Transportation Technologies

for a Sustainable Future

Renewable energy options for road, rail, marine and air transportation

Online at: https://doi.org/10.1088/978-0-7503-5306-9

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Transportation Technologies
for a Sustainable Future
Renewable energy options for road, rail, marine and air transportation

Richard A Dunlap
Department of Physics and Atmospheric Science, Dalhousie University,
Halifax, Nova Scotia, Canada

IOP Publishing, Bristol, UK

ª IOP Publishing Ltd 2023

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ISBN 978-0-7503-5306-9 (ebook)

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 Contents

Preface xi
Author biography xiii

1 Our current transportation technologies and the need 1-1

for change
1.1 Introduction 1-1
1.2 A breakdown of transportation energy use 1-3
1.3 Future energy needs 1-6
1.4 Pollution and global climate change 1-9
1.4.1 Chemical and particulate pollution 1-9
1.4.2 The greenhouse effect 1-11
1.4.3 The consequences of global climate change 1-15
1.5 Future fossil fuel use 1-18
1.5.1 Reserve-to-production ratios 1-19
1.5.2 Hubbert theory 1-19
1.5.3 Analysis of future fossil fuel demand 1-23
1.6 Sustainable energy sources for the future 1-25
1.6.1 Hydroelectric energy 1-25
1.6.2 Wind energy 1-26
1.6.3 Solar energy 1-29
1.6.4 Nuclear fission 1-32
1.6.5 Biofuels 1-35
1.6.6 Carbon footprints of energy technologies 1-36
1.6.7 Utilization of carbon-free electricity 1-38
1.6.8 The need for increased energy storage capacity 1-41
1.7 Atmospheric carbon removal 1-42
1.7.1 Ocean storage 1-42
1.7.2 Underground storage 1-43
1.7.3 Chemical storage 1-43
1.7.4 Reforestation or afforestation 1-43
1.7.5 Humus 1-43
1.7.6 Biochar 1-44
1.8 The way forward 1-44
References 1-46

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 Transportation Technologies for a Sustainable Future

2 Battery electric vehicles 2-1

2.1 Introduction 2-1
2.2 Primary and secondary batteries 2-1
2.3 Battery chemistry 2-2
2.4 Basic battery science 2-4
2.5 Battery electric vehicle characteristics 2-7
2.6 The history of the battery electric vehicle 2-12
2.6.1 The development of road vehicles 2-12
2.6.2 Early electric vehicles 2-14
2.6.3 The Henney Kilowatt 2-15
2.6.4 The General Motors EV1 2-15
2.6.5 The Toyota RAV4 EV (first-generation) 2-18
2.6.6 The REVA/REVAi 2-20
2.6.7 The Nissan Leaf 2-22
2.6.8 The Tesla Roadster 2-22
2.7 Current battery electric vehicles 2-24
2.7.1 Neighborhood electric vehicles 2-25
2.7.2 Highway-capable electric vehicles 2-26
2.7.3 Two-wheeled battery electric vehicles 2-27
2.7.4 Battery electric trucks and buses 2-31
2.8 Battery electric vehicle infrastructure 2-34
2.8.1 Private slow chargers 2-34
2.8.2 Public slow chargers 2-35
2.8.3 Public fast chargers 2-35
2.8.4 Charging time 2-35
2.8.5 Swappable batteries 2-38
2.8.6 Electric road 2-38
2.9 More about lithium batteries 2-41
2.9.1 Types of lithium-ion battery 2-41
2.9.2 Lithium–sulfur batteries 2-42
2.9.3 Lithium and other battery resources 2-44
2.10 Advanced batteries and related technologies 2-47
2.10.1 Sodium batteries 2-47
2.10.2 Magnesium batteries 2-51
2.10.3 Aluminum–air batteries 2-52
2.10.4 Flow batteries 2-53
2.10.5 Supercapacitors 2-55

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 Transportation Technologies for a Sustainable Future

2.11 Hybrid vehicle technology 2-60

2.11.1 Parallel hybrids 2-62
2.11.2 Series hybrids 2-63
2.11.3 Plug-in hybrids 2-67
2.11.4 Diesel–electric hybrids 2-68
2.11.5 Supercapacitor hybrids 2-69
2.12 Summary 2-70
References 2-71

3 Hydrogen and its derivatives 3-1

3.1 Introduction 3-1
3.2 The properties of hydrogen 3-2
3.3 Hydrogen storage 3-3
3.3.1 Compressed hydrogen 3-3
3.3.2 Liquefied hydrogen 3-4
3.3.3 Cryo-compressed hydrogen 3-5
3.3.4 Hydrogen storage in solids 3-5
3.4 The production of hydrogen 3-12
3.4.1 Steam reforming 3-13
3.4.2 Methane pyrolysis 3-13
3.4.3 Electrolysis 3-14
3.4.4 Biological hydrogen production techniques 3-18
3.4.5 Colors of hydrogen 3-20
3.5 Hydrogen internal combustion engine vehicles 3-21
3.5.1 BMW 3-21
3.5.2 Mazda 3-23
3.5.3 Other hydrogen internal combustion engine vehicles 3-26
3.6 Fuel cells 3-26
3.6.1 Alkaline fuel cells 3-27
3.6.2 Polymer electrolyte membrane fuel cells 3-28
3.6.3 Phosphoric acid fuel cells 3-28
3.6.4 Solid oxide fuel cells and molten carbonate fuel cells 3-29
3.6.5 Hybrid fuel cell systems 3-30
3.7 Hydrogen fuel cell vehicles 3-31
3.8 Hydrogen infrastructure 3-38
3.9 Ammonia 3-44
3.9.1 The properties of ammonia 3-44

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 Transportation Technologies for a Sustainable Future

3.9.2 Ammonia-fueled internal combustion engine vehicles 3-45

3.9.3 Onboard cracking 3-46
3.9.4 Direct ammonia-fuel-cell-powered vehicles 3-47
3.10 Methanol and dimethyl ether 3-47
3.10.1 The properties of methanol 3-47
3.10.2 The production of methanol 3-48
3.10.3 Methanol as a fuel 3-51
3.10.4 Dimethyl ether 3-57
References 3-58

4 Biofuels 4-1
4.1 Introduction 4-1
4.1.1 First-generation biofuels 4-1
4.1.2 Second-generation biofuels 4-2
4.1.3 Third-generation biofuels 4-2
4.1.4 Fourth-generation biofuels 4-2
4.2 Bioethanol 4-2
4.2.1 Properties of ethanol 4-2
4.2.2 Uses of ethanol 4-3
4.2.3 Methods of ethanol production 4-4
4.2.4 Ethanol as a fuel 4-7
4.2.5 Fuel ethanol and its environmental consequences 4-13
4.3 Biodiesel 4-20
4.3.1 Methods for the production of biodiesel 4-20
4.3.2 The use of biodiesel as a transportation fuel 4-25
4.3.3 Biodiesel production 4-27
4.3.4 Environmental aspects of biodiesel use 4-28
4.3.5 Straight vegetable oil as a fuel 4-29
4.4 Renewable diesel 4-30
4.5 Biogas and biomethane 4-33
4.5.1 The production of biogas and biomethane 4-33
4.5.2 The applications of biomethane 4-35
4.5.3 The environmental aspects of biomethane 4-39
4.6 Biomethanol and biodimethyl ether 4-41
4.6.1 The production of biomethanol 4-42
4.6.2 The use of biomethanol as a transportation fuel 4-44

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 Transportation Technologies for a Sustainable Future

4.6.3 Biodimethyl ether 4-45

4.7 An overview of biofuels 4-45
References and additional reading 4-47

5 Other modes of transportation 5-1

5.1 Introduction 5-1
5.2 Rail transportation 5-1
5.2.1 Current railway locomotive designs 5-1
5.2.2 Sustainable railway technologies 5-6
5.2.3 The current and future use of rail transportation 5-13
5.3 Maritime transportation 5-14
5.3.1 Current marine propulsion systems 5-15
5.3.2 Sustainable marine propulsion systems 5-17
5.4 Air transportation 5-29
5.4.1 Current aviation fuels 5-29
5.4.2 Battery electric aircraft 5-31
5.4.3 Hydrogen-powered aircraft 5-34
5.4.4 Alternative aviation fuels 5-36
References 5-40

6 The future of transportation 6-1

6.1 Introduction 6-1
6.2 What we need to do 6-4
6.2.1 Solar energy 6-8
6.2.2 Wind energy 6-8
6.2.3 Nuclear fission 6-8
6.2.4 Our future energy mix 6-8
6.3 Vehicle efficiency analysis and grid capacity 6-9
6.4 A summary of road vehicle technologies 6-16
6.4.1 Vehicle efficiency 6-17
6.4.2 Fuel cost 6-17
6.4.3 Cost of vehicle production 6-18
6.4.4 Infrastructure development and maintenance costs 6-18
6.4.5 Environmental effects, vehicle performance, 6-22
and convenience
6.4.6 Road vehicle technology analysis 6-25

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 Transportation Technologies for a Sustainable Future

6.5 A summary of other modes of transportation 6-26

6.5.1 Rail transportation 6-26
6.5.2 Maritime transportation 6-27
6.5.3 Air transportation 6-27
6.6 The future 6-28
References and further reading 6-29

Appendix A: Powers of ten A-1

Appendix B: Power and energy B-1

Appendix C: Units of power and energy C-1

Appendix D: Energy contents of various fuels D-1

Appendix E: Battery characteristics E-1

x
 Preface

From the time when our ancient ancestors first made use of fire for heating and
cooking, we have depended on energy extracted from nature to provide for our
needs. Until the end of the 19th century, this energy was provided mainly by the
combustion of wood. Around 1900, coal supplanted wood as our major source of
energy, and this was replaced by petroleum products around 1950. In the latter part
of the 20th century, it became increasingly obvious that our sources of energy could
not remain the same indefinitely. By the end of the 20th century, it also had become
obvious that anthropogenic emissions, largely carbon dioxide from fossil fuel use,
were responsible for global climate change. By this time, it had become apparent,
both from a resource utilization standpoint and from an environmental standpoint,
that it was necessary for human society to transition to sustainable energy sources.
Considerable work has been undertaken over the past few decades on the
development of sustainable low-carbon energy sources. Much of this has dealt
with electricity produced by harvesting energy from the environment.
Hydroelectricity, solar photovoltaics, and wind energy are the principal examples
of such developments. At present, about one quarter of the electricity generated
globally comes from these low-carbon renewable sources, while another 10% comes
from low-carbon nuclear power stations. However, about two-thirds of the world’s
electricity is still produced by the combustion of fossil fuels. Going forward, the
replacement of fossil-fuel-fired electricity generating facilities with environmentally
sustainable electricity sources will be a major task.
Transportation is a major component of our energy use and accounts for more
than a third of the global total. At present, about 95% of transportation energy
comes from fossil fuel sources, and any comprehensive approach intended to reduce
fossil fuel use must deal with transportation energy needs. To date, comparatively
little progress has been made towards converting transportation technologies to low-
carbon energy sources. This is, to a large extent, due to the particular requirements
for transportation energy. In nearly all cases, the source of energy for transportation
must be portable and of sufficient specific energy density. Fossil fuels are ideal in this
respect and, thus far, have remained relatively inexpensive. The economics of
transportation energy technologies are quite different than those of electricity
generation. In the case of electricity generation, infrastructure is developed by the
utility provider and the consumer has little direct input into the technology that is
utilized to produce the electricity that is delivered to their home. In the case of
transportation, at least for private vehicles, industry provides most of the fueling
infrastructure, such as bioethanol stations or public electric vehicle charging
stations, while the consumer makes decisions concerning the choice of vehicle.
The incentive to develop a fueling infrastructure depends on the availability of
customers with appropriate vehicles, while the incentive for consumers to purchase
specific vehicles depends on the availability of fuel. This situation has been at least
one factor in the lack of growth of technologies such as hydrogen-fueled vehicles.
There are numerous options for low-carbon energy that may be considered in the

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context of various modes of transportation, including road transportation, rail

transportation, marine transportation, and air transportation. The path forward
requires a careful consideration of the advantages and disadvantages of each of these
options.
This book begins with a review of our energy use and its implications for future
resource availability and the global environment. It also reviews possible future
approaches to our overall energy system. The various approaches to low-carbon
transportation energy are considered for the different major modes of transporta-
tion. The advantages and disadvantages of each approach are analyzed, and the
book provides an objective overview of the options that are available or could be
available in the near future to provide guidance for the reader in making their own
transportation choices. Finally, the way in which transportation energy require-
ments can be integrated into our overall approach to sustainable and environ-
mentally friendly energy is considered.
This book is intended for a general reader with some background in high-school-
level science. Some background material is covered in more technical detail in the
appendices.

