Chapter 10 Outline

10.1 Challenges and Impacts of Human Energy Use

10.2 Types of Fossil Fuels and their Impact

10.3 Nuclear Energy – An Alternative?

10.4 Renewable Energy Sources

10.5 Global Climate Change

10.6 Chapter Summary

Learning Outcomes

After studying this chapter, each student should be able to:

• 10.1 Describe challenges humans have related to energy use, in terms of health, environmental damage, and geopolitical problems
• 10.2 Understand the types of fossils fuels and the challenges each one of these nonrenewable energy sources pose to our health and environment
• 10.3 Discuss major pros and cons related to the use of nuclear energy
• 10.4 Describe and evaluate forms of renewable energy, in terms of their global capacity, environmental impact, and potential for growth
• 10.5 Explain what global climate change is, list major gases contributing to this problem, identify how fossil fuel use alters the natural carbon cycle, and describe predicted effects of climate change.
•      10.6 Be able to summarize the major ideas of this chapter.

10.1 Challenges and Impacts of Human Energy Use

Energy for lighting, heating and cooling our buildings, manufacturing products, and powering our transportation systems comes from a variety of natural sources. The earth’s core provides geothermal energy. The gravitational pull of the moon and sun create tides. The sun emits light, which creates wind, powers the water (hydrologic) cycle, and enables photosynthesis. Plants, algae, and cyanobacteria utilize solar energy to grow and create biomass that can be burned and used for biofuels, such as wood, biodiesel, bioethanol. After being buried for millions of years and being subjected to intense heat and pressure, biomass can create energy-rich fossil fuels.

Each of these types of energy can be defined as renewable or non-renewable. Renewable energy sources can be replenished within human lifespans. Examples include solar, wind, and biomass energy. Non-renewable energy sources are finite and cannot be replenished within a human timescale. Examples include nuclear energy and fossil fuels, which take millions of years to form.

All energy sources, regardless of whether they are from renewable or non-renewable sources, have some environmental and health costs and the distribution of energy resources is not equally distributed among all nations, which can lead to political conflicts. The environmental, health, and political impacts begin with the extraction of the resource and continues with its processing, purification, transportation, and disposal of waste generated during use.

Extraction of fossil fuels can be used as a case study because its use has significant impacts on the environment. As we use up the easily accessible reservoirs of these resources, we are forced to mine deeper into mountains, farther out at sea, and farther into pristine habitats, compromising these ecosystems. Fossil fuels are often located far from where they are utilized so they need to be transported by pipeline, tankers, trains, or trucks. These all present the potential for accidents, leakage and spills. When transported by train or truck, energy must be expended and pollutants are generated. Processing of petroleum, gas, and coal generates various types of emissions and wastes, as well as utilizes water resources. Production of energy at power plants emits pollution that may impact air and water.

The use of fossil fuels has allowed much of the global population to reach a higher standard of living. However, this dependence on fossil fuels results in many significant impacts on society. If supplies become limited or extremely costly, our economies are vulnerable. If countries do not have fossil fuel reserves of their own, they incur even more risk as they are dependent upon foreign nations for their energy resources.

10.2 Types of Fossil Fuels and Their Major Impacts

Fossil fuels come from the organic matter (fossils!) of plants, animals, algae, and cyanobacteria that was buried, heated, and compressed under high pressure over millions of years. The process transformed the biomass of those organisms into the three types of fossil fuels: oil, coal, and natural gas. These forms of energy are nonrenewable in the sense that they cannot be created by humans today, so the earth’s supplies will eventually be used up.

Petroleum (oil)

Thirty-seven percent of the world’s energy consumption and 43% of the United States energy consumption comes from oil. Today’s world reserves of oil are enough to last about 45 more years at the current level of production.

Oil is usually found one to two miles (1.6 – 3.2 km) below the Earth’s surface, whether that is on land or ocean. Once oil is found and extracted from the earth, it must be refined, which separates and prepares the mix of crude oil into the different types for gas, diesel, tar, and asphalt. Oil refining is one of the top sources of air pollution in the United States for volatile organic hydrocarbons and toxic emissions, and the single largest source of carcinogenic benzene (Figure 1).

Figure 1. Refinery in south Texas. (Credit: Photo from Paul Bosch, placed in Public Domain.)

When petroleum is burned as gasoline or diesel, to make electricity, or to power boilers for heat, it produces a number of emissions that have a detrimental effect on the environment and human health:

Carbon dioxide (CO₂) is a greenhouse gas and the major reason there is human caused climate change.

Sulfur dioxide (SO₂) causes acid rain, which damages plants and animals that live in water, and it increases or causes respiratory illnesses and heart diseases, particularly in vulnerable populations like children and the elderly.

Nitrous oxides (NO_X) and Volatile Organic Carbons (VOCs) contribute to ground level ozone, which is an irritant and causes damage to the lungs.

Particulate Matter (PM) produces hazy conditions in cities and scenic areas, and combines with ozone to contribute to asthma and chronic bronchitis, especially in children and the elderly. Very small, or “fine PM,” is also thought to penetrate the respiratory system more deeply and cause emphysema and lung cancer.

Lead (Pb) can have severe health impacts on the nervous system, such as the brain and central nervous system, especially for children.

As the United States tries to extract more oil from its own dwindling resources, they are drilling even deeper into the earth, sometimes from offshore areas of the ocean, which increases the environmental risks (Figure 2). The largest United States oil spill to date began in April 2010 when an explosion occurred on the Deepwater Horizon Oil Rig that killed 11 employees. The rig was drilling exploratory oil wells at a depth of approximately 5000ft in the Gulf of Mexico off the coast of Louisiana. The depth of the well made sealing the leak extremely difficult. It took more than three months to stop the leaking oil, ultimately spilling nearly 200 million gallons of oil into the Gulf of Mexico before the well could be capped. Wildlife, ecosystems, and people’s livelihoods were adversely affected and large amounts of money and energy were expended on clean-up efforts. The long-term impacts are still not known.

Figure 2. Photograph of an offshore oil rig. (Credit: Pixabay CCO in public domain.)

