization of this fuel. First, clean coal technology refers to a variety
of approaches designed to remove contaminants from coal (such as mercury, sulfur, and arse-
nic) before it is burned. However, these technologies do nothing to address the issue of CO2
pollution associated with coal use. For that, a second approach known as carbon capture
and storage (CCS), or carbon sequestration, is being proposed and tested. CCS involves
technologies that can capture CO2 emissions from coal burning before it leaves the smoke-
stack. This CO2 gas is then converted to a liquid and pumped underground for long-term stor-
age. Early tests of CCS have had mixed results, but they have also proved to be quite expensive.
This added expense undercuts one of the only advantages coal has in its favor: its relatively
low price. Therefore, it’s not clear whether the current decline in coal use, at least in countries
like the United States, will ever be reversed.

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Section 7.4 Oil

7.4 Oil

Most people alive today have lived their entire life in what could be called the “age of oil.” Not
only are we reliant on oil for our cars and transportation, we also depend on this resource in
countless other ways. Oil is the raw material for many forms of plastic and synthetic fibers,
and our industrial agricultural system could not operate without massive inputs of oil for fer-
tilizer production. Therefore, it’s critical to consider the ways in which we extract and utilize
oil, its environmental impacts, and whether we are nearing a period of “peak oil.”

Today’s oil deposits originate from the remains of phytoplankton and other microorganisms
that lived in shallow seas and swamps hundreds of millions of years ago. As these organisms
died and sank to the bottom, they formed thick layers of organic material that was even-
tually buried under layer after layer of sediment. As this organic material was subjected to
increased heat and pressure, it was transformed into a waxy substance known as kerogen
and then eventually into oil or natural gas, depending on temperatures and pressure levels.
Oil collects in underground or underwater oil reservoirs, where it is trapped under a layer
of impermeable rock that holds it in place and prevents it from seeping upward. Despite what
the name sounds like, an oil reservoir is not a large pool of liquid oil but rather a porous rock
formation that holds small drops of oil in its pores the way a sponge holds water. The current
geographic distribution of large-scale oil deposits reflects those areas of the world that have
the right geological conditions to have allowed oil to form millions of years ago and collect in
oil reservoirs.

The BP Statistical Review of World Energy estimated global oil consumption in 2017 to be
roughly 36 billion barrels. BP also reported global proven reserves of oil at the end of 2017
of 1,696 billion barrels, resulting in an R/P ratio of a little under 50, meaning that at current
rates of consumption we have roughly 50 years of oil remaining. Two factors could lead to this
number either overestimating or underestimating how many years of oil supply we actually
have left. On the one hand, global demand for oil has been increasing at rapid rates, and this
could mean we deplete reserves faster than expected. On the other hand, new drilling and
oil extraction technologies could make oil deposits that are currently not counted in proven
reserves available for exploitation, extending the life span of global oil reserves.

Extraction
Oil is extracted from underground reservoirs by drilling oil wells. When an oil reservoir is
first tapped, there tends to be enough natural pressure in the deposit to push the oil up to the
surface. This first volume of oil extracted from an oil well through natural pressure is known
as primary oil recovery, and about 20% to 30% of oil in a reservoir can be extracted this way.
Oil companies will then make use of secondary oil recovery techniques, such as injecting
fluids into a reservoir to increase pressure, in order to extract another 10% to 20% of the oil

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Section 7.4 Oil

in a deposit. Since many major oil deposits around the world have already gone through pri-
mary and secondary oil recovery processes, oil companies are now using even more extreme
measures known as tertiary oil recovery (for example, injecting heated fluids or gases into
an oil reservoir) to extract another 10% to 20% of oil from a reservoir. As one would expect,
the EROI for oil extraction declines as oil companies move from primary to secondary and
eventually tertiary oil recovery techniques. Primary oil recovery practices may have an EROI
of 25:1, but this declines to about 10:1 for secondary oil recovery and as low as 5:1 for tertiary
oil recovery. As a result, oil companies will typically resort to tertiary oil recovery techniques
only when oil prices are high enough to justify the extra effort and expense.

Another trend in global oil production is the
increasing exploitation of unconventional
oil deposits from oil shale and oil sands (also
called tar sands). Oil shale is a rock forma-
tion that holds oil but is not porous enough
to allow movement of oil through the forma-
tion. In the past 20 years, oil companies have
developed a technique known as hydraulic
fracturing, or fracking, to remove oil and
natural gas from shale deposits. In fracking,
liquids mixed with sand are pumped into oil
shale deposits under extremely high pres-
sures. This fractures and cracks the shale
formations, while the sand keeps the cracks
open just enough to allow the oil and gas to

begin to flow (see Figure 7.2). Oil sand, or tar sand, formations are found near the surface
and contain a tar-like substance known as bitumen. These sands can be heated to extract the
bitumen, which can be refined into oil. Large-scale tar sand production in Alberta, Canada,
supplies oil refineries in the United States via the Keystone Pipeline. Expansion of the pipe-
line has been a highly controversial issue in the northern and central United States in recent
years. Both oil shale and tar sand production have lower EROI rates than oil production from
conventional deposits, and both of these techniques have greater environmental impacts as
well. For example, we learned in Chapter 5 that fracking of oil shale formations is linked with
water-quality problems. Tar sand production involves completely stripping the surface of any
vegetation and is also linked with local water pollution problems.

Once oil is extracted from the ground, it still needs to be refined before it can be used. The
raw material that comes out of the ground is known as crude oil, and oil refineries are used
to break that material down into different petroleum products like jet fuel, gasoline, asphalt,
and lubrication oil. Oil refineries are basically giant distillation plants where crude oil is
heated in what are known as distillation columns. Roughly 70% of crude oil sent to refiner-
ies is converted into gasoline or diesel fuel, and these fuels are used almost exclusively in the
transportation sector.

dan_prat/iStock/Getty Images Plus
The tar sands operation in Alberta, Canada, is
massive.

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Section 7.4 Oil

Figure 7.2: Fracking

Fracking, or hydraulic fracturing, involves pumping water, sand, and chemicals at extremely high
pressures into shale oil and gas deposits. This causes the shale to crack and allows the oil or gas to flow
to the surface.

Source: Adapted from normaals/iStock/Getty Images Plus.

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Section 7.5 Natural Gas

Impact and Future
As with coal mining and use, oil extraction and use results in a number of environmental
problems. Chapter 6 described the challenges associated with oil spills and oil pollution of
the world’s oceans. In addition, development of unconventional oil deposits like oil shale and
tar sands results in habitat destruction, water and air pollution, and other environmental
issues. Finally, burning petroleum products like gasoline and diesel produces some of the
same air pollution and greenhouse gas emission problems as burning coal. However, burning
petroleum products is somewhat less polluting than using coal to produce the same amount
of energy.

The future of oil use will depend on a number of factors. As with coal and natural gas, ongoing
use of oil for decades to come may be limited by the issue of global climate change and the
need to control greenhouse gas emissions. Because oil is used mainly in millions of vehicles
dispersed all over the world, CO2 emissions cannot be captured and stored in ways that are
being tested for coal-fired power plants. Finally, with only about 50 years of proven reserves
of oil estimated to be available, there are questions about whether we are nearing a point of
“peak oil.” Peak oil refers to the point in time when global oil production and use reaches
its highest point before beginning a period of permanent decline. For these reasons—and
because of the significant environmental impacts associated with oil extraction, transport,
refining, and use—many energy experts are calling for a more rapid shift away from internal
combustion engines to a greater reliance on EVs.

7.5 Natural Gas

Natural gas has a geologic origin similar to that of crude oil, except that it came about in loca-
tions where ancient organic material was buried deeper underground and subjected to even
higher temperatures and pressures. As a result, natural gas deposits that we exploit today
are often located in the same geographic regions as oil deposits. In fact, it used to be common
practice for oil-drilling companies to simply “burn off ” or flare natural gas that is released
during the process of drilling for oil. Today, however, that natural gas is considered too valu-
able to waste in this way, so it is either captured and shipped to market through pipelines or
reinjected into the oil deposit to increase pressure and the flow of oil.

Natural gas consists mainly of methane (CH4) and is generally a cleaner burning fuel than
either oil or coal. Burning natural gas produces only about half of the CO2 as burning the
energy equivalent of coal. This is one of the reasons why demand for natural gas has been
growing worldwide, and specifically why natural gas has been displacing so much coal used
in the electric power sector in the United States. The share of natural gas in the global energy
economy increased from 22% in 2007 to 24% in 2017, according to the BP Statistical Review
of World Energy. In the United States the share of natural gas has increased from 23% to 29%
in the same time period.

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Section 7.5 Natural Gas

Current global proven reserves of natural gas are estimated to be 194 trillion cubic meters
(254 cubic yards), and global consumption rates are 3.67 trillion cubic meters (4.8 cubic
yards) a year. This yields an R/P ratio of 53 years. In the United States the current R/P ratio is
only about 12, suggesting only about 12 years of natural gas supply remaining at current rates
of consumption. However, as we’ll see in the following section, new natural gas extraction
technologies like fracking are expanding proven reserves in many places. Some of the largest
remaining deposits of natural gas are in Russia, Iran, Qatar, and Turkmenistan.

Extraction
Like oil, natural gas is extracted from underground deposits by drilling wells, and like oil,
hydraulic fracturing (or fracking) is being used to extract natural gas from shale deposits.
Once natural gas is pumped out of a reservoir, it is shipped by pipeline to a refinery, where it
is cleaned of impurities. From there, natural gas is shipped to end users like electric power
plants or residential furnaces through even more pipelines. In the United States about 34%
of natural gas supply is used for electric power production, 16% for home heating and hot
water, 12% for commercial applications, 3% for transportation (mainly natural gas–powered
city buses), and 35% for industrial purposes (such as raw material for plastic, synthetic fiber,
and fertilizer production).

One challenge with natural gas is that, unlike oil, it cannot be easily shipped across oceans.
As a result, billions of dollars are being invested in facilities to convert natural gas into a liq-
uid compound known as liquefied natural gas (LNG). LNG is produced by chilling natural gas
to !160 °C (!260 °F). Once chilled to this temperature, LNG takes up only about 1/600 the
space of its gaseous form. LNG can then be shipped across oceans in specialized tankers and
converted back to a gaseous form in facilities in the receiving country. Converting natural gas
to LNG does require more energy, which therefore lowers the EROI for this energy source.

Impact and Future
The future for natural gas as an energy source will depend in large part on how this fuel is
extracted and utilized. Because natural gas produces so much less CO2 than an equivalent
amount of coal, it’s often described as a clean energy source that can act as a “bridge” to
an energy future powered mainly by renewable sources. The clean energy bridge argument
for natural gas is used as justification for increased hydraulic fracturing of shale deposits in
places like North Dakota (Bakken shale deposit), Texas (Barnett shale deposit), and Pennsyl-
vania (Marcellus shale deposit). Natural gas proponents correctly point out that gas extracted
from these shale deposits is displacing coal in electric power plants and thereby helping the
United States reduce its CO2 emissions. However, the clean energy bridge justification has
been called into question based on a 2018 report published in the journal Science. That report
found that methane (CH4) leaks from natural gas wells, pipelines, and other facilities were
60% higher than previously estimated (Alvarez et al., 2018). Because methane is also a green-
house gas that can be up to 80 times more effective at trapping heat than CO2, some of the
clean energy advantages of natural gas use appear to be canceled out.