xii
 Author biography

Richard A Dunlap
Richard A Dunlap received a BS from Worcester Polytechnic
Institute (Physics 1974), an A.M from Dartmouth College
(Physics 1976), and a PhD from Clark University (Physics
1981). Since 1981, he has been a professor in the Department of
Physics and Atmospheric Science at Dalhousie University and
currently holds a position as Research Professor. He was Faculty
of Science Killam Research Professor from 2001 to 2006 and
Director of the Dalhousie University Institute for Research in
Materials from 2009 to 2015. Professor Dunlap’s research interests include nuclear
spectroscopies, magnetic materials, quasicrystals, critical phenomena, and advanced
battery materials. He has published more than 300 refereed research papers and his
previously published books include Experimental Physics: Modern Methods (Oxford
1988), The Golden Ratio and Fibonacci Numbers (World Scientific 1997), An
Introduction to the Physics of Nuclei and Particles (Brooks/Cole 2004), Sustainable
Energy (Cengage, 1st edn 2015, 2nd edn 2019), Novel Microstructures for Solids
(IOP/Morgan & Claypool 2018), Particle Physics (IOP/Morgan & Claypool 2018),
The Mössbauer Effect (IOP/Morgan & Claypool 2019), Lasers and Their Application
to the Observation of Bose–Einstein Condensates (IOP/Morgan & Claypool 2019),
Electrons in Solids—Contemporary Topics (IOP/Morgan & Claypool 2019), and
Energy from Nuclear Fusion (IOP Publishing 2021).

xiii
 IOP Publishing

Transportation Technologies for a Sustainable Future

Renewable energy options for road, rail, marine and air transportation
Richard A Dunlap

Chapter 1
Our current transportation technologies and
the need for change

1.1 Introduction
Human society uses large amounts of energy. It is now an essential component of
our daily lives. The earliest humans used only the energy that was provided by their
own bodies. This came from the food that they consumed and typically amounted to
about 2000 calories per day, which is equivalent to an average continuous power
expenditure of about 100 W (for a discussion of the relationship between energy and
power, see appendix B). Throughout history, human energy consumption has
increased, first with the use of fire for heating and cooking and later with the
domestication of animals for agricultural needs and transportation. This was
followed by the widespread use of fossil fuels. At present, the average person in
an industrialized country has a continuous consumption of about 10 kW, i.e.
100 times that of early humans. About half of this energy consumption might be
considered to be personal energy, while about half may be considered to be societal
energy. Personal energy is the energy that we use in our homes for heating, cooking,
and appliances, as well as our personal transportation. Societal energy is energy that
is used in industry for manufacturing, businesses, and commercial transportation; it
is averaged over society. One of the most important uses of energy is for trans-
portation. This is also the use that poses some of the greatest challenges for the
future development of new energy technologies and is the subject of this book.
It is important to consider in some detail what energy is used for. It turns out
that most of the energy that we use is wasted. Energy exists in a number of different
forms, such as thermal energy associated with objects that are hot, mechanical
energy associated with things that are moving, and chemical energy that is associated
with the bonds between atoms. Energy is wasted because the energy that we get
from nature is generally not in the form that we want to use, and the conversion
processes that convert one form of energy into another are not 100% efficient.

doi:10.1088/978-0-7503-5306-9ch1 1-1 ª IOP Publishing Ltd 2023

 Transportation Technologies for a Sustainable Future

Overall, energy is conserved (in the case of nuclear energy, it is the total mass/energy
that is conserved) but conversion processes typically do not convert all of one form of
energy into the form that we want. In addition, in many cases we have to input
additional energy into the process in order to effectively make use of the energy
that nature provides. We can see these features in a couple of common examples of
energy use.
First, we can consider the use of a rechargeable LED flashlight. Its energy may
begin as chemical energy contained in a coal deposit. The coal is mined and
transported to a power station. The coal is then burned, and the chemical energy is
converted into heat. The heat is used to produce steam which turns a turbine.
The turbine then turns a generator which produces electricity. The electricity is
distributed to the grid, and we use that electricity to charge the battery in the
flashlight. This process converts electrical energy into stored chemical energy.
When we turn on the flashlight the chemical energy is converted back into
electrical energy and the LED converts this electrical energy into light. This
process ultimately converts chemical energy into light, but you can see that there
are many steps in between. Some important points to note in this example are
that energy needs to be input into the process, primarily for the mining and
transport of the coal.
A second example is driving an automobile. Transportation of any kind inevitably
represents mechanical energy, because an object is moved from one point to another.
In the case of a gasoline-powered vehicle, the energy begins as chemical energy stored
in an oil deposit. The oil is extracted and transported to a refinery where gasoline and
other hydrocarbons are separated. The gasoline is transported to a service station and
delivered to the customer. The automobile engine burns the gasoline, converting
chemical energy to heat and the heat drives the pistons in the engine to produce
mechanical energy, which moves the vehicle. Again, we see the need to input
processing energy and the various energy conversion processes involved.
The above examples emphasize an important point, namely, the difference
between primary energy sources, i.e. the energy that we extract or harvest from
nature (such as the chemical energy associated with coal or crude oil), and end-user
energy, such as the light produced by the flashlight or the mechanical energy that
transports a vehicle from one point to another.
In both of these examples, there are a number of energy conversions between the
primary energy that is extracted from nature and the end-user energy that is required
in each particular case. While the overall efficiency of each application depends on
all the conversions that are required, the most notable loss of energy is in the
conversion of heat into mechanical energy that is achieved by burning a fossil fuel. It
is, therefore, important to look in more detail at the conversion of heat into
mechanical energy. Any device, such as the steam turbine or the internal combustion
gasoline engine, which converts heat to mechanical energy is referred to as a ‘heat
engine.’ Heat engines can never be 100% efficient, as they always leave some of the
heat unconverted. A diagram of the energy flow in a heat engine is shown in
figure 1.1. A steam turbine might be 35% efficient and a gasoline engine is typically
only about 20% efficient. An analysis of the energy conversions involved in a

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 Transportation Technologies for a Sustainable Future

Figure 1.1. Energy flow in a typical heat engine which converts thermal energy to mechanical energy, showing
the loss of energy due to waste heat.

particular transportation technology is a crucial component of understanding its

viability and will form an important part of the discussions throughout this book.

1.2 A breakdown of transportation energy use

Energy use, i.e. the amount of energy used and the sources of that energy, varies in
different countries according to the specific needs of that country. Some factors that
affect energy use include the per capita gross domestic product (GDP), types of
industry, population density, climate, and natural resources. In general, countries
with a high per capita GDP are highly industrialized and consume more energy per
capita than countries with a low per capita GDP. Countries with heavy industries,
such as automobile manufacturing, use more energy than countries with light
industries, such as small electronics production or banking. Countries with low
population density typically use more energy than countries with high population
density because people tend to travel more, and goods must be transported over
greater distances. Countries with extreme climates, particularly those with cold
climates, use more energy because of the greater need for heating or air conditioning.
Finally, the energy sources that are most commonly used are often governed by the
resources that are available nationally. The major countries that consume the most
energy per capita are Norway and Canada. Both have high per capita GDPs, cold
climates, and relatively low population densities. It is also interesting that both
countries have extensive hydroelectric resources and generate the majority of their
electricity by this method, which accounts for 98% of the electricity generated for
Norway and 60% for Canada. While the overall primary energy sources differ
considerably between countries on the basis of the above considerations, the energy
breakdown for the United States serves as a good example of the situation that is
common in many industrialized countries. Table 1.1 shows the distribution of
primary energy sources in the United States as of 2019. The table shows that 80% of
all primary energy used in the United States comes from fossil fuels. This is very
close to the worldwide average for the percentage of fossil fuel use, 84% in 2019
(BP 2020).

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 Transportation Technologies for a Sustainable Future

Table 1.1. Breakdown of primary energy sources in the United States in

2019. Data are adapted from https://flowcharts.llnl.gov/content/assets/
images/energy/us/Energy_US_2019.png.

Energy source Percentage of total use

Petroleum 36.6
Natural gas 32.0
Coal 11.4
Nuclear fission 8.4
Biofuels 5.0
Wind 2.7
Hydroelectric 2.5
Solar 1.0
Geothermal 0.2

Table 1.2. Breakdown of energy use by sector in the United States in 2019.
Data are adapted from the U.S. Energy Information Administration (EIA
2019).

Sector Percentage of total use

Electricity generation 34.3

Transportation 23.9
Industrial 22.2
Residential 12.2
Commercial 7.2

A breakdown of end-user energy use in the United States is shown in table 1.2.
Transportation includes personal vehicles as well as commercial vehicles, rail-
ways, marine transportation, and aircraft. A further breakdown of transportation
energy is discussed below. Commercial energy includes retail stores and office
buildings, while residential energy primarily includes heat for single-family
homes and apartment buildings. Industrial energy is that which is used in
manufacturing.
Transportation is an essential component of our modern society. While we are
probably most familiar with the personal transportation that we use in the form of
passenger vehicles, buses, and commercial aircraft, there is also an enormous
transportation infrastructure that moves goods to support our society. Table 1.3
gives a breakdown in terms of the energy consumed by the different modes of
transportation that are used worldwide. The next three chapters of the present book
deal primarily with road transportation, as this comprises the largest fraction of
transportation energy use. Other modes of transportation, i.e. rail, marine, and air,
are discussed in chapter 5.
We can also look at the sources of energy used for transportation. Table 1.4 shows
a breakdown of the energy sources used for transportation in the United States.

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 Transportation Technologies for a Sustainable Future

Table 1.3. Percentages of world energy used for different types of transportation.
Data are adapted from www.eia.gov/outlooks/ieo/pdf/transportation.pdf.

Type of transportation Percentage of total

Passenger vehicles 62.2

Road freight 22.4
Air 9.5
Marine 4.1
Rail 1.7

Table 1.4. Breakdown of the energy used for transportation in the United States
in 2019. Data are adapted from https://flowcharts.llnl.gov/content/assets/images/
energy/us/Energy_US_2019.png.

Energy % Total

Fossil fuels 94.7

Biofuels 4.8
Electricity 0.5

At present, about 95% of transportation energy comes from fossil fuels (petroleum or
natural gas), about 5% comes from biofuels (for example, ethanol additives to
gasoline), and less than 1% from electricity.
There are two factors that require serious consideration when dealing with
transportation energy: efficiency and portability. With regard to efficiency, it is
interesting to go back and look at the difference between primary energy and
end-user energy as it specifically relates to transportation. It is obvious that
transportation energy must ultimately take the form of mechanical energy in order
to move objects from one location to another. While there are cases in which we can
harvest mechanical energy from the environment, for example, using wind turbines,
in virtually all cases, conversion of the harvested energy into other forms is necessary
in order for it to be utilized for transportation. Since, at present, nearly all
transportation energy is obtained from either fossil fuels or biofuels, this primary
energy must be converted into mechanical energy by means of a heat engine. This is
obviously the case for vehicles powered by internal combustion engines, but it is also
the case for many electric vehicles which utilize electricity that has been produced by
a coal-fired power plant to charge batteries. Since the efficiency of a heat engine is
limited by the basic laws of thermodynamics, the conversion of primary energy to
transportation energy is much less than 100% efficient. In fact, at present, about two
thirds of the primary energy that is used for transportation is lost as wasted heat
given off to the environment. This has two adverse consequences: first, much more
primary energy must be extracted from the environment than is ultimately needed
for transportation, and second, the excess heat that is deposited in the environment
may have adverse environmental effects.

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 Transportation Technologies for a Sustainable Future

The second transportation factor that requires consideration is portability. This is

most important for road transportation, such as passenger vehicles, trucks, and
buses. It is necessary for vehicles to utilize an energy source that has sufficiently high
energy density that a reasonable amount (i.e. by mass and volume) of onboard fuel
can provide an acceptable vehicle range. Portability is less of a concern for marine
transportation, where the mass and/or volume of fuel is somewhat less critical, and
in rail transportation, where an external energy source, i.e. a third rail or catenary,
may be feasible.
In the next two sections, the need to change the transportation energy infra-
structure is discussed in terms of resource availability and environmental
consequences.

1.3 Future energy needs

In order to understand how energy choices will affect our future environment, it is
important to consider several points. These include:
• the amount of energy we will need in the future;
• the sources of energy that will be used in the future;
• strategies to reduce atmospheric greenhouse gases.