Two-thirds of oil consumption is devoted to transportation, providing fuel for cars, trucks, trains and airplanes. For the United States and most developed societies, transportation is woven into the fabric of our lives, a necessity as central to daily operations as food or shelter. The concentration of oil reserves in a few regions of the world makes much of the world dependent on imported oil for transportation. The rise in the price of oil in the last decade makes dependence on imported energy for transportation an economic and a political issue. The United States, for example, now spends upwards of $350 billion annually on imported oil, a drain of economic resources that could be used to stimulate growth, create jobs, build infrastructure and promote social advances at home.

Coal

Unlike oil, coal is a solid. Due to its relatively low cost and abundance, coal is used to generate about half of the electricity consumed in the United States. Coal is the largest domestically produced source of energy and production has doubled in the United States over the last sixty years. Currently, the United States has about 30% of the world’s coal reserves, therefore, it is a major fuel resource that the United States controls domestically.

Coal is plentiful and for many years has been relatively inexpensive, when looking only at the market cost relative to the cost of other sources of electricity.  But when one considers the environmental impact of extraction, transportation, and use, other significant hidden costs come into play. Burning coal emits sulfur dioxide, nitrogen oxide, and mercury, which have been linked to acid rain, smog, and negative health impacts. Burning of coal also emits higher amounts of carbon dioxide (CO₂) per unit of energy than the use of oil or natural gas. Coal accounted for 35% of the total United States emissions of carbon dioxide released into the Earth’s atmosphere in 2010. Ash generated from combustion contributes to water contamination, negatively impacting water quality and aquatic ecosystems.

Traditional underground mining involves opening one or more portals or shafts into the earth that follow or intercept coal seams, that are too deep for surface mining methods (Figure 3). This form of coal mining is risky to mine workers due to health risks such as pneumoconiosis (black lung), caused by breathing in coal dust, which can causes shortness of breath and leads to over 1000 premature deaths per year. There is also a risk of entrapment or death , averaging  18-48 fatalities per year, according the U.S. Mine Safety and Health Administration. Twenty-nine miners died on April 6, 2010 in an explosion at the Upper Big Branch coal mine in West Virginia. In other countries, with less safety regulations, accidents occur more frequently. Prolonged exposure to coal dust also increases a worker’s risk of developing black lung disease (pneumoconiosis), which causes coughing, shortness of breath, and increased risk of early mortality. There are also significant health effects and risks to those living in the vicinity of coal mines, due to pollution of mines and streams and increased particulate matter in the air they breath.

Figure 3. An underground coal mine. (Credit: coal mine – 1626368 in public domain; Geological Society of London)

Strip mining, called euphemistically “surface mining” by the coal industry, is another way to obtain coal. This method begins by removing all plants, animals, and all other living things from the surface of the area to be mined, and then removing the underlying soil and rock to access the coal deposits below (Figure 4).

Figure 4. Machinery used to remove layers of soil and rock to reach coal below (Credit: This image is in the public domain.)

Strip mining accounts for about two-thirds of coal obtained in the United States. Although both underground and strip mining are detrimental to the environment, strip mining is particularly destructive, obliterating entire ecosystems and depositing soil and rock in nearby areas, causing air and water pollution and myriad forms of long lasting environmental damage. Both the areas mined and the areas where debris are dumped are very difficult and sometimes impossible to reclaim. The Environmental Protection Agency reported that 724 miles of Appalachian streams were buried in fill from strip mines from 1985 to 2001. In the US alone, over a period of 70 years, strip mining has severely altered over 2.4 million hectares of natural landscape, most of which was originally deciduous forest (Figure 5).

Figure 5. This strip mine covers over 25,000 square miles in Montana, the largest strip mine in the United States. (Credit – Attribute: The Environmental Protection Agency – U.S. National Archives and Records Administration)

Mountaintop mining (MTM), is a form of surface mining practice involving the removal of mountaintops to expose coal seams and disposing of the associated mining waste in adjacent valleys. While less dangerous to miners, it is very damaging to the environment because it removes the tops of mountains, destroying the existing habitat, and changing forever the very geology of large regions of our planet. Additionally, the debris from MTM is dumped into valleys burying streams and other important habitats.

Natural Gas

Natural gas meets 20% of world energy needs and 25% of the United States’ needs. The current reserves are enough to last about 110 years at the 2009 rate of U.S. consumption. Natural gas is mainly composed of methane (CH₄) and is a very potent greenhouse gas, when it escapes into the atmosphere.  Natural gas is created in a variety of ways. It can be formed at shallow depths as a product of bacteria anaerobically breaking down organic matter, like landfill gas. Or it can be formed like other fossil fuels; from the compression of organic matter and deep heat underground. This kind of natural gas is found with petroleum in reservoir rocks and with coal deposits, and these fossil fuels are extracted together.

Natural gas is released into the atmosphere from coal mines, oil and gas wells, natural gas storage tanks, pipelines, and processing plants (Figure 6). These leaks are the source of about 25% of total U.S. methane emissions, which translates to three percent of total U.S. greenhouse gas emissions. Burning natural gas releases carbon dioxide into the atmosphere, which is another greenhouse gas.

Figure 6. The Trans-Alaska Pipeline is an aboveground pipeline that transports oil from Prudhoe Bay to Valdez where they are taken up by tankers (oil-hauling ships) for export. (Credit: Kylet Perry; National Geographic Society)

Natural gas production can also result in the production of large volumes of contaminated water. This water has to be properly handled, stored, and treated so that it does not pollute the environment. As natural gas prices increase, it has become more economical to extract the gas from shale. Shale refers to oil and natural gas trapped in fine-grained sediment buried underground. Extraction of shale gas is more problematic than traditional sources due to a process nicknamed fracking, or fracturing of wells, since it requires large amounts of water (Figure 7). This technique of resource removal uses high-pressure fluids to fracture the normally hard shale deposits and release gas and oil trapped inside the rock. If mismanaged, hydraulic fracturing fluid, which contains potentially hazardous chemicals such as hydrochloric acid, glutaraldehyde, petroleum distillate, and ethylene glycol, can be released into the environment, negatively affecting aquatic resources, especially groundwater.

