We humans need a lot of energy to maintain our modern civilization. We will need even more energy in the future, because billions of people living in developing nations will require a lot more energy in order to raise their standard of living to that of the developed world.

Nevertheless, it is possible, because we already have technologies that could in principle allow us to meet all our energy needs without continued use of fossil fuels. Broadly speaking, we can separate these technologies into three major categories:

• Energy efficiency
• Renewable energy
• Nuclear energy

In the rest of this section, we’ll briefly investigate these technologies, along with their benefits and drawbacks.

Energy Efficiency

The cheapest and easiest way to make headway against global warming (and all related energy issues) is to reduce the demand for energy. After all, if we can live our lives while using less energy, then it will be much easier to find ways to generate the energy we need.

Note that the goal of energy efficiency is to reduce energy use, not to reduce quality of life. In fact, when done well, efficiency can improve quality of life. Broadly speaking, there are two basic ways to do this:

• Adopting technologies that use energy more efficiently, meaning that they require less energy to perform the same (or better) functions.
• Making lifestyle choices that allow us to live better and healthier lives while using less energy and/or reducing emissions of greenhouse gases.

We’ll consider a few examples of each.

Energy-Efficient Technology

 

 
 
 
 
 
 
 
 

Figure 7.3.1–2 – These pictures show examples of three common lighting technologies.

Similar savings of both energy and cost are possible in many other ways. Here are just a few examples:

• Installing better insulation and better windows can dramatically decrease the energy needed to keep a building warm in the winter and cool in the summer.
• Replacing appliances like refrigerators, washers, and dryers with more efficient models can greatly reduce electricity use.
• Driving a car that has better fuel economy (meaning it can go a longer distance on a particular amount of gas) means using less gasoline and therefore lower carbon dioxide emissions. Replacing a gasoline car with an electric car is generally even better, for two reasons: First, electric car engines are generally much more efficient than gasoline-powered engines, so the same total amount of energy will go much farther in an electric car. Second, if you get the electricity from a non-fossil source, such as solar panels on your roof, a wind power station, or a nuclear power station, then driving an electric car will not produce any greenhouse emissions at all.

Overall, improved energy efficiency is what you might call a “no-brainer”: It saves both energy and money, with no reduction in benefits or lifestyle. Moreover, because it means less total energy use, it can help reduce the future amount of global warming even if some of our energy is still coming from fossil fuels. And, of course, improved energy efficiency will make it easier to transition away from fossil fuels, since we’d need fewer new energy sources to replace the fossil fuels.

Lifestyle Choices and Carbon Footprint

The second general way we can reduce energy usage and greenhouse emissions is through lifestyle choices. Since our focus is on global warming, we will consider what is called your carbon footprint, which means the total amount of greenhouse gas that is added to the atmosphere as a result of the way you live your life. The same idea can be applied more broadly to groups of people, businesses, or communities.

There are many ways that you can reduce your carbon footprint. Slide show 7.3.1-3 shows just a few examples, and you can surely think of many more possibilities. Be sure to notice that while some of these choices might seem like they require lifestyle sacrifices, in many cases they can also enhance your life. For example, driving less by walking or riding a bike can keep you healthier, and taking mass transit to school gives you time to study on the way and reduces the risk of getting stuck in traffic.

Slide Show 7.3.1–3 – There are many ways to reduce your energy use and your carbon footprint. These slides offer just a few examples.

Renewable Energy

The most fashionable alternatives to fossil fuels are renewable energy sources such as wind, solar, geothermal, hydroelectric, and biofuels. While none of these sources are perfect — for example, solar panels contain toxic chemicals, wind turbines can kill birds and bats, and dams for hydroelectric power can damage river ecosystems — they have the advantage of producing energy without increasing the concentration of carbon dioxide or other greenhouse gases in our atmosphere. Debates about renewables therefore focus on how much energy they can realistically provide, whether they are cost-effective, and their relative pros and cons.

As we discuss renewable (and other) energy sources, it will be helpful if you review the units we use to measure energy and power in Section 4.2.3. (It will also help to do the Activity below.) Recall that current total world power consumption is approximately 15 terawatts, meaning that as a civilization, we use about 15 trillion joules of energy each second.

Wind

We’ll look briefly at each of the five major types of renewable energy, starting with wind power. You have probably seen huge wind turbines that can generate electricity. They can be installed either on land or offshore (Figure 7.3.1–4).

 
 

Figure 7.3.1–4 – Wind turbines can be located either on land or offshore. Offshore winds are often steadier, but of course they are available only along coastlines.