In this section, we look at predictions for the amount of energy that will be needed in
the future. The second point is considered in sections 1.4–1.6, and the final point is
considered in section 1.7.
It is, perhaps, most informative to begin by looking at the per capita primary
energy consumption of some countries, as shown in figure 1.2. It is clear from the
figure that around 1970 there was a significant increase in the per capita energy
consumption in North America. This was due to an increase in mobility and the use
of electronics during that period. There has also been a slight downward trend in
North American per capita energy use since around 2000. This is due to an increased
awareness of future energy concerns and an increase in conservation efforts and
device efficiency. Figure 1.3 shows the total energy use in different regions. It can be
seen that the total energy use in North America has remained more or less constant
for the past 20 years. This is because the slight decrease in per capita energy
consumption has been compensated for by a slight increase in population. The
situation in many other highly industrialized countries is similar, as can be seen in
the data for Europe shown in figure 1.3.
Energy consumption in many less industrialized countries follows somewhat
different trends. Figure 1.2 shows that since about 2000, the per capita energy
consumption in China has approximately tripled. A somewhat smaller although still
significant increase has occurred in India. This trend results from an increase in
industrialization and an increase in personal energy consumption in these countries.
This trend in per capita energy use, combined with significant population growth,
has resulted in the total energy consumption trend as shown in figure 1.3 for Asia.
Thus, it is clear from the above examples that the total world energy consumption
in the future will be a function of population growth and the per capita energy

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Figure 1.2. Per capita annual primary energy consumption in Canada, the United States, and China along
with the world average from 1965 to 2019. Note 100 000 kWh = 360 GJ. Reproduced from OurWorldInData
(2022). CC BY 4.0.

Figure 1.3. Total annual primary energy consumption in different regions of the world. Note 100 000
kWh = 360 GJ. Reproduced from OurWorldInData (2022). CC BY 4.0.

consumption in various countries. While we might generally expect relatively

constant overall energy use in highly industrialized countries, as has been the case
in recent years, we might also expect increasing total energy use in developing

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countries that have not yet reached the same degree of industrialization as North
America and Europe. The combined uncertainty of the results obtained from models
of population growth and per capita energy needs in different parts of the world
leads to a considerable range of possible energy requirements in the future.
Figure 1.4 shows the mean of a number of predictions for future energy use through
the end of the current century. The mean predicted primary energy consumption
worldwide in 2100 is about 1650 EJ per year, compared to the current consumption
of about 580 EJ per year and shows an increase by a factor of 2.7 over the next
80 years. In determining the need to develop new energy infrastructure in the future,
it is important to account for this anticipated growth. The figure also shows that
there is a substantial range of predicted values for world energy consumption in 2100
ranging from a low of 514 EJ per year (slightly less than the current value) to over
2200 EJ per year, based on different population and economic growth models.
The mean value for world energy use in 2100 from figure 1.4 can be viewed in the
context of per capita energy use. Using the United Nations (2019) estimate of
11 billion for the world population in 2100, the data from the figure gives an average
per capita primary energy consumption of about 150 GJ per year. This may be
compared to the current world average per capita annual energy consumption of
81 GJ and is close to current values for most European countries and Japan.

Figure 1.4. Predicted total world primary energy use until the end of the 21st century. The line gives the mean
of the models considered and the vertical bar at year 2100 shows the range of predicted values in that year.
Based on models described in IPCC (2000).

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This increase in per capita energy consumption is basically indicative of the increase
in industrialization and expected living standards in developing countries. Details of
energy needs based on the ratio of primary energy to end-user energy are discussed
in chapter 6.

1.4 Pollution and global climate change

Our choices for future energy sources largely depend on two factors:
• a consideration of the environmental consequences of energy use;
• the availability of resources.

The first point is considered in this section and the second point is considered in
section 1.5.
The utilization of energy by society has a number of adverse environmental
effects. The most significant among these is the emission of various pollutants that
occurs during the combustion of fossil fuels. A discussion of the major chemical and
particulate pollutants that result from fossil fuel use follows. Specific pollutants that
act as greenhouse gases are then discussed, along with their environmental
consequences.

1.4.1 Chemical and particulate pollution

Carbon monoxide—Carbon monoxide results from the incomplete combustion of
carbon-containing fuels. This is described by the reaction
2C + O2 → CO,
which typically occurs when there is insufficient oxygen present to produce complete
oxidization of the carbon. The production of carbon monoxide is most common
when the combustion of carbon-containing compounds occurs in an enclosed space,
such as in an internal combustion automobile engine. Carbon monoxide is an
important pollutant because of its adverse health effects when it is inhaled. Carbon
monoxide reacts readily with hemoglobin in the blood and displaces oxygen. In
sufficient quantities, it can be fatal.
Nitrogen compounds—Nitrogen–oxygen compounds may be formed whenever
any material undergoes combustion in air. If the temperature exceeds about 1100 °C,
nitrogen in the atmosphere is oxidized by the process
N2 + O2 → 2NO,
thereby forming nitric oxide. The conditions that lead to the formation of nitric
oxide are common in internal combustion engines. The nitric oxide may be further
oxidized to form nitrogen dioxide by reaction with ozone in the atmosphere:
NO + O3 → NO2 + O2 .
Nitrogen dioxide is a toxic brown gas that is responsible for the color of the smog
that collects in many cities.

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Hydrocarbons—Hydrocarbons form under the same conditions as carbon mon-

oxide and represent the unburned component of hydrocarbon-containing fuels. As is
the case with carbon monoxide, hydrocarbon pollution is most commonly produced
by internal combustion automobile engines. Hydrocarbon pollution is a contrib-
utory factor to lung disease.
Sulfur dioxide—Sulfur dioxide is produced by the oxidation of sulfur impurities
that are common in many fossil fuels. This situation is most common for coal-fired
power stations. Sulfur dioxide reacts with oxygen in the atmosphere according to the
process
2SO2 + O2 → 2SO3,
which is followed by a reaction with water vapor, namely
SO3 + H2O → H2SO4 .
The final product of these reactions is sulfuric acid, which is highly corrosive. The
acid rain that results from the formation of sulfuric acid in the atmosphere is highly
damaging to stone and concrete structures, as well as painted surfaces.
Particulate matter—The combustion of solid fuel, such as wood and coal, results
in the production of particulate matter pollution. As the chemical composition of the
particulate matter depends on the composition of the fuel, its environmental effects
are somewhat uncertain. However, this form of pollution typically acts as a
respiratory irritant.
Carbon dioxide—Carbon dioxide is the principal emission that results from the
combustion of any fuel that contains carbon. For pure carbon, the reaction is
C + O2 → CO2 .
Virtually all potential fuels, with the exception of hydrogen and ammonia (which
are discussed later in this book), contain carbon and produce carbon dioxide.
Carbon dioxide pollution is discussed in detail in the section below on the
greenhouse effect.
It is clear from the above discussions that some pollutants are closely associated
with our current transportation technologies. These include carbon monoxide,
nitrogen compounds, and hydrocarbons. Other pollutants, such as sulfur com-
pounds and particulates, are more closely related to the use of coal. Table 1.5 gives

Table 1.5. Current percentages of various pollutants in the United States

that result from vehicle use. Data adapted from Dunlap (2019).

Pollution Percentage produced by vehicles

Carbon monoxide 60
Nitrogen compounds 35
Hydrocarbons 35
Sulfur dioxide ~0
Particulate matter ~0

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Table 1.6. Improvement in passenger vehicle emissions in the United States as a result of
government emission control standards between 1970 and 2004. Data are in grams per
kilometer. Adapted from Dunlap (2019).

Year Carbon monoxide Nitrogen oxides Hydrocarbons

1970 21.1 3.1 2.5

2004 1.1 0.04 0.056

the percentages of the various pollutants that have been described above that result
from the energy used for transportation. It is clear that transportation has an
important impact on hazardous pollutants in the environment. Emission control
standards that have been imposed on vehicle manufacturers over the years have
done much to mitigate the emission of pollutants, especially from light-duty vehicles.
Examples of improvements made in vehicle emissions over the past half century or
so are given in table 1.6. In addition to environmental improvements that have
resulted from increased emission control standards for vehicles, much has been done
in recent years to reduce pollution from power stations, particularly those which are
coal-fired. Scrubbers are effective at reducing sulfur dioxide emissions by reacting
power station exhaust gases with calcium-containing compounds such as CaO or
CaCO3. Mechanical filters or electrostatic precipitators are effective at reducing the
particulate matter in power station exhaust gas.
Despite advances in emission controls in many countries, pollution remains an
important concern and can have serious adverse effects on human health, which are
typically concentrated in urban and industrial areas. Such effects are often
temporary, occurring primarily at particular times of the day or week and are often
exacerbated during particular seasons or by certain weather conditions.

1.4.2 The greenhouse effect

Clearly, the most serious environmental effect of our energy use is global climate
change. This is the result of the greenhouse effect and is caused by the presence of
certain pollutants in our atmosphere. The greenhouse effect arises because of the
wavelength dependence of the interaction of electromagnetic radiation with certain
molecules. Radiation from the Sun has wavelengths in the range of about 200 nm to
2000 nm. This radiation includes the ultraviolet region (<380 nm), the visible region
(380 nm–700 nm), and the infrared region (>700 nm) and has a maximum intensity
at around 480 nm (in the yellow region of the visible spectrum). The sunlight that is
incident on the Earth’s outer atmosphere interacts with the Earth in different ways.
It may either be reflected back into space by the atmosphere, absorbed by the
atmosphere, transmitted through the atmosphere and reflected by the Earth’s
surface, or transmitted through the atmosphere and absorbed by the Earth’s surface.
The radiation that is absorbed by the surface warms the Earth. This warm surface
reradiates energy at a much longer wavelength than that of the incident solar
radiation and has a peak intensity at about 9.7 μm. Without the presence of the

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Figure 1.5. Illustration of the greenhouse effect. Reproduced from EPA (2022). Image stated to be in the
public domain.

atmosphere, this reradiated energy would be lost to space. However, with the
atmosphere, this reradiated energy can be transmitted through the atmosphere, or it
can be reflected back to the Earth, further increasing the surface temperature. The
greenhouse effect occurs because certain molecular species in the atmosphere are
relatively transparent to short-wavelength radiation (i.e. solar radiation) but more
reflective to long-wavelength radiation (i.e. energy reradiated from the surface).
Thus, the presence of these molecular species (referred to as greenhouse gases) traps
solar energy near the Earth’s surface and raises its temperature. This is the same
effect that occurs when an automobile is left in the Sun. The vehicle’s windows act
similarly to the Earth’s atmosphere because they transmit short-wavelength radia-
tion and reflect long-wavelength radiation, thereby trapping solar energy inside the
vehicle and raising the temperature. The details of the greenhouse effect in the
Earth’s atmosphere are shown graphically in figure 1.5.
The most important greenhouse gases in the Earth’s atmosphere are given in
table 1.7. The table shows the relative infrared absorptions per molecule for the
different greenhouse gas species, the current concentrations of these gases in the
atmosphere, and their relative contribution to the greenhouse effect. Clearly, more
than two thirds of the greenhouse effect is the result of carbon dioxide in the
atmosphere, primarily because of its large concentration. However, other green-
house gases are significant, mainly because of their greater infrared absorption per
molecule. The presence of greenhouse gases in the atmosphere (specifically carbon
dioxide) is essential for the existence of life on the planet. Without the greenhouse
effect that the atmosphere provides, the equilibrium temperature of the Earth’s
surface would be about −19 °C, which is inconsistent with the evolution of life.

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Table 1.7. The relative importance of greenhouse gases. Data adapted from Dunlap (2019) and www.eea.
europa.eu/data-and-maps/indicators/atmospheric-greenhouse-gas-concentrations-10/assessment.