Figure 7. Graphic illustration of the process of hydraulic fracturing. (Source: Al Granberg, ProPublica)

The raw gas from a well may contain many other compounds besides the methane that is being sought, including hydrogen sulfide, a very toxic gas. Natural gas with high concentrations of hydrogen sulfide is usually flared, or burned, at the source, which produces carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen oxides, and many other compounds. Natural gas wells and pipelines often have engines to run equipment and compressors, which produce additional air pollutants and noise.

Despite the pollution released by the extraction and use of natural gas, it is a preferred fossil fuel when considering its environmental impacts. Specifically, when natural gas is burned, much less carbon dioxide, nitrogen oxides, and sulfur dioxide are omitted than from the combustion of coal or oil.

The Future of Coal and Natural Gas

The future development of coal and natural gas depend on the degree of public and regulatory concern for carbon emissions, and the relative price and supply of fuels. Supplies of coal are abundant in the United States, and the transportation chain from mines to power plants is well established. The primary unknown factor is the degree of public and regulatory pressure that will be placed on carbon emissions. Strong regulatory pressure on carbon emissions would favor retirement of coal and addition of natural gas power plants. This trend is reinforced by the recent dramatic expansion of shale gas reserves in the United States due to advances in drilling technology. Greater United States production of shale gas and the ability to extract petroleum from fracking techniques has reduced fossil fuel imports and made the United States a net exporter of fossil fuels since 2019.

The following video gives a brief review of the various kinds of fossil fuels and how they are formed:

 

National Geographic (2017, Aug 29) What are fossil fuels? [Video – YouTube] https://youtu.be/YTnE0OQPTEo

10.3 Nuclear Power – an alternative?

Nuclear power is energy released from the radioactive decay of elements, such as uranium. Nuclear power plants produce no carbon dioxide and, therefore, are often considered an alternative fuel (fuels other than fossil fuels). Currently, world production of electricity from nuclear power is about 19.1 trillion KWH, with the United States producing and consuming about 22% of that. Nuclear power provides about 9% of the electricity in the United States.

Even though nuclear power does not release carbon dioxide, there are still environmental challenges associated with nuclear power. Mining and refining uranium ore and making reactor fuel demands a lot of energy. Also, nuclear power plants are very expensive and require large amounts of metal, concrete, and energy to build. The main environmental challenge for nuclear power is the disposal of radioactive waste produced during energy production. These materials have long radioactive half-lives. The half life of a radioactive element is the time it takes for 50% of the material to radioactively decay. A long radioactive half-life means the material will remain a threat to human health for thousands of years

There are many other regulatory precautions governing permitting, construction, operation, and decommissioning of nuclear power plants due to risks from an uncontrolled nuclear reaction. The potential for contamination of air, water and food is high should an uncontrolled reaction, called a meltdown, occur.

Debating Nuclear Energy

From a sustainability perspective, nuclear energy presents an interesting dilemma. On the one hand, nuclear energy produces no carbon emissions, a major sustainable advantage in a world facing anthropogenic climate change. On the other hand, nuclear energy produces dangerous waste that 1) must be stored away from the natural environment for thousands of years, 2) can produce bomb-grade plutonium and uranium that could be diverted by terrorists or others to destroy cities and poison the environment, and 3) threatens the environment through accidental leaks of long-lived radiation. Thoughtful scientists, policy makers, and citizens must weigh the benefit of this source of carbon-free electricity against the environmental and societal risks of radiation.

Following the development of nuclear technology at the end of World War II for military purposes, nuclear energy quickly acquired a new peacetime path for relatively inexpensive production of electricity. Eleven years after the end of World War II, a very short time in energy terms, the first commercial nuclear reactor produced electricity at Calder Hall in Sellafield, England.

Although the price of building nuclear power plants grew tremendously since that first plant in England, the number of nuclear reactors around the world increased steadily to over 430 by the 1980s. The accident and partial nuclear meltdown experienced by the Three Mile Island nuclear power plant in Pennsylvania in 1979 galvanized opposition by the public to build new nuclear power plants. This accident, which released small amounts of radioactive gases, along with cost overruns of over 200% experienced by governmental and private organizations involved in building nuclear power plants , brought most construction to a stand-still. The explosion and nuclear meltdown at the Chernobyl Nuclear Power Plant in Ukraine in 1986 had far greater negative impact on the environment, spewing radioactive products far into the air which landed in many different countries and other locations downwind of this plant. This was a worst case scenario for a nuclear disaster at a nuclear power plant, making a large area near Chernobyl unlivable even today, and poisoning thousands of acres of our planet with nuclear fallout (Figure 8). Since 1990, the number of operating reactors has remained approximately flat, with new construction balancing decommissioning due to public and government reluctance to proceed with nuclear electricity expansion plans.

More recently, the nuclear accident in Fukushima, Japan in March 2011, showed that unlikely circumstances can cause life threatening accidents at even the safest nuclear power plant. The Fukushima nuclear disaster was caused by an earthquake, followed by a tsunami, that disabled the cooling system for a nuclear energy complex. This loss of cooling caused a partial meltdown of some of the reactor cores and the release of significant amounts of radiation into the air and water.

Figure 8. The town of Pripyat, Ukraine, including this amusement park, was abandoned after the Chernobyl Nuclear Power Plant explosion and meltdown in 1986, due to dangerous levels of radiation released into the environment. (Credit: Andre Joosse – Reports from Chernobyl Exclusion Zone – this image is in the public domain)

Today, as we experience the negative consequences of global warming, there are arguments by scientists and some political figures that we should increase our reliance on nuclear power, since it does not emit greenhouse gases, and thereby reduce the number of fossil fuel burning electric plants. This debate will certainly focus on safety issues and cost, and its outcome will determine whether the world experiences a nuclear renaissance or continues to decommission and reduce the number of nuclear power plants.

The following video reviews some of the pros and cons of using nuclear energy:

 

MooMooMath and Science (2021, Dec 7) Nuclear energy – pros and cons. [Video – YouTube] https://youtu.be/a__E88op6cc

10.4 Renewable Energy Sources

Although renewable energy is often classified as hydroelectric, solar, wind, biomass, geothermal, wave and tide power, all forms of renewable energy arise from just three sources: the light of the sun, the heat of the earth’s crust, and the gravitational attraction of the moon and sun. Sunlight is by far the largest contributor to renewable energy. The sun provides the heat that drives the weather, including the formation of high- and low-pressure areas in the atmosphere that make wind. The sun also generates the heat required for vaporization of ocean water that ultimately falls over land creating rivers that drive hydropower, and the sun is the energy source for photosynthesis, which creates biomass. Solar energy can be directly captured for water and space heating, for driving conventional turbines that generate electricity, and as excitation energy for electrons in semiconductors that drive photovoltaics. The sun is also responsible for the energy of fossil fuels, created from the organic remains of plants and sea organisms compressed and heated in the absence of oxygen in the earth’s crust for tens to hundreds of millions of years. The time scale for fossil fuel regeneration, however, is too long to consider them renewable in human terms.