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Section 7.6 Nuclear Energy

7.6 Nuclear Energy

All three fossil fuels—coal, oil, and natural gas—face some of the same challenges. Fossil fuels
are nonrenewable and will not last forever. The most abundant of these fuels, coal, is also the
dirtiest and most polluting. Extraction and use of all fossil fuels have immediate environmen-
tal impacts in the form of habitat destruction and water and air pollution—as well as long-
term impacts in the form of climate change and global warming.

The remainder of this chapter will focus on the changes we need to make and the renewable
energy sources that need to be developed and deployed globally to avoid the worst conse-
quences of climate change. But first we will explore a source of energy that some say will play
a critical role in the transition away from fossil fuels. Nuclear energy, or nuclear power, is
electricity produced through a nuclear reaction. Because nuclear power can generate elec-
tricity without directly emitting carbon dioxide or other greenhouse gases, some have touted
it as a “climate-friendly” source of energy. However, concerns over nuclear safety, the proper
disposal of highly radioactive nuclear waste, and the high cost of nuclear construction have all
combined to hinder a more rapid development of this energy source.

History
The nuclear age began with the detonation of two atomic bombs over Japan near the end
of World War II in 1945. In the years after the war, scientists began harnessing the same
basic technology used to produce atomic bombs in order to develop nuclear energy. The first
commercial nuclear power plants went into operation in the 1950s, and at the time it was
expected that this energy source would produce electricity so inexpensively that it would be
“too cheap to meter.” Optimism over the future of nuclear power continued into the 1960s and
1970s as electric power companies placed
hundreds of orders for new plants.

The rate of growth in nuclear power plant
construction began to ease, however, due
to rising construction costs, public worries
over nuclear safety, and questions about
what to do with growing stockpiles of
nuclear waste. Nuclear accidents at Three
Mile Island in Pennsylvania in 1979 and
Chernobyl in Ukraine in 1986 underscored
these concerns, and nuclear power produc-
tion slowed further. On March 11, 2011, an
earthquake and tsunami off the coast of
Japan caused radioactive material to pour
out of the Fukushima Daiichi Nuclear Power
Plant complex into the surrounding air and
sea, reigniting the debate over the safety
and future of nuclear energy.

Animaflora/iStock/Getty Images Plus
Nuclear energy is touted by some as climate
friendly because it produces electricity without
emitting carbon dioxide. However, nuclear
facilities are costly to construct, potentially
dangerous to maintain, and result in radioactive
waste that must be handled with great care.

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Section 7.6 Nuclear Energy

Today nuclear power provides about 10% of global electric power production, down from
a high point of 17% in the mid-1990s. The United States has the highest number of nuclear
power plants at 100, followed by France (58), Japan (43), China (36), and Russia (36). Of
these countries, France derives the highest percentage of its electricity from nuclear power,
with this energy source meeting 72% of that country’s electricity demand.

How It Works
While the specific design of nuclear power plants varies across countries, they all operate on
the basic principle of nuclear fission. Nuclear fission occurs when the nucleus of an atom
is split to form two smaller nuclei, releasing energy in the process. To generate electricity,
nuclear power plants initiate and control nuclear fission inside devices known as nuclear
reactors.

In most reactors, nuclear fission starts with uranium-235 (U235). U235 is created when uranium
is mined and purified to reach a concentration that can sustain a series of nuclear fissions,
known as a nuclear chain reaction. Uranium atoms are unstable and will split, or undergo
fission, when struck by subatomic particles known as neutrons. Neutrons are released in
a reactor core to split uranium atoms, in the process releasing energy and more neutrons.
Those neutrons then trigger even more splitting or fission of other uranium atoms, releasing
even more energy and neutrons. This sets in motion a nuclear chain reaction that releases
tremendous amounts of energy in the process. In order to prevent this chain reaction from
getting out of control, reactor cores also contain a cooling solution or moderator that slows
the reactions down. They also have control rods made of material like boron that absorb neu-
trons and help slow or control the reaction. When the earthquake and tsunami struck the
Fukushima nuclear complex in Japan, it crippled the cooling system in the reactor core of the
plant. The runaway nuclear chain reaction then led to a nuclear “meltdown” and the release
of radioactive material.

The entire purpose of generating a controlled nuclear chain reaction is simply to boil water.
The energy released during fission heats water in the reactor core to a high enough tem-
perature to produce steam. That steam is used to spin a large turbine attached to an electric
generator, producing electricity. The same basic idea is at work in a coal- or natural gas–fired
electric power plant, except that steam is produced in those plants by the combustion of these
fuels rather than by a nuclear chain reaction.

Advantages and Disadvantages
In terms of the advantages and disadvantages of nuclear power, it’s appropriate to compare
this energy source to coal, since both are used almost exclusively to generate electricity (see
Table 7.1).

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Section 7.6 Nuclear Energy

Both nuclear and coal-fired electricity generation start with mining—of uranium and coal,
respectively. Because so much more coal has to be mined to generate the same amount of
electricity, coal generally leads to greater habitat destruction and land disturbance. Both
types of mining contribute to health risks for miners: black lung disease for coal miners and
radiation exposure for uranium miners.

Once these fuels reach a power plant and are used to generate electricity, nuclear power is far
cleaner than coal and basically produces no air pollution or CO2 emissions. It should be noted,
however, that mining uranium, enriching uranium, and building and operating a nuclear
power plant do produce pollution and CO2 emissions, even if the actual generation of electric-
ity does not. In addition, nuclear power production results in radioactive waste that will be
dangerous for thousands of years. This waste needs to be stored and monitored to prevent
radioactive material from escaping to the surrounding environment.

Table 7.1: Coal versus nuclear

Coal Nuclear

Land disturbance from mining Extensive, especially from
mountaintop removal mining

Less extensive

Greenhouse gas emissions Significant, a major source of CO2
emissions globally

None from electric power
generation; limited from plant
construction and uranium
mining

Other air pollution Significant (see Chapter 8) None from electric power
generation; limited from plant
construction and uranium
mining

Radiation emissions None or limited None or limited, with the
exception of severe accidents

Radioactive waste None Significant, requiring long-term
storage and management

Worker health and safety Serious risks and dangers from
coal mining

More limited risks in mining,
but potentially greater long-
term risk in nuclear power plant
operations

Health impacts on nearby
residents

Significant due to air pollution None or limited, with the
exception of severe accidents

Effects of accident or terrorist
attack

None or limited Possibly catastrophic

Fuel supply 200–300 years, based on known
estimates

Uncertain; depends on potential
for reprocessing of used nuclear
fuel

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Section 7.7 The Energy Transition

Finally, nuclear power plants themselves become radioactive over time and have to undergo
an expensive decommissioning process at the end of their operation. In addition, the radioac-
tive material from the decommissioning process has to be stored safely for hundreds of years.

Impact and Future
Overall, nuclear power produces electricity with fewer immediate environmental impacts
compared with coal. The main exception relates to radioactive waste management and dis-
posal. One other difference, however, is the very small risk of a nuclear accident and what
the consequences of such an event would be. Aside from large nuclear accidents—such as
those at Three Mile Island, Chernobyl, and Fukushima—smaller incidents and minor radia-
tion leaks are more common. This “small risk–big impact” reality of nuclear power is largely
responsible for public opposition to this energy source and has also contributed to the rising
cost of nuclear power.

The future potential of nuclear energy is highly uncertain. Many of the roughly 400 nuclear
power plants currently generating electricity around the world are nearing the end of their
expected operational life and will soon start to undergo decommissioning. The high cost of
construction and financial risks associated with building and operating a new nuclear power
plant have driven electric utility companies in the United States and other countries to cancel
orders for new reactors. However, given the urgency of global climate change, some energy
experts and even some prominent environmentalists are calling for a new look at nuclear
energy. New reactor designs and so-called next-gen nukes that have inherent safety features
and lower construction costs are also fueling renewed interest in nuclear power. The question
remains as to whether public distrust of nuclear power and private sector nervousness about
the financial risks can be overcome. A lot will depend on how rapidly the world can continue
to develop renewable energy sources.

Learn More: The Debate Over Nuclear Energy

This TED Talk presents a debate over the need for nuclear energy between two experts in the
field.

• https://www.youtube.com/watch?v=UK8ccWSZkic

7.7 The Energy Transition

Long before we ever “run out” of fossil fuels like coal, oil, and natural gas, we will have to tran-
sition away from a reliance on these fuels to different energy sources. Unless we do so, atmo-
spheric concentrations of the main greenhouse gas carbon dioxide will reach levels exceed-
ing 550 or 600 ppm, triggering catastrophic climate change with massive and unpredictable
consequences. At current rates of consumption, this means that we have just a few decades to

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Section 7.7 The Energy Transition

achieve roughly an 80% reduction in our use
of fossil fuels, since our energy choices will
become increasingly “carbon constrained.”
While we have undergone energy transi-
tions in the past, the transformation of the
energy landscape in the decades ahead will
be far more massive and will have to occur
faster than anything we have ever witnessed
before. It’s no exaggeration to state that we
are on the verge of not just an energy transi-
tion but an actual energy revolution.

The energy sources and technologies
needed to replace fossil fuels are currently
available, commercially viable, and see-

ing increased use the world over. These include what are sometimes referred to as “tradi-
tional” renewable energy sources like hydropower, geothermal energy, and biomass energy.
They also include “new” renewables like solar energy, wind power, and ocean energy. These
renewable energy sources have a massive potential. The total energy contained in one hour
of sunlight striking the Earth’s surface is more than all the commercial energy consumed on
the planet in an entire year. Likewise, the energy contained in the wind blowing at any time
across the planet is more than 15 times the global energy demand in that moment. However,
unlike the highly “energy-dense” fossil fuels, renewable energy sources are diffuse and inter-
mittent. We have to deploy technologies like solar panels and wind turbines over wide areas
to capture enough of this energy to meet demand and to develop methods to collect and store
that energy for later use.

The renewable energy transition or revolution faces a number of other challenges as well. As
with all new technologies, the development and deployment of renewable energy is held back
by uncertainties over the technology itself. As these technologies have become more wide-
spread, some of the hesitation associated with adopting them has also diminished. Second,
renewable energy sources have often been more expensive than fossil fuel energy sources,
and this has limited investment in and adoption of these technologies. That situation has
changed rapidly in just the past decade as renewable energy sources like wind and solar have
become cost competitive with fossil fuels in most applications. Third, recall the concept of
external costs and the idea that all fossil fuel use (especially coal) imposes externalities in the
form of air pollution, water pollution, health impacts, and habitat destruction. The presence
of these external costs means that fossil fuels appear to be cheaper than they actually are, or
put a different way, renewable energy sources might be even more cost competitive than we
believe them to be.

