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Climate Change

To contextualize carbon capture, it is important to understand some of the fundamentals of climate change. Unfortunately, climate change has become very politicized since the beginning of this century, and the debate has extended well beyond the public policy options to the fundamentals, such as whether or not climate change is induced by humankind. However, there is a strong consensus in the scientific community on many key aspects of climate change. Much of this consensus comes from the series of assessment reports put out by the Intergovernmental Panel on Climate Change (IPCC), with hundreds of leading scientists from around the world working on each report; for this work, the IPCC was awarded the Nobel Peace Prize in 2007.1 It is this consensus on climate change that I will present in this chapter. While the detailed scientific analysis is quite complex, the scientific concepts discussed below are relatively straightforward and easy to grasp.

Let us start with the Earth’s energy balance. Energy enters the Earth’s atmosphere in the form of solar radiation. About 30 percent of this radiation is immediately reflected back to outer space, but the Earth’s land, ocean, and atmosphere absorb the rest. This absorbed heat is eventually re-radiated back to outer space in the form of infrared radiation. As long as the outgoing energy is equal to the incoming energy, the planet will neither heat up nor cool down.

This brings us to the greenhouse effect. Certain gases in the atmosphere called “greenhouse gases” absorb the outgoing infrared radiation from the Earth’s surface and then re-radiate it in all directions. This has the effect of putting a blanket over the Earth to make it warmer. If there were no greenhouse gases in the Earth’s atmosphere, the temperature of the Earth would be approximately −18°C, making the planet too cold to support life as we know it. Instead, it is a much more comfortable 15°C, thanks to this natural greenhouse effect.2

The most important greenhouse gases—water vapor (H2O), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)—occur naturally in our atmosphere. Since the Industrial Revolution, man has been adding to the amount of carbon dioxide, methane, and nitrous oxide through the burning of fossil fuels, land use changes like deforestation, and agricultural practices such as fertilizer use. The addition of these gases to the atmosphere warm the Earth beyond the temperature of the natural greenhouse effect. In terms of the “blanket” analogy, we are making the blanket thicker; this is the enhanced greenhouse effect, and it is affecting our climate.

Scientists have known about the enhanced greenhouse effect for well over a century. In 1896, the Nobel Prize–winning Swedish scientist Svante Arrhenius published an article calculating that the Earth’s temperature could rise several degrees Celsius if the amount of CO2 in the atmosphere doubled.3 Back then, the amount of fossil fuels being burned was a small fraction of what they are today, so this doubling would take more than a thousand years to arrive. At the time, Arrhenius’s calculation was an interesting theoretical exercise, but no one really considered it of practical interest. Our use of fossil fuels has increased drastically in the last century and a quarter, making the enhanced greenhouse effect much more than an interesting theoretical exercise. In fact, there is a good chance it will be the number one public policy issue of the twenty-first century.

The Climate Diamond

I have found figure 1 very helpful in explaining climate change and the options for doing something about it; I call it the “climate diamond,” because it looks like a baseball diamond. Due to human activity, the concentration of greenhouse gases in the atmosphere is rising. My focus in this book will be on CO2: the greenhouse gas emitted by human activity that is the main contributor to climate change. The largest source of this CO2 is the burning of fossil fuels in power plants, industry, automobiles, our homes, and more. The concentration of CO2 in the atmosphere in preindustrial times was about 275 parts per million (ppm). Today that number has surpassed 400 ppm—an increase of 45 percent. There is good data on the usage of fossil fuels worldwide and their associated emissions of CO2; for the United States, the Department of Energy’s Energy Information Administration has detailed energy use data going back to 1950.4 Internationally, most countries gather similar data, and the International Energy Agency maintains databases of energy use worldwide. In addition, since March of 1958, the Mauna Loa observatory in Hawaii has made precise measurements of the atmospheric concentration of CO2. As a result, there is a very high level of understanding of the link between human activity and the concentration of CO2 in the atmosphere.

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Figure 1 The climate diamond, showing the interactions in the climate system and possible intervention strategies.

Due to the greenhouse effect, an increasing amount of greenhouse gases in the atmosphere will cause the global temperature to rise. The term “climate sensitivity” describes how much the Earth will warm on average for a doubling of CO2. In his paper, Arrhenius calculated this number to be about 4°C. Today, we use sophisticated computer models of the atmosphere and oceans to predict the climate sensitivity. Despite the vast amounts of computing power devoted to estimate climate sensitivity, its exact value is uncertain, but, according to the IPCC, it “is likely in the range 1.5°C to 4.5°C with high confidence.”5 Due to the complexity of the climate system, this uncertainty is not surprising. Every year our understanding improves, but there is still much work left to do.