Geothermal energy refers to heat rising to the surface from earth’s molten iron core created during the formation and compression of the early earth as well as from heat produced continuously by the radioactive decay of uranium, thorium, and potassium in the earth’s crust. Tidal energy arises from the gravitational attraction of the moon and the more distant sun on the earth’s oceans, combined with rotation of the earth.

Hydropower

Hydropower (hydroelectric power) relies on falling water, usually at dams, to spin turbines and create electricity. It provides 35% of the United States’ renewable energy (Figure 9). Hydropower is considered a clean and renewable source of energy because it does not directly produce pollutants and because the source of power is regenerated naturally by the water cycle. However, hydropower dams and the reservoirs they create can have environmental impacts. For example, dams can obstruct migration of fish to their upstream spawning areas. This problem can be partially alleviated by using “fish ladders” that help fish get around the dams. Fish traveling downstream, however, can get killed or injured as water moves through turbines in the dam. Reservoirs and dam operation can also affect aquatic habitats due to changes in water temperature, depth, chemistry, flow characteristics, and sediment loads, all of which can lead to significant changes in the ecology and physical characteristics of the river both upstream and downstream. As reservoirs fill with water it may cause natural areas, farms, cities, and archeological sites to be inundated with water and force populations to relocate.

Figure 9. View of the Hoover Dam and Power Plant on the Colorado River as seen from above. (Credit: U.S. Department of the Interior)

Solar Energy

Solar power converts the light energy of the sun into electrical energy and has minimal impact on the environment, depending on where it is placed. In 2022, 4.5% of the world’s renewable energy generated for electricity was from solar power,  while this source of energy amounted to 3.4% of the electricity generated in the United States.

Often solar arrays are placed on roofs of homes or buildings, over parking lots or pedestrian areas, or integrated into construction in other ways. This kind of placement minimizes additional impact to the environment above and beyond the impact of building construction that would likely happen in any case (Figure 10).

Figure 10. Rooftop solar installation on Douglas Hall at the University of Illinois at Chicago has no effect on land resources, while producing electricity with zero emissions. (Credit: Office of Sustainability, University of Chicago)

However, large systems may be placed on otherwise undeveloped land where fragile ecosystems could be damaged if care is not taken (Figure 11). Some solar thermal systems use potentially hazardous fluids (to transfer heat) that require proper handling and disposal. Concentrated solar systems may need to be cleaned regularly with water, which is also needed for cooling the turbine-generator. Using water from underground wells may affect the ecosystem in some arid locations. The manufacturing of photovoltaic (PV) cells generates some hazardous waste from the chemicals and solvents used in processing.

Figure 11. The Ivanpah Solar Power Facility, located in the Californian desert, is the world’s largest concentrating solar power plant. (Credit: U.S. Department of Energy)

Wind

Wind energy is a renewable energy source that is clean and has very few environmental challenges. Wind turbines (often called windmills) convert wind energy into electricity without releasing emissions that pollute the air or water (with rare exceptions), and they do not require water for cooling (Figure 12). These tall windmills are becoming a prominent sight across the United States. As of 2020, the U.S. wind industry provided more than 20% of installed wind power around the globe. According to the American Wind Energy Association, over 35% of all new electrical generating capacity in the United States since 2006 was due to wind, surpassed only by natural gas.

Figure 12. An example of a wind farm in the United States. (Credit: U.S. Department of Energy)

Because a wind turbine has a small physical footprint relative to the amount of electricity it produces, many wind farms are located on crop and pasture land. They contribute to economic sustainability by providing extra income to farmers and ranchers, allowing them to stay in business and keep their property from being developed for other uses. For example, energy can be produced by installing wind turbines in the Appalachian mountains of the United States instead of engaging in mountain top removal for coal mining. Offshore wind turbines on lakes or the ocean may have smaller environmental impacts than turbines on land.

Wind turbines do have a few environmental challenges, though. There are aesthetic concerns to some people when they see them on the landscape. A few wind turbines have caught on fire, fallen down, and some have leaked lubricating fluids, though this is relatively rare. Some people do not like the sound that wind turbine blades make. Turbines have been found to cause bird and bat deaths particularly if they are located along their migratory pathway, which is of particular concern if these are threatened or endangered species. Ways to mitigate that impact that are currently being researched. There are some small impacts from the construction of wind projects or farms, such as the construction of service roads, the production of the turbines themselves, and the concrete for the foundations. However, overall analysis has found that turbines make much more energy than the amount used to make and install them.

Biomass and Biofuels

Biomass refers to material made by organisms, such as cells and tissues (typically from plants), which can be burned to convert the energy of these organisms into electrical energy. Biomass is a renewable energy source because those plants can be grown again! The burning of biomass does release carbon dioxide into the atmosphere, but growing the biomass removes carbon dioxide from the atmosphere. So the removal of CO₂ that occurs during the process of photosynthesis matches the CO₂  released when it is burned. This results in zero net carbon dioxide added to the atmosphere. Burning biomass, however, does have a downside, as smoke can contain harmful pollutants like carbon monoxide (CO) and particulate matter.

For biomass to be a truly sustainable option, it needs to come from waste material, such as lumber mill sawdust, paper mill sludge, yard waste, oat hulls from an oatmeal processing plant, and manure and human waste. It is not sustainable, for example, to cut down large swaths of forests just for energy production, because our energy demands are so great that we would quickly deforest the world, destroying critical habitat.