Fortunately, many of these challenges that have been holding back the adoption of renewable
energy sources are diminishing, and we are seeing examples of cities, states, and even entire
countries meet a growing percentage of their energy demand through renewable sources. For
example, the city of Orlando, Florida, is covering rainwater collection ponds with solar panels
and has set a goal of meeting all its energy needs from “carbon-free” sources by 2050. The
state of California is on track to generate 50% of its electricity with renewable energy sources
within the next few years. And countries like Germany and Denmark are already meeting one
third or more of their electricity needs with renewable energy sources like solar and wind.

valio84sl/iStock/Getty Images Plus
Solar farms such as this one might well play an
important role in the energy transition.

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Section 7.8 Energy Efficiency and Conservation

Much of the remainder of this chapter will take a closer look at the renewable energy tech-
nologies that will play the biggest part in the energy transition away from fossil fuels. This
includes solar energy, wind power, biomass energy, hydropower, geothermal energy, and
ocean and tidal energy. However, we’ll start the discussion of renewables with a focus on
energy efficiency and conservation. By first reducing levels of energy demand through better
lighting, appliances, windows, and insulation, we can reduce the quantity and magnitude of
the renewable energy devices that need to be deployed to meet that energy demand.

Learn More: The Energy Transition

In the first link, energy theorist Amory Lovins lays out a 40-year plan to move away from our
dependence on oil in an engaging TED Talk. The second website provides examples of how
the energy transition is under way all over the world.

• https://www.youtube.com/watch?v=ZHOyfyGwpes
• https://energytransition.org

7.8 Energy Efficiency and Conservation

Energy conservation and energy efficiency are related but are also different concepts. Energy
conservation refers to a process of changed behavior that reduces energy consumption by,
for example, turning down the heat or walking instead of driving. Energy efficiency is defined
as achieving the same outcome—heating a room, driving to work—while using less energy
in the process. Therefore, energy efficiency depends on changes in technology or conditions,
such as better insulation or a more fuel-efficient vehicle.

Energy efficiency and conservation are sometimes referred to as the “fifth fuel” after coal,
oil, natural gas, and renewable energy sources since they help us achieve desired energy out-
comes. But energy efficiency and conservation are the most immediate and the least costly
means for reducing greenhouse gas emissions from energy use. The logic behind the pursuit
of energy efficiency and conservation is simple: Lowering energy demand means reducing
the need to produce energy in the first place, regardless of where that energy is actually com-
ing from. In other words, rather than focus on the energy supply side by increasing energy
production, energy efficiency and conservation represent a shift in focus to the demand side.
Put another way, it could be said that the most “environmentally responsible” power plant
that can be built is the one that doesn’t need to build. We can find examples of energy conser-
vation and efficiency all around us.

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Home

Section 7.8 Energy Efficiency and Conservation

Transportation Sector
In the transportation sector, designing communities and neighborhoods in a way that pro-
motes walking, biking, and/or the use of mass transit options is a great way to promote
energy conservation. Unfortunately, in many regions of the United States, the opposite is the
case, and citizens are left with little choice but to rely on personal vehicles for most or all of
their transportation needs. In terms of energy efficiency, internal combustion engines have
become much more efficient over the past few decades. However, some of these efficiency
gains have been canceled out by a move to greater use of sport-utility vehicles and trucks by
consumers. In 1975 over 80% of the personal vehicles sold in the United States were cars, but
today that figure is under 50%. As a result, the overall efficiency of the personal vehicle fleet
in the United States has only increased from 22 miles per gallon (mpg) in 1985 to just under
25 mpg in 2017.

Looking into the future, greater use of gasoline–electric hybrid vehicles, plug-in hybrid auto-
mobiles, and electric vehicles is being touted as a way to reduce environmental impacts in
the transportation sector. The gasoline–electric and plug-in hybrid vehicles are equipped
with both an internal combustion engine and an electric motor powered by batteries. The
gasoline–electric battery system is constantly recharged as the brakes are applied, whereas
batteries in a plug-in hybrid are charged by plugging into an electric outlet. Both kinds of
hybrid vehicles rely on the internal combustion engine for higher speed driving and battery
power for slower speed, city driving. And both kinds of hybrid vehicles can achieve fuel effi-
ciencies of 40 to 60 mpg. Finally, EVs depend entirely on battery power and emit no pollu-
tion or greenhouse gases when in operation. However, the overall environmental impact of
a switch to EVs depends in large part on how the electricity used to charge the batteries is
generated in the first place (see the Close to Home feature box).

Close to Home: Considering Sources and Benefits of Electricity

Electricity is an incredibly useful form of energy, and it can accomplish many of our daily
tasks more efficiently than fossil fuels can. Consider car travel. A typical gasoline-powered
car might be around 20% efficient. In other words, only 20% of the energy contained in
gasoline is successfully harnessed to move things around. The rest is lost as waste heat to
the surrounding environment. EVs use electric motors that can be more than 90% efficient
(Hanley, 2018), so nearly all the electricity stored in a car’s battery system can be converted
into powering the car.

(continued)

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Section 7.8 Energy Efficiency and Conservation

Close to Home: Considering Sources and Benefits of Electricity
(continued)

Heating buildings can be more efficient with electricity as well. Most homes use furnaces and
boilers that warm air and water with natural gas or oil. Heat pumps are electrical appliances
that can move heat from one location to another with incredible efficiency. In many
situations, heat pumps can reduce energy use by 30% to 60% (U.S. Department of Energy,
n.d.b). Because electricity is so efficient, many experts believe that electrifying our economy
is one of the best things we can do for the environment. They argue that if we cook, heat, and
transport ourselves with more electricity and fewer fossil fuels, we will require fewer energy
resources and have less of an environmental impact.

However, there are some important factors to consider, including where the electricity comes
from. Some places use emissions-free technologies like nuclear, wind, solar, and hydroelectric
to produce electricity, but most locations still rely on coal and natural gas power plants.
These fossil fuel sources are only 30%–50% efficient, so a lot of energy can be lost (and a lot
of emissions can be produced) when we generate electricity in the first place. The benefits of
electricity depend on the specific technologies that are supplying the electrical grid.

Consider the benefits of driving an EV in different locations in the United States. A typical U.S.
car owner drives an average of 37 miles per day (Federal Highway Administration, 2018),
which results in about 31 pounds of CO2 emissions per day when using a typical gasoline-
powered car (U.S. Department of Energy, 2018). EVs might emit anywhere from 0 pounds
per day, if their electricity comes from an emissions-free power source, to 25 pounds per day,
if their electricity comes from a coal-fueled power plant (U.S. Department of Energy, n.d.a,
2016). Twenty-five pounds per day is still an improvement, but in this case, it might make
more sense to upgrade the power plant before investing heavily in a new transportation
system.

To explore the benefits of electricity use in different locations, take a look at the EPA’s Power
Profiler website. This resource contains data from electrical grid regions all over the United
States. The mix of energy resources utilized by each region is provided in the Fuel Mix chart,
and you can find where these regions are located by using the map toward the bottom of the
page. Grid emissions are presented in the Emission Rates chart, which provides the pounds
of CO2 that are produced for every megawatt-hour of electricity. Using both charts, we can
see that some regions, like the SRMW in Missouri and Illinois, rely predominantly on coal and
create large amounts of greenhouse gas emissions. Other regions, like the NYUP in New York,
utilize hydroelectric and nuclear technologies and produce much cleaner electricity.

You can also use the Power Profiler to explore your grid region in greater detail. If you enter
your zip code on the left-hand side, the website will compare the fuel mix and emission rate
in your grid region to those of the national average. To put your region’s emission rate into
perspective, the national average value is 998.4 pounds per megawatt-hour, which would
result in roughly 13 pounds per day for the average EV owner. To find the driving impact of
EVs in your location, just multiply your region’s emission rate by the 0.0125 megawatt-hours
per day that a typical EV will require.

Now that you have a better sense of where your electricity is coming from, do you think it is
important to convert more energy systems to electricity in your location? Should your region
focus on transitioning to cleaner forms of power production first? Are there other ways
you can capitalize on the environmental benefits of electricity to make your lifestyle more
sustainable?

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

https://www.epa.gov/energy/power-profiler

https://www.epa.gov/energy/power-profiler

Section 7.8 Energy Efficiency and Conservation

The Building and Residential Sector
Energy conservation and efficiency can also be achieved in the
building and residential sector. While turning off lights and control-
ling the thermostat are commonsense ways to conserve energy (and
save money), they are just the tip of the iceberg in reducing building
and residential energy consumption. Energy efficiency investments
like adding insulation, installing energy-efficient windows, switch-
ing to energy-efficient appliances, and using energy-efficient light-
ing can dramatically lower energy consumption and energy bills in
just about any home or building. So-called net zero energy build-
ings are constructed to be highly energy efficient and outfitted with
renewable energy devices like solar panels, with the overall goal of
having the building produce as much energy as it consumes.

Despite the apparently obvious advantages to promoting energy
conservation and achieving greater energy efficiency, there are a
number of barriers to doing so. First, becoming more energy effi-
cient can often involve significant up-front investments. While insu-
lating a home, installing energy-efficient windows, or buying a more
efficient refrigerator can save a consumer money over the long term,
they require spending money now, and not everyone can afford
such investments. Likewise, it’s not always clear to consumers what
the most energy-efficient options are. While many of us are familiar
with the yellow EnergyGuide labels found on new appliances, we’re
not always able to process that information in a way that allows for
a true and accurate comparison across different products. Unfor-
tunately, it appears that these up-front cost and information bar-
riers to energy efficiency have a disproportionate impact on low-
and moderate-income households, exactly the families that would
benefit the most from lower energy consumption and energy bills
(Bagley, 2019). Government programs offer one way to overcome this challenge. For example,
one program in California directs a portion of energy tax revenue to clean energy projects in
low-income neighborhoods.

Consumer Information, Federal
Trade Commission. This image

is not subject to copyright
protection.

EnergyGuide labels
such as this one are
intended to help
consumers make
informed decisions,
but people don’t
always understand
the information being
presented. The key
is to focus on the
“estimated yearly
energy cost” and
compare that figure to
other appliances being
considered.

Learn More: Energy Justice in California

California’s effort to help fund investment in energy efficiency and renewable energy in low-
income communities is an example of what’s being called “energy justice.” Learn more about
the program at these sites.

