In addition to the existing technologies that we discussed in the prior section, researchers and entrepreneurs around the world are investigating many other technologies that could in principle provide us many more ways to address the problems of global warming. Some of these are “modest” extensions of existing technologies that are very likely to happen within the next couple of decades. For example:

• Offshore wind technology is rapidly advancing, so in the future we will likely be able to make much more use of offshore wind.
• Solar photovoltaic technology is also rapidly advancing, which should allow us to make solar panels that will convert a higher percentage of the sunlight they receive into electricity.
• Huge advancements are also occurring in the technology for tidal power, which could make it a substantial source of energy in the future.
• Battery and other energy storage technologies are rapidly advancing, which will make it much easier to make use of renewable energy sources.

But remember that we want you think long term, out toward the year 2100 and beyond. For that, it is worth thinking about some technologies that are only beginning to be developed today, but that have tremendous potential for the future. In the rest of this section, we’ll briefly discuss four of these technologies: microbe-based biofuels, solar energy from space, nuclear fusion, and active removal of carbon dioxide.

Algae-based Biofuels

We’ve already discussed existing biofuels (such as those made from corn, sugar cane, sorghum, and soybeans). Recall that while these biofuels can in principle replace some of our fossil fuel usage, they also have some notable drawbacks. In particular, the way they have been grown to date has not been truly carbon neutral, and they use land and water that could otherwise be used for food production.

Future biofuels may be much better. In particular, many researchers are working to develop biofuels made from microbes such as algae. Algae are rich in natural oils that, in principle, can be “refined” into fuels that could directly replace petroleum-based fossil fuels. Moreover, algae can much more easily be grown in a truly carbon neutral way, in which they absorb just as much carbon dioxide during growth as they release later when burned. In fact, it may even be possible to produce algae-based biofuels in a way that is carbon negative, meaning that some of the carbon dioxide the algae absorb during growth is converted into a form (sometimes called “hydrochar”) that can be used or buried in a way that does not return this carbon dioxide to the atmosphere. If so, then these biofuels might help us eventually begin to lower the carbon dioxide concentration from its current high levels.

A further advantage of algae-based fuels is that they can be grown almost anywhere — perhaps even in floating, enclosed “ponds” in the ocean — and they can be grown with seawater or wastewater. This means that, unlike existing biofuels, they should not have any negative consequences for the availability of food or fresh water.

Unfortunately, despite these attractive features of algae-based biofuels, they’ve also proven to be technologically challenging to produce. More than a decade ago, numerous new companies were working to produce algae-based biofuels, and these fuels were successfully tested in cars, airplanes, and ships. However, none of these companies were able to scale up the production to a level that was commercially viable, and most of them have either gone out of business or have changed their product focus.

Nevertheless, algae-based biofuels still hold promise. and they may yet prove to be an important future technology for fossil fuel replacement. Video 7.3.2–1 describes some ongoing research in the development of these fuels.

Solar Energy from Space

As we’ve discussed, one of the major drawbacks to solar energy on Earth is the fact that it is intermittent, working only in the daytime when it is not cloudy. But it’s never cloudy in space, and if you put solar panels in a high enough orbit, it is never nighttime either. So another idea for solving our energy and global warming problems is to launch solar panels into high Earth orbit (Figure/Video 7.3.2–2), where they would absorb sunlight and beam the energy down to collecting stations on Earth. Recall that the power of sunlight shining on Earth is more than 20,000 times current world power usage, and there is even more power available from high orbits. Therefore, solar energy from space could easily meet almost any future energy need that we can imagine.

Figure/video 7.3.2–2 – The amount of solar energy available in Earth orbit is tens of thousands of times as much we need on Earth today. Therefore, if we could harness solar energy from space, it could in principle meet all our future energy needs even as we vastly raise living standards for people around the world.

It would obviously be expensive to launch solar panels into space, but perhaps not as expensive as you might guess. The “panels” for use in space might well be no thicker than a thin film of plastic wrap, so enormous panels could potentially be unfurled from lightweight spools that could be launched by existing rockets. Moreover, these panels would not degrade in space the way they would on Earth, so once launched into orbit, they would likely provide energy for decades (or more) without the need for replacement. Overall, the total launch costs for enough panels to meet all global energy needs for decades might well be less than we spend (globally) on energy in a single year at present.

The greater challenges to using solar energy from space probably lie in the technology for transmitting the energy to Earth, in building the collecting stations for that energy, and in tying those stations into a power grid that could distribute the energy around the world. But none of these challenges appear to be insurmountable, and proponents of solar energy from space argue that we could start implementing it now if we were willing to make a concerted effort on it. Indeed, in 2020, the U.S. Naval Research Laboratory launched the first test of a device for beaming solar energy from space down to Earth (click here for a short video about this mission).

Nuclear Fusion

Recall that all current nuclear power plants are based on nuclear fission, in which atoms of heavy elements such as uranium are split apart. But what if we could instead tap nuclear fusion , which is the power source of the Sun and other stars? In other words, imagine that we could in essence create power plants that would act like miniature suns, fusing hydrogen to make helium.