Bioethanol and Biodieselare liquid biofuels manufactured from plants. Bioethanol can be easily fermented from sugar cane juice, as is done in Brazil or can be fermented from broken down corn starch, as is mainly done in the United States. The economic and social effects of growing plants for fuels need to be considered, since the land, fertilizers, and energy used to grow biofuel crops could be used to grow food crops instead. The competition of land for fuel vs. food can increase the price of food, which has a negative effect on society. It could also decrease the food supply increasing malnutrition and starvation globally. Also, in some parts of the world, large areas of natural vegetation and forests have been cut down to grow sugar cane for bioethanol and soybeans and palm-oil trees to make biodiesel, which is not sustainable land use. Biofuels may be derived from parts of plants not used for food, such as stalks and can be made from used vegetable oil, thus reducing that impact.

Landfill gas (biogas) refers to methane (often referred to as natural gas) that is formed as a result of biological processes in sewage treatment plants, waste landfills, anaerobic composting, and livestock manure management systems. This gas can be captured and burned to produce heat or electricity. The electricity may replace electricity produced by burning fossil fuels and result in a net reduction in CO₂ emissions. The only environmental impacts are from the construction of the plant itself, similar to that of a natural gas plant.

Municipal solid waste (MSW) is commonly known as garbage and can be burned directly to produce electricity. Waste to energy processes are gaining renewed interest as they can solve two problems at once: disposal of waste and production of energy from a renewable resource. Many of the environmental impacts are similar to those of a coal plant, including air pollution and ash generation. However, because the fuel source is less standardized than coal and hazardous materials may be present in MSW, the EPA regulates that incinerators and waste-to-energy power plants clean the gases of harmful materials before release. If the ash is clean enough it can be “recycled” as an MSW landfill cover or to build roads, cement block and artificial reefs

Geothermal Energy

Five percent of the United States’ renewable energy comes from geothermal energy: using the heat of Earth’s subsurface to provide endless energy. Geothermal systems utilize a heat-exchange system that runs about 20 feet (5 meters) below the surface where the ground is at a constant temperature. The system uses the earth as a heat source (in the winter) or a heat sink (in the summer). This reduces the energy consumption required to generate heat from gas, steam, hot water, and conventional electric air-conditioning systems. The environmental impact of geothermal energy depends on how it is being used. Direct use and heating applications have almost no negative impact on the environment.

Geothermal power plants do not burn fuel to generate electricity so their emission levels are very low. They release less than 1% of the carbon dioxide emissions of a fossil fuel plant and they use scrubber systems to clean the air of hydrogen sulfide that is naturally found in the steam and hot water. They emit 97% less acid rain-causing sulfur compounds than are emitted by fossil fuel plants. After the steam and water from a geothermal reservoir have been used, they are injected back into the earth.

Oceans – Tidal and Wave Energy

Tidal energy is produced by the rise and fall of ocean waters, so is a renewable and clean source of energy. During the 20th century, engineers developed ways to use tidal movement to generate electricity in areas where there is the greatest amount of tidal range – the difference in between high tide and low tide. The first was located in La Rance, France and the largest facility is the Sihwa Lake Tidal Power Station in South Korea. These locations use special turbines and generators to convert moving water from tidal changes into electricity  (Figure 13). So far the United States does not have any tidal power plants, but locations with large tidal movements, such as Alaska and Maine are being considered for this purpose.

 

a.    b.

Figure 13.  a. Diagram of how tidal power can be harvested to produce electricity. b. Tidal power plant in use along the Rance River in France (Credit: Adapted from the National Energy Education Development Project [public domain])

The following video reviews some of the major ideas about renewable energy sources:

 

National Geographic (2017, Sept 21) Renewable Energy 101. [Video – YouTube] https://youtu.be/1kUE0BZtTRc

Interest in Renewable Energy

Strong interest in renewable energy in the modern era arose in response to the oil shocks of the 1970s, when the Organization of Petroleum Exporting Countries (OPEC) imposed oil embargos and raised prices in pursuit of geopolitical objectives. The shortages of oil, especially gasoline for transportation, and the eventual rise in the price of oil by a factor of approximately 10 from 1973 to 1981 disrupted the social and economic operation of many developed countries and emphasized their precarious dependence on foreign energy supplies. The reaction in the United States was a shift away from oil and gas to plentiful domestic coal for electricity production and the imposition of fuel economy standards for vehicles to reduce consumption of oil for transportation. Other developed countries without large fossil reserves chose to emphasize nuclear power or to develop domestic renewable resources such as hydropower, wind, geothermal, solar, and biomass. As oil prices collapsed in the late 1980s, interest in renewables, such as wind and solar that faced significant technical and cost barriers, declined in many countries, while other renewables, such as hydropower and biomass, continued to experience growth.

The increasing price and volatility of oil prices and the increasing dependence of many developed countries on foreign oil, spurred renewed interest in renewable alternatives to ensure energy security. A new concern, not considered by many in previous oil crises, added further motivation: our knowledge of the emission of greenhouse gases when oil is burned and its growing contribution to climate change. These energy security, carbon emission, and climate change concerns drive significant increases in fuel economy standards, fuel switching of transportation from uncertain and volatile foreign oil to domestic electricity and biofuels, and production of electricity from low carbon sources.

Recall that carbon compounds contain energy. Many of these compounds, from dead plants, animals, and algae that have fossilized over millions of years, form the fossil fuels of oil, coal, and natural gas. Since the beginning of the Industrial Revolution in the 1800s, the demand for Earth’s limited fossil fuel supplies has risen. Burning fossil fuels for energy releases carbon from a reservoir where it has been stored underground for millions of years as carbon dioxide into the atmosphere, altering the natural carbon cycle. This drastic increase in carbon dioxide traps more heat in the Earth’s atmosphere. This is associated with climate change and is a major environmental concern worldwide.

10.5 Global Climate Change

The earth’s temperature depends on the balance between energy entering and leaving the atmosphere. Many factors, both natural and human made, can cause changes in Earth’s energy balance, including:

• variations in the amount of the sun’s energy reaching Earth
• changes in the reflectivity of Earth’s atmosphere & surface
• changes in the make up of the earth’s atmosphere, especially the presence of greenhouse gases, which affects the amount of heat retained by the earth.

Scientists have pieced together a picture of Earth’s climate, dating back hundreds of thousands of years, by analyzing a number of indirect measures of climate such as ice cores, tree rings, glacier size, pollen counts, and ocean sediments. Scientists have also studied changes in Earth’s orbit around the sun and the activity of the sun itself.