• https://calepa.ca.gov/envjustice/ghginvest
• https://e360.yale.edu/features/green-upgrade-how-california-is-pioneering

-renewable-energy-justice-cap-and-trade

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

https://calepa.ca.gov/envjustice/ghginvest

https://e360.yale.edu/features/green-upgrade-how-california-is-pioneering-renewable-energy-justice-cap-and-trade

https://e360.yale.edu/features/green-upgrade-how-california-is-pioneering-renewable-energy-justice-cap-and-trade

Section 7.9 Solar Energy

7.9 Solar Energy

Of all the renewable energy sources discussed in this chapter, the potential for solar energy—
energy from the sun—is probably the greatest. In addition to being abundant, solar energy
helps drive processes that enable other forms of renewable energy; for example, the wind,
the water cycle (hydropower), and photosynthesis (biomass energy). The main challenge we
face with solar energy is finding ways to take this abundant—but also diffuse and intermit-
tent—energy source and concentrate it in a form that we can use in transportation, building,
industrial, and commercial applications. This requires technologies that can capture, collect,
convert, store, and transport solar energy when and where it is needed.

How It Works
One major benefit of solar energy is that it can be utilized in a number of different ways.
Passive solar energy refers to approaches that use sunlight directly without any mechani-
cal devices, such as when sunlight is used to illuminate or heat interior spaces. Active solar
energy approaches capture sunlight using mechanical devices and then convert it to useful
heat or electric power (referred to as solar power).

Passive Solar Energy
Human societies have long been aware of
the potential for passive solar energy appli-
cations. A well-known example of this is the
Anasazi cliff dwellings found in the south-
western United States. These dwellings
are located on south-facing cliffs with rock
overhangs, providing direct solar heating of
the space in cooler winter months when the
sun is low in the sky and shade in the sum-
mer months from the hot desert sun.

In modern homes the same principle can be
achieved by orienting the building to receive
maximum sunlight in winter months and
less during the summer. For example, large areas of south-facing windows will let in the win-
ter sun and help warm interior spaces. Extended overhangs or window treatments (such as
solar-blocking shades that are easy to open and close) can then be used to block some of
that sun from entering in the summer to help keep the space cool. Deciduous trees can also
be planted around a building, since they drop their leaves in the winter—allowing sunlight
through—but shade the building in the summer.

bboserup/iStock/Getty Images Plus
The ancient Anasazi cliff dwellings are an
example of passive solar construction in that
they provide optimum solar heating and sun
protection at different times of the day and year.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

Section 7.9 Solar Energy

Active Solar Energy
Active solar energy devices include flat plate solar collectors for space heating or hot water
production. Flat plate collectors are mounted on rooftops and consist of a glass surface, dark-
colored backing, and a series of tubes for circulating water or air. Sunlight striking the col-
lector heats the water or air, which is then pumped into the building and used to provide hot
water to the tap or heat for space heating. Flat plate solar collectors for hot water heating
are relatively inexpensive and easy to install, and they are especially popular in sunny, warm
climates.

Perhaps the greatest potential for solar energy, however, is with the generation of electricity, or
solar power. Solar energy can be used to generate electricity through two main approaches—
solar photovoltaic and concentrating solar power technologies. Solar photovoltaic (PV) cells
convert sunlight into electricity (see Figure 7.3). The photovoltaic effect occurs when light
energy causes certain materials to emit electrons and generate an electric current. Most PV
cells are made of two silicon plates and small amounts of other metals. As sunlight hits a PV
cell, it strikes one of the silicon plates and releases electrons, and as these electrons move
toward the second silicon plate, they create an electric current. An individual PV cell is a tiny,
wafer-shaped plate just a couple of inches across that is able to generate an electrical current
roughly equivalent to that of a size D flashlight battery.

Figure 7.3: Photovoltaic effect

Solar PV panels are made out of PV cells and are used to generate electricity.

Source: Adapted from ser_igor/iStock/Getty Images Plus.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

Section 7.9 Solar Energy

PV cells are grouped into modules a few feet across, and modules are combined to form a PV
panel. PV panels are then grouped together to form PV arrays, which can range in size from
a handful of panels on a residential rooftop to thousands of panels deployed across the land-
scape by electric utility companies in what are known as PV farms. The Longyangxia Dam
Solar Park in China and the Kurnool Ultra Mega Solar Park in India are believed to be the
largest solar PV complexes in the world, and both occupy a land area of roughly 25 square
kilometers in size (about the size of 260 football fields). Each of these PV farms deploys about
4 million solar PV panels and generates enough electricity to power approximately 200,000
households.

Concentrating solar power (CSP) systems are another way to generate electricity from the
sun. CSP systems are large-scale complexes that use mirrors to concentrate the sun’s rays
on a tank or series of pipes filled with water or another fluid. The concentrated sunlight is

so intense that it brings this fluid to a boil,
producing steam. The steam can then be
used to spin a turbine and generate elec-
tricity in much the same way as is done in
a conventional or nuclear power plant. The
world’s largest CSP system (also about 25
square kilometers in size), the Noor com-
plex, is located in Morocco and can generate
enough electricity to meet the needs of over
1 million people. The largest CSP facility in
the United States is the Ivanpah Solar Elec-
tric Generating System in the Mojave Desert
of California; it is about two thirds the size
of the Noor complex.

Advantages and Disadvantages
Solar energy offers a number of significant advantages over fossil fuel energy sources. Solar
is infinitely renewable and does not directly produce any air pollution or greenhouse gases.
Solar PV panels are easily adaptable and can be installed on roofs, over parking lots, in aban-
doned industrial areas, or across unused farmland and open space. The solar energy industry
employs close to 250,000 Americans, more than double the number employed in this sector
in 2012 and roughly 70,000 more than are employed in the entire coal industry. The solar
energy industry also contributed almost $20 billion to the U.S. economy in 2018.

At the same time, solar energy has a number of disadvantages and faces a handful of chal-
lenges. Solar energy is unevenly distributed (see Figure 7.4) and may not be as economical
in some places as in others. At the household level, installing a rooftop solar PV system can
have an up-front cost of $10,000 or more. While such a system will pay for itself over time, the
ability of many households to afford such an up-front investment is limited. Large-scale solar
PV farms and CSP complexes are generating electricity at prices that are nearing equivalency

liorpt/iStock/Getty Images Plus
This concentrating solar power system uses
thousands of mirrors to focus the sun’s rays on
a collector tower.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

Section 7.9 Solar Energy

with coal- and natural gas–fired power plants, but they are still slightly more expensive than
these energy sources (ignoring the external costs associated with fossil fuel use). Finally, while
solar power is essentially pollution free once in operation, the manufacture and production of
solar PV and CSP systems do involve some fossil fuel energy consumption and environmental
impacts. These impacts are small compared to those associated with the direct use of fossil
fuels, but they need to be taken into consideration.

Figure 7.4: U.S. solar resource map

Solar energy is unevenly distributed. In this map of the United States, the darker the area, the more solar
energy that region receives.

Source: “Solar Maps,” by National Renewable Energy Laboratory, n.d. (https://www.nrel.gov/gis/solar.html).

The solar energy sector has seen rapid growth in the United States and worldwide in recent
years, and there is every indication that this trend will continue. New solar installations have
accounted for 30% to 40% of all new electric generating capacity installed in the United States
since 2013, driven by consistently declining prices for solar PV and CSP systems. Solar power
systems already generate enough electricity to power over 12 million homes in the United
States, and there are now more than 2 million solar installations across the country.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

https://www.nrel.gov/gis/solar.html

Section 7.10 Wind Energy

7.10 Wind Energy

Humans have long been aware of the power and potential of wind energy, harnessing it for
thousands of years to sail ships and turn windmills for grinding grain or pumping water. As
with solar energy, the worldwide potential for wind energy is great, but as with solar, the
challenge is how to capture, convert, and transport that energy to where it’s needed when
it’s needed. Wind energy could actually be considered a form of solar energy, since winds
are caused by uneven heating of the planet’s surface combined with differences in topogra-
phy and the Earth’s rotation. As a result, some areas of the planet are better suited for wind
energy development than others.

How It Works
To convert wind energy into electrical wind power, we make use of wind turbines. Wind tur-
bines are large mechanical assemblies that convert the wind’s kinetic energy into electrical
energy (see Figure 7.5). Electric utilities and wind power companies mount wind turbines on
tall towers to take advantage of higher wind speeds and less turbulent wind conditions higher
above the ground. As winds hit the blades or rotor of a wind turbine, the kinetic energy in the
wind begins to spin the blades. The rotor blades are mounted on a shaft connected to a gear-
box and generator; as the shaft rotates, it drives the generator, producing electricity. Today’s
utility-scale wind turbines are massive, mounted as high as 220 meters (720 feet) above the
ground and with rotor blades that are 100 meters (330 feet) in length. A single wind turbine
of this size can generate enough electricity to power as many as 5,000 homes. However, elec-
tric utilities typically cluster wind turbines together in a specific geographic area known as a
wind farm. The largest wind farm in the world is located in China, where 7,000 wind turbines
produce enough electricity to power over 5 million households. The largest wind farm in
the United States (covering roughly 13 square kilometers, or 5 square miles) operates 600
turbines in Kern County, California, and generates enough electricity to power more than 1
million homes.

Wind power is the fastest growing source of electricity generation in the world today and
currently meets about 4% of global electricity demand. China has the largest installed wind
power capacity of any country in the world, but the United States is still the top producer
of electricity from wind. This is because China has been building new wind farms in more
remote regions of that country without fully integrating them into the national electric power
grid. Other leaders in wind power production include Germany, Spain, India, and the United
Kingdom. In terms of the share of overall electricity produced by wind power, Denmark, Por-
tugal, Spain, Ireland, and Germany top the rankings. With nearly 40% of its electricity coming
from wind power, Denmark is proving that with the right planning and management of the
electric power grid, even an intermittent source of energy like wind can make a major contri-
bution to meeting electrical demand.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

Section 7.10 Wind Energy

Advantages and Disadvantages
Wind energy offers many of the same benefits and advantages as solar power—it is non-
polluting, does not directly result in greenhouse gas emissions, and employs over 100,000
Americans. At current rates of production, wind power in the United States is responsible for
a reduction in greenhouse gas emissions that is the equivalent of taking over 20 million cars
off the road. Since wind turbines can be placed on open fields or grazing lands, they can also
be a good source of additional income for farmers and ranchers, who can receive annual roy-
alty payments of $3,000 to $4,000 for every turbine placed on their land. Lastly, wind turbines
are a relatively efficient way to generate electricity, with an EROI of over 20:1.

Figure 7.5: Wind turbine

Wind turbines convert the wind’s kinetic energy into electrical energy.

Source: Adapted from “The Inside of a Wind Turbine,” by Office of Energy Efficiency and Renewable Energy, n.d. (https://www.energy.gov
/eere/wind/inside-wind-turbine).