Moreover, the cost of wind power has dropped dramatically in the past couple decades, and it is now generally cheaper to produce energy with wind than with fossil fuels. As a result, wind has been generating a rapidly growing (though still small) fraction of the world’s electricity. Figure 7.3.1-5 shows data on the installed wind capacity, meaning the total power that could be generated if all the installed wind turbines were operating at the same time.

So is wind the solution to all our problems of global warming? While it has great potential, wind also faces numerous challenges. Try the following questions to see what you already know or can figure out about some of the challenges of wind power and how they might be met.

Discuss the following questions with a classmate. Then click to open the answers to see if they agree with what you came up with.

It’s also worth noting that while wind power has many advantages over fossil fuels, the installation of wind turbines often faces local opposition, primarily due to aesthetics (for example, claims that they’ll ruin a beautiful landscape), the land they require, or the noise they can generate. This type of opposition has stalled numerous proposed wind projects. On the other hand, wind is often popular with farmers and ranchers, because they can earn money by leasing their land for wind turbines while still making use of most of their land.

Solar
Like wind energy, solar energy has become much less expensive in recent years. As a result, you can now see solar energy in use in most parts of the world. Broadly speaking, there are three major ways in which people are tapping solar energy today (Figure 7.3.1–6):

Figure 7.3.1–6 – These photos show three major ways in which sunlight is used to supply energy for human activities.

The global potential for solar energy is enormous. The total amount of solar power reaching Earth in the form of sunlight is more than 20,000 times current world power usage. In other words, if we could somehow tap just 1/20,000 of the energy that reaches Earth in the form of sunlight, it could meet all of our energy needs. Because the amount of available solar energy varies by location (largely due to latitude and weather), and because solar systems cannot convert 100% of the sunlight that hits them into energy, capturing this much solar energy would require solar systems covering roughly 1/1,000 of Earth’s surface. Figure 7.3.1–7 shows one way of envisioning what this land area looks like to scale on a world map. Although the required area is small compared to the world’s total area, it is still quite significant. For example, even if we put solar panels on every rooftop in the world, it would still add up to only a few percent of this needed area.

Besides the challenge of covering enough area to make a large dent in fossil fuel use, the other main challenge of solar is the same challenge we face with wind: it is an intermittent energy source, available only in daytime and when it is not cloudy. This can create particular challenges at high latitudes (such as in northern Europe), because these latitudes get very little daylight during the winter, and while they get plenty of sunlight in summer, there is not currently an easy way to store that energy for later use.

Despite the challenges, solar power is likely to play a large role in a transition away from fossil fuels. Aside from land use, its only other significant downside is in the materials that must be mined, manufactured, and eventually disposed of or recycled (once they exhaust their useful lifetimes). Some of these include toxic metals and other chemicals, which makes recycling particularly important for solar panels, since otherwise these would leach into the environment.

Geothermal

The third renewable energy source we’ll discuss is geothermal energy , which means energy extracted from Earth. There are two major but very different ways to take advantage of geothermal energy.

The first is to use heat from deep within the Earth. This heat can be used to generate clean and efficient energy, but it is generally available only near volcanoes, geysers, or hot springs. Still, that means a lot of places, and geothermal energy is becoming increasingly common in such areas. Iceland, for example, now gets the vast majority of its energy from geothermal power plants (Figure 7.3.1–8).

The second way of getting energy from Earth is much simpler and can be used almost anywhere. It is often called a geothermal heat pump (or “ground source” heat pump), and it simply takes advantage of the fact that if you drill down just two to three meters, the ground stays at an almost uniform temperature all year round. It is therefore possible to use a simple “heat exchanger” to extract heat from the ground in winter and dump heat into the ground in summer, which means that it can provide both heating and air conditioning. Video 7.3.1–9 explains how these systems work. If more widely implemented, these systems could meet much of the world’s residential and business needs for heating and cooling.

Hydroelectric

Hydroelectric power means electricity produced with water, such as that produced by dams on rivers. A dam basically uses gravity to generate energy: It forces downhill-flowing water through openings that drive turbines to make electricity. Figure 7.3.1–10 and the accompanying video show the basic operation of a dam-based hydroelectric power system.

 
 
 
 
 
 

Hydroelectric power is currently the world’s largest source of renewable energy, because it is both clean and relatively inexpensive. However, while it does not produce any greenhouse gases directly, the construction of dams can in some cases lead to substantial emissions (as explained in the above video). In addition, dams can have damaging effects on river ecosystems, and breaches of dams can cause damaging floods. As a result, the building of dams for hydroelectric power is often controversial.