Relative infrared Current atmospheric

absorption per concentration by Relative atmospheric
Greenhouse gas molecule volume in 2015 (ppm) greenhouse effect (%)

Carbon dioxide (CO2) 1 402.9 68

Methane (CH4) 25 1.835 19
Nitrous oxide (N2O) 298 0.3277 7
Chlorofluorocarbon 10 900 0.000 530 6
(CCl2F2)

The presence of greenhouse gases in the atmosphere raises the Earth’s mean surface
temperature to about +15 °C. Increasing the concentration of greenhouse gases in
the atmosphere obviously increases the Earth’s surface temperature, and this will
affect the environmental conditions on Earth in a way that will be detrimental to our
society.
Human activity is the major contributor to increasing greenhouse gases at present
and energy production is the most significant source of the greenhouse gases that are
produced by human society. Figure 1.6 shows the relative contributions of different
human activities in the United States to the production of greenhouse gases.
Transportation is the largest single contributor to greenhouse gases, followed closely
by electricity generation. It is clear that carbon dioxide is the most significant
(although not the only important) greenhouse gas. Transportation, along with
electricity generation, account for over half of the carbon dioxide that is emitted
worldwide. Human activities are also a major contributor to atmospheric methane,
the second most important greenhouse gas. These activities include agriculture,
biomass burning, organic landfill waste, and methane that escapes during fossil fuel
production.
The correlation between anthropogenic greenhouse gas emissions and global
climate has been studied in significant detail for the past several decades. Figure 1.7
shows the results of an extensive study of ice cores from Antarctica. The data show
periodic variations in temperature that have occurred over the past 400 000 years
that are very well correlated with atmospheric carbon dioxide and methane levels.
The reasons for these fluctuations in atmospheric chemistry and climate are not
precisely known, but it is obvious that these are not the result of industrialized
human activity. There is, however, some evidence that relates these climatic
variations to changes in the cosmic ray flux that results from the rotation of the
Sun around the galactic core. What is most significant in this analysis is a
comparison of this historical data based on ice core samples with more recent ice
core and direct measurements of the concentrations of these greenhouse gases.
Figure 1.7 shows that over the past 400 000 years or so, atmospheric carbon dioxide
levels have varied between about 180 ppm and 300 ppm, while atmospheric methane
levels have varied between about 0.35 ppm and 0.7 ppm. Recent measurements of

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Figure 1.6. Distribution of the sources of greenhouse gases in the United States in 2020. Reproduced from
EPA (2022). Image stated to be in the public domain.

atmospheric carbon dioxide and methane concentrations are shown in figures 1.8
and 1.9, respectively. In addition, figure 1.8 shows the recent correlation between
global temperature and atmospheric carbon dioxide concentration. Both these
figures show that recent greenhouse gas levels have been increasing consistently in
recent years and that current concentrations, namely, over 400 ppm for carbon
dioxide and about 1.85 ppm for methane, are well above the historical values for the
past 400 000 years.
Three conclusions are obvious from the analysis of the above data:
• levels of atmospheric greenhouse gases are higher at present than they have
been at any time during the past 400 000 years;
• levels of atmospheric greenhouse gases are currently increasing;
• there is a clear correlation between atmospheric greenhouse gas concentra-
tions and global temperatures.

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Figure 1.7. A comparison of historical atmospheric carbon dioxide (CO2) and methane (CH4) levels and
temperature anomalies, as determined from the analysis of ice core samples from Vostok, Antarctic.
Reproduced from NASA (2005). Image stated to be in the public domain.

Figure 1.8. Correlation between atmospheric carbon dioxide levels (gray line) and temperature anomalies
(blue and red bars) for the past 140 years. Reproduced from NOAA Climate.gov (2022). Image stated to be in
the public domain.

The reasons for the features noted above are not directly obvious from an analysis of
the data. However, the overwhelming scientific consensus is that the recent rises in
carbon dioxide and other greenhouse gas concentrations in the atmosphere are the
results of human activity.

1.4.3 The consequences of global climate change

It is clear from the above discussion that the major manifestation of increased
greenhouse concentration in the atmosphere is an increase in global temperatures.

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Figure 1.9. Measured atmospheric methane levels since about 1983. Reproduced from NOAA (2022). Image
stated to be in the public domain.

The effects of these climatic changes are very far-reaching and influence many
aspects of the environment. Some of the most significant environmental changes that
are related to greenhouse gas emissions are discussed briefly below.

1.4.3.1 Decreased number and extent of glaciers

Increasing global temperatures have resulted in glacial melting. This is most obvious
from a visual observation of glacial extents. A significant example of glacial melting
has occurred in Iceland, where Okjökull (meaning ‘Ok glacier’ in Icelandic) has
decreased in area from about 38 km2 to less than 1 km2 between the early 20th
century and the early 21st century. In 2019, Okjökull was officially declassified as a
glacier.

1.4.3.2 Ice sheet loss

Along the same lines as glacial melting, global warming has also resulted in the loss
of ice mass in the Arctic and Antarctic. This is most noticeable from the Greenlandic
and Antarctic ice sheets, where current annual loss rates are 286 Gt and 127 Gt,
respectively.

1.4.3.3 Increased ocean heat content

As global temperatures increase, the heat absorbed by the upper layers of the ocean
increases, leading to an increase in the total heat content of the oceans. The
corresponding increase in ocean temperature can have significant effects on ocean
ecology.

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1.4.3.4 Arctic sea ice decline

Increasing ocean temperatures have resulted in the melting of sea ice. This is most
apparent in the Arctic, where, according to current trends, it is expected that much
of the Arctic will be ice-free during summer months by the end of the century.

1.4.3.5 Increased sea level

The melting of sea ice and ice sheets that results from global warming will give rise to
increased sea levels. The thermal expansion of water will also contribute to increased
ocean water volume. Since the late 19th century, sea levels have been observed to rise
by about 20 cm. The continuation of this trend due to increased greenhouse gas
concentration in the atmosphere can have highly adverse effects on both the natural
habitat as well as human society in coastal regions. Because of its large heat
capacity, the ocean will respond more slowly to global temperature changes than the
atmosphere and, as a result, sea levels will continue to rise for many decades, even if
greenhouse gas levels are reduced.

1.4.3.6 Ocean acidification

When the concentration of carbon dioxide in the atmosphere is increased, its
partial pressure in the atmosphere is also increased. In order to maintain
equilibrium between the carbon dioxide in the atmosphere and that which is
dissolved in the oceans, the concentration of carbon dioxide in seawater will
increase. About 45% of the carbon dioxide that is released into the atmosphere
remains in the atmosphere, about 35% is dissolved in the oceans, while the
remaining 20% or so is sequestered by terrestrial plants. Some of the carbon
dioxide that is dissolved in the ocean forms carbonic acid (H2CO3). Some of this
carbonic acid will dissociate by the process
H2CO3 → 2H++CO32−,
and the resulting H+ ions will increase the acidity of seawater. Since seawater is
normally alkaline, increasing the concentration of H+ ions will bring it closer to
neutral. It has been estimated that since industrialization, the surface ocean pH has
changed from about 8.25 to 8.14. Decreasing ocean pH can have adverse effects on
calcifying marine organisms, such as corals and those that have calcium carbonate
(CaCO3) exoskeletons (e.g. crustaceans and molluscs). This, in turn, can have
adverse consequences for organisms that are higher up in the food chain.

1.4.3.7 Ocean deoxygenation

Phytoplankton produce oxygen in the surface layers of the ocean by photosynthesis.
This oxygen is normally carried to lower layers of the ocean by the mixing of the
surface layer with the denser layers below it. The increased ocean stratification that
results from increased temperature and decreased salinity of surface layers due to
global warming and the input of fresh water from melting ice sheets, respectively,
reduces mixing and decreases oxygen concentration in the lower layers of the ocean.
This leads to a decrease in the ability of marine organisms to survive in the lower
regions of the ocean.

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1.4.3.8 Altered ocean circulation patterns

Changes in ocean temperature and salinity gradients, as noted above, will lead to
changes in ocean circulation patterns. Perhaps the most notable of these will be
changes to the Gulf Stream and its northern extension, the North Atlantic Drift,
which brings warmer water from the Gulf of Mexico to north Atlantic regions,
including eastern Canada and northwestern Europe. Models suggest that global
climate change could lead to a weakening of the Gulf Stream and a corresponding
cooling of some regions, such as Scandinavia.

1.4.3.9 Changes in precipitation patterns

Changes in weather patterns will result in increased precipitation in some regions
and decreased precipitation in others. These precipitation features will lead to
increased drought and floods. Decreased precipitation in many agricultural regions,
such as the Midwest and the Southwest in the United States, will lead to decreased
crop production. Wildfires will occur with increased frequency and severity in
regions with reduced precipitation.

1.4.3.10 More frequent and severe hurricanes

Global climate change is expected to result in more frequent extreme weather events.
Perhaps the most notable of these will be the increased frequency, severity, and
duration of hurricanes. These effects have been observed since the early 1980s.

1.4.3.11 Altered geographic ranges of some species

Ecological changes, such as temperature changes and changes in precipitation
patterns affect the habitats of wildlife and can lead to decreased populations or
even extinction of some species, as well as changes in their geographical range.

1.4.3.12 Thawing of permafrost

Permafrost is ground that is continuously frozen in regions where the ambient
temperature remains sufficiently low. It occurs primarily in the Northern
Hemisphere in the Arctic regions of Alaska, Canada, Greenland, and Siberia.
Substantial quantities of greenhouse gases including carbon dioxide, methane, and
nitrous oxide are trapped in permafrost. When permafrost melts as a result of global
warming, these gases will be released to the atmosphere, leading to further global
warming.

1.5 Future fossil fuel use

As discussed above, the vast majority of our current energy is supplied by fossil fuels.
This is particularly true for the energy used for transportation. Fossil fuel resources
are limited and at some point will no longer be able to fulfill a significant portion of
our energy needs. We may also decide to transition to other energy sources before
fossil fuels are depleted. This transition may be linked to environmental concerns but
may also be linked to the rising fossil fuel prices that will result from diminishing
supplies. Determining future fossil fuel use is an important component of predicting

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the environmental impact of our energy use. There are two approaches to under-
standing how fossil fuels may be used in the future. We can look at available fossil
fuel resources, as this will limit what is available for use, or we can look at the future
demand for fossil fuels. Here, we consider two fairly straightforward approaches
to predicting future fossil fuel production based on resource availability. These are:
(a) an analysis of reserve-to-production ratios and (b) Hubbert theory. We then
consider different scenarios for future fossil fuel demand.

1.5.1 Reserve-to-production ratios

The simplest method of estimating the longevity of our fossil fuel resources is to
calculate the ratio of how much of the resource is remaining and how much we use
per year at present. This is known as the reserves-to-production ratio, as
summarized in table 1.8 for the different fossil fuels; it gives the number of years
of use that remain at the current rate of consumption. This approach may not be
accurate, as it assumes that fuel will be utilized at a constant rate and that all
known reserves are equally viable. However, this method can provide a rough
estimate of the longevities of the different fossil fuels. A more mathematical
approach is described next.

1.5.2 Hubbert theory

In the 1950s, American geophysicist Marion King Hubbert developed a mathemat-
ical approach to describing the utilization of natural resources, specifically oil in the
United States. This model can, in general, be applied to any resource and has been
successful in describing the utilization of coal, petroleum, and natural gas. There are
three basic assumptions behind the Hubbert model:
1. The utilization of a resource begins slowly when the resource is determined to
be useful. This is because the infrastructure required to use the resource must
be developed.
2. The utilization of the resource increases as the infrastructure is developed
and reaches a maximum when half of the available resource has been
consumed.
3. The utilization of the resource decreases after half of the resource has been
consumed and falls to zero when the resource has been exhausted or becomes
no longer viable. This is because, as the resource becomes depleted, the
efficiency of its extraction decreases and the cost of its use increases.

Table 1.8. Reserve-to-production (r/p) ratios for fossil fuels for 2019. Data adapted from BP (2020) and IEA
(2020). Note: bbl = barrels = 158.97 L, t = 103 kg = 2025 lbs.

Resource Known reserves (r) (2019) Annual production (p) (2019) r/p (years) End year

Oil 1.73 × 1012 bbl 3.47 × 1010 bbl 50 2069

Natural gas 1.99 × 1014 m3 3.93 × 1012 m3 51 2070
Coal 1.07 × 1012 t 7.92 × 109 t 135 2154

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Further mathematical details of the Hubbert model may be found in Dunlap

(2020a). Typically, the annual production rate of a resource is taken as an indicator
of its utilization, and in the Hubbert model the production rate of a resource is
expected to follow the logistic curve shown in figure 1.10.
The validity of the Hubbert model has been tested on a variety of subsets of fossil
fuel data. Figure 1.11 shows the data for the annual production rate of Pennsylvania
anthracite coal. Anthracite coal is the most desirable form of coal because it has the
highest carbon content (and hence highest energy content) as well as the lowest
concentration of impurities (which reduce the energy content and add to the
emission of chemical pollutants). Pennsylvania had the most significant anthracite
coal resources in the United States, and these were utilized extensively beginning
around the middle of the 19th century, as illustrated in figure 1.11. The utilization
data shows good agreement with the shape of the curve predicted by the Hubbert
model, except for an additional small peak during the 1940s that corresponds to
increased production as a result of increased demand related to World War II.
Production diminished to near zero by the beginning of the 21st century as a result of
the depletion of economically viable resources. At present, Pennsylvania anthracite
production amounts to about 1.6 Mt per year out of a total U.S. anthracite
production of about 4.5 Mt per year (note Mt = 106 metric tonnes = 109 kg). These
numbers may be contrasted with the Pennsylvania anthracite production of about
90 Mt per year around the time of World War I. The Hubbert model is also
applicable to a number of other natural resources such as whale oil and whale bone
(see Höök 2010), the production of which decreased and ended when it became
unviable for economic, environmental, and social reasons.