Rotor
blades

Gearbox
Grid

connection

Generator

Tower

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https://www.energy.gov/eere/wind/inside-wind-turbine

https://www.energy.gov/eere/wind/inside-wind-turbine

Section 7.10 Wind Energy

But just as with solar energy, wind power also has some drawbacks and challenges. Like
solar, wind energy is intermittent and unevenly distributed (see Figure 7.6), making it a more
viable option in some regions than others. Another challenge is that some individuals find
wind power facilities, especially large-scale wind farms and associated electrical transmis-
sion wires, to be aesthetically unpleasing. People living near wind farms may also complain
about the noise from the spinning turbines, although sound measurements suggest they are
no louder than many familiar background noises like refrigerators and nearby traffic. Lastly,
wind turbines are known to be a cause of bird and bat deaths as a result of collisions, and the
frequency of this problem is growing with the expansion of wind power. Proponents of wind
power acknowledge this problem but also point out that the thousands of bird deaths each
year from wind turbines are just a tiny fraction of the millions of deaths caused by domestic
cats, auto traffic, and collisions with windows and buildings. Nevertheless, the wind power
industry is paying increasing attention to issues of aesthetics, noise, and nearby bird and bat
populations as it makes decisions about the appropriate siting and placement of wind tur-
bines and wind farms.

Figure 7.6: U.S. wind resource map

Wind energy is unevenly distributed. In this map of the United States, wind speed is generally highest
along the coasts and in the Midwest.

Source: “Wind Maps,” by National Renewable Energy Laboratory, n.d. (https://www.nrel.gov/gis/wind.html).

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https://www.nrel.gov/gis/wind.html

Section 7.11 Biomass Energy

As the cost of generating electricity with wind turbines continues to decline, wind power
production is expected to continue to increase. It’s already the case that in locations with
favorable wind conditions, the cost of producing electricity with wind turbines is lower than
generating it in a coal, natural gas, or nuclear power plant. Because there is no “price” for
the wind, the cost of producing wind power is also not subject to the same sort of market
fluctuations in price experienced by coal- and natural gas–powered electricity production.
In the years ahead, offshore wind farms located in areas of open water are expected to grow
in importance. Offshore wind farms offer a number of advantages over onshore locations.
Namely, offshore locations tend to have more consistent and higher wind speed conditions,
and they can be located far enough off the coast to minimize noise and aesthetic concerns.

7.11 Biomass Energy

Of all the forms of energy described in this chapter, biomass energy has the longest history
of human use. Biomass energy, or bioenergy, is any form of energy derived from living,
organic material. Throughout history we have burned wood and other plant-based material
to cook, illuminate the darkness, and keep warm, and wood was humankind’s main source of
energy until just a few hundred years ago. We can say that bioenergy is a form of solar energy
since it originates with the chemical energy produced through photosynthesis.

How It Works
We can use bioenergy to generate heat and electricity or to create gaseous or liquid fuels.
Direct combustion of firewood, charcoal, and agricultural residues for cooking and space
heating is still widespread in many developing countries of the world. The FAO estimates that
over 2 billion people worldwide still rely on these forms of “traditional” bioenergy. World-
wide consumption of firewood and other biomass energy in traditional applications still rep-
resents about 10% of global primary energy use each year. In addition, biomass energy in
the form of wood waste and agricultural residues is used in larger scale facilities to gener-
ate electricity and for industrial heating purposes. For example, in the United States wood
waste from sawmills and forestry operations is used to generate electricity and as a fuel in
pulp and paper operations. In Brazil, the Philippines, and other tropical countries, the residue
from sugarcane production, known as bagasse, is burned for electricity production and as an
industrial fuel in sugar mills.

Biomass can also be converted to gaseous fuels (biogas) or liquid fuels (biofuels). Biogas is
produced in “digesters,” tanks that are filled with sewage sludge, manure, and other organic
wastes. Because the tanks do not allow oxygen to enter, the waste material inside undergoes
anaerobic decomposition, producing a gas that is mostly methane (the major component of
natural gas). Small-scale biogas digesters are a common feature on farms in China, India, and
other developing countries, although the potential for large-scale biogas production in places
like the United States is great. Biogas production is another of those win-win-win technolo-
gies since it addresses a waste problem (from sewage sludge and animal manure), gener-
ates useful energy in the form of biogas, and produces a residual sludge that makes excellent
fertilizer.

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Section 7.11 Biomass Energy

Biofuels are the most widespread form of
bioenergy, and the most common form of
biofuel is ethanol. Ethanol is produced by
fermenting carbohydrate-rich crops like
corn and sugarcane. Brazil is a world leader
in ethanol production and meets about 50%
of its fuel needs for cars and light trucks
with this biofuel. Virtually all the ethanol
production in Brazil comes from sugar-
cane. Some cars in Brazil are modified to
run entirely on ethanol, while others make
use of a blended fuel that is 75% gasoline
and 25% ethanol. The United States is actu-
ally the leading global producer of ethanol,
mostly from corn, and ethanol accounts for
about 10% of motor vehicle fuel consump-
tion in this country. Most ethanol used in the United States comes in the form of a blended fuel
known as E10 that is 90% gasoline and 10% ethanol. Together, the United States and Brazil
produce 85% of the world’s ethanol.

Another kind of biofuel is known as biodiesel. Biodiesel can be produced from plant oils and
animal fats and burned in diesel automobile and truck engines. The most common “feed-
stock” for biodiesel production is soybeans, although canola oil, palm oil, coconut oil, and
even waste cooking oil from fast-food restaurants can be used to produce this fuel. Similar to
ethanol, biodiesel is typically used in a blend of 80% diesel and 20% biodiesel. Biodiesel use
worldwide is only about half that of ethanol, with European countries making far greater use
of this fuel than other regions.

Advantages and Disadvantages
Because bioenergy comes in so many different forms and is derived from so many differ-
ent types of material, it is not as straightforward to assess the environmental and economic
advantages and disadvantages of this energy source. One obvious advantage of bioenergy is
that it is abundant and can be produced from so many different forms of organic material,
much of which goes unused or is wasted each year. Another advantage is that biofuels can be
used in existing internal combustion engines—unlike solar or wind energy, which can only
power our transportation system if we convert to EVs.

Overall, one of the main theoretical benefits of all forms of bioenergy is that it has the poten-
tial to be a “carbon-neutral” form of energy. When firewood, agricultural waste, biogas, or bio-
fuels are combusted, they do release the greenhouse gas carbon dioxide. However, the carbon
in biomass and biofuels got there in the first place through photosynthesis, so presumably the
same amount of carbon released during combustion is “recaptured” when new trees or crops
are grown to replace the ones being burned or converted to biofuels. In reality it’s not always
as straightforward as this. For example, when wood from mature forests is burned, it releases
carbon that has been stored for decades or even centuries, and new forest growth will take a
long time to offset those emissions.

Bigpra/iStock/Getty Images Plus
Biofuels are liquid fuels derived from organic
materials such as plants. Biodiesel is derived
from plant oils or animal fats.

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Section 7.11 Biomass Energy

A related problem with biofuels, especially ethanol, has to do with the “net energy” gains from
using these fuels. Recall that EROI is the amount of useful energy extracted from a resource
divided by the amount of energy it took to produce it. It turns out that a significant amount of
fossil fuel energy is utilized to plant and harvest some of the crops used for ethanol, and then
again in the fermentation process used to convert those crops into ethanol fuel. Some studies
have estimated that burning corn ethanol might actually result in even greater carbon dioxide
emissions than just burning regular gasoline in the first place (Murphy, 2010). Other research
suggests that using corn ethanol does reduce carbon dioxide emissions in the transportation
sector but only by small amounts (Murphy, 2010). Sugarcane is a far less energy-intensive
crop, and therefore sugarcane ethanol is better from a carbon dioxide standpoint and has a
significantly higher EROI than corn ethanol.

Another disadvantage with biofuels has to do with a variety of land-use impacts. As discussed
in Chapter 4, growing crops like corn on large-scale monoculture farms can have significant
environmental effects in terms of soil erosion, water pollution, and downstream impacts like
eutrophication and dead zones. Growing substantially more corn to produce relatively mod-
est amounts of biofuel therefore does not seem to make a lot of sense. However, U.S. farm
policy designed to help corn farmers has resulted in government mandates on ethanol pro-
duction, and as much as 40% of the corn grown in the United States already goes to produce
ethanol. Even if we were to allocate 100% of U.S. corn production to ethanol, it would still
only produce about 25% of our transportation fuel needs; the same amount of fuel could be
saved by simply improving automobile fuel efficiency by just 4 mpg (Conca, 2014). Mean-
while, shifting more corn production to ethanol creates ripple effects in other markets, since
corn is also used to produce food for human consumption, sweeteners, and animal feed. Like-
wise, growing more soybeans, canola, coconuts, or palm for biodiesel production can also
have land-use and environmental impacts at the farm level. We learned in Chapter 1 about the
impacts on tropical forests from the expansion of palm oil production. Some of the expansion
of palm oil in places like Southeast Asia is being driven by increased demand for biodiesel in
Europe. As a result, we need to consider the ways in which biofuel production might be reli-
ant on crops that are either better used for food consumption or have significant and negative
environmental and land-use impacts.

Two other methods for producing biofuels appear to offer a number of advantages over cur-
rent approaches. Unlike regular corn ethanol, for example, which is derived from the kernels
or “food” portion of the corn plant, cellulosic ethanol is made from fermenting a variety of
less useful plant parts and material like corn stalks and grasses. Cellulosic ethanol production
can be based on agricultural waste products and grasses grown to reclaim abandoned farm-
land, and therefore it does not have the same negative environmental and land-use impacts. It
also has a much higher EROI than regular ethanol and is far better in terms of net greenhouse
gas emissions. The main challenge with cellulosic ethanol is developing enzymes that can
break down the tougher plant material—cellulose—found in stalks and grasses. Likewise,
there is growing interest in producing biodiesel and/or ethanol from algae. Algae is fast grow-
ing and can be modified to grow in open ponds or even in vertical tubes and tanks in urban
settings.

Overall, various forms of bioenergy will continue to play a major role in the global energy
economy for the foreseeable future. Current usage of corn-based ethanol in places like the
United States appears to be based far more on political considerations and farm support pro-
grams than on any environmental or economic logic. Therefore, it would seem wise to begin

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Section 7.12 Hydropower, Geothermal Energy, and Ocean Energy

to shift some of the resources and focus from current approaches to newer and less destruc-
tive forms of bioenergy. Biogas production from municipal sewage and animal feedlots, cel-
lulosic ethanol, sustainably produced wood energy, and algae-based biodiesel production are
all examples of such approaches.

7.12 Hydropower, Geothermal Energy, and Ocean Energy

Decades before modern solar panels and wind turbines were developed, we used the energy
contained in running water and from under the Earth’s surface. Hydroelectric power
(hydropower) harnesses the kinetic energy of moving water to generate electricity. For well
over a century, dams have been built to exploit this energy resource. Geothermal power
makes use of heated water from deep underground reservoirs to produce steam to generate
electricity. More recently, geothermal applications have been expanded to take advantage of
the near constant temperatures found just underneath the Earth’s surface to heat and cool
buildings. In addition, there is growing interest in exploiting the energy found in the waves
and tides, known as ocean energy. Because the water cycle keeps water constantly moving,
and because the processes that produce geothermal, tidal, and wave energy will continue to
do so indefinitely, these forms of energy are also considered renewable.

