The purpose of this lesson is for you to review key concepts from Lesson 1 (Energy and Sustainability) of EMSC 240N. I strongly encourage you to at least browse through Lesson 1 [1] of EMSC 240N, though that is not required.

Learning Outcomes

By the end of this lesson, you should be able to:

• provide a basic description/definition of the following terms/concepts: energy, thermodynamics, the First Law of Thermodynamics, energy efficiency, renewable energy, non-renewable energy, carbon-free, carbon neutral, sustainability, Brundtland Commission, 3 Es, intergenerational equity, and systems thinking;
• identify examples of the above concepts in contemporary culture;
• apply the above concepts in analyses of contemporary issues;
• identify and describe different forms of energy;
• describe how energy can be converted from one form to another; and
• analyze energy-focused charts and graphs.

Lesson Roadmap

Questions?

If you have any general course questions, please post them to our HAVE A QUESTION discussion forum located under the Discussions tab in Canvas. I will check that discussion forum regularly to respond as appropriate. While you are there, feel free to post your own responses and comments if you are able to help out a classmate. If you have a question but would like to remain anonymous to the other students, email me through Canvas.

If you have something related to the material that you'd like to share, feel free to post to the Coffee Shop forum, also under the Discussions tab in Canvas.

Thermodynamics is defined by NASA [2] as "the study of the effects of work, heat, and energy on a system." Any time you discuss energy transfer, assess the efficiency of a piece of equipment, or analyze the conversion of energy from one form to another, it involves thermodynamics.

Energy and Forms of Energy

Energy

Energy is defined as "the ability to do work," and work is the transfer of energy or the application of force across a distance. If this were a Physics or Thermodynamics course, we'd be more concerned about work, but for better or worse it is not, so we will stick to focusing on energy. For the purposes of this course, there are a few important things to remember about energy:

• Energy "makes things happen". Energy is required for a computer screen to light up, a car to move, the sun to make plants grow, and your brain to comprehend this sentence. In short, energy is involved in everything that humans can sense (sights, sounds, movement, thoughts, etc.) and many things that humans cannot sense (bacteria digesting waste, atoms holding together, mountains building, etc.). Everything physical around us either has or uses energy.
• Energy cannot be created or destroyed. It can only change forms. This is the First Law of Thermodynamics, sometimes known as the Law of Conservation of Energy. For a summary of the different forms of energy, see below.
• Since energy is the ability to do work, it can be quantified. More energy provides the ability to do more work; less energy provides the ability to do less work.
• Energy can be expressed in a number of different units, and one energy unit can be converted to any other energy unit as long as the unit conversion is known. More on this later in the course.

Forms of Energy

The following discussion of energy forms is taken nearly word-for-word from EM SC 240N. Direct quotes are from this reading from the National Energy Education Development (NEED) Project [3], which you are welcome, but not required, to read. 

The two categories of energy are potential and kinetic. Potential energy is stored energy and kinetic energy is energy in motion. The forms of energy are as follows:

Forms of Potential Energy

• Chemical energy is stored in the bonds between atoms and molecules. Common examples include the energy stored in food, fossil fuels, and batteries, but anything that is made of more than one atom has chemical energy. Practically speaking, everything made of matter has chemical energy.
• Mechanical energy is "stored in objects by the application of a force." Common examples include a wound spring, a stretched out rubber band, and compressed air.
• Nuclear energy is "stored in the nucleus of atoms," and is what holds the nucleus together. Anything made of matter has nuclear energy, but most of the nuclear energy converted by humans comes from the fission (splitting) of uranium atoms and is used to generate electricity. Most of the energy used by humans, however, comes from nuclear fusion (fusing of atoms) in the sun.
• Gravitational energy is "energy of position or place." Common examples include water (e.g., in a river) at a high(er) elevation, a ball sitting on top of a hill, and you sitting on your chair right now. If you see naturally flowing water, it is moving downhill (tides and waves notwithstanding), so hydroelectric energy (electrical energy generated from flowing water) starts out as gravitational potential energy.