Figure 1.10. Logistic curve described by the Hubbert model for the utilization of a resource. This image
(Rubber Duck 2015) has been obtained by the author from the Wikimedia website, where it is stated to have
been released into the public domain. It is included within this chapter on that basis.

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Figure 1.11. Production of Pennsylvania anthracite. Reproduced with permission from Rutledge (2011).
Available at: http://rutledge.caltech.edu/.

Figure 1.12. United States crude oil production for the contiguous 48 states (green curve) and Hubbert’s
prediction from 1956 (red curve). Oil produced in Alaska is not included, as this was not included in Hubbert’s
original analysis. Note: 1 barrel = 158.97 L. This image (Plazak 2015) has been obtained by the author from
the Wikimedia website where it was made available under a CC BY-SA 4.0 licence, https://creativecommons.
org/licenses/by-sa/4.0/deed.en. It is included within this chapter on that basis. It is attributed to Plazak.

The Hubert model must be applied to resource utilization data with some caution.
An example of a case in which the application of the model is not straightforward is
crude oil production in the United States. These data are shown in figure 1.12.

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While there was some increased production around 1970 as a result of increased
demand for vehicle fuel, the data shows reasonably good agreement with the
Hubbert model shown by the red curve in the figure up until the early 2000s. After
that, the production curve is substantially greater than the Hubbert prediction.
Such deviations can occur for several reasons. First, significant previously
unknown resources may be discovered and thereby increase the total amount of
the resource available. Second, as is the case in figure 1.12, new technologies may
be developed that allow resources that were previously considered economically or
technically unusable to become viable. In figure 1.12, the red curve, which follows
the original prediction from the 1950s by Hubbert, considers the utilization of
what is referred to as ‘conventional’ oil. Around 2000, technologies that allowed
for the extraction of what is referred to as ‘tight’ oil became common. Tight oil
includes oil that is more difficult to extract from underground resources as well as
oil that is trapped in shale, i.e. shale oil. Fracking and oil shale processing
technologies have made these sources of crude oil economically viable. The
availability of these resources, as well as the desire of the United States to reduce
dependency on imported foreign oil, led to substantially increased production from
tight oil sources. It is interesting to note that if only conventional oil production is
plotted, the production curve continues to be reasonably well described by the
Hubbert curve. While the addition of fracking and other non-conventional
technologies has very noticeably increased oil production, the total amount of
oil available (given by the area under the curve) has been increased by only a fairly
modest amount. This is because, as the graph shows, the new peak is quite narrow
(in years) and the overall longevity of the resource has not been increased very
significantly. In order to properly analyze data such as that shown in figure 1.11 it
is necessary to incorporate two Hubbert curves, one for conventional oil and one
for tight oil. Additional Hubbert curves can be incorporated to account for
additional resource discoveries or other new technologies, and such analysis is
referred to as a multi-Hubbert analysis.
The application of suitable multi-Hubbert analyses to world fossil fuel production
provides some highly significant information related to the anticipated longevity of
these resources. Table 1.9 gives the half-peak years for oil, natural gas, and coal
resources worldwide based on a 2012 analysis (Maggio and Cacciola 2012). The
half-peak year is the year in which production rate will drop to one half of the peak
production rate, which is also the time at which about 85% of the total resource will

Table 1.9. Half-peak years for world oil, natural gas,

and coal production based on a multi-Hubbert analysis.
Data are adapted from Maggio and Cacciola (2012).

Resource Half-peak year

Oil 2052
Natural gas 2078
Coal 2115

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have been used. The half-peak years shown in the table are in reasonable agreement
with the results of the simple reserve-to-production ratios. Both approaches suggest
that on a timescale of 40–50 years, oil and natural gas resources will be severely
depleted, and coal resources will be severely depleted on a timescale of about
100 years.

1.5.3 Analysis of future fossil fuel demand

The analysis based on the Hubbert model as described above provides some
interesting insight into future energy use. However, it is far from perfect.
Production is more or less driven by demand, and it can be seen that in periods
of increased demand there is a corresponding increase in production which results in
deviations from the Hubbert model. It is also clear that the results of the analysis
depend critically on the validity of the assumptions and the input parameters. Since
Hubbert’s first analysis in the 1950s, the estimated time of peak production has
moved forward more or less continuously. This is due to the discovery (or
utilization) of new resources (e.g. offshore oil or Alaskan oil) or the implementation
of new technologies that make more of the resource viable (e.g. fracking, oil
extraction from tar sands). This is clearly the reason for the non-logistic-curve
behavior shown in figure 1.12. Although many limited sets of data, such as that
shown in figure 1.11, are reasonably well described by the Hubbert model, it has also
been questioned whether this approach is generally a valid method of analyzing
energy resource utilization (Sorrell et al 2009).
Moving forward, the Hubbert model gives us some expectations concerning the
longevity of available resources, within the limits described above. However, an
assessment of the effects of our energy use on the environment is related to our
actual energy use, rather than the energy resources that are available. It has,
therefore, become beneficial to analyze future energy demand as a measure of
environmental impact. The demand (for fossil fuel resources) may be less in the
future than the availability of such resources would imply. This can occur for several
(somewhat related) reasons including:
• reduction in future fossil fuel use as a means of mitigating climate change;
• reduction in fossil fuel use as a result of an increase in the capacity of low-
carbon energy sources;
• reduction in fossil fuel use because of increasing costs relative to more
sustainable options.

The last point can result from increasing fossil fuel costs due to decreasing supply;
alternatively, it can result from decreasing sustainable energy costs due to improved
technologies. Thus, determining future fossil fuel energy demand depends on a
number of factors, most of which are not easy to predict. These not only include a
number of scientific and technical issues related to renewable energy development
but also political, economic, and social factors. It is possible, however, to estimate
future demand based on different energy development scenarios. As an example,
figure 1.13 shows some general features for world oil demand based on

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Figure 1.13. Global oil demand as a function of time: (1) historical production driven by demand, (2) future
demand limited by resources, (3) sustainable future demand, and (4) net zero future demand.

considerations discussed in BP (2021) and IEA (2022). Historical data is shown up to

about 2021 (curve 1), and various scenarios for future oil demand are illustrated. In
the case of demand limited by resources (curve 2), current predictions along the lines
of the Hubbert analysis of past oil production are shown; these illustrate peak
production occurring within a decade or so. Sustainable future demand (curve 3)
refers to the case in which the global temperature increases by the end of the century
are limited to a maximum of 2.0 °C, which may be further reduced to a maximum of
1.5 °C if effective atmospheric carbon capture technology is implemented (as
discussed in section 1.7). The net zero case (curve 4) represent the most aggressive
reduction in fossil fuel use and results in a maximum global temperature increase of
1.5 °C, independent of carbon capture.
The discussion above clearly indicates that the use of fossil fuels in the future is
dictated by demand, as long as this remains below the limits of availability. This
demand is, at least to some extent, governed by the choices that society makes in its
approach to energy sources, as well as economic and technical considerations.
In recent years it has become apparent that there are other factors that can have a
direct influence on our energy use. The COVID-19 pandemic which spread world-
wide in 2020 influenced overall energy use. Travel restrictions, as well as the
economic downturn, that resulted from the pandemic reduced overall energy use and
fossil fuel use in particular. This trend is apparent in figure 1.13, where a slight
decrease is seen around 2020. It has been speculated that fossil fuel use will return to
its pre-COVID-19 trends, but this has not occurred as of mid-2022.

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Beginning in early 2022, the war in Ukraine has had severe effects on energy use
in many parts of the world as a result of the disruption of fossil fuel distribution. The
future short-term and long-term effects of this war and the COVID-19 pandemic on
our overall energy use and the transition to carbon-free energy sources required to
address global climate change still remain to be seen.

1.6 Sustainable energy sources for the future

The discussion above has emphasized two important reasons for the development of
new energy sources: the depletion of world fossil fuel resources and the environ-
mental consequences of continued carbon emissions. It is clear that our current
energy mix will not be sustainable very far into the future and that transitioning to
low-carbon energy sources as soon as possible is essential to minimize the effects of
global climate change.
Sustainable low-carbon energy sources typically either produce electricity or a fuel
in which chemical energy is stored. These two forms of energy are readily applicable to
transportation as, for example, electricity for battery electric vehicles or fuel for
internal combustion engine vehicles, respectively. In addition, renewable energy may
make a minor contribution in the form of mechanical energy harvested from the wind
that is used to power marine vehicles. A brief description of the carbon-free energy
technologies that produce electricity or chemical fuels is given below. Nuclear energy,
although not renewable, is low-carbon and is included in the list.
At present about 65% of electricity worldwide is produced from fossil fuels, about 25%
is produced from renewable energy sources and about 10% is produced from nuclear
energy. In this section, major low-carbon electricity-producing technologies are discussed
in order of decreasing total world installed capacity, as summarized in table 1.10.

1.6.1 Hydroelectric energy

Hydroelectricity is the most extensively utilized renewable energy resource. It is also
the oldest renewable source of electricity and was first developed as a commercial
supplier of electricity to the public in the 1880s. Figure 1.14 shows the Milltown
Hydroelectric Station, which is the oldest operational hydroelectric generating

Table 1.10. Installed worldwide generating capacities of the

major carbon-free electricity sources at the end of 2019. Data
adapted from Dunlap (2019), the International Atomic Energy
Agency (IAEA 2020), and the International Renewable Energy
Agency (IRENA 2020).

Energy source World capacity (GW)

Hydroelectric 1190
Wind 623
Solar 586
Nuclear fission 392
Biofuels 124

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Figure 1.14. Milltown Hydroelectric Station located on the Canada–United States border between New
Brunswick and Maine. Image: Richard A Dunlap.

facility in North America. It was constructed in 1881 and has a generating capacity
of 4 MW.
Hydroelectric facilities can be roughly divided into two categories: high head
facilities and run-of-the-river facilities. High head facilities are large-capacity
installations in which a substantial dam is used to create a reservoir. Water from
the reservoir flows to turbines and generators located at the bottom of the dam,
thereby generating electricity. Run-of-the-river facilities have a minimal dam or no
dam and largely use the kinetic energy of the flowing water of the river to turn
turbines to generate electricity.
While hydroelectric power does not in itself generate greenhouse gases, it can
contribute to global climate change indirectly. First, high head facilities in particular
are constructed using enormous quantities of concrete. The production of concrete
involves the heating of limestone (CaCO3) to produce CaO by the reaction
CaCO3 → CaO + CO2 ,
thereby emitting CO2 to the atmosphere. The creation of a reservoir utilizes land
that in many cases was previously occupied by forests or other vegetation.
Reservoirs for high head facilities can cover a very large area. For example, the
reservoir that supplies the Three Gorges Dam on the Yangtze River in China covers
an area of 1084 km2. The creation of a reservoir eliminates vegetation that would
otherwise sequester carbon dioxide from the atmosphere. In addition, organic
matter that is covered by water decays and thereby emits carbon dioxide and
methane. This problem is most significant in tropical regions. Run-of-the-river
facilities do not share these environmental concerns, but typically have more
variable capacity factors, as discussed below.
In recent years, there has been considerable growth in the utilization of hydro-
electric energy in some developing countries. Figure 1.15 shows that this growth is
notable in China and Brazil. At present, hydroelectric energy represents the largest
component of renewable electricity generated worldwide (about 17% of total
electricity generation).

1.6.2 Wind energy

As shown in table 1.10, wind currently has the second largest installed capacity of all
low-carbon electricity sources. Figure 1.16 also shows that installed wind capacity

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Figure 1.15. Growth of hydroelectric power in the top five countries. This image (Plazak 2013) has been
obtained by the author from the Wikimedia website where it was made available under a CC BY-SA 3.0
licence, https://creativecommons.org/licenses/by-sa/3.0/deed.en. It is included within this chapter on that basis.
It is attributed to Plazak.