Let’s assume for a moment that we could do fusion the same way that the Sun does, using ordinary hydrogen. In that case, we could simply extract the hydrogen fuel from any source of water (since water is H₂O). For example, if we had a miniature fusion power plant hooked up to your kitchen sink faucet, we could in principle extract hydrogen from the water flowing through it. So to get a sense of the potential of fusion as a power source, take a guess at how much power we could in principle generate simply by using the hydrogen extracted from the water from your kitchen faucet. That is, before continuing on, try the multiple choice question in Figure 7.3.2–3.

In reality, we will probably do fusion slightly differently than the way it occurs in the Sun. Instead of fusing ordinary hydrogen, as the Sun does, future fusion power will probably start with the form (isotope) of hydrogen called deuterium . However, deuterium can also be extracted from ordinary water, because about 1 out of every 6,400 hydrogen atoms is actually a deuterium atom. Therefore, instead of the water flow of a single kitchen faucet, you’d need the flow of 6,400 faucets to get the same answer to the question in Figure 7.3.2–3. This still isn’t much water, as it is only about the flow of a typical small creek.

The tremendous power potential of fusion is only the beginning of its advantages. For example:

• The final product of nuclear fusion is helium, which is not only safe and nontoxic, but actually quite useful. This means that fusion is not only a carbon-free power source, but it produces no other pollutants at all.
• The fact that we can get all the hydrogen or deuterium fuel we need from a small amount of water means there is no mining needed for fusion, which means it does not have any of the downsides even of even wind or solar energy.
• Fusion produces very little radioactive waste compared to fission , and the waste decays more rapidly, so it poses less of a challenge for safely burying away.
• Fusion power is completely safe, because it is physically impossible for a nuclear fusion plant to go out of control and have a meltdown.
• Fusion power plants would not be prone to any of the other concerns we discussed for existing nuclear fission power either. For example, because the fuel and byproducts are simply hydrogen (or deuterium) and helium, they would be worthless to terrorists or bomb makers.

Overall, fusion is almost undoubtedly the safest, cleanest, and most abundant energy source that we could potentially make use of. Moreover, because the fuel can be extracted from water, the operating costs of a nuclear fusion power plant would be very low. Therefore, if we could build nuclear fusion power plants cheaply enough, fusion would provide us with a virtually unlimited and almost free source of energy.

Given such incredible potential, you might wonder what’s stopping us, and the answer is simple: Despite decades of effort, no has yet figured out how to tap nuclear fusion for commercial power. However, a lot of progress is being made. One particularly promising project is the International Thermonuclear Experimental Reactor, or ITER, which is currently under construction in France with the goal of demonstrating commercially viable nuclear fusion within about a decade. Numerous other research teams around the world, including many at universities and even private companies, are working to try to develop fusion power. Watch the following three, short videos to get a little deeper understanding of fusion and the work currently being done to develop it as a future energy source.

Videos 7.3.2–4 – You can find many videos and documentaries about nuclear fusion, but we’ve chosen these three to give you a short (about 10 minutes total) overview of fusion and the ITER project.

Active Carbon Dioxide Removal

Imagine for a moment that we successfully implement carbon neutral technologies like those we’ve discussed so far, so that we are no longer adding carbon dioxide or other greenhouse gases to the atmosphere. Does that mean the problem of global warming will have been solved?

Unfortunately, that alone may not do it. To understand why, look again at Figure 7.1.2–4, repeated below. Notice that, even if we were to stop carbon dioxide emissions immediately, it would still leave us far above the pre-industrial carbon dioxide concentration of 280 parts per million. That means we’ll continue to suffer all the consequences of global warming that we are already experiencing. In fact, models indicate that the global average temperature will continue to rise — and the consequences continue to worsen — for at least several decades after we stop adding greenhouse emissions to the atmosphere.

Therefore, a more complete solution to the problem of global warming requires not only stopping our ongoing carbon dioxide emissions, but also finding a way to remove some of the carbon dioxide we’ve already added. Based on current climate models, most climate scientists think that we could alleviate most or all of the negative consequences of global warming if we could bring the carbon dioxide level back down to about 350 parts per million.

So how might we remove carbon dioxide from the atmosphere? One obvious way is to plant more trees, since trees store carbon dioxide as they grow (Figure 7.3.2–5). Improved farming practices could also store more carbon dioxide in soil. However, while both of these are worthwhile strategies, they probably cannot by themselves bring the carbon dioxide level down as much as we would like.

The difficulty with these ideas is the scale at which they would need to be implemented. For example, direct air capture would require vast numbers of carbon capture machines placed all around the world. Moreover, these machines would require a lot of energy to run (by some estimates, they might require up to half of the world’s current energy usage), which means they would not be practical unless we first had abundant, carbon neutral energy available.

Nevertheless, you should recognize good news here: While we will need new technological advances to do it, it seems reasonable to assume that we’ll eventually develop ways of restoring Earth’s natural carbon dioxide balance. If we can do this quickly enough, you might end up living much of your life in a “post-global warming world,” meaning a world in which the devastating consequences of global warming have been put behind us.

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