Forms of Kinetic Energy

• Electrical energy is "the movement of electrons." The most common example of this is electricity moving through a wire, but discharging static electricity and lightning are also electrical energy.
• Radiant energy is also called electromagnetic energy. It travels in transverse waves and is produced by anything with a temperature above absolute zero. Common examples include light, sunlight, microwaves, radio waves, and radiant heat emanating in all directions from a fire.
• Thermal energy is the vibration of the molecules of a substance. As an object or substance gets heated up, the molecules vibrate more rapidly; as it cools, they slow down. Humans cannot see this vibration because it happens at a molecular level, but we can feel it, or at least the results of it. Have you ever accidentally touched a hot stove and gotten burned? That unpleasant sensation is the result of the quickly vibrating molecules of the stove imparting their thermal energy into your skin. Anything above absolute zero has thermal energy, so it is all around us all the time, including everything you see right now.
• Motion energy is the energy in moving objects. Anything with mass that is moving has motion energy. Moving cars, flowing water, a falling object, and even wind (air is made of matter, after all!) are common examples.
• Sound energy moves in waves and is produced by vibrating objects. When you hear something, it is the result of the bones in your ear absorbing and converting these waves into motion energy, which your brain then interprets as sound. Despite what you may have heard, if a tree falls in the woods and there is no one there to hear it, it does generate a sound! Well, it generates sound energy, at least.

Differentiating the various forms of energy is usually straightforward, but I have noticed that people often confuse thermal and radiant energy. This is probably because most people associate "thermal" with "heat," so when something generates heat, it is assumed that thermal energy is being released. Please keep in mind that radiant energy travels in waves, and is released by everything above absolute zero (humans have never observed absolute zero). Radiant energy emanates in all directions from everything, and the hotter the object, the more and more intense radiant energy it emits.  All radiant energy is invisible to the human eye except for energy in the visible spectrum. Thermal energy, on the other hand, is energy in the vibrating molecules of a substance. Again, everything above absolute zero has thermal energy, i.e., its molecules are vibrating. Thermal energy is contained within the molecule(s) and is not emitted.

Figure 1.1: As the metal of this pellet furnace heats up, the metal gains thermal energy. However, most of the heat that gets to the room is released as radiant energy, which emanates in all directions from the hot furnace. Incidentally, the brick hearth also heats up as it absorbs the radiant energy from the furnace, increasing its thermal energy. It slowly releases this through radiation after the furnace is turned off. Bricks have a high thermal mass, and so are slow to warm up and cool down.

Credit: Mike, CC BY-ND 2.0 [4]

Energy Transfer

Energy is constantly changing forms all around you (and everywhere else on earth) all of the time. All forms of energy can end up as all other forms of energy, and recall that the First Law of Thermodynamics dictates that all energy, irrespective of its form, comes from somewhere else. Again, the following is taken almost word-for-word from EM SC 240N.

We could go on and on. But as you probably know, these are all examples of kinetic energy. There are also a number of types of potential energy around you. Think of some examples of potential energy around (and in) you right now. You are able to move and think because of chemical (potential) energy inside of your body. In fact, everything around you has chemical potential energy. Any object on the wall, on a table, attached to the ceiling, or just above the ground has gravitational (potential) energy because it is above the ground. There is also nuclear (potential) energy in all matter because all matter has at least one nucleus. Again, we could go on and on, but the point is that everything around you has potential energy, and thus has the ability to do work, i.e., “to make things happen.”

All of the examples of energy that were noted above came from somewhere else. The light coming from a light bulb is converted from electrical energy running through a wire. The heat radiating from non-living things around you was absorbed from another source such as sunlight or the heating system of the building. The motion and electrical energy your body has right now come from the chemical energy inside of your body. The gravitational energy of things around you came from motion energy required to lift the objects. And so on. And recall that each time energy was transferred, work was done.

Energy Efficiency

Efficiency is an often used term when discussing energy, e.g., "I have an efficient car," "How efficient is your furnace?", and "The average efficiency of a coal-fired power plant is around 33%." Though the term is thrown around a lot, it has a specific meaning. Energy efficiency is the amount of useful output per unit of input. The "useful" part of that definition is important since the First Law of Thermodynamics requires that all energy that goes into something must go somewhere.