Figure 1.16. Increase in electricity produced by wind since the mid-1990s. This image (Delphi234 2014) has
been obtained by the author from the Wikimedia website, where it is stated to have been released into the
public domain. It is included within this chapter on that basis.

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has increased substantially over the past two decades in almost all regions of the
world. At present, about 15% of worldwide wind capacity is offshore, most of this
located in Europe, where high population densities in many countries make offshore
locations attractive.
Wind energy has a number of very attractive characteristics. Some of the most
significant are as follows:
Cost-effective—Wind is a cost-effective method of generating electricity (see
below).
Well-established technology—Wind turbine technologies are well established,
although research to increase generator efficiency and improve turbine design
continues.
Wide distribution of resources—While not all locations are ideal for the placement
of wind turbines, most countries have wind resources, either onshore, offshore, or
both, that are suitable for wind energy development. Offshore locations are
attractive because their wind velocities are typically greater than those of onshore
locations, and the use of land resources in areas of high population density can be
avoided. However, as discussed later in the chapter, economic factors favor onshore
wind energy development.
Potential dual land use—Wind farms typically consist of large numbers of
individual turbines, and these must be spaced adequately in order to effectively
make use of wind energy. The land between wind turbines can be utilized for other
purposes, such as agriculture.
Low risk—While all methods of harvesting and utilizing energy involve some
degree of risk, wind energy is one of the safest energy technologies. Since the 1970s,
there have been about 200 human fatalities related to the wind power industry,
mostly involving occupational workers. The risk of wind energy to the general
public is quite small and typically involves accidents related to broken turbine blades
or ice throws.
Although the potentially adverse effects that result from the utilization of wind
energy are typically less severe than for many other energy sources, the more
significant concerns are described below.
Noise—The potential for possible health risks associated with the noise produced
by wind turbines has been one of the major concerns for the widespread imple-
mentation of this technology. In most jurisdictions, regulations are in place that
prohibit the construction of wind turbines within certain distances of residential
buildings. At 1 km, the sound level is about 30 dB, comparable to the ambient sound
level in a quiet rural area.
Shadow flicker—On a sunny day, the shadows of the blades of a wind turbine
move, leading to a flickering as viewed by an observer on the ground. This flickering
typically occurs once every second or so (depending on the rotational frequency of
the turbine) and causes annoyance to residents living in its path. This, combined
with noise levels as well as the potential for blade accidents or ice throws, requires
the placement of turbines at suitable distances from residential areas.
Effects on wildlife—While bird (and bat) fatalities are used as an argument
against the development of wind energy, recent studies by the U.S. Fish and Wildlife

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Table 1.11. Estimated bird mortality from some different

anthropogenic causes in the United States. Data adapted
from the U.S. Fish and Wildlife Services (2020).

Hazard Bird deaths per year

Domestic cats 2 400 000 000

Windows 599 000 000
Vehicles 214 500 000
Electric power lines 25 500 000
Wind turbines 234 012

Services (2020), summarized in table 1.11, give the estimated bird mortalities from
different anthropogenic causes. It is clear that the number of bird fatalities from
other causes is much more significant than from wind turbines. Another way to look
at this issue is to compare bird mortality for different energy technologies per unit
energy generated. Specifically, fossil-fuel-generated electricity causes bird death as a
result of mining operations, air pollution, and global warming and results in about
17 times the bird mortality per unit of electricity generated than that of wind-
generated electricity (Sovacool 2009).
Deforestation—The removal of trees for the purpose of constructing a wind farm
has the potential effect of decreasing carbon sequestration from the atmosphere.
Thus, the choice of locations for wind farms should consider this possible negative
environmental consequence.

1.6.3 Solar energy

Solar energy will undoubtedly be a major component of power in a sustainable future.
Solar energy has been effectively used on a residential and community scale to provide
direct thermal energy. It is, however, most likely to contribute in a substantial way to
future energy as a source of electricity. There are two approaches to producing
electricity from solar energy: thermal generation (sometimes called concentrated solar
power), which uses solar radiation to heat a working fluid and generates electricity
using a heat engine and photovoltaics, which generate electricity directly using
semiconducting devices. At present, more than 99% of the installed solar grid capacity
utilizes photovoltaic technology, and this is discussed further in this section.
The extensive development of solar photovoltaics began in the early 1990s, as
illustrated in figure 1.17. This figure shows that over the past thirty years or so, the
growth of photovoltaic capacity worldwide has been exponential (as evidenced by
the approximately straight line on the semi-log plot). While most photovoltaic cells
have been made of silicon, the technology has shifted from monocrystalline silicon
to multicrystalline silicon over this time frame, as seen in figure 1.18. A major factor
that has contributed to the growth of photovoltaics has been the cost of photovoltaic
cells. Figure 1.19 shows the decrease in the cost of cells per unit power output. At
present, solar photovoltaics is one of the most cost-effective methods of electricity
generation for the grid.

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Figure 1.17. Total world installed photovoltaic capacity as a function of year from 1992 to 2018. This image
(Rfassbind 2014a) has been obtained by the author from the Wikimedia website, where it is stated to have been
released into the public domain. It is included within this chapter on that basis.

Figure 1.18. Different photovoltaic technologies used as a function of time from 1990 to 2013. Crystalline silicon
includes monocrystalline silicon (mono-Si) and multicrystalline silicon (multi-Si), while thin-film technologies
include amorphous silicon, CdTe, and copper–indium–gallium–selenide (CIGS). This image (Rfassbind 2014b)
has been obtained by the author from the Wikimedia website, where it is stated to have been released into the
public domain. It is included within this chapter on that basis.

Solar energy has a very low density at the surface of the Earth, and, as a result, a
substantial land area is required to produce quantities of electrical power that are
comparable to those generated by fossil fuel or nuclear power stations. In the United

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Figure 1.19. Price history chart of crystalline silicon solar cells in USD per watt since 1977. This image
(Rfassbind 2015) has been obtained by the author from the Wikimedia website, where it is stated to have been
released into the public domain. It is included within this chapter on that basis.

States, for example, the average annual 24 h radiation ranges from about 150 W m−2
in the Northeast and Northwest to about 245 W m−2 in the Southwest. This means
that an area of between about 20 km2 and 35 km2 would be required to produce the
same average output as a typical coal-fired power station (~1 GW). A typical solar
photovoltaic installation is illustrated in figure 1.20.
At first glance the utilization of solar energy through the application of photo-
voltaic technology would seem to have few potentially adverse environmental
consequences. While this is generally true, it is important to consider the negative
effects of extensive global solar power generation. The large number of photovoltaic
panels and the corresponding large land area that are needed to provide significant
electrical power have certain drawbacks. While this is also the case for wind power,
the situation for solar power is somewhat different, as the panels block the Sun’s
light from directly reaching the land beneath them. This makes land use for large-
scale agriculture incompatible with solar photovoltaics. However, the spaces
between the rows of solar panels can be used to grow grass, and pilot projects
have involved the use of this land for grazing by livestock such as sheep. Although
the significant manufacturing and infrastructure construction means that the risks
associated with solar photovoltaics, particularly for occupational workers, are
greater than might be expected, they are somewhat less than for wind power.

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Figure 1.20. A portion of the Dau Tieng Solar Power Project, Tay Ninh Province, Vietnam. This facility has a
capacity of 600 MW and covers an area of 5 km2. Note that the electricity generated is related to the capacity
factor, as discussed below. This image (TammyLe 2019) has been obtained by the author from the Wikimedia
website where it was made available under a CC BY-SA 4.0 licence, https://creativecommons.org/licenses/by-
sa/4.0/deed.en. It is included within this chapter on that basis. It is attributed to TammyLe.

Some of the reasons for this relate to their less demanding transportation require-
ments (as no huge components, such as wind turbine rotors, need to be transported
as single units) and less hazardous maintenance conditions.

1.6.4 Nuclear fission

Nuclear fission refers to nuclear reactions in which a heavy nucleus is broken up into
two (usually lighter) nuclei. Since the sum of the nuclear binding energy is greater for
the two lighter nuclei than for the original heavier nucleus, excess energy is given off
as kinetic energy of the nuclei. This kinetic energy is ultimately turned into heat
when the reaction by-products interact with the atoms in a working fluid such as
water. This heat may be used to produce electricity by means of a heat engine in the
same way that heat from the combustion of coal is used to produce steam to run
turbines and generate electricity.
Fission reactors designed for the purpose of producing electricity were first
constructed in the 1950s and became common in many countries in the 1970s.
Figure 1.21 shows the Seabrook Nuclear Generating Station in New Hampshire, a
typical example of a pressurized water reactor. The construction of this station
began in the mid-1970s during the period of the largest growth of nuclear fission
energy, but it did not become operational until 1990. The variation in interest in
nuclear power is illustrated in figure 1.22, where the number of new reactor
construction starts are plotted as a function of year from 1954 to 2015. After
around 2000, there has been a worldwide increase in the number of new nuclear
reactors, but this activity must be balanced against aging reactors that have been
decommissioned. In fact, as shown in figure 1.23, the total number of nuclear power

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Figure 1.21. Seabrook Nuclear Generating Station in Seabrook, New Hampshire. This facility is a 1246 MW
pressurized water reactor. Construction began in 1976 and the station became operational in 1990. Image:
Richard A Dunlap.

Figure 1.22. The number of new nuclear power station construction starts per year from 1954 to 2015. This
image (Ypna 2013) has been obtained by the author from the Wikimedia website where it was made available
under a CC BY-SA 3.0 licence, https://creativecommons.org/licenses/by-sa/3.0/deed.en. It is included within
this chapter on that basis. It is attributed to Ypna.

reactors and the total nuclear generating capacity have changed very little since the
late 1980s.
When assessing the future contribution of nuclear fission to our energy supply, it
is necessary to consider resource availability, safety, security, and waste disposal, as
discussed below.
Fission energy resources—The vast majority of operational fission power
reactors worldwide are thermal neutron reactors. These reactors utilize energy
derived from the fission of 235U, which accounts for only 0.72% of naturally
occurring uranium. At present, nuclear power provides about 11% of all electricity
worldwide and this represents about 4% of all energy. A simple analysis based on the

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Figure 1.23. Installed global nuclear reactor capacity, along with actual generated output (top) and number of
operational nuclear reactors and reactors under construction (bottom), from 1955 to 2007. This image (Rhode
2007) has been obtained by the author from the Wikimedia website where it was made available under a CC
BY-SA 3.0 licence, https://creativecommons.org/licenses/by-sa/3.0/deed.en. It is included within this chapter on
that basis. It is attributed to Robert A Rohde.

reserve-to-production ratio provides a lifetime for the remaining uranium resources

of about 53 years (Dunlap 2021). Thus, under these conditions, we cannot expect
nuclear fission power to provide a long-term solution for carbon-free electricity. A
fast breeder reactor can use 238U (which accounts for the remaining 99.28% of
naturally occurring uranium) or naturally occurring thorium-232 (232Th) as a fuel.
At present, there are two operational commercial fast breeder reactors, compared to
about 450 thermal neutron reactors worldwide. Certainly, expanding the use of fast
breeder reactors would greatly increase the longevity of fission power by enabling
the use of more plentiful fuels.
Safety—There have been numerous incidents and accidents at commercial power
reactor facilities as a result of equipment failure or human error. The three most
serious and well-known accidents are those that occurred at Three Mile Island in
1979, Chernobyl in 1986, and Fukushima in 2011. These accidents are certainly
cause for concern, and there are no guarantees that similar or even more serious
events will not happen in the future. However, current fission reactor designs are
much improved over the older designs that were involved in these accidents and have
implemented technology to drastically reduce the possibility of such future events.
Security—Nuclear fission reactors utilize fuel containing fissile material, partic-
ularly 235U. Such materials can be utilized for the construction of nuclear weapons.
It is therefore important for international agencies, such as the International Atomic
Energy Agency (IAEA) to monitor uranium production programs worldwide in

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order to distinguish between activities related to peaceful energy production and

those related to the preparation of fissile material for nuclear weapons.
Waste disposal—Perhaps the greatest concern for the continuation of nuclear
fission power is the question of waste disposal. The by-products of the fission
process are radioactive and can present a significant health risk for many tens or
hundreds of years. Thus, the spent reactor fuel must be stored safely until the
activity level has decreased to a point where it is no longer a danger. A portion of
the spent fuel can be reprocessed and reused as reactor fuel, although this may
cause additional security concerns related to the possible illicit acquisition of
weapons-grade material. At present most spent fuel is stored in sealed containers in
underground locations. It is of interest to note the quantity of waste that is
produced by nuclear reactors. Since around 1970, the total amount of high-level
radioactive waste that has been generated by all of the fission reactors worldwide is
about 400 000 tonnes. About 100 000 tonnes of this has been reprocessed, leaving
about 300 000 tonnes for disposal. This corresponds to the volume of a cube about
40 m on a side.
As noted previously, nuclear fission reactor construction has decreased consid-
erably since its high point in the early 1970s (see figure 1.22). Although the nuclear
accidents at Three Mile Island (in 1979) and Chernobyl (in 1986) were a factor in
swaying public opinion against nuclear power, a fairly continuous decline from the
mid-1970s to the early 2000s can be seen in the figure. Recent analyses, however,
(see, for example, Ritchie (2020) and the references therein) have concluded that
nuclear fission energy is among the safest low-carbon options for future electricity
generation (as well as one of the least carbon producing). Since around 2000, there
has been some growth in new reactor starts, including reactors with improved safety
features, as well as fast breeder reactors.