Changes in the Sun’s Energy Affect how Much Energy Reaches Earth

Climate can be influenced by natural changes that affect how much solar energy reaches Earth. These changes include changes within the sun and changes in Earth’s orbit. Changes occurring in the sun itself can affect the intensity of the sunlight that reaches Earth’s surface, causing either warming (during periods of stronger solar intensity) or cooling (during periods of weaker solar intensity). The sun follows a natural 11-year cycle of small ups and downs in intensity, but the effect on Earth’s climate is small.

Changes in the shape of Earth’s orbit as well as the tilt and position of Earth’s axis can also affect the amount of sunlight reaching Earth’s surface. These changes are likely what caused past cycles in which Earth has experienced long periods of cold temperatures (ice ages), as well as shorter interglacial periods (periods between ice ages) of relatively warmer temperatures.

Changes in solar energy continue to affect climate. However, solar activity has been relatively constant, aside from the 11-year cycle, since the mid-20th century and therefore does not explain the recent warming of Earth. Similarly, changes in the shape of Earth’s orbit as well as the tilt and position of Earth’s axis affect temperature on relatively long timescales (tens of thousands of years), and therefore cannot explain the recent warming that has occurred in the past couple of centuries.

The recent changes in climate and warming of the earth are due to the increase in greenhouse gases into the atmosphere, caused by burning fossil fuels and other human induced changes, as will be explored in the rest of this chapter. 

Changes in Reflectivity Affect How Much Energy Enters Earth’s System

The term albedo refers to the amount of solar radiation reflected from an object or surface. The composition of Earth’s surface and atmosphere affect its overall albedo. Light-colored objects and surfaces, like snow and clouds, have a high albedo, which results in a cooling effect as the sun’s energy is reflected back into space. Darker objects and surfaces, like the ocean and forests, have a low albedo, meaning less energy is reflected and more is absorbed, resulting in a warming effect.

The Earth’s overall albedo is determined by a number of natural and anthropogenic (human caused) factors. Snow, clouds, particles released by volcanic eruptions into the atmosphere, and sulfur emissions from burning coal all have a high albedo. Oceans, forests, and soot have a low albedo. Natural changes in albedo, like the melting of sea ice, increases in cloud cover, or volcanic eruptions have contributed to climate change in the past. Currently, human changes in land use and land cover have also changed Earth’s albedo. Processes such as deforestation, reforestation, desertification, and urbanization alter albedo, contributing to changes in climate in the places they occur.

The historical record shows that the climate varies naturally over a wide range of time scales, and climate changes prior to the Industrial Revolution in the 1700s can be explained by natural causes, such as changes in solar energy, volcanic eruptions, and natural changes in greenhouse gas (GHG) concentrations. More recent changes in climate, however, cannot be explained by natural causes alone. Rather, it is extremely likely that human activities, especially our combustion of fossil fuels, explains most of that warming. The scientific consensus is clear: through alterations of the carbon cycle, humans are changing the global climate by increasing the effects of something known as the greenhouse effect.

The Greenhouse Effect Causes the Atmosphere to Retain Heat

The greenhouse effect is the idea that the sun’s light energy can pass through glass into a contained area, but this energy can be trapped as it is converted to heat (infrared energy). Gardeners that live in moderate or cool environments use actual greenhouses because they trap heat and create an environment that is warmer than outside temperatures. Greenhouses contain glass or plastic that allow visible light from the sun to pass through. This light energy is absorbed by plants, soil, and various surfaces and heats them. Some of that heat energy is then radiated outwards in the form of infrared radiation, a different form of energy. Although the glass allowed  visible light to enter the greenhouse, that same glass blocks infrared radiation, thereby trapping the heat energy, and causing the temperature within the greenhouse to increase.

The same phenomenon happens inside a car on a sunny day. Have you ever noticed how much hotter a car can get compared to the outside temperature? Light energy from the sun passes through the windows and is absorbed by the surfaces in the car such as the seats and dashboard. Those warm surfaces then radiate infrared radiation, which cannot leave through that same glass. This trapped infrared energy causes the air temperatures in the car to increase. This process is commonly known as the greenhouse effect.

The greenhouse effect also happens with the entire Earth. Of course, our planet is not surrounded by glass windows. Instead, the Earth is wrapped with an atmosphere that contains greenhouse gases (GHGs). Much like the glass in a greenhouse, GHGs allow incoming visible light energy from the sun to pass through, but they block the infrared radiation from leaving the atmosphere (Figure 14). In this way, they help trap heat energy that subsequently raises air temperature. The greenhouse effect is not entirely a negative phenomenon. Scientists estimate that the average temperature on Earth would be -18ºC without naturally-occurring GHGs, which would make Earth inhospitable for most organisms alive today. However, human activities have altered the amount of greenhouse gases in the atmosphere, leading to higher than normal temperatures, and profound changes in worldwide climate.

Figure 14. This figure shows how climate change is occurring. (Credit:  AP Environmental Science)

The following video helps to explain what climate change is and why it is happening:

 

Click View (2021, Apr 19) What is climate change? Explore the Causes of Climate Change. [Video – YouTube] https://youtu.be/EuwMB1Dal-4

 

The Main Greenhouse Gases

Greenhouse gases have a physical molecular structure that allows them to be transparent to visible light, but absorb wavelengths of infrared radiation. Some notable greenhouse gases are water vapor (H₂O), carbon dioxide (CO₂), and methane (CH₄).

Carbon Dioxide (CO₂)

Carbon dioxide (CO₂) is the primary greenhouse gas that is contributing to recent global climate change. Although CO₂ is a natural component of the carbon cycle, human activities, primarily the burning of fossil fuels and changes in land use, release large amounts of CO₂ into the atmosphere that would not otherwise be there, causing its concentration in the atmosphere to rise. Atmospheric CO₂ concentrations have increased by 45% since pre-industrial times, from approximately 280 parts per million (ppm) in the 18th century to 420 ppm in 2023. The current CO₂ level is higher than it has been in at least 800,000 years, based on evidence from ancient atmospheric gases trapped in ice (Figure 15 & 16). Human activities currently release over 37 billion metric tons of CO₂ into the atmosphere every year. While naturally occurring phenomena, such as volcanic eruptions, released large quantities of CO₂ in the distant past, the U.S. Geological Survey (USGS) reports that human activities now emit more than 135 times as much CO₂ as volcanoes each year.