• For example, the average internal combustion engine is 28% - 32% efficient, according to the U.S. Department of Energy [5] (U.S. DOE). This means that of all the energy that goes into the engine (chemical energy in the gasoline), only 28% - 32% results in motion energy to move the wheels and electrical energy to operate the various electrical components. Most of the rest is wasted as heat. (Note that only 16% - 25% of the chemical energy ends up actually moving the wheels due to the drivetrain and other losses.)
• Modern natural gas furnaces can be upwards of 97% efficient, which means that 97% of the chemical energy in the natural gas is converted to useful heat that can be delivered to the building, with the remaining 3% lost as waste heat and latent heat in the exhaust. (It is not uncommon for 30% of this energy to be lost in the ducts, according to the U.S. DOE [6], by the way.) Older natural gas furnaces often operate in the 70% - 80% efficiency range. 
• According to the U.S. EIA [7], the average coal-fired power plant in the U.S. is about 33% efficient, which means that only about 33% of the chemical energy in the coal ends up as electrical energy. Almost all of the rest is wasted as heat. If you are so inclined, see the video below for a thorough explanation and animation of how a coal-fired power plant works.

All energy-using (and generating) technologies have an efficiency - TVs, light bulbs, solar panels, cell phones, wind turbines, airplane engines, electric motors, you name it. One important aspect to know is that when energy is converted, it is physically impossible to convert all of the energy into useful output. In other words, it is not possible for anything to be 100% efficient. This is dictated by the Second Law of Thermodynamics. The Second Law has other implications, but they are not important in the context of this course. If you'd like to learn more about the Second Law, see the video below and/or this [8]link.

Renewable and Non-Renewable Energy

Renewable energy is defined by the U.S. Environmental Protection Agency [9] thus: "Renewable energy includes resources that rely on fuel sources that restore themselves over short periods of time and do not diminish." Non-renewable energy is energy that cannot restore itself over a short period of time and does diminish. It is usually easy to distinguish between renewable and non-renewable, but there are some exceptions (more on that in a minute).

Non-Renewable Energy

Fossil Fuels

Fossil fuels are fossilized hydrocarbons made from organic material. They are considered "fossilized" because they take millions of years to form, they are hydrocarbons because they are made mostly of hydrogen and carbon, and of course organic material refers to living or recently living things.

The three primary fossil fuels used in the world are coal, oil, and natural gas. (As noted in EM SC 240N, oil and natural gas are technically made up of multiple hydrocarbons, but they are each conventionally referred to as individual hydrocarbons.) Feel free to read through the U.S. Energy Information Administration's (U.S. EIA's) summaries of coal [10], oil [11], and natural gas [12] before reading the summaries below.

• Coal is formed when organic material (almost entirely plants) dies and sinks to the bottom of swampy areas, and is subsequently buried under sediment for millions of years. There are four main types of coal, listed from lowest to highest heat content (i.e., lowest to highest chemical potential energy per ton): lignite, sub-bituminous, bituminous, and anthracite. Anthracite coal is the shiny black rock that most people probably think of when they think of coal, and the rest are shades of dull black or brown. Anthracite has very high carbon content (86% - 97%, according to the U.S. EIA [10]), and lignite has the lowest at around 25% - 35% carbon. Anthracite is mainly used in the metals industry, and the rest are primarily used to generate energy.
• Oil (aka petroleum, which means "rock oil") is formed when dead organic material (mostly microscopic photosynthetic organisms) die and sink to the bottom of shallow seas, are buried under sediment (usually sand and/or silt), and changed by heat and pressure over millions of years. Most of the oil extracted in the world is found in the pores of rock layers - sandstone (formed from sand grains) and increasingly from shale (formed from silt grains). Shale oil is extracted through hydraulic fracturing ("fracking"), which will be discussed in a future lesson.
• Natural gas is formed by the same process as oil. Natural gas naturally exists as a gas, and like oil is found inside the pores of rocks. Oil and natural gas are almost always found together.

Since all fossil fuels started out as plants or animals, all of their energy comes from the sun. The solar energy (all radiant energy) is stored as chemical energy when the plant undergoes photosynthesis, then is stored as chemical energy in the fossil fuel itself. It is (usually) released when the fuel undergoes combustion, which results in thermal and ultimately radiant energy release. Note that the physical material of fossil fuels does not come from the sun - the carbon, for example, is pulled from the atmosphere during photosynthesis - but the energy that is released when coal, oil, or natural gas is burned was once solar energy.

Nuclear

Nuclear energy, as discussed above, is the energy that holds the nucleus of atoms together. Nuclear energy in nuclear power plants is extracted using fission of uranium atoms. Fission releases radiant energy, which is used to heat water to steam and turn a turbine, which spins a generator and generates an electrical current. The sun utilizes fusion (fusing hydrogen together to form helium atoms), which then releases radiant energy.