1.6.5 Biofuels
Biofuels can contribute to future transportation energy needs in two ways: first, as a
fuel for power stations that contribute to grid power, which can then be used for
battery electric vehicles (as discussed in chapter 2) or vehicles that utilize electrofuels
(as discussed in chapter 3) and second, for direct use in vehicles using internal
combustion engines or fuel cells.
The use of incinerators to burn municipal solid waste as an alternative to other
means of waste disposal, such as landfill, has been in use for well over a hundred years.
In the later part of the 20th century the use of heat from such combustion became of
interest for the production of electricity, and today there are over 500 such facilities
worldwide. This process is referred to as waste-to-energy (WTE), although the term
WTE is also used to designate the process of converting solid waste to liquid or
gaseous fuels (see chapter 4). Figure 1.24 shows a WTE plant in northeast England
that burns 390 000 tonnes of municipal waste per year. The overall environmental
benefits of WTE are uncertain (see Dunlap (2019)), although the production of carbon
dioxide from the combustion of waste is generally considered to be a desirable
alternative to the production of methane during its decomposition in a landfill site.

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Figure 1.24. Teesside Energy from Waste Plant is a WTE power station in Haverton Hill, UK. It began
operation in 1998 and has a capacity of 29.2 MW. This image (Fintan264 2009) has been obtained by the
author from the Wikimedia website where it was made available under a CC BY-SA 3.0 licence, https://
creativecommons.org/licenses/by-sa/3.0/deed.en. It is included within this chapter on that basis. It is attributed
to Fintan264.

In recent years, wood has been used as a fuel for electricity generation. In this
case, wood is either burned directly to produce heat for a steam boiler or it is heated
to produce a gaseous fuel by gasification, which is then burned (see section 4.6).
Wood fuel typically takes the form of wood chips or waste from construction or land
clearing. Wood-fired power stations may be purpose-built facilities or may be former
coal-fired power stations that have been converted to burn wood. The Bay Front
Generating Station in Ashland, Wisconsin is an example of the latter category of
facility and is illustrated in figure 1.25. Wood-fired power stations tend to be small
(typically tens of MW) compared to coal-fired stations, which usually have
capacities in the range of hundreds of MW to 1 GW.
The alternative approach to using biomass for transportation energy is the
production of a liquid or gaseous fuel that can be used directly in an internal
combustion engine or to power a fuel cell. This approach includes the use of
purpose-grown crops, such as corn, to produce ethanol or the use of municipal or
agricultural waste to produce biogas. Details of the possible use of biomass to
produce transportation fuel are presented in chapter 4 for road vehicles and in
chapter 5 for other modes of transportation.

1.6.6 Carbon footprints of energy technologies

As noted in the sections above for various sustainable electricity options, there are
some potential environmental concerns for a number of these technologies. These
environmental concerns include the potential contribution of these technologies to

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Figure 1.25. The Bay Front Generating Station in Ashland, Wisconsin is a 28 MW facility that was converted
from burning coal to burning waste wood in the early 2010s. A pile of wood fuel is located to the left of the
facility. This image (Chris857 2018) has been obtained by the author from the Wikimedia website where it was
made available under a CC BY-SA 4.0 licence, https://creativecommons.org/licenses/by-sa/4.0/deed.en. It is
included within this chapter on that basis. It is attributed to Chris857.

global greenhouse gas emissions. For example, as noted above, potential defores-
tation can contribute to greenhouse gases by eliminating a component of natural
carbon sequestration. It is also possible that carbon dioxide or other greenhouse
gases such as methane may be emitted during the manufacture of infrastructure, and
this contribution should be amortized over the lifetime of the facility. In order to
fully understand the greenhouse gas implications of different technologies, it is
necessary to undertake a life-cycle analysis. This analysis evaluates the greenhouse
gas contribution during all stages of infrastructure construction, system operation,
and eventual end-of-life processing. In order to account for the fact that different
aspects of the system life may produce different greenhouse gases, the results of this
analysis are often given in terms of the equivalent concentration of carbon dioxide in
accordance with the relative infrared absorption of each gas, as given in table 1.7.
Table 1.12 shows the results for greenhouse gas emissions per unit electrical energy
generated as determined by life-cycle analysis for different electricity generation
technologies. As different facilities utilizing the same energy technology may be of
different designs and sizes and may be at different geographical locations, there is a
range of carbon dioxide emissions associated with each technology. The table gives
minimum, median, and maximum values obtained from the life-cycle analyses.
It is clear from the data in the table that all ‘carbon-free’ electricity sources are not
created equal from an environmental standpoint, although most have a greenhouse
gas footprint that is smaller than that of either natural gas or coal by an order of
magnitude. Two notable exceptions to this trend are biofuels and the maximum

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Table 1.12. Life-cycle analysis of equivalent CO2 greenhouse gas emissions for different electricity-producing
technologies. Data adapted from Krey et al (2014) and Schlömer et al (2014).

CO2 emissions (g kWh−1)

Energy source Minimum Median Maximum

Hydroelectric 1 24 2200
Wind (onshore) 7 11 56
Wind (offshore) 8 12 35
Solar (photovoltaic) 18 48 180
Biofuels 130 230 420
Geothermal 6 38 79
Nuclear fission 3.7 12 110
Natural gas 410 490 650
Coal 740 820 910

amount of greenhouse gases that can be produced by hydroelectric energy. Biofuels

can represent a very diverse collection of different technologies, and fuels can be
produced from very different feedstocks using very different technologies. A detailed
analysis of different biofuels has been presented by Scharlemann and Laurence (2008).
While hydroelectric facilities are generally very environmentally friendly, the discussion
above has pointed out that high head facilities with large reservoirs, particularly those
in tropical regions, may be a source of excessive atmospheric greenhouse gas
contributions. This situation is responsible for the extreme maximum value given in
the table, which shows that the adverse environmental effects of such installations can
exceed those of conventional fossil fuel use. It might be noted that many of the early
hydroelectric facilities were constructed at a time when the addition of significant
amounts of economical electrical generating capacity was a more important consid-
eration than environmental sustainability. It is significant that the median value of the
greenhouse gas emissions for hydroelectric facilities falls well within the range of values
for other renewable energy resources, which shows that hydroelectric power is, for the
most part, a suitable source of renewable and sustainable electricity.
A related concept is that of embodied energy (see, for example, Thomitzek et al
(2019)), which is the total energy required to produce a manufactured item. This
includes the energy utilized in the mining and production of the component
materials, as well as the energy involved in the manufacturing process itself. This
concept is useful in understanding the overall energy needs for different technologies
and is a useful tool for material selection and for improving manufacturing
techniques. In the case of transportation, embodied energy is one factor in a
comparison of the overall environmental impact of different technologies.

1.6.7 Utilization of carbon-free electricity

It is clear that the use of electricity generated by carbon-free technologies has
increased considerably in recent years. However, it still remains a small fraction of

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Table 1.13. Typical capacity factors for some energy technologies. The data are
average values for the United States for 2019 and are from the U.S. EIA (2020a).

Energy source Capacity factor (%)

Hydroelectric 41.2
Wind 34.3
Solar 24.1
Biofuels 61.0
Geothermal 69.6
Nuclear fission 93.4

that produced from fossil fuels. In evaluating the importance of alternative energy
sources for the generation of electricity, it is important to understand the
distinction between installed capacity and actual electricity generated. This is
because all forms of electricity production do not produce electricity at the
maximum capacity all of the time. This is particularly the case for many types
of renewable energy. The ratio of the actual energy output from a device to the
energy that would be produced if it operated continuously at its maximum output
is referred to as the capacity factor (often quoted as a percentage). Table 1.13 gives
some typical capacity factors for some carbon-free electricity generation technol-
ogies in the United States. Thus, in assessing the overall ability of an energy source
to contribute to our energy needs, the capacity factor as well as the total installed
capacity must be considered. Some comments, as given below, will help to put this
information in context.
Although we might think of hydroelectric facility output as a constant quantity,
there are actually substantial seasonal fluctuations in hydroelectric output due to
fluctuations in river flow rate. At times of reduced flow, the generator facility will
provides less than the maximum output. The maximum capacity of the facility can
be designed to optimize the actual output, but there will always be times of less than
maximum capacity, leading to a capacity factor of less than 100%. These fluctua-
tions in river flow are more significant for run-of-the-river power stations because
they have no reservoir, and this leads to a typically lower capacity factor for these
facilities. As a general rule, less than half of the installed capacity of hydroelectric
facilities translates into actual energy produced.
Wind velocities typically show both daily as well as seasonal variability. This
leads to variability in the generator output and capacity factors of less than 100%.
It is interesting to note that wind power is proportional to the cube of the wind
velocity, thus it is important to design the wind turbine so that it is efficient during
periods of large wind velocity, as this is the time when the most wind energy is
available. The range of operating velocities for the turbine must match the wind
conditions at the site in order to optimize the capacity factor. Generally, wind
turbines positioned offshore have better capacity factors because the wind velocities
are more consistent than they are on land and the turbine can be designed to take
advantage of the prevailing wind conditions.

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 Transportation Technologies for a Sustainable Future

Photovoltaics utilize solar energy that has considerable temporal variations.

There are several factors that affect the power output of a photovoltaic panel. These
include:
• the latitude;
• the day of the year;
• the time of day;
• the orientation of the panel.

These factors determine the angle of incidence of sunlight on the panel as a function
of time. In addition, local weather conditions can influence the amount of sunlight
that is incident on the panel. Tracking collectors that follow the Sun to ensure that
sunlight is incident normal to the surface of the panel improve the capacity factor
but at the expense of significant additional cost and design complexity.
As illustrated in table 1.13, nuclear energy shows, by far, the greatest capacity
factor. In this case the loss of capacity results largely from periods of maintenance
and refueling.
The relative importance of different electricity generation technologies is,
perhaps, better represented by the actual amount of electrical energy generated
over the course of a year, rather than the installed capacity. The electrical energy
generated is a measure of both the installed capacity and the average capacity factor.
Table 1.14 shows the percentages of electricity that were generated worldwide in
2017 by different generating technologies. This table shows that fossil fuels are
clearly the leading source of electricity worldwide. The relative percentages for
renewable electricity and nuclear are the result of their installed capacities and their
capacity factors, as described above.
It is important for the development and incorporation of new electricity
generation technologies that they are, at least in the long run, economically viable.
Based on an analysis of low-carbon technologies, the cost per unit electricity
generated has been estimated by the United States Energy Information
Administration. The results of their estimates for new facilities entering service in

Table 1.14. Percentages of world electricity generated by different sources in

2018. ‘Other’ includes tidal and solar thermal. Calculated from information
available at www.iea.org/data-and-statistics?country=WORLD&fuel=Electricity
%20and%20heat&indicator=ElecGenByFuel.

Energy source Fraction of electricity (%)

Fossil fuels 63.9

Hydroelectric 16.2
Nuclear 10.1
Wind 4.8
Solar (photovoltaics) 2.1
Biofuels 1.9
Geothermal 0.3
Other 0.2

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Table 1.15. Estimated average cost of electricity in the United States

produced by various methods for new facilities entering service in 2025
(in 2019 USD). Government tax incentives are not included. Data adapted
from EIA (2020b, 2020c).

Source Electricity cost ($ kWh−1)

Solar (photovoltaics) 0.036

Geothermal 0.037
Wind (onshore) 0.040
Hydroelectric 0.053
Natural gas 0.067
Coal (advanced) 0.076
Nuclear fission (advanced) 0.082
Biofuels 0.095
Wind (offshore) 0.122

2025 are summarized in table 1.15. Solar photovoltaics and wind (at least onshore)
are seen in the table to be among the most economical electricity-producing
technologies. Thus, the two renewable technologies that have shown significant
growth in recent years are likely to continue to show growth.