Hydropower
The most common form of hydropower is known as an impoundment hydroelectric plant.
This involves building a dam across a river to store or “impound” water behind the dam in a
reservoir (see Figure 7.7). When water is released through openings in the dam, it flows down-
hill to where a turbine is located. The kinetic energy of the moving water spins the turbine to
generate electricity. A less common approach to hydropower is to divert a portion of flowing
water from a river to a hydroelectric plant (without using a dam), a technique known as run-
of-river hydropower. Hydropower currently meets 16% of global electricity demand, with
China, Brazil, Canada, and the United States as the largest producers. Hydropower accounts
for nearly 100% of electricity production in some countries, like Norway and Paraguay, while
meeting over 60% of Brazil’s and 50% of Canada’s electricity demand. Hydropower accounts
for 7% of electricity generation in the United States.

The main advantage of hydropower is that it generates electricity without fossil fuel com-
bustion, so there are no direct emissions of air pollutants or greenhouse gases. However,
because hydropower usually involves the construction of a dam to create a reservoir, it can
have a number of ecological and social impacts. These include the destruction of wildlife habi-
tat as well as modifications to river flow patterns. This can impact water temperature and
water quality, disrupt fish migration patterns, and alter downstream ecosystems that have
evolved over time to specific river flow patterns. Furthermore, large hydroelectric reservoirs
in tropical regions have been linked to increased methane emissions, canceling out some of
the benefits of reduced CO2 emissions (Hurtado, 2016). In this sense it might be fair to say
that hydropower is renewable but not necessarily sustainable. Because many of the best sites
for hydropower development have already been exploited, and because large dam projects
can generate significant public opposition, it’s not likely that hydropower production will
increase in the future at the same rates as solar and wind energy.

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Section 7.12 Hydropower, Geothermal Energy, and Ocean Energy

Geothermal Energy
Geothermal energy resources can be used in large-scale power plants to produce electricity
or at a smaller scale to heat and cool homes and other buildings. Geothermal power plants
utilize steam from hot water reservoirs found miles below the Earth’s surface to spin a tur-
bine and generate electricity. These types of power plants are very location specific, since
they rely on certain geologic conditions that allow hot magma from deep within the Earth’s
interior to flow near enough to the surface to heat water. The top geothermal power produc-
ers in the world are the United States, the Philippines, Indonesia, Mexico, and New Zealand.

A different form of geothermal energy that is not as location specific is known as ground-
source heating and cooling, or ground-source heat pumps (GSHPs). GSHPs operate on the
very basic principle that the ground just 2 to 3 meters (6 to 10 feet) below the surface main-
tains a fairly constant, year-round temperature of 10 °C to 15 °C (50 °F to 60 °F). In temperate
regions with changing seasons, this ground temperature is warmer than outside air in the
winter months and cooler than outside air during summer months. GSHP systems use a heat
pump and a series of underground plastic pipes to circulate water or another fluid between

Figure 7.7: Hydroelectric dam

An impoundment hydroelectric dam converts the kinetic energy of the falling water into electricity.

Building a tall dam
allows water to fall
from a great height,
producing more
energy. 1

As water flows in,
it spins the turbine
blades, generating
a current from the
coils of wire found
in the generator. 2

The current then goes
to the transformer,
where the voltage
travels over power
lines to power homes
and businesses. 3

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Section 7.12 Hydropower, Geothermal Energy, and Ocean Energy

a building and the underground space around that building (see Figure 7.8). In the summer
months the water or fluid in those pipes transfers warm air from the building underground
to be cooled and brought back into the building. In the winter months it does the opposite,
transferring heat from underground into the building. There are already well over 1 million
GSHP systems installed in homes, schools, hospitals, and other buildings in the United States,
and another 60,000 to 80,000 new systems are added each year.

Figure 7.8: Ground-source heat pump

GSHPs circulate water or another fluid through a series of underground pipes to heat air in the winter
and cool air in the summer.

Source: Adapted from “Geothermal Heating and Cooling Technologies,” by US Environmental Protection Agency, 2016 (https://www.epa
.gov/rhc/geothermal-heating-and-cooling-technologies).

Cooling modeHeating mode

Circulation

Heat absorption

Recirculation

Heat exchange
and use

1

4

2

3

Recirculation
Heat discharge

Circulation Heat pump

Heat exchange
and absorption

4

2

3

1

Heat pump

Both geothermal power and ground-source heating/cooling systems help reduce air pollution
and greenhouse gas emissions. They both also have fairly minimal environmental impacts,
although construction of large-scale geothermal power plant complexes can be disruptive to
local ecosystems. Unlike with hydropower, there is still a fair amount of untapped geothermal
power potential to be developed in those regions of the world with favorable conditions. Like-
wise, demand for GSHP systems continues to remain strong, even if installing these systems
in homes encounters the same up-front cost problem associated with residential PV systems.

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https://www.epa.gov/rhc/geothermal-heating-and-cooling-technologies

https://www.epa.gov/rhc/geothermal-heating-and-cooling-technologies

Section 7.13 Energy Markets and Policies

Ocean Energy
The two main approaches to harnessing the energy of the oceans is to exploit the kinetic
energy of the tides (tidal power) and the waves (wave power).

Tidal power can be harnessed in a few different ways. A tidal barrage is basically a dam that
is constructed across the mouth of a tidal basin. As the tide rises, the gates of the barrage are
opened to allow water in, and at high tide the gates are closed to impound that water behind
it. After the water on the other side drops during low tide, the barrage gates are opened again
to release the water that’s impounded and generate electricity through spinning turbines. A
tidal fence, which resembles a turnstile, is placed underwater in narrow channels, where tidal
currents spin the blades to produce electricity. Likewise, tidal turbines operate like underwa-
ter wind turbines, except that their blades are spun by tidal currents rather than the wind.

Wave power systems are either offshore or onshore. Offshore wave power systems rely on the
bobbing, up-and-down motion of waves to power a pump that generates electricity. Onshore
wave energy systems are built along the coastline and are powered by the energy of breaking
waves. This is typically accomplished by constructing a chamber filled with air and open to
the sea. As waves enter the chamber, they push the air past a turbine, which spins to produce
electricity.

Ocean energy systems are clean and renewable. However, tidal barrage systems are only via-
ble in a small number of places around the world with the right combination of geography
and tidal swings. Tidal fence and turbine systems can be located in a larger number of geo-
graphic locations, but they can be costly to build and maintain and are challenging from an
engineering standpoint. Wave power systems are also still mostly experimental, given some
of the technical and engineering issues facing large-scale deployment of these technologies.

7.13 Energy Markets and Policies

What investments in energy efficiency and renewable energy sources have in common is
that they represent what could be called a “no-regrets” or “win-win-win” approach to energy
policy. Even if we took the issue of global climate change out of the picture, energy efficiency
and renewable energy are good for our economy, enhance national security, and help address
known and immediate environmental problems like air and water pollution. (The Apply Your
Knowledge feature explores how to determine which energy option is best.)

Overall, the renewable energy approaches and technologies described in this chapter offer
the two main advantages of being clean and virtually inexhaustible and renewable. Some of
these technologies are experiencing rapid growth and are already making major contribu-
tions to meeting our energy needs. Others have more limited potential for geographic, geolog-
ical, or engineering reasons, but they can play an important part in meeting localized energy
demand. The fact that we are not undergoing an even more rapid energy transition despite
these advantages and win-win-win outcomes has much to do with energy policy and politics
in our country and around the world.

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Section 7.13 Energy Markets and Policies

Apply Your Knowledge: Which Energy Option Is Best?

Some experts believe we should invest in zero-carbon energy sources like wind, solar, and
nuclear, while others promote more energy-efficient buildings and transportation systems.
It can be hard to tell which technologies would be best for the environment, especially when
you try to consider the economic costs of different solutions. Fortunately, we can use some
math to compare options and prioritize the most effective technologies.

To begin our analysis, let us first compare the environmental benefits of different
technologies using a common metric. In this exercise, we will measure environmental
benefits using the amount of CO2 emissions that are avoided by implementing different
technologies. For example, putting a moderate-sized solar panel system on your roof might
prevent local power plants from releasing the equivalent of 20 metric tons of CO2 into the
atmosphere over the course of that system’s lifetime.

To help us consider the economics of different options, we consider the costs and savings
associated with each technology. Your rooftop solar system would cost a certain amount of
money to install and maintain, but it would also save you money on electricity. Depending on
the specific costs and savings at a particular location, the overall system might gain or lose
money over the course of its lifetime. In this activity, we will consider the net costs (the total
costs minus the total savings) of implementing different technologies.

To take our analysis one step further, we can divide the net costs by our emissions reductions
to estimate the cost of avoiding 1 metric ton of CO2. This final value is called an abatement
cost. When it is a positive value, it means that it will cost money to avoid 1 metric ton of CO2.
When it is a negative value, money is being saved.

Now that we have a good metric for comparing sustainable energy solutions, let us take
a look at some data in what is called an abatement curve. In Figure 7.9, various energy
technologies are represented as rectangles stacked side by side along the x-axis. The
rectangle widths represent the average annual emissions reductions that could be achieved
by these technologies in the United States. The rectangle heights represent the estimated
abatement costs of these measures if they were to be implemented before the year 2030.
Based on this information, what energy measures and technologies do you think the United
States should prioritize going forward?

We can learn a lot of valuable information when we look at abatement curves like Figure 7.9.
For one thing, we can see that energy efficiency measures are generally more cost effective
than replacing existing power plants. This helps illustrate that even if certain technologies
receive a lot of media attention, they may not necessarily be the most cost effective ways to
increase sustainability. Figure 7.9 also shows that there are several options with negative
abatement costs. These options are mostly energy efficiency measures, and the numbers
suggest that they will actually save money over time. Energy efficiency represents a win-
win in terms of cost and emissions, and it is a great place to start when planning and
implementing better energy systems.

(continued)

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Section 7.13 Energy Markets and Policies

Apply Your Knowledge: Which Energy Option Is Best?
(continued)

Decisions that individuals and businesses make about how much and what types of energy to
use are shaped in large part by the prices of different energy sources. In a perfectly free mar-
ket, those energy prices would reflect the true cost of what it takes to develop, distribute, and
utilize a specific energy resource. In reality, energy markets in the United States and around
the world are far from free and are influenced and shaped by government policies. For exam-
ple, the Organisation for Economic Co-operation and Development estimates that worldwide
government subsidies to fossil fuel companies were as high as $373 billion in 2015 (Timper-
ley, 2018). The International Monetary Fund, using a broader definition of subsidies, put this
figure at close to $5 trillion in that year (Coady, Parry, Le, & Shang, 2019). Regardless, subsi-
dies help artificially reduce the price of the energy resource being subsidized.

Figure 7.9: 2030 U.S. abatement curve

Abatement costs of greenhouse gas (GHG) reductions measures. The width of the rectangles
shows estimated average annual emissions reductions of each measure. The height of the
rectangles and their position along the y-axis shows the projected cost of the measure if
implemented before 2030. “CO2e” refers to carbon dioxide equivalents, which allows us to
consider all greenhouse gases in this discussion.