Renewable Energy

As noted above, renewable energy sources "restore themselves over short periods of time and do not diminish." For a thorough explanation of many renewable energy sources, see this site from the U.S. EIA [13]. A more thorough explanation of these sources is provided later in this course.

• Solar [14]energy comes directly from the sun. (Recall that it results from nuclear fission, and arrives at the earth as radiant/electromagnetic energy.) Solar photovoltaics (PV) convert solar energy directly to electricity. Solar thermal technologies absorb solar energy and convert it to thermal energy in water or other fluids. Passive solar energy is a form of solar thermal and is when a home or other building uses the sun's energy to heat the inside of the building. Solar energy is constantly replenished, and so is renewable. It is intermittent, of course, which is its main limitation, along with being limited in power output. There is only so much energy per area available at a given time.
• Wind [15]energy is the motion energy in moving air. Air has mass, and when moving has velocity and thus kinetic energy. The wind energy used by humans is mostly harvested using wind turbines, which utilize wind energy to spin blades, which spins a generator that generates electricity. Air moves from areas of higher pressure to areas of lower pressure. This pressure difference is caused by differential heating (and cooling), which is the result of solar energy as it is absorbed and released by the irregularly shaped earth and different materials the earth is made of. Thermodynamically speaking, kinetic energy in the wind starts out solar energy, and so is renewable. Like solar, the wind is intermittent and limited in amount, but does not "run out."
• Hydropower [16]is energy in moving water (again, mass that has a velocity has kinetic energy). Most of the hydropower used by humans is used to generate hydroelectricity, which is when moving water spins a turbine, which spins a generator that generates electricity. Hydropower also comes from the sun: Water gets its kinetic energy from gravitational energy that causes it to flow downhill. This gravitational energy is the result of water being elevated. The only way water naturally goes uphill is through evaporation, which is almost entirely the result of direct solar energy or wind energy, and evapotranspiration by plants, which is also the result of solar energy. Any way you slice it, hydropower starts as solar energy. Hydropower is limited in scale and location (many places do not have flowing water), but where it does flow, it will often continue to do so, and is thus renewable.
• Biomass [17]is energy from living or recently living things. There are many ways that humans use biomass: burning wood, collecting biogas from sewage and animal waste, converting corn or switchgrass to ethanol, converting vegetable oil or algae to biodiesel, and burning food or agricultural waste are all ways to utilize biomass to generate useful energy. All living things get their energy from the sun - plants directly so, and animals ultimately get their energy from plants. Biomass is thus renewable but is limited in scale and supply. Plants only grow so fast, so if you harvest biomass faster than it is replenished, it is not being used at a renewable rate.
• There are other minor renewable energy sources such as geothermal (thermal energy from the earth), tidal energy (kinetic energy in tides, which results from gravitational energy from the sun and the moon), and wave energy (the result of wind energy that moves over bodies of water).

Carbon Free and Carbon Neutral Energy Sources

As you are no doubt aware, a primary sustainability concern regarding energy use is carbon dioxide (CO₂) emissions. A carbon-free energy source emits no carbon when energy is being generated. Solar, wind, hydroelectric, and nuclear energy are commonly used carbon-free sources. Carbon neutral sources release CO₂ but have no net impact on the CO₂ concentration of the atmosphere because they release no more CO₂ than was absorbed from the same atmosphere. Biomass is the only carbon-neutral source of energy. Recall that biomass gets its energy from the sun by virtue of it being used by photosynthetic organisms to grow. Biomass is made mostly of carbon, which is integrated into the biomass when CO₂ is absorbed from the surrounding air. When said biomass is converted to useful thermal/radiant energy via combustion, the same or less CO₂ is released, resulting in a net zero impact on carbon dioxide concentrations. To summarize:

• Carbon-free energy sources: solar, wind, hydropower, wave, geothermal, tidal, nuclear
• Carbon-neutral energy source: biomass
• Carbon-emitting energy sources: coal, oil, natural gas

Key Sustainability Concepts

As I'm sure you are aware, the terms sustainable and green are used in many contexts and in many sectors of society. Sustainable growth, sustainable energy, green business, sustainable fashion, green cars, sustainable food, and sustainable consumption are just a small sample of how the terms are used. Many people in the sustainability field (myself included) are concerned that the term has been overused to the point that it is almost meaningless. Robert Engelman, President of the Worldwatch Institute [19], refers to this phenomenon as "sustainababble" in his "Beyond Sustainababble [20]" chapter from Is Sustainability Still Possible?. While this excessive usage of the term is undesirable, it is in some ways understandable because a) sustainability relates to everything that humans do and b) it has become an effective way to market products. Selling stuff to the masses drives the economy (consumer spending historically [21] constitutes around 65% - 70% of U.S. GDP), though such rampant consumerism ironically has a largely negative impact on sustainability. You may recall that EM SC 240N was largely designed to cut through a lot of this "sustainababble," and help you understand what sustainability really means. This course will offer a review of a lot of the concepts in that course, as well as provide some additional ones.