Figure 15. Scientists drill for ice cores in polar regions. The ice contains air bubbles and biological substances that provide important information for researchers. (Credit: a: Helle Astrid Kjær; b: National Ice Core Laboratory, USGS)

Figure 16. This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO₂ has increased since the Industrial Revolution. (Credit: Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO₂ record.)

Methane (CH₄)

Methane (CH₄) is a powerful greenhouse gas (28 time more potent than CO₂) that is produced through both natural and human activities. For example, wetlands release methane naturally, but agricultural activities and fossil fuel extraction and transport emit large amounts of CH₄. Methane is more abundant in Earth’s atmosphere now than at any time in at least the past 650,000 years. Due to human activities, CH₄ concentrations increased sharply during most of the 20th century and are now 2.5 times more abundant than pre-industrial levels.

Water Vapor (H₂O)

Water Vapor (H₂O) is the most abundant greenhouse gas and also the one that contributes the most to the natural greenhouse effect, despite having a short atmospheric lifetime. Some human activities can influence local water vapor levels. However, on a global scale, the concentration of water vapor is controlled by temperature, which influences overall rates of evaporation and precipitation. Therefore, the global concentration of water vapor is not substantially affected directly by human emissions.

Scientific Consensus: Global Climate Change is Real

Data show that Earth’s temperature is increasing, but there is debate regarding the cause of the increase, whether human activities are to blame, and whether steps can or should be made to mitigate it. The Intergovernmental Panel on Climate Change (IPCC), created in 1988 by the United Nations Environment Programme and the World Meteorological Organization, is charged with the task of evaluating and synthesizing the scientific evidence surrounding global climate change. Hundreds of leading scientists from around the world have reviewed thousands of peer-reviewed, publicly available studies and the scientific consensus is clear: global climate change is real and humans are the cause for this change.

Additionally, the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and the US National Research Council agree that climate change is occurring and that humans are driving it. This doesn’t necessarily mean that every scientist sees eye to eye on each component of climate change, but broad agreement exists both in the United States and abroad. Critics of climate change, driven by ideology instead of evidence, try to suggest to the public that there is no scientific consensus on global climate change. Such an assertion is patently false.

The Effects of Global Climate Change

You may wonder why humans should care about climate change. Human societies have adapted to the relatively stable climate we have enjoyed since the last ice age which ended several thousand years ago. But global warming is already having far reaching negative effect on human populations. The increase in earth’s average temperature has:  (1) changed current precipitation amounts and patterns, leading to drought and wildfires in some areas, and floods in others, (2) reduced the amounts of permafrost, ice, snow, and glaciers, raising sea level, and 3) warmed the oceans while increased CO ₂ concentrations have acidified ocean water, damaging coral reefs and other ocean life. These changes and many others affect our ability to grow food (agriculture), our water supplies, health and safety, power and transportation systems, along with causing widespread damage to the natural environment.

The magnitude and rate of future climate change will primarily depend on the rate at which levels of greenhouse gas concentrations in our atmosphere continue to increase, how strongly features of the climate (e.g., temperature, precipitation, and sea level) respond to the expected increase in greenhouse gas concentrations, and natural influences on climate (e.g., from volcanic activity and changes in the sun’s intensity), and natural processes within the climate system (e.g., changes in ocean circulation patterns).

The warmer it gets, the greater the risk for more severe changes to the climate and Earth’s systems. Although it’s difficult to predict the exact impacts of climate change, what’s clear is that the climate we are accustomed to is no longer a reliable guide for what to expect in the future.

Past and Present-day GHG Emissions Will Affect Climate Far into the Future

Many greenhouse gases stay in the atmosphere for long periods of time. As a result, even if human greenhouse gas emissions stopped increasing or even decreased, atmospheric greenhouse gas concentrations would continue to remain elevated for hundreds of years and surface air temperatures would continue to warm. This is because the oceans, which store heat, take many decades to fully respond to higher greenhouse gas concentrations. Modeling future ecological changes is a challenging field of study, due to the many variables and unknowns associated with climate studies. The next several paragraphs will address scientific predictions of how increased greenhouse gases will affect future global temperatures, precipitation amounts and patterns and storm events, ice, snowpack, and permafrost levels, sea level change, ocean acidification, and the spread of disease.

It is easy to feel helpless against climate change, however it is important to remember that changes made today may be able to slow the rate of the change and reverse the negative impacts faster than if we stay the course!

Future Temperature Projections

Climate models project that average global temperatures are expected to increase by 2 to 11.5°F by 2100, depending on the level of future greenhouse gas emissions. By 2100, global average temperature is expected to warm at least twice as much as it has during the last 100 years. Ground-level air temperatures are expected to continue to warm more rapidly over land than oceans and some parts of the world are projected to see larger temperature increases than the global average.

Future Precipitation and Storm Events

Temperature changes will also likely lead to changes in the patterns of precipitation and storm events, including both rain and snowfall. Some regions may have less precipitation, some may have more precipitation, and some may have little or no change. The amount of rain falling in heavy precipitation events is likely to increase in most regions, while storm tracks are projected to shift towards the poles. The intensity of storms will also likely increase on average. This will be particularly pronounced in tropical and high-latitude regions, which are also expected to experience overall increases in precipitation. The strength of the winds and the amount of precipitation associated with tropical storms are likely to increase.

Future Ice, Snowpack, and Permafrost

Increased temperatures will also lead to sea ice, glaciers, ice caps, and permafrost melting. Arctic sea ice is already declining drastically, the area of snow cover in the Northern Hemisphere has decreased since 1970, and permafrost temperature has increased over the last century, making it more susceptible to thawing. Over the next century, it is expected that sea ice will continue to decline, glaciers will continue to shrink, snow cover will continue to decrease, and permafrost will continue to thaw (Figure 17). For every 2°F of warming, models project about a 15% decrease in the average amount of annual sea ice.