While most existing hydropower comes from rivers (and most of that from dams), it is also possible to generate hydropower from tides. In this case, the inflow and outflow of water with the tides is used to turn turbines and generate electricity. Tidal power has so far been tapped only in a few places around the world, though it has great potential for the future (Video 7.3.1–11).

Biofuels

The final category of renewable energy that we’ll discuss is biofuels, which represents any use of organic matter — such as crops, wood, manure, or food waste — for generating energy . The particular type of organic matter that is used is called the feedstock for the biofuel. Common crop feedstocks include corn, sugar cane, sorghum, and soybeans.

The main reason for interest in biofuels as a replacement for fossil fuels is that they can often be used in existing engines for transportation (such as in cars, buses, boats, and airplanes). In other words, instead of having to replace existing gasoline-powered cars with electric cars, we could in principle just replace the gasoline with biofuel.

The key question, then, is whether and how much this really helps to combat global warming. Biofuels are certainly “renewable” in the sense that the feedstocks used to make them can be regrown. But whether they are renewable in a carbon neutral way (meaning a way that does not add to the atmospheric carbon dioxide concentration) depends on the details of how they are grown. More specifically, biofuels are carbon neutral only if growing the feedstock absorbs the same amount of carbon dioxide from the atmosphere that is later released when the biofuels are burned.

Unfortunately, most biofuels used to date have not been used in a carbon neutral way. In some cases the reason is that land has been cleared of forest to make room for the feedstocks, and deforestation adds carbon dioxide to the atmosphere. In other cases the reason is that it can take a lot of energy to produce the biofuels, and this energy has generally come from fossil fuels. Moreover, using land to grow crops for biofuels means that land is not being used for food production. As a result, biofuel production has in some cases led to a smaller food supply and higher food prices. Video 7.3.1–12 summarizes some of the uses and issues of biofuels.

Nuclear Energy

Our third existing technology (after energy efficiency and renewable energy) for solving global warming is nuclear energy . Nuclear energy is a potential solution to global warming for four key reasons:

These four facts explain why nuclear power has strong support from climate scientists, and has also received strong support from the Intergovernmental Panel on Climate Change (IPCC). Nevertheless, nuclear energy has been very controversial. Let’s look briefly at some of the issues around nuclear energy.

Basics of Nuclear Energy

Nuclear energy is a real-life example of Einstein’s famous equation E = mc² (discussed earlier in this Take it to the Next Level box), because the energy comes from converting a small amount of mass into energy. There are two basic processes that can release nuclear energy (Figure 7.3.1–13):

• Nuclear fission is the splitting of a large atomic nucleus (such as that of uranium) into smaller ones.
• Nuclear fusion is the process of combining two or more small nuclei into a larger one. This is the energy source of the stars; for example, the Sun generates energy through nuclear fusion of hydrogen to make helium.

All current nuclear power plants generate energy through nuclear fission, though many scientists and engineers are working hard to develop fusion as a power source (we’ll discuss fusion in Section 7.3.2).

The basic principle of a nuclear power plant is fairly simple:

• The nuclear reactions (always fission in today’s nuclear power plants) occur in a structure called the nuclear reactor , where the energy released by the reactions creates heat.
• The heat generated in the reactor is used to heat water to make steam, which turns a turbine that is used to generate electricity (see this earlier box).

Video 7.3.1–14 explains this basic operation. If you’d like to know more about the nuclear reactions themselves, see the Take it to the Next Level box below.

Nuclear Concerns and Counterpoints

The controversy about nuclear energy can be traced to several concerns. Here, we’ll briefly describe each of the major concerns, along with counterpoints to those concerns cited by supporters of nuclear energy.

Concern — Radiation (during normal operation): The uranium fuel used in nuclear reactors is radioactive, as are many of the by-products of uranium fission. This fact has led many people to fear that living near a nuclear power plant would mean a danger from the radiation produced inside the power plant.

Counterpoint: While entering the core of a nuclear reactor would be exceedingly dangerous, the structure that contains the reactor prevents this radiation from escaping. Therefore, as long as the plant is operating normally, its radiation poses no danger either to people working at the plant or to the public in surrounding areas. This fact surprises many people, but you can understand it by remembering (from Chapter 4 and this box) that virtually all rocks contain at least some radioactive material. This means there is natural background radiation at all times and in all places. Measurements show that the radiation you would receive even living next door to a nuclear power plant is much, much smaller than the radiation we all receive from the natural environment around us (see the I was Wondering box for details).