Source: Adapted from Reducing U.S. Greenhouse Gas Emissions: How Much at What Cost? by McKinsey and Company, 2007,
p. 42 (https://www.mckinsey.com/business-functions/sustainability/our-insights/reducing-us-greenhouse-gas
-emissions).

Car
efficiency

Residential
lighting

0

100

75

50

25

0

-25

-50

-75

-100

100

A
b

at
em

en
t

co
st

(
$/

to
n

C
O

e
)

200 300

Power plant
efficiency

New building
efficiency

Residential
insulation

Industrial process
improvements Nuclear Biomass

Wind Solar

Carbon capture coal

400 500 600 700

GHG reductions (million tons CO e/year)2

2

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https://www.mckinsey.com/business-functions/sustainability/our-insights/reducing-us-greenhouse-gas-emissions

https://www.mckinsey.com/business-functions/sustainability/our-insights/reducing-us-greenhouse-gas-emissions

Section 7.13 Energy Markets and Policies

When you combine government intervention with a consideration of external costs—those
costs associated with the use of an energy resource but not factored into market price—you
end up with fossil fuel energy prices that are significantly lower than what they actually cost
society. This is because taxpayers pay for the subsidies, and we all eventually pay for the
external costs. These artificially low fossil fuel prices distort decision making by consum-
ers and businesses, inflate demand for fossil fuels, and make renewable energy alternatives
appear more expensive and less competitive than they actually are.

Given the clear environmental, economic, and social benefits associated with shifting from
an overreliance on fossil fuels to greater use of clean, renewable energy sources, how can
government policy be altered to speed up the energy transition? Energy economists offer a
number of possible suggestions.

Full-Cost Pricing
Full-cost pricing of energy refers to “internalizing” the external costs associated with the use
of a particular energy resource. For example, if you live in an area that relies mainly on coal
for electricity generation, it is almost certain that you are not currently paying the full cost for
that electricity. As discussed earlier in the chapter, coal mining destroys habitats and causes
serious water pollution problems, while coal combustion results in local/regional air pollu-
tion and greenhouse gas emissions. These environmental impact costs are not, for the most
part, factored into the price that power companies pay for coal or that consumers pay for
electricity produced with that coal. This makes coal and coal-fired electricity appear cheaper
than they actually are and distorts our decisions in the process.

One way to achieve full-cost pricing in this case would be to impose an energy tax or carbon
tax on coal in an amount that would reflect some of these external costs. Revenue from that
tax could be used to restore habitat damaged by coal mining, clean water supplies polluted
by mining, fund health care in places polluted by coal combustion, or offset higher electricity
costs for low-income consumers.

Subsidy Reform
Subsidy reform refers to diverting subsidies to cleaner energy resources. Historically, fossil
fuels and nuclear power have received far more in the way of U.S. government subsidies and
tax breaks than renewable energy sources. One study estimated that from 1918 to 2009, the
oil and gas industry received close to $500 billion in subsidies and tax breaks, while the figure
for nuclear power was nearly $200 billion (Pfund & Healey, 2011). Most subsidies to renew-
able energy came in the form of funding ($30 billion) for biofuels, a policy that as mentioned
earlier has less to do with energy and more to do with farm support. Under $6 billion in sub-
sidies and tax breaks went to renewable energy sources like wind and solar during that time
period. This situation has begun to change as more focus has been put on renewable energy
sources in recent years. Given that one of the main policy goals of subsidies should be to
speed up the development and deployment of new and innovative technologies, focusing the
bulk of government funding and tax breaks on long-established energy sources like oil, coal,
and nuclear power might not make the most sense.

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Section 7.13 Energy Markets and Policies

Feed-In Tariffs
Feed-in tariffs require electric power companies to buy electricity at a guaranteed price from
any individual or business that can generate it and “feed” that electricity back into the power
grid. For example, home owners and businesses can install a PV system on their roof know-
ing that any electricity generated by that system will be purchased by the power company.
This makes it much easier to acquire bank financing for the up-front cost of installing such a
system, since the revenue from the electricity sales can be used to pay off the loan. After that,
home owners and businesses can actually meet their own electricity needs while also profit-
ing from the sale of any excess electricity. As a result of a feed-in tariff policy, solar and wind
power installations have skyrocketed in Germany and made that country a world leader in
renewable energy adoption.

Renewable Portfolio Standard
A renewable portfolio standard (RPS) is simply a government mandate (city, state, or fed-
eral) that a certain percentage of energy use in that location come from renewable energy
sources. In the United States 38 states have some sort of RPS in place, and dozens of cit-
ies ranging in size from New York to Reno have also adopted an RPS. RPS mandates create
increased demand for renewable energy sources and create incentives for private investors
to finance these technologies. Even without RPS mandates, there was already a clear trend of
private venture capital moving increasingly toward renewable energy investment. In 2016 it’s
estimated that private investors accounted for 92% of the $263 billion that was invested in
renewable energy that year (International Renewable Energy Agency, 2018).

Other Approaches
Beyond full-cost pricing, subsidy reform, feed-in tariffs, and renewable portfolio standards,
there are a handful of other policy approaches that can help speed up the energy transition.
These include supply-side approaches aimed at increasing the amount of renewable energy
being generated, like research and development funding, tax credits for renewable energy
production, and tax credits to home owners and businesses that install solar PV panels or
GSHPs. There are also demand-side approaches to reduce energy consumption and improve
efficiency. These include increasing fuel efficiency standards in cars, promoting more efficient
appliances, and providing tax credits to home owners to insulate their homes and improve
energy efficiency. What all these policies have in common is that they create a market envi-
ronment that is more favorable to renewable energy sources than has historically been the
case. While free-market advocates may argue against such an approach, the reality is that
our energy markets are already distorted and influenced by government tax and regulatory
policies. Those tax and regulatory policies favor the continued use of fossil fuels and ignore
many of the negative environmental, economic, and social impacts of using these fuels. What
is needed is a new policy approach that recognizes the critical need to move toward a greater
reliance on renewable energy sources.

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In 2011 energy experts Mark Jacobson of Stanford University and Mark Delucchi of the Uni-
versity of California–Davis published a comprehensive, two-part paper on whether it was
possible and what it would take to move the world to 100% reliance on renewable energy
sources by the year 2050 (Jacobson & Delucchi, 2011a, 2011b). Jacobson and Delucchi
examined issues of technology, geography, energy markets and economics, energy storage
and distribution systems, and political and cultural barriers to change and concluded that
a transition to 100% renewable in the next few decades was possible. Their overall conclu-
sion was not only that such a shift was technically possible but that it could actually result in
improved economic conditions as well.

While not all energy experts agree with the assumptions or conclusions reached by Jacob-
son and Delucchi, their research has generated an interesting discussion about our energy
future. Our current reliance on fossil fuel energy sources is both environmentally destruc-
tive and unsustainable, given the limited and finite supplies of these energy sources. While
renewable energy technologies like wind and solar energy still only account for a small
percentage of our energy supply, they are technically and economically viable and poised for
continued rates of rapid growth. We must speed up the transition away from fossil fuels and
toward renewable energy sources to mitigate the impacts on air quality and climate change.
Those impacts, and the urgency of the situation, are the focus of the next chapter.

Additional Resources

Our Energy System

In addition to the EPA Power Profiler introduced in the Close to Home feature box, the New
York Times has an interesting interactive feature that allows you to see how the electricity
used in your state is produced and how that has changed over time.

• https://www.nytimes.com/interactive/2018/12/24/climate/how-electricity
-generation-changed-in-your-state.html

The EIA has a good page explaining how electricity is produced and distributed to end users.

• https://www.eia.gov/energyexplained/index.php?page=electricity_generating

Natural Gas

Natural gas has been hailed as an “energy bridge to the future” because of its relatively low
CO2 emissions relative to coal. The idea is that we can use more natural gas instead of coal in
order to allow time for renewable energy sources like wind and solar to be more fully devel-
oped. However, this claim only focuses on CO2 emissions from natural gas, whereas a recent
study in Science of natural gas production and distribution systems found large emissions of
methane (another greenhouse gas) from this energy source (Alvarez et al., 2018). The first
link summarizes the findings; the second link is to the journal article itself.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

https://www.nytimes.com/interactive/2018/12/24/climate/how-electricity-generation-changed-in-your-state.html

https://www.nytimes.com/interactive/2018/12/24/climate/how-electricity-generation-changed-in-your-state.html

https://www.eia.gov/energyexplained/index.php?page=electricity_generating

• https://insideclimatenews.org/news/21062018/methane-leaks-oil-gas-climate
-change-risks-natural-gas-slcp-global-warming-pollution-science-edf-study

• https://www.edf.org/media/new-study-finds-us-oil-and-gas-methane-emissions
-are-60-percent-higher-epa-reports-0

Nuclear Energy

Nuclear power can seem like a challenging concept to grasp, but the basic idea behind it is
quite simple. These sources help explain how electricity is produced through nuclear fission
reactions.

• https://www.ucsusa.org/nuclear-power/nuclear-power-technology/how-nuclear
-power-works

• https://www.nei.org/fundamentals/how-a-nuclear-reactor-works
• https://www.energy.gov/ne/articles/nuclear-101-how-does-nuclear-reactor-work

The debate over the prospects for nuclear power and whether it has role to play in meeting
future energy needs has really heated up in recent years. These sources present both sides
of the argument.

• https://e360.yale.edu/features/why-nuclear-power-must-be-part-of-the-energy
-solution-environmentalists-climate

• https://e360.yale.edu/features/industry-meltdown-is-era-of-nuclear-power
-coming-to-an-end

• https://www.washingtonpost.com/outlook/i-oversaw-the-us-nuclear-power
-industry-now-i-think-it-should-be-banned/2019/05/16/a3b8be52-71db-11e9
-9eb4-0828f5389013_story.html

Solar Energy

Solar energy can be used for illumination, heating, and producing electricity (solar power).
These sources help explain how some of the technologies that make solar energy possible
actually work.

• https://www.energy.gov/science-innovation/energy-sources/renewable-energy
/solar

• https://www.energy.gov/eere/solar/articles/solar-energy-technology-basics
• https://www.energy.gov/eere/solar/downloads/solar-power-basics
• https://www.ucsusa.org/clean-energy/renewable-energy/how-solar-energy-works

Wind Energy

These sources help explain how wind power works and how a wind turbine is designed to
convert the energy in wind into electricity.