1.6.8 The need for increased energy storage capacity

It is clear from the previous discussion that both wind and solar energy exhibit
fluctuations on both a daily timescale and longer timescales, such as seasonal
variations. Similarly, hydroelectric energy shows some seasonal fluctuations. It is
clear that the widespread use of these energy sources requires careful consideration.
On a seasonal scale, average wind velocities tend to be lower in the summer (in the
Northern Hemisphere) and higher in the winter. The opposite is true for solar
energy. In many cases, hydroelectric energy tends to peak in late spring when river
flows are at their largest due to runoff from melting snow. Thus, these natural
seasonal fluctuations in renewable electricity tend to even out some of the seasonal
fluctuations in capacity if a suitable mix of different energy sources is implemented.
It is, however, the short-term variations in renewable electricity that require the
greatest consideration in order to fulfill our electricity needs and, in particular, to
satisfy baseload requirements. Three factors also exacerbate this situation: first, as
noted above, an increase in total energy consumption due to population increase and
increased industrialization; second, the shift away from fossil fuels and towards
renewable energy sources that will be necessitated by resource limitations and
environmental factors; finally, the likelihood of required increases in grid capacity in
order to accommodate changing transportation needs, as discussed in detail in
chapter 6.
All of these factors point to the need to develop energy storage facilities in parallel
with the development of renewable energy resources. The major grid-scale electrical
storage approaches are pumped hydroelectric storage and battery storage.

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 Transportation Technologies for a Sustainable Future

Considerable pumped hydroelectric storage is already in place, and in recent years

there has been a considerable expansion of battery electrical storage worldwide.
Other approaches that might be applicable to some specific situations include
compressed-air energy storage, superconducting magnets, and hydrogen.
Compressed-air energy storage requires specific locations where substantial under-
ground chambers are available to store compressed air; at present there are two such
major facilities, one in Germany and one in the United States. Both facilities utilize
the combustion of natural gas to heat the air as it expands during energy recovery
and are, therefore, not carbon-free technologies. The use of superconducting
magnets is becoming common as a means of grid stabilization and small-scale
grid storage. Future developments in high-temperature superconducting magnet
technology may make this approach compatible with large-scale grid storage.
Hydrogen may be appropriate for specific applications such as electricity storage
for remote locations. The use of hydrogen as an energy storage medium is discussed
in detail in chapter 3. Dunlap (2020b, 2020c) recently provided a review of energy
storage technologies.

1.7 Atmospheric carbon removal

There are two approaches that we can take in order to reduce greenhouse gas
concentrations in the atmosphere. The best approach would be to eliminate the
sources of anthropogenic greenhouse gases by eliminating the use of fossil fuels. This
requires the total replacement of our fossil fuel energy infrastructure with carbon-
free energy technologies.
Until fossil fuel use is eliminated entirely, it will be possible to capture carbon
dioxide and remove it from the atmosphere. Thus far, this strategy has primarily
been used to capture and sequester carbon dioxide that is produced by fossil fuel
(e.g., coal-fired) power plants, or other facilities such as geothermal wells, where
substantial amounts of carbon dioxide are released at a single location. More
recently, some facilities have been constructed for the direct air capture of carbon
dioxide. In this case, carbon dioxide that is not associated with any specific source is
removed from the atmosphere. Carbon dioxide that is captured can either be
sequestered by one of the methods described below or it can be utilized for the
production of synthetic fuels, such as e-methanol, as described in section 3.10. In the
latter case, the process returns the carbon to the atmosphere when the synthetic fuel
is burned. Thus, the process is overall carbon-neutral and there is no net change to
the atmospheric carbon concentration. The most important carbon sequestration
methods are described below.

1.7.1 Ocean storage

The longevity of ocean storage is uncertain. Studies have shown that carbon dioxide
dissolved in the oceans may diffuse back into the atmosphere on a timescale of a few
hundred years. In addition, carbon dioxide dissolved in seawater lowers the pH,
leading to ocean acidification and the accompanying environmental consequences as
described above.

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 Transportation Technologies for a Sustainable Future

1.7.2 Underground storage

This approach requires the identification of appropriate underground caverns. One
possibility is depleted oil and natural gas wells. At present, carbon dioxide is
routinely pumped into existing oil wells. This provides storage for some greenhouse
gas emissions but is mainly done in order to increase the efficiency of oil extraction.
The longevity of carbon dioxide storage underground requires detailed
investigation.

1.7.3 Chemical storage

Carbon dioxide may be stored in a solid form using reactions such as
CO2 + CaO → CaCO3
and
CO2 + MgO → MgCO3.
At present, world carbon dioxide emissions related to energy production are
about 33 Gt (or 3.3×1013 kg) per year. To sequester all of this carbon dioxide would
require about 42 Gt (1.3×1010 m3) of CaO or about 30 Gt (8.4×109 m3) of MgO.
This means that about 10 km3 of material would have to be processed and stored.
Only about one third of carbon emissions are from power stations, so from a
practical standpoint about 3 km3 of storage material would be needed to cover this
component of carbon emissions. This is still a huge and expensive undertaking. An
additional complicating factor is that the reactions above do not proceed fast
enough to be useful at room temperature. The sequestering material must be heated
to fairly high temperatures, thereby increasing the complexity and cost of the process
and also requiring the input of additional energy.
The final approach to dealing with atmospheric greenhouse gases is to capture
them after they are released to the atmosphere. There are several potentially viable
approaches for removing greenhouse gases, particularly carbon dioxide, which are
already present in the atmosphere. These methods have recently been reviewed by
Geden and Schenuit (2020) and are discussed briefly below.

1.7.4 Reforestation or afforestation

Reforestation refers to the growth of new trees in areas where the number of trees
has diminished, while afforestation refers to establishing trees in areas where they
previously did not grow. This may be done for the purpose of sequestering carbon
dioxide from the atmosphere. Estimates of the effectiveness of this approach suggest
that extensive reforestation could sequester up to 3.6 Gt CO2 per year.

1.7.5 Humus
Humus is the component of soil that is produced by the decomposition of plant
material by microorganisms. Humus is the major organic fraction of soil that is
without the distinct cellular structure of plant matter. Humus is capable of storing

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 Transportation Technologies for a Sustainable Future

significant quantities of carbon, but this carbon is typically released during

cultivation using modern agricultural techniques. The development of appropriate
agricultural methods could allow humus to retain 2 Gt–5 Gt CO2 per year.

1.7.6 Biochar
Biochar is a high-carbon charcoal that is produced by the pyrolysis of biomass.
Pyrolysis is the heating of a material in a low-oxygen or oxygen-free environment
and this process produces a mixture of biochar, bio-oil, and syngas. The ratio of the
three products can be varied by adjusting the heating temperature. Temperatures in
the range of about 400 °C to 500 °C optimize biochar production. Syngas, which is a
mixture of mainly hydrogen and carbon monoxide, may be used as a fuel for the
production process. Biochar has been used for many years to increase the
agricultural productivity of soil. It is also effective at sequestering carbon dioxide
from the atmosphere, and recent experiments have shown that the widespread use of
biochar in agriculture could remove 0.5 Gt–2 Gt of CO2 per year.
The amount of carbon dioxide that can be removed from the atmosphere by these
methods can be put in context by comparing it with the current world annual carbon
dioxide emissions of 33 Gt CO2. Thus, the amount of carbon dioxide that can be
removed from the atmosphere by the methods described above would amount to a
maximum of only about one third of our current emissions. It is also important to
see how these emissions and the possibility of mitigating them compare with the
total atmospheric carbon that is consistent with minimizing the effects of global
climate change. The Paris Agreement (see UNFCCC (2015)) specified that global
temperatures should not increase by more than 2 °C above pre-industrialized levels
and, if possible, that the increase should be less than 1.5 °C. There have been
numerous studies of the relationship between total carbon dioxide in the atmosphere
and global temperatures in order to estimate the remaining atmospheric carbon
budget that would likely limit global temperature increases to 1.5 °C. Kriegler et al
(2018) have recently reviewed the literature on this topic. Remaining carbon dioxide
budgets (adjusted to 2020) range from −248 Gt CO2 to 752 Gt CO2 in various recent
studies. The negative value indicates that the total atmospheric carbon dioxide has
already exceeded the amount that is consistent with the requirements of the Paris
Agreement. The mean value resulting from these studies gives a remaining carbon
dioxide budget of around 234 Gt CO2 (adjusted to 2020), corresponding to about
seven years at the current rate of emission. This is consistent with the estimated
remaining carbon dioxide budget of of 202 Gt CO2 (adjusted to 2020) provided by
the Intergovernmental Panel on Climate Change (IPCC 2014). Clearly, continuing
along our current path of extensive fossil fuel use beyond about 2030 will make it
difficult to maintain atmospheric carbon dioxide at levels consistent with minimizing
the adverse effects of climate change.

1.8 The way forward

It is clear from the above discussion that the longevity of fossil fuels is limited, but
that it is essential for environmental reasons to transition to low-carbon energy

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 Transportation Technologies for a Sustainable Future

sources as soon as possible. Since our overall energy consumption is expected to

increase, as shown in figure 1.4, any decrease in fossil fuel energy must be more than
compensated for by the implementation of alternative energy resources. Since oil,
natural gas, and coal serve different purposes to some extent, their impacts on
alternative energy technology development should be viewed somewhat independ-
ently. Oil, for example, is used extensively for transportation, while coal is used
primarily for electricity generation, and natural gas is used for electricity generation
as well as residential heating and industrial processes.
The relative importance of dealing with different fossil fuels from an environ-
mental standpoint is summarized by the information in table 1.16. In this analysis,
we have taken the idealized compositions of coal, gasoline, and natural gas to be
C (carbon), C8H18 (octane) and CH4 (methane), respectively. These fuels contain
additional components, but this simple assumption gives us considerable insight into
their importance for greenhouse gas emissions. The combustion processes for these
three fuels are as follows:
carbon: C + O2 → CO2

octane: 2C 8H18 + 25O2 → 16CO2 + 18H2O

methane: CH 4 + 2O2 → CO2 + 2H2O.

The table shows the energy content of each fuel and the amount of carbon dioxide
emitted per unit energy generated. Clearly, coal produces the greatest greenhouse
gas emissions per unit energy, followed by gasoline and then natural gas. There is a
simple intuitive way of looking at this fact. The energy generated by the combustion
of these different fuels can be thought of as the sum of the energy generated by the
oxidation of the carbon component plus the energy generated by the oxidation
of the hydrogen component. The oxidation of carbon produces carbon dioxide,
while the oxidation of hydrogen produces water. Therefore, the amount of carbon
dioxide produced per unit energy is inversely related to the hydrogen-to-carbon ratio
of the fuel.
As shown in table 1.16, the combustion of coal produces about 2.3 times as much
carbon dioxide per unit energy generated as natural gas. This certainly provides
motivation to phase out the use of coal sooner than natural gas. This has been the
selling point for many governments in favor of the development of natural gas
infrastructure to replace coal infrastructure. Certainly, from a greenhouse gas

Table 1.16. Carbon dioxide emissions per unit energy for different fossil fuels. Energy content from Dunlap
(2019).

Ideal H/C Energy Molecular

Fuel composition ratio content (MJ kg−1) mass (g mol−1) (kg CO2)/(MJ)

Coal C 0:1 32.8 12 0.112

Gasoline C8H18 2.25:1 46.8 114 0.066
Natural gas CH4 4:1 55.8 16 0.049

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standpoint, this is advantageous but not as advantageous as moving to carbon-free

energy sources, such as solar, wind, or even nuclear. Attempts to rationalize the
continued extensive use of coal by promoting ‘clean coal’ technology may reduce
particulate matter and sulfur dioxide pollution but have no effect on greenhouse gas
emissions and are motivated by economic rather than environmental concerns.
The use of carbon-free energy sources for transportation is essential in order to
eliminate the adverse effects of global climate change. This could include the use of
renewable sources or nuclear power for electricity generation as well as the direct use
of biofuels. However, as pointed out in chapter 6, a detailed analysis of environ-
mental factors, as well as an evaluation of the efficiency of different transportation
technologies, is essential when choosing the most viable approach.

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Full list of references

Chapter 1
BP 2020 Statistical Review of World Energy, 69th edn (London: BP). Available online at: www.bp.
com/en/global/corporate/energy-economics/statistical-review-of-world-energy.html
BP 2021 Statistical Review of World Energy, 70th edn (London: BP). Available online at: www.bp.
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