Concern — Accidents and “Meltdown”: Nuclear power plants may be safe when operating normally, but accidents can lead to the release of much more radiation. The most significant accidents are those in which the core undergoes what is often called meltdown , in which fuel rods in the core begin to melt and large amounts of radiation can be released into the environment. There have been three major accidents involving meltdown at nuclear power plants: Three Mile Island (Pennsylvania, USA) in 1979, Chernobyl (in Ukraine, then part of the Soviet Union) in 1986, and Fukushima (Japan) in 2011. Chernobyl was by far the worst, having released so much radiation that it forced tens to hundreds of thousands of people to permanently leave their homes and is likely to have caused thousands of premature cancer deaths (Figure 7.3.1–15). Because there no way to prevent all accidents, even with the best safety precautions, many people argue that nuclear power is simply too dangerous to be acceptable.

Counterpoint: Everyone agrees that accidents will inevitably occur, so the main counterpoint focuses on comparative danger. Consider, for example, the three major nuclear accidents mentioned above. While both Three Mile Island and Fukushima did indeed release significant amounts of radiation, there is no evidence to date of anyone in the general public having received a dosage large enough to cause cancer or other shortening of life span. Indeed, the only known deaths from nuclear power plant accidents came from Chernobyl: at least 30 workers died from radiation-related illnesses within months of the accident, and it is likely that the radiation has caused or will cause thousands more people to die prematurely from radiation-induced cancers. Therefore, as bad as these nuclear accidents have been, the sum total of deaths attributable to nuclear power in all of history is far smaller than the estimated 5 to 10 million premature deaths that occur every single year as a result of air and water pollution caused by the use of fossil fuels.

In fact, per unit of energy generated, nuclear power appears to be about as safe or safer even than most renewable sources. For example, thousands of people have been killed (and millions more displaced from their homes) in building dams for hydropower, and even wind and solar can lead to deaths during the mining of their materials and in people falling from wind towers or roofs. Figure 7.3.1–16 compares estimated death rates from various power sources.

Moreover, new technologies should make it possible to make nuclear power plants much safer. In particular, the danger of meltdown arises from the fact that existing nuclear power plants use what is called active cooling to prevent their nuclear fuel from overheating. This means that if an accident causes a problem in which the cooling system fails, it can lead to a meltdown and release of radioactive materials. However, new reactor designs have been developed to use passive cooling (for example, mixing the fuel with salt so that it expands if the temperature rises, thereby slowing the reactions), in which the power plant would automatically turn itself off if a similar accident occurred. These and other engineering improvements offer the potential to make new nuclear power plants far safer than those built in the past. In many cases, it may also be possible to retrofit existing nuclear power plants with these new, safer technologies.

Concern — Nuclear waste: Just as you have to refill a car’s fuel tank (or recharge its batteries), nuclear power plants need fuel “refills” as well, and that means the “used up” fuel must be discarded. This discarded fuel is usually called nuclear waste , and this waste will remain dangerously radioactive for tens of thousands of years. It will therefore pose a danger to future generations unless we find a way to keep it isolated enough that no one will ever come across it by accident. So far, no one has come up with a way to permanently and safely deal with this nuclear waste.

Second, it turns out that because nuclear “waste” is still radioactive, it can in principle be used to generate further energy until the remaining radioactivity is extremely low. While existing nuclear power plants can’t do this, it is possible that future nuclear power plants will be able to. In other words, instead of having to dispose of nuclear waste, we may be able to keep using it until no longer poses much danger. An added advantage of this approach is that it means we wouldn’t have to mine as much new uranium, because we would instead use existing waste as nuclear fuel. Video 7.3.1–17 summarizes the main counterpoints regrading nuclear waste.

Concern — Nuclear terrorism or sabotage: The radioactive fuel used in nuclear power plants could be used to cause great damage if terrorists were to sabotage a nuclear power plant or to steal the fuel either from a plant or while it is being transported to a plant.

Counterpoint: This threat is a major concern, especially if we expand the use of nuclear power, since that would mean more radioactive material being transported around the world. The main counterpoint is that, in general, we successfully protect many other critical supplies and sites (such as airports and government buildings). Therefore, if we are diligent, it should be possible to protect nuclear power as well.