See below for a summary of key sustainability points from Lesson 1 of EM SC 240N:

1. There is no single, universal definition of "sustainable," "sustainability," or "green." This lack of definition allows for the ubiquitous use noted above. There is no authority that monitors and/or limits the terms' use, and thus it can be attached to nearly anything. That stated, there are a few important definitions/conceptualizations that you should know:
   • If something cannot be done for at least the foreseeable future, then it should not be considered sustainable. The example of sustained yield management used in EM SC 240N is useful here: If trees (or any naturally replenishing resource such as fish, freshwater, soil nitrogen, etc.) are harvested faster than they can be replenished, then they are not sustainable. On the flip side, if a waste product is being emitted faster than it can naturally be reabsorbed by the environment, it is not sustainable. Rising CO₂ levels are a good example of this - the earth cannot absorb carbon dioxide at the rate it is being emitted by humans.  
   • The most universally recognized definition of sustainability (technically it is the definition for sustainable development, but the terms can generally be used interchangeably) is from the so-called Brundtland Commission, which was the United Nations committee headed by Gro Harlem Brundtland that published Our Common Future in 1987. Their definition is that sustainable development "meets the needs of the present without compromising the ability of future generations to meet their own needs" (Credit: Is Sustainability Still Possible? p. 3. Original source: Our Common Future [22], World Commission on Environment and Development).
   • There are many other helpful definitions of sustainability. One that I think is particularly robust is from the U.S. EPA [23]: "To pursue sustainability is to create and maintain the conditions under which humans and nature can exist in productive harmony to support present and future generations."
2. Front and center of the Brundtland Commission's definition is intergenerational equity, a very important concept in sustainability. Intergenerational equity mandates that we consider the impacts of our actions on future generations. This expands the basic concept of sustainability (Can we keep doing what we are doing indefinitely?) to include whether or not we are promoting a good quality of life for future generations. Not only should future generations survive, but they should thrive.
3. Achieving intergenerational equity is fraught with difficulty. What is a need? To what degree do we sacrifice the needs and wants of the current generation in order to maximize the chances of future generations to live a good quality of life? How can we know the exact impact on the future? Though these are difficult questions to answer, true sustainability requires that we address all of them.
4. Sustainability metrics/indicators help get rid of some of the "fuzziness" of sustainability definitions. Indicators quantify things that impact sustainability so that we can ascertain whether or not we are on a sustainable path, e.g. the number of resources remaining, the concentration of wastes, rates of consumption, population trends, etc. This is addressed in more detail in other lessons, but atmospheric CO₂ levels are a good example of this (see below).
5. Systems thinking is another essential concept in sustainability. The following is from EM SC 240N: 
   1. There is difficulty in satisfying both present and future needs. Ridding the world of abject poverty is at the forefront of sustainability goals, but unfortunately economic growth and sustainability - particularly environmental sustainability - are often at odds. For example, increasing access to fossil fuels generally helps facilitate improving economic conditions, but causes unsustainable emissions. Even current and future sustainability can be at odds, e.g. when Engelman notes that: "Safe water may be reaching more people, but potentially at the expense of maintaining stable supplies of renewable freshwater in rivers or underground aquifers for future generations."
   2. This all indicates the importance of systems thinking. There is a lot of literature about systems thinking, and it does not have a single definition. (If only the world of sustainability were so simple!) It can be thought of as analyzing the world around us as a collection of interrelated systems, and not considering phenomena as isolated and unrelated to other phenomena. In other words, systems thinking requires consideration of connections.
   3. There is an old saying that "the biggest cause of problems is solutions," which is important to keep in mind when analyzing sustainability issues. From a sustainability perspective, systems thinking means that you should at least always a) consider the short- and long-term impacts of actions, both in space and time, and b) consider the possible causes of issues. It is unwise to address a problem or situation without thinking about the possible causes and consequences.