• https://www.energy.gov/eere/wind/how-do-wind-turbines-work
• https://www.energy.gov/videos/energy-101-wind-turbines
• https://www.energy.gov/maps/how-does-wind-turbine-work
• https://www.ucsusa.org/clean-energy/renewable-energy/how-wind-energy-works

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

Oil and Gas Fields Leak Far More Methane than EPA Reports, Study Finds

Oil and Gas Fields Leak Far More Methane than EPA Reports, Study Finds

https://www.edf.org/media/new-study-finds-us-oil-and-gas-methane-emissions-are-60-percent-higher-epa-reports-0

https://www.edf.org/media/new-study-finds-us-oil-and-gas-methane-emissions-are-60-percent-higher-epa-reports-0

https://www.ucsusa.org/nuclear-power/nuclear-power-technology/how-nuclear-power-works

https://www.ucsusa.org/nuclear-power/nuclear-power-technology/how-nuclear-power-works

https://www.nei.org/fundamentals/how-a-nuclear-reactor-works

https://www.energy.gov/ne/articles/nuclear-101-how-does-nuclear-reactor-work

https://e360.yale.edu/features/why-nuclear-power-must-be-part-of-the-energy-solution-environmentalists-climate

https://e360.yale.edu/features/why-nuclear-power-must-be-part-of-the-energy-solution-environmentalists-climate

https://e360.yale.edu/features/industry-meltdown-is-era-of-nuclear-power-coming-to-an-end

https://e360.yale.edu/features/industry-meltdown-is-era-of-nuclear-power-coming-to-an-end

https://www.washingtonpost.com/outlook/i-oversaw-the-us-nuclear-power-industry-now-i-think-it-should-be-banned/2019/05/16/a3b8be52-71db-11e9-9eb4-0828f5389013_story.html

https://www.washingtonpost.com/outlook/i-oversaw-the-us-nuclear-power-industry-now-i-think-it-should-be-banned/2019/05/16/a3b8be52-71db-11e9-9eb4-0828f5389013_story.html

https://www.washingtonpost.com/outlook/i-oversaw-the-us-nuclear-power-industry-now-i-think-it-should-be-banned/2019/05/16/a3b8be52-71db-11e9-9eb4-0828f5389013_story.html

https://www.energy.gov/science-innovation/energy-sources/renewable-energy/solar

https://www.energy.gov/science-innovation/energy-sources/renewable-energy/solar

https://www.energy.gov/eere/solar/articles/solar-energy-technology-basics

https://www.energy.gov/eere/solar/downloads/solar-power-basics

https://www.ucsusa.org/clean-energy/renewable-energy/how-solar-energy-works

https://www.energy.gov/eere/wind/how-do-wind-turbines-work

https://www.energy.gov/videos/energy-101-wind-turbines

https://www.energy.gov/maps/how-does-wind-turbine-work

https://www.ucsusa.org/clean-energy/renewable-energy/how-wind-energy-works

These two sources help explain the basics behind large-scale geothermal power systems as
well as smaller scale ground-source heat pumps.

• https://www.energy.gov/eere/videos/energy-101-geothermal-energy
• https://www.energy.gov/eere/videos/energy-101-geothermal-heat-pumps

The Energy Transition

April 2019 was a milestone month for renewable energy in the United States. This was the
first month in which, collectively, renewable energy sources like hydropower, solar energy,
and wind power produced more energy than coal. This is further evidence of the energy
transition that is under way in the United States and around the world. You can learn more
about this event at these sites.

• https://grist.org/article/renewable-energy-outpaced-coal-in-april-for-the-first
-time-ever

• https://www.forbes.com/sites/andystone/2019/06/30/as-clean-energy-surpasses
-coal-us-energy-transition-locks-into-place/#1ec0ba8a2ef7

Energy Efficiency and Conservation

Zero-energy homes and buildings are structures that produce as much energy as they con-
sume. These sources help explain the basics behind the zero-energy concept.

• https://www.energy.gov/eere/buildings/zero-energy-buildings
• https://zeroenergyproject.org/buy/zero-energy-homes

Energy justice initiatives are occurring all over the nation, as these articles discuss.

• https://e360.yale.edu/features/energy-equity-bringing-solar-power-to-low
-income-communities

• https://grist.org/article/pueblo-colorado-renewable-energy-future

Renewable Portfolio Standards

Renewable portfolio standards are one way to promote greater use of renewable energy
sources. You can learn more about RPS programs and whether your state has an RPS at
these sites.

• http://www.ncsl.org/research/energy/renewable-portfolio-standards.aspx
• https://www.seia.org/initiatives/renewable-energy-standards
• http://eta-publications.lbl.gov/sites/default/files/2018_annual_rps_summary

_report.pdf

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

https://www.energy.gov/eere/videos/energy-101-geothermal-energy

https://www.energy.gov/eere/videos/energy-101-geothermal-heat-pumps

https://grist.org/article/renewable-energy-outpaced-coal-in-april-for-the-first-time-ever

https://grist.org/article/renewable-energy-outpaced-coal-in-april-for-the-first-time-ever

https://www.forbes.com/sites/andystone/2019/06/30/as-clean-energy-surpasses-coal-us-energy-transition-locks-into-place/#1ec0ba8a2ef7

https://www.forbes.com/sites/andystone/2019/06/30/as-clean-energy-surpasses-coal-us-energy-transition-locks-into-place/#1ec0ba8a2ef7

https://www.energy.gov/eere/buildings/zero-energy-buildings

What are Zero Energy Homes?

https://e360.yale.edu/features/

energy-equity-bringing-solar-power-to-low-income-communities

energy-equity-bringing-solar-power-to-low-income-communities

https://grist.org/article/pueblo-colorado-renewable-energy-future

http://www.ncsl.org/research/energy/renewable-portfolio-standards.aspx

https://www.seia.org/initiatives/renewable-energy-standards

http://eta-publications.lbl.gov/sites/default/files/2018_annual_rps_summary_report.pdf

http://eta-publications.lbl.gov/sites/default/files/2018_annual_rps_summary_report.pdf

active solar energy The use of mechanical
and electrical equipment to convert
sunlight to heat and electric power.

biodiesel A biofuel made from
plant oils and animal fats.

bioenergy Energy derived from
living, organic material. Also
known as biomass energy.

biofuels Liquid fuels derived from biomass.

biogas Gaseous fuel derived from biomass.

biomass energy See bioenergy.

carbon capture and storage
(CCS) Approaches intended to capture
carbon dioxide emissions from coal burning,
convert them into liquid, and pump the
liquid underground for long-term storage.

carbon sequestration See carbon
capture and storage (CCS).

carbon tax A tax or fee on carbon-based
fuels (coal, oil, and natural gas) that is
intended to reduce carbon emissions.

cellulosic ethanol A biofuel made
from grasses or the less useful parts of
a plant, such as the stalks and leaves.

clean coal technology Approaches
designed to remove contaminants
from coal before it is burned.

coal seams Layers of coal.

concentrating solar power (CSP)
systems Large-scale complexes that
generate solar power using mirrors to
concentrate the sun’s rays on a tank or series
of pipes filled with water or another fluid.

conventional deposits Sources of
fossil fuels that can be accessed using
traditional drilling or mining techniques.

crude oil Unrefined oil that has
just been extracted from the ground
before being sent to an oil refinery.

energy conservation The
reduction of energy consumption
through changes in behavior.

energy conversion The process of
changing one form of energy into another.

energy conversion efficiency The
percentage of primary energy
converted to secondary energy.

energy efficiency The process of using
less energy to achieve the same outcome.

energy end-use efficiency The
percentage of primary energy
used in its final destination.

energy return on investment (EROI) The
amount of useful energy extracted from
a resource divided by the amount of
energy it took to produce that energy.

energy transition A transformation
of energy systems.

feed-in tariff A program whereby
energy producers are paid for the
electricity they send to the grid.

fossil fuels Fuels formed from the remains
of organisms over millions of years.

fracking See hydraulic fracturing.

geothermal power Power derived
from heated water from deep
underground reservoirs.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

ground-source heat pump (GSHP) A
heating and cooling system that
transfers heat to or from the ground.

hydraulic fracturing A technique
for removing oil and natural gas from
shale deposits; it involves pumping a
liquid–sand mixture into deposits in
order to crack the shale open so oil and
gas can flow. Also known as fracking.

hydroelectric power Power derived
from the kinetic energy of moving
water. Also called hydropower.

hydropower See hydroelectric power.

impoundment hydroelectric plant A
power plant that generates electricity
by releasing water from a dam.

mountaintop removal mining A form
of strip mining that involves removing the
top portion of a mountain to expose the
coal underneath and dumping the material
(overburden) into surrounding valleys.

nonrenewable energy Fossil
fuels; energy sources that, once
consumed, are no longer available.

nuclear chain reaction A series
of nuclear fissions that releases
a large amount of energy.

nuclear energy See nuclear power.

nuclear fission The reaction that
occurs when the nucleus of an atom
is split to form two smaller nuclei,
releasing energy in the process.

nuclear power Electricity produced
through a nuclear reaction.

nuclear reactors Devices used
by nuclear power plants to initiate
and control nuclear fission.

ocean energy The energy
found in waves and tides.

oil refineries Distillation plants
where crude oil is broken down
into different products.

oil reservoirs Porous rock formations
that hold small drops of oil in their pores.

oil sands Formations found near the
surface that contain a tar-like substance
known as bitumen, which can be refined
into oil. Also known as tar sands.

oil shale A rock formation that holds
oil and gas but is not porous enough to
allow movement of oil or gas through it.

passive solar energy The use of sunlight
directly, without mechanical devices,
to illuminate or heat interior spaces.

peak oil The point in time when
global oil production and use reaches
its highest point before beginning
a period of permanent decline.

photovoltaic (PV) cells Devices that
convert sunlight into electricity.

primary energy Energy that is
stored in natural resources.

primary oil recovery The initial process
extracting oil through natural pressure.

proven reserves The quantities of an
energy source that can be extracted
from known deposits, using current
technology, at current prices.

renewable energy Energy sources that
are replenished in a human timescale.

renewable portfolio standard (RPS) 
A government mandate that a certain
percentage of energy use come from
renewable energy sources.

© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

reserves-to-production (R/P) ratio A
measure of how long a resource will last.

run-of-river hydropower A power
plant that generates electricity by
diverting water from a river.

secondary energy Energy that
is converted from primary energy
into a more useful form.

secondary oil recovery The process of
extracting oil once primary oil recovery
methods are exhausted, including injecting
fluids into a reservoir to increase pressure.

solar energy Energy from the sun.

solar power The use of solar energy
to generate electric power.

strip mining See surface mining.

subsurface mining See
underground mining.

surface mining The process of
using giant earth-moving machines
to scrape away vegetation, topsoil,
and rock to reveal a shallow coal
seam. Also known as strip mining.

tar sands See oil sands.

tertiary oil recovery The process of
extracting oil once secondary oil recovery
methods are exhausted, including injecting
heated fluids or gases into a reservoir
to increase pressure even further.

tidal power The power derived from
the kinetic energy of the ocean tides.

unconventional deposits Sources
of fossil fuels that cannot be accessed
using traditional methods.

underground mining The process
of digging tunnels or shafts into the
ground to reach coal seams that are
deeper than 60 meters (200 feet).
Also known as subsurface mining.

wave power The power derived from
the kinetic energy of the ocean waves.

wind power The power derived from
the kinetic energy of the wind.

wind turbines Large mechanical
assemblies that convert the wind’s
kinetic energy into electrical energy.

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© 2020 Zovio, Inc. All rights reserved. Not for resale or redistribution.

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