As the global temperature rises, it will have an impact on Earth systems. The temperature rise is not uniform, with the rise in the Polar Regions much greater than in the Tropics. We have already seen a dramatic reduction of sea ice in the Arctic Ocean, larger than predicted even a decade ago. One reason for this accelerated melting is that the dark ocean absorbs much more heat than the white ice; therefore, as the ice melts, the Arctic absorbs more heat, which melts more ice, which then absorbs even more heat, and so on. This is an example of a positive feedback loop. Major changes in Earth systems include sea-level rise, shifts in rainfall patterns leading to an increase in both floods and droughts, more intense storms, migration of ecosystems, and extinction of species. While the understanding of the general trends are good, there is still great uncertainty in the timing and magnitude of these changes. For example, predictions for sea-level rise by 2100 range from 0.26 to 0.55 m for a low emissions scenario to 0.45–0.82 m for a high emissions scenario.6

Finally, these changes in Earth systems will have an impact on human activity. Some will be positive, but many will be negative. More violent storms can increase death tolls and require stricter and more expensive building codes. Since about 40% of the Earth’s population lives by an ocean, sea-level rise is of great concern. Already, it seems inevitable that some island states like the Tuvalu and the Marshall Islands will disappear underwater. The incidence of vector-borne disease like dengue fever, West Nile virus, Lyme disease, and malaria will increase. Crop yields may decrease in certain areas, but increase in others. The list goes on, but it is safe to say that climate change will eventually affect everyone on Earth.

Figure 1 also shows an interaction between the atmospheric greenhouse gas concentrations and the Earth systems. This encompasses what is known as the carbon cycle, where carbon is exchanged between the atmosphere, the terrestrial biosphere (i.e., vegetation and soils), and the oceans. In the exchange, greenhouse gases can go in either direction. Plants remove CO2 from the atmosphere during photosynthesis, using sunlight to turn CO2 and H2O into carbohydrates. When the plants die or deforestation occurs, they release greenhouse gases to the atmosphere. The oceans contain about 60 times the amount of carbon found in the atmosphere. Due to natural physical processes, about 80 percent of the anthropogenic CO2 emitted to the atmosphere today will eventually end up in the oceans. There is fear that rising temperatures would melt the permafrost in the Arctic, thereby releasing the methane frozen in the permafrost. Methane is a very potent greenhouse gas, which would accelerate warming.7 While scientists think the probability extremely low, in a worst-case scenario the melting of the permafrost could lead to a doomsday scenario of a runaway greenhouse effect. Today, the terrestrial biosphere and oceans serve as “carbon sinks,” meaning that the net exchange of CO2 is from the atmosphere to the terrestrial biosphere and oceans. Without these carbon sinks, the rise in atmospheric greenhouse gas concentrations would be even more dramatic than it is today.

Intervention Strategies

In addition to depicting the key interactions necessary to understand climate change, figure 1 also illustrates the major intervention strategies at the disposal of humankind. Mitigation is the reduction of greenhouse gas emissions that go into the atmosphere from human activity. Adaptation is the changing of human activity to adjust to the changes in the Earth systems. Carbon Dioxide Removal (CDR) is the removing of CO2 from the atmosphere. Finally, Solar Radiation Management (SRM) is the deployment of programs to increase the amount of incoming sunlight reflected immediately back into space. Geoengineering has become a popular term to encompass both SRM and CDR. Carbon capture is a major option for both mitigation and CDR.

Mitigation

When people talk about reducing their carbon footprint, they are talking about mitigation. Mitigation is the most important intervention strategy because it deals directly with the root cause of the problem: our emissions of greenhouse gases. The more mitigation we undertake, the less of the other three strategies we will need to deploy. On December 12, 2015, 194 countries signed the Paris Agreement that contained the aspirational goal of keeping the global temperature rise well below 2°C.8 To accomplish this, we need to reduce our carbon emissions to near zero sometime in the latter half of this century. There is no silver bullet to achieve this; instead it will require utilizing every mitigation option at our disposal.

For most air pollutants, once the emissions stop, the pollutant will disappear and the impacts will go away. However, this is not the case for CO2, which stays in the atmosphere for centuries. Therefore, to limit the temperature rise to a certain level, we must limit the amount of total CO2 we emit; this is the carbon budget. Because the exact value of climate sensitivity—which relates the amount of CO2 in the atmosphere to long-term temperature rise—is uncertain, the carbon budget is given in probabilistic terms. To ensure a 50 percent chance of limiting warming to 2°C, the carbon budget starting in 2013 is 1,550 billion tonnes (gigatonnes or Gt) CO2.9 For 3°C, the number is 3,300 GtCO2.10 In other words, there is a 50 percent chance that we will exceed the 2°C goal of the Paris Agreement in 2056 if we continue at the current emissions rate of 36 GtCO2 per year.