Figure 17. The effect of global warming can be seen in the continuing retreat of Grinnel Glacier. The mean annual temperature in the park has increased 1.33 °C since 1900. The loss of a glacier results in the loss of summer meltwaters, sharply reducing seasonal water supplies and severely affecting local ecosystems. (Credit: modification of work by United States Geological Survey)

Future Sea Level Change

Warming temperatures contribute to sea level rise by expanding ocean water, and melting mountain glaciers and ice caps. Since 1870, global sea level has risen by about 8 inches. Estimates of future sea level rise vary for different regions, but global sea level for the next century is expected to rise at a greater rate than during the past 50 years.

Regional and local factors will influence future relative sea level rise for specific coastlines around the world. For example, relative sea level rise depends on land elevation changes that occur as a result of subsidence (sinking) or uplift (rising), in addition to things such as local currents, winds, salinity, water temperatures, and proximity to thinning ice sheets.

Future Ocean Acidification

Carbon dioxide dissolves in water, making the ocean a major reservoir for carbon. Originally, this was considered beneficial, as oceans removed carbon dioxide from the atmosphere. However, when carbon dioxide dissolves in water, it forms carbonic acid, and over time, the oceans have become more acidic. The pH level of the oceans has decreased by approximately 0.1 pH units since pre-industrial times, which is equivalent to a 25% increase in acidity. The pH level of the oceans is projected to decrease even more by the end of the century as CO₂ concentrations are expected to increase for the foreseeable future.

Spread of Disease

Colder temperatures typically limit the distribution of certain species, such as the mosquitoes that transmit malaria, because freezing temperatures destroy their eggs. Therefore, a rise in global temperatures will increase the range of disease-carrying insects and the viruses and pathogenic parasites they harbor. This spread has already been documented with dengue fever, a disease that affects hundreds of millions per year, according to the World Health Organization. Other diseases, including malaria, yellow fever, West Nile virus, zika virus, and chikungunya, are expected to spread to new portions of the world as the global climate warms. Not only will the range of some disease-causing insects expand, the increasing temperatures will also accelerate their life cycles, which allows them to breed and multiply quicker, and perhaps evolve pesticide resistance faster.

Climate Change affects Everyone

The spread of disease has an obvious effect on human populations as more people may get sick or die. However, the effects of increased temperatures, changing precipitation patterns, melting glaciers, sea level rise, and ocean acidification on humans may seem more abstract. However, everyone around the world will likely be impacted by climate change in one way or another.

Increased temperatures lead to heat-related illnesses, such as heat stroke and humans will be more reliant on technology to live comfortably. This results in a positive feedback loop as more technology requires more energy production, which contributes additional greenhouse gases to the atmosphere if it is obtained from unsustainable sources.

Changing patterns and intensity of precipitation can lead to flooding in areas that previously did not experience flooding and more severe floods in areas already prone to flooding. Agriculture will be affected as farmers have to increase irrigation efforts in some areas, leading to strain on water resources, or worry about fields being washed out by storms. Infrastructure will need to be adapted to deal with changing water levels and surface flow.

Melting ice and snow may cause increased interactions between humans and wildlife. This is already the case in the Arctic, where polar bears are forced to encroach upon human civilizations in search of food due to sea ice forming later and melting earlier than in the past (Figure 18). Melting ice also leads to sea level rise, which will destroy homes on the coast of large landmasses and may completely inundate smaller islands.

Figure 18. Polar bears rely on vanishing amounts of sea ice for hunting. (Credit: PLOS – image is in the public domain)

Ocean acidification decreases the amount of calcium carbonate available in the water. Calcium carbonate is a compound needed by marine organisms such as plankton, mollusks, shellfish, and corals to make their shells and skeletons. These organisms serve as the base of many marine ecosystems. Their demise could result in a collapse of marine food webs, which would negatively impact the over one billion people on Earth who rely on fish as their main source of protein.

You Can Take Action

By making choices that reduce greenhouse gas pollution, and preparing for the changes that are already underway, we can reduce risks from climate change. Our decisions today will shape the world our children and grandchildren will live in. You can take steps at home, on the road, and in your place of employment to reduce greenhouse gas emissions and the risks associated with climate change. Many of these steps can also save you money. Some, such as walking or biking to work, can even improve your health! You can also get involved on a local or state level to support energy efficiency, clean energy programs, or other climate programs.

The following video explores various topics related to climate change, and some of the actions humans can take to reduce climate change:

 

Miltonberger, Matt (2017, May 19) Climate change – we are the problem and the solution. [Video- YouTube] https://youtu.be/-D_Np-3dVBQ

10.6 Chapter Summary

Humans rely on energy for survival. Energy allows people to travel around in the environment, grow, harvest, and cook food, and run technology that increases quality of life. Energy can come from a variety of sources that can be classified as either non-renewable or renewable. Non-renewable sources are finite and irreplaceable in human timelines and include fossil fuels, such as oil, coal, and natural gas. Nuclear power, the power emitted by the nuclei of atoms, is also a non-renewable resource. Renewable resources are those that can be readily replaced and include hydropower, solar, wind, biomass, and geothermal. All forms of energy have benefits and drawbacks based on how they are extracted, transported, and used. However, the detrimental effects of the increase in fossil fuel use since the industrial revolution is a looming concern. Burning fossil fuels releases carbon dioxide into the atmosphere, where it contributes to the greenhouse effect, resulting in global climate change.

Attribution

Content in this chapter includes original work created by Lauren Roberts and Paul Bosch as well as from the following sources, with some modifications:

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EEA. (2013). Combined heat and power. Retrieved from http://www.eea.europa.eu/data-and-maps/indic ators/combined-heat-and-power-chp-1. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from original.

EPA. (n.d.). Climate change. Accessed August 31, 2015 at http://www.epa.gov/climatechange/. Modified from original.

Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher.

Theis, T. & Tomkin, J. (Eds.). (2015). Sustainability: A comprehensive foundation. Retrieved from http://cnx.org/contents/1741effd-9cda-4b2b-a91e003e6f587263@43.5. Available under Creative Commons Attribution 4.0 International License. (CC BY 4.0). Modified from original.

University of California College Prep. (2012). AP environmental science. Retrieved from http://cnx.org/content/col10548/1.2/. Available under Creative Commons Attribution 4.0 International License. (CC BY 4.0). Modified from original.