Figure 1.2: Global average temperature and atmospheric carbon dioxide concentrations since 1880. Atmospheric carbon dioxide concentration is one of the most prominent sustainability metrics we have available to us, with most climate scientists agreeing that we are at or approaching dangerous levels.

Credit: NOAA [24]

The Three Es of Sustainability

Sustainability and sustainable development are often thought of as having three core components: environment, economy, and equity. These are commonly referred to as the "3 Es" of sustainability. The 3 Es is a useful way to provide an analytical framework for sustainability. This 3E framework is useful because it provides questions that can be asked when investigating whether or not something is sustainable. While even these terms can be defined in various ways, we will use the following definitions from the reading when analyzing the sustainability implications of something:

• Is it "environmentally sustainable, or viable over the very long term"? (environment)
• Is it "economically sustainable, maintaining living standards over the long term"? (economy)
• Is it "socially sustainable, now and in the future"? (social equity)

Figure 1.3: Sustainability can be visualized as the intersection of all 3 Es.

Credit: D. Kasper

The following provides a few more details about each of the 3 Es:

• The environment is the least confusing of the three. If we can keep doing ___________ without compromising the integrity or functioning of the environment (e.g. by not emitting wastes faster than they can be absorbed and not using natural resources faster than they can be replenished), then it can be considered environmentally sustainable. Later in this course, we will go over the concept of regenerative sustainability, which refers to taking this a step further and improving natural conditions.
• Equity refers to the fairness of opportunity and access to resources like education, health care, a clean environment, political participation, social standing, food, shelter, and others. It does not mean equal distribution of resources. There will always be inequality, whether we want it or not. In a socially equitable society, everyone has reasonable access to things that are generally considered conducive to a good quality of life. Whether or not they take advantage of them is another story. There is an important difference between being uneducated because of laziness and because of lack of access to good schools. Making this happen is easier said than done, but the distinction is important to make.
• Economic sustainability refers both to a) engaging in actions that are economically sustainable (if businesses do not make enough money to continue, they will not be in business for long) and b) promoting an economy that provides and maintains a reasonably high quality of life for all over the long term. From a sustainability perspective, money should be seen as a means to an end, and that end should be quality of life and environmental sustainability. If I run a business that makes me a lot of money but negatively impacts the quality of life for current and/or future generations, it is not considered economically sustainable from a 3E perspective.

Energy, Sustainability, and Society

I have a challenge for you: think of something that you did in the past week that did not involve energy.

Okay, so that's not really a fair challenge. Everything we do, even thinking about things that we might do, requires energy. Here's a more reasonable challenge: think of something that you did in the past week that did not involve the use of non-renewable energy.

Any food you eat almost certainly required non-renewable energy. There are obvious connections like farm machinery, artificial fertilizers, and herbicides, transporting food, refrigerating food, cooking food, and packaging food. But even if you grow your own, you likely used a tool or fencing that was manufactured using non-renewables, seeds that were processed and shipped with fossil fuel-using machines, packaging that was made using non-renewable energy, or maybe even plastic row markers made with petroleum-based plastics. Almost all transportation uses non-renewables, most businesses run on non-renewable energy sources (either directly or indirectly through electricity generation), almost all of the products you buy contain materials either made of or that are processed with fossil fuels. The electronic device you are looking at right now is partially made of and manufactured using fossil fuels. In short, modern society is very dependent upon access to non-renewable energy, particularly fossil fuels. As Asher Miller notes in The Post Carbon Reader:

Look around and you'll see that the very fabric of our lives - where we live, what we eat, how we move, what we buy, what we do, and what we value - was woven with cheap, abundant energy. (p. xiv)

The charts below provide some insight into the U.S. and global energy regimes. The first chart is from the International Energy Agency, and the other is from the U.S. EIA. Both are excellent sources of energy information. Please take a look at them and read through the descriptions, and keep in mind that there is one final summative point provided below.

Global Energy Use

Figure 1.4: 1973 and 2015 fuel shares of TPES Click for a text description.

In 1973, the total was 6,101 Mtoe distributed in the following way: Coal: 24.5%, Hydro: 1.8%, Oil: 46.1%, Biofuels and waste: 10.5%, Natural gas: 16.0%, Nuclear: 0.9%, Other: 0.1%. In 2015, the total was 13,647 Mtoe distributed in the following way (2014 percentages in parentheses): Coal: 28.1% (28.6%), Hydro: 2.5% (2.4%), Oil: 31.7% (31.4%), Biofuels and waste: 9.7% (10.3%), Natural gas: 21.8% (21.2%), Nuclear: 4.9% (4.8%), Other: 1.5% (1.4%).