In terms of technological approaches to reducing CO2 from energy usage, three major mitigation pathways exist: reducing energy use, shifting to low carbon energy sources, and carbon dioxide capture and storage (CCS), referred to throughout this book as “carbon capture.” Improved energy efficiency has the biggest potential to reduce energy use, but behavioral changes, ranging from adjusting commuting methods to modifying eating habits, can also reduce energy use.

There are a myriad of ways to improved energy efficiency. They include replacing incandescent lightbulbs with modern LED lights, increasing the fuel economy of our automobiles, improving the efficiency of our household appliances. Between 1949 and 2016, the energy intensity of the US economy, measured in energy use per unit of Gross Domestic Product (GDP), decreased at a rate of about 1.5 percent a year.11 Going forward, the challenge will be to decrease energy intensity even faster. To meet climate change goals, energy intensity improvements will probably need to at least double the historical rate.

The second major mitigation pathway is to shift to low- or no-carbon energy sources. This includes nuclear power and renewable energies such as wind, solar, biomass, geothermal, and hydro; it also involves shifting from coal to natural gas. All of these options offer significant potential to reduce CO2 emissions, but they also offer challenges, as described in the examples below.

A natural gas-fired power plant will emit about half the CO2 per unit of electrical output than that of a coal-fired power plant. Steered by cheap natural gas prices, coal-to-gas has been a major driver in the reduction of CO2 emissions in the United States over the past decade. In 2005, coal produced 1992 terawatt hours of electricity (TWhe) and natural gas 684 TWhe in the United States. By 2016, coal dropped 38 percent to 1230 TWhe while natural gas surpassed coal by increasing 87 percent to 1280 TWhe.12 However, significant coal-to-gas switching has been limited to North America because natural gas prices are higher in other parts of the world. In the long-term, to reach the 2°C goal of the Paris Agreement, even the emissions from natural gas-fired power plants will become unacceptable unless they are capturing their carbon.

Wind and solar have made great gains in recent years, due in large part to favorable policies like renewable portfolio standards and tax credits. This has led to improvements in these technologies, including significant cost reductions. Despite their high growth rates, wind provided just under 6 percent and solar less than 1 percent of electric sector power production for the United States in 2016.13

The largest single supplier of carbon-free energy today is nuclear power, but its future is controversial. Some countries, like China, are increasing their installed capacity, but others, like Germany, are phasing out all their nuclear units. In the United States, we have approximately one hundred nuclear reactors with a combined capacity of about 100,000 megawatts of electricity (MWe). However, our nuclear fleet is aging and reactors are slowly being retired. Over the next two to three decades, most of the current capacity could be lost. At the same time, it is doubtful that we will build more than a handful of new nuclear reactors. That leaves a lot of carbon-free energy to replace.

The third mitigation pathway is carbon capture. In this scenario, society still burns fossil fuels, but captures its CO2 emissions before they go up the smokestack. The best sources for CCS are power plants and large industrial processes such as refineries, cement plants, steel mills, and fertilizer plants. The captured CO2 can in some instances be utilized, or more likely injected deep underground for permanent storage. I will discuss the strengths and weaknesses of CCS in detail in later chapters.

Adaptation

Greenhouse gases in the atmosphere have already increased enough so that some adaptation is inevitable. While mitigation and adaptation are two sides of the same coin, their politics are very different.

If a country implements a mitigation strategy, that country bears the costs, but the whole world shares in the benefit. This is why international agreements like the one reached in Paris are critical to the success of mitigation. If a large enough percentage of the world’s countries commit to mitigation, then the benefits grow for all of them, making each country’s mitigation program easier to sell.

Adaptation measures are more localized and the benefits more immediate. If sea level rise threatens flooding in a city, that city can decide to spend money on various flood control activities. All the costs accrue to it, but so do all the benefits. Furthermore, the city does not even need to acknowledge that climate change is the problem. Citizens see that flooding is on the increase and they deal with that problem, whether the cause is climate change or something else. Politically, adaptation is a much easier sell than mitigation.