Concern — Spread of nuclear weapons: The fuel used in nuclear power plants cannot be used to make nuclear bombs, because it doesn’t contain enough of the bomb-making material (uranium-235). However, as discussed in the Take it to the Next Level box above, making the fuel for nuclear power plants requires a process called “enrichment,” and this same process could in principle be continued to the point where the uranium could be used for a bomb. This fact creates concern about the spread of nuclear weapons to nations or groups that don’t currently have them (which is called “nuclear proliferation”), because it makes it difficult to distinguish whether nuclear power capabilities are being built solely to generate energy or also to build nuclear weapons.

Counterpoint: Again, this is a real concern. However, there are two main counterpoints. The first is based on international agreements designed to prevent the spread of nuclear weapons. Enrichment is a complex process that requires large machines, which means these machines are not easy to hide. Therefore, as long as any nation doing enrichment for nuclear power agrees to international inspections (which are currently conducted by the International Atomic Energy Agency), it should be possible to verify that enrichment is being done only to the point of making fuel for power plants, not for making bombs. Alternatively, enrichment might be allowed in only a few places where it could be carefully controlled, with the fuel distributed for nuclear reactors around the world.

The second counterpoint is that nuclear power plants could actually help the world reduce or eliminate nuclear weapons, because existing nuclear weapons can be dismantled and have their material “de-enriched” to be used as nuclear fuel. In fact, this has already been done: From about 1991 to 2013, about 10% of the electricity used in the USA was generated by nuclear power with fuel recovered from dismantled nuclear bombs . Estimates indicate that dismantling the world’s remaining nuclear weapons could provide enough nuclear fuel to power the entire world for many years.

Concern — Nuclear power costs too much: Building nuclear power plants is very expensive (Figure 7.3.1–18), and money must also be set aside for dealing with their waste and for their eventual decommissioning, when they must be safely shut down and dismantled. As a result, nuclear power has historically proven to be much more expensive than most other energy sources, including both fossil fuels and renewables like wind and solar.

Counterpoint: This has indeed been true, but it is not inevitable that nuclear power should remain so expensive. At least part of the reason for nuclear power’s high cost can be traced to public fears (that is, all the other concerns above). These fears mean that anyone trying to build a nuclear power plant is taking a risk that the plant will be delayed or stopped by public opposition, and this type of delay ends up costing a lot of money. If public fears can be overcome (that is, if people accept the counterpoints above), the cost of nuclear power might drop dramatically, especially if accompanied by a concerted effort to standardize and improve nuclear construction.

Moreover, even if wind and solar remain cheaper, they still have the problems of being intermittent, which means they generally need “backup” from another power source. Today, that backup source is almost always fossil fuels, which are the main cause of global warming. Therefore, even if nuclear is more expensive than wind and solar, it may be necessary as a backup to those energy sources. After all, whatever the cost of nuclear power, it is almost certain to be less than the human and economic costs of global warming.

To summarize, there are several real and legitimate concerns about nuclear power, but each of them has counterpoints that might alleviate the concern.

Summary — Existing Solutions to Global Warming

We’ve covered a lot of ground in here in Section 7.3.1, so it’s worth looking back to summarize what you’ve hopefully learned.

The first and most important lesson is this:

We already have technology that, at least in principle, could allow us to almost completely eliminate the emissions of greenhouse gases that cause global warming while still having plenty of energy to maintain and improve living standards around the world.

These technologies fall into three basic categories: energy efficiency, renewable energy, and nuclear energy. The first category (energy efficiency) can in principle greatly reduce our energy needs without any downsides, but efficiency alone cannot eliminate greenhouse emissions, since we will still need a lot of energy.

Therefore, in terms of replacing the fossil fuels that are causing global warming, our two basic options are renewables, especially wind and solar, and nuclear. We’ve discussed the pros and cons of these options in some detail, but at the risk of oversimplifying, the debate comes down mainly to the following:

• Wind and solar:
  Pro: There is in principle plenty of energy available to meet all our energy needs through these clean, renewable sources.
  Con: Scaling up use of these sources to replace fossil fuels is an enormous challenge, and one that might not be possible to meet without new technological developments for battery or other storage.
• Nuclear:
  Pro: It should be much easier to scale up to replace fossil fuel power, mainly because it provides the same type of steady (not intermittent) energy and doesn’t require any more land or material than fossil fuel power plants.
  Con: The public has many fears about nuclear power, some of them very legitimate, and unless we can overcome these fears, it will be difficult to build new nuclear power plants.

So we’ll leave this section with the most important question of all: What technologies do you think we should use to solve the problem of global warming?