Credit: International Energy Agency [25]

There are a few interesting things to point out from the chart above.

• These charts provide what is referred to as an energy fuel mix. The term "fuel mix" refers to the percent breakdown of energy sources for a given area or sector. 
• Total Primary Energy Supply (TPES) refers to all original or primary energy consumed. For example, if your electricity is supplied by a power plant, the energy your electronic device is using right now is not primary energy because the electricity was converted from an original source (e.g. coal, oil, natural gas, nuclear). Given that electricity generation is always less than 100% efficient (sometimes much less, per the previous section), the primary energy used by your device is greater than what shows up on your electric bill.
• Biofuels are lumped together with "waste." In many parts of the world, including many states in the U.S., if you burn garbage to produce heat and/or electricity, it is considered a biofuel, and thus renewable.
• Wind and solar are lumped into the "other" category, at a measly 1.5%. This has improved since 2015 (and was 1.1% of the total in 2012), and in fact has been growing at an all-time high rate, but there is still a long way to go before wind and solar make a major dent in the global energy regime.

U.S. Energy Fuel Mix

The charts below provide rather dramatic evidence of how important non-renewable energy is to the U.S. Both charts are from the EIA's Annual Energy Outlook (AEO) series, which are published on a yearly basis. A few things worth pointing out:

• The first chart is from the 2015 version of the AEO. Though a bit outdated, I put it here because the chart style (distinct color-coding and percentages) makes it very easy to see the dominance of non-renewable energy sources. The second chart is from the most recent report but is not quite as easy to interpret.
• These charts include both historical use and projected future use. Any way you slice it, the charts make clear that non-renewable energy (in particular fossil fuels) has played, and will (likely) continue to play, a dominant role in society.
• Aside from recessions (e.g., the early 1980s and 2007-8), energy use continues to increase over time. Despite consistent increases in energy efficiency, the U.S. can't seem to level off, never mind reduce overall consumption. This is also something that will have to be addressed if we are going to have a sustainable energy future.

Figure 1.5: As you can see, over 90% of the total energy supply in the U.S. was from non-renewable energy in 2013, and about 83% of the total is fossil fuels. The EIA clearly does not think this will change much by 2040, with the exception of a little more total renewable and natural gas use. Click here for a text description

Primary Energy Consumption By Fuel in the Reference Case, 1980-2040 Energy Supply 1990 Natural Gas: 23%, Renewables: 7%, Liquid Biofuels: 0%, Nuclear: 7%, Coal: 23%, Petroleum and Other Liquids: 40%, Energy Supply 2013 Natural Gas: 27%, Renewables: 8%, Liquid Biofuels: 1%, Nuclear: 8%, Coal: 18%, Petroleum and Other Liquids: 36%, Projected Energy Supply 2040 Natural Gas: 29%, Renewables: 10%, Liquid Biofuels: 1%, Nuclear: 8%, Coal: 18%, Petroleum and Other Liquids: 33%.

Credit: US EIA, Annual Energy Outlook 2015 [26]

Final Thought on Energy and Sustainability

It should be clear that the vast majority of energy used worldwide comes from non-renewable sources, and this is unlikely to change any time soon. This has a lot of sustainability implications, which we will address in more detail later. From systems thinking perspective, it is important to realize that everything you do requires energy, and it is important to think about where that energy comes from and what the sustainability implications are.

Summary

That's it for Lesson 1! Hopefully this review helped solidify these concepts for you. By now you should be able to:

• provide a basic description/definition of the following terms/concepts: energy, thermodynamics, the First Law of Thermodynamics, energy efficiency, renewable energy, non-renewable energy, carbon free, carbon neutral, sustainability, Brundtland Commission, 3 E's, intergenerational equity, and systems thinking;
• identify examples of the above concepts in contemporary culture;
• apply the above concepts in analyses of contemporary issues;
• identify and describe different forms of energy;
• describe how energy can be converted from one form to another; and
• analyze energy-focused charts and graphs.

Reminder - Complete all of the Lesson 1 tasks!

Double-check the to-do list on the Lesson 1 Overview page [28] to make sure you have completed all of the activities listed there before you begin Lesson 2.