Adaptation is not a substitute for mitigation. It does not address impacts to the natural ecosystems, where the plants and animals may not have the ability to adapt. Developed countries like the United States have the ability to much better adapt than developing countries like Bangladesh, where sea level rise could be devastating. The developed countries have been the major emitters of greenhouse gases, but the developing countries will suffer much more from the impacts. There is no doubt that the world will need to implement adaption strategies to deal with climate change, but it should not be at the expense of mitigation.

Carbon Dioxide Removal (CDR)

The interest in CDR is growing. Why is this? Because it is becoming apparent that we are not going to reduce our CO2 emissions fast enough to avoid surpassing the 2°C goal. As a result, if we exceed the carbon budget associated with 2°C warming, CDR technologies could remove CO2 from the atmosphere to bring the carbon budget back into balance. Since pulling the CO2 out of the atmosphere is generally more expensive than most of the mitigation options, it becomes apparent that this interest in CDR is being driven by the desire not to exceed 2°C warming, coupled with insufficient mitigation efforts.

The above rationale leads to a question: Does the world end if we exceed 2°C warming? The answer is an emphatic no, but it is a slippery slope. The more warming there is, the bigger the changes to the Earth systems and the bigger the risks we take of causing irreversible changes in these systems. This will result in bigger impacts on human activity, bigger costs for adaption, and bigger outlays for damages. The greatest fear, though, is going past some tipping point, such as initiating a runaway greenhouse effect, as discussed earlier.

To implement CDR, we need to develop negative emissions technologies (NETs).14 Many NETs deal with enhancing natural sinks, specifically vegetation, soils, and the oceans. Examples include planting trees to fix atmospheric carbon in biomass and soils, adopting agricultural practices like no-till farming to increase carbon storage in soils, and fertilizing the ocean to increase biological activity to pull carbon from the atmosphere into the ocean. Another approach is enhancing the weathering of minerals, where CO2 in the atmosphere reacts with silicate minerals to form carbonate rocks. This weathering occurs naturally on timescales of hundreds of thousands of years, so the challenge is to speed up this process at an acceptable cost. One more NET involves converting biomass to biochar and using the biochar as a soil amendment. This results in removing carbon from the atmosphere and storing it in the soils. Two proposed NETS directly involve CCS: bioenergy with carbon capture and storage (BECCS), and direct air capture (DAC) of CO2 from ambient air by engineered systems. Chapter 6 analyzes BECCS and DAC in detail.

There is much uncertainty to the cost, scale, and effectiveness of each of these NETs. If we continue on our current trajectories and bust our carbon budget for 2°C in a big way, there is no guarantee that we can remove enough CO2 from the atmosphere to bring the budget back in balance.

Solar Radiation Management (SRM)

By far the most controversial intervention strategy is solar radiation management. The idea is to block incoming sunlight to cool the Earth, in order to counterbalance the warming caused by the enhanced greenhouse effect. The inspiration for this strategy comes from nature, where volcanoes cool the planet by spewing ash and sulfates high up into the atmosphere; this cooling can last for a year or two. In New England, 1816 is known as “The Year without a Summer.” The cause of the unusually cold temperatures was an event on the other side of the globe: the eruption of Mount Tambora in Indonesia in April 1815. More recently, the eruption of Mount Pinatubo in the Philippines in June 1991 depressed global temperatures by about 0.5°C for a couple of years.

SRM mimics nature by injecting particles high up in the atmosphere to block incoming sunlight. Proponents claim that this is relatively cheap and buys us time to get our carbon budget back in line. Opponents say that this would be a big experiment with unknown consequences, ranging from ozone layer destruction to geopolitical conflicts. The proponents reply that we are already conducting a big experiment with unknown consequences by putting greenhouse gases into the atmosphere.

While SRM could bring down the global temperature, there are many questions about its impact at local, regional, and even global levels. A major problem is that ocean acidification, a result of CO2 emissions, would be unaffected by SRM. In addition, it is highly unlikely that the pattern of cooling from SRM will match the pattern of warming caused by greenhouse gases. For example, SRM could introduce drought to a region that would otherwise be fine. The cooling caused by the volcanos only lasts a year or two, so any SRM strategy must continue year after year. Stopping SRM abruptly after it is established may be worse than never using SRM in the first place.

One of the biggest complaints of SRM’s opponents is that people will use it as an excuse not to mitigate. In response, most proponents agree that SRM is not a substitute for mitigation, but given the reality of where global temperatures are headed, they say we must prepare for the future, by researching options for SRM now. I look at SRM as a Hail Mary pass in football: it rarely works, but when it is your only option, you try it. I think the best strategy for humankind is to not get in a position where we need a Hail Mary pass. This means we must mitigate, mitigate, and mitigate some more. That is where carbon capture can make a big contribution.

Notes