Reframing our understanding of carbon dioxide emissions can help clear the path for practical approaches to reducing carbon in the atmosphere.
The physical problem underlying climate change is very simple: dumping carbon dioxide and other greenhouses gases into the air raises their concentrations in the atmosphere and causes gradual warming. In the several decades since climate change has been an important international political issue, the necessary solution to this simple problem has been viewed as equally simple: the world must radically reduce its emissions of carbon-carrying gases.
Here we explore a different perspective, and a different type of solution. Carbon dioxide is a waste product; dumping it into the open air is a form of littering. Dumping can be avoided or cleaned up with technological fixes to our current infrastructure. These fixes do not require drastic reductions in energy use, changes in lifestyle, or transformations in energy technologies. Keeping carbon dioxide out of the atmosphere is a waste management problem. The rapid mixing of carbon dioxide in the atmosphere simplifies this waste management problem compared with others, such as sewage or municipal garbage, where local buildup of waste is deleterious and therefore requires the disposal of the specific waste material as it is generated. By contrast, carbon dioxide does not create local damage, and it does not matter where carbon dioxide molecules are removed from the atmosphere as long as the amount removed equals the amount added.
Waste management was introduced for other effluents because uncontrolled dumping caused serious and irreparable harm. For example, the introduction of sewer systems in European cities in the nineteenth century was driven by the recognition that cholera and typhoid were caused by water contamination. Introducing sewer systems had to overcome arguments that they were too expensive and that the causal relationship between waste and disease was not fully understood. As cause and effect became clear, sewer systems were built.
Nobody can buy a house today without a sanctioned method for sewage handling, and household garbage must be properly disposed of. Residents typically pay a fee to their local government to cover the costs of sewage removal and treatment. In many locations, private companies collect household garbage. Their successful business models rely on the fact that simply dumping garbage on the street is societally unacceptable, recognized as deleterious to health and well-being, and therefore illegal.
Even when the consequences of ignoring waste streams are not as drastic as with sewage, a majority of people may still agree on the societal value of cleaning up. For example, in modern societies, littering along highways is unacceptable. The consensus is visible in the fines established for littering.
From a waste management perspective, carbon dioxide emissions represent the metabolic by-product of industrial activities on which billions of people depend to survive and thrive. Now we must learn to safely dispose of this by-product.
For global climate change, a change in primary focus from emissions reduction and resource conservation to waste disposal changes the approach to the carbon problem. Current policies tend to encourage and reward reductions in carbon dioxide emissions. If the world were to consider carbon dioxide like sewage, this would not be the case. Rewarding people for going to the bathroom less would be nonsensical. Low-flow toilets would certainly be encouraged, but the reduced flow must still be properly channeled into a sewage system. Similarly, the alternative to littering is to properly dispose of (or recycle) trash, not to expect that people let trash accumulate in their cars. As a policy response, parking lots at scenic overlooks feature garbage bins.
The focus on reducing emissions to address climate change has typically included with it a moral judgment against those who emit. Such a moral stance makes virtually everyone a sinner, and makes hypocrites out of many who are concerned about climate change but still partake in the benefits of modernity. A waste management perspective makes it unnecessary to demonize or outlaw activities that create waste streams. It’s okay for people to use toilets and generate garbage; society in turn provides appropriate means of waste disposal to protect the common good. From a waste management perspective, carbon dioxide emissions represent the metabolic by-product of industrial activities on which billions of people depend to survive and thrive. Now we must learn to safely dispose of this by-product.
Another key element of a carbon dioxide waste management approach is that it does not demand a global transformation of existing energy infrastructures and technologies. Waste management demands only the construction of a parallel infrastructure to collect the carbon dioxide and dispose of it safely and permanently. The waste management perspective therefore does not threaten the political, social, and economic interests associated with the fossil energy system—and does not automatically trigger opposition from those interests.
Nor does a waste management orientation require the type of large-scale, coordinated effort that has dominated climate change policy initiatives to date. Because energy systems and transport systems are highly integrated and coordinated, efforts to reduce emissions must be integrated and coordinated as well. For example, adding renewable energy capacity to an electricity grid will not necessarily reduce emissions if the back-up power system necessary to balance intermittencies is still fossil-based. A waste management approach does not demand large-scale coordination; it requires only that individuals and companies start finding ways to dispose of or recycle carbon.
But is it real?
Are there affordable technologies for implementing carbon waste management? Would companies recognize a business model around carbon waste management? And can consumers be convinced that carbon waste management is necessary and that claims of carbon disposal can be trusted?
The centerpieces of carbon waste managements are technologies for carbon dioxide capture and disposal. Such technologies already exist. Disposal is often referred to euphemistically as carbon storage. Carbon can be stored in many ways. It can be tied up in mineral carbonates or biomass; it can be injected underground; it can be stored in waste-disposal sites or bound up in materials that are used in the built infrastructure. Geological storage, the injection of carbon dioxide into underground reservoirs, has been demonstrated, is known to be affordable, and is virtually permanent. Geological surveys indicate that the storage capacity in diverse localities is sufficient for the large-scale introduction of carbon disposal. Most options other than geological storage are not yet well developed. They vary in cost, scalability, and permanence. Biomass options often fall short on storage capacity and permanence. Mineral sequestration is often too expensive, and substantial storage in the built infrastructure would require big changes in its design.
The most expensive part of managing carbon waste, however, is the capture of carbon dioxide. Most capture technologies have been developed for point sources, such as coal-fired power plants, but such capture cannot address emissions from distributed sources, such as cars or homes. This leaves behind roughly half of all emissions. Distributed emissions require technologies that can take carbon back from the environment, specifically from the air.
Capture of carbon dioxide from air is technically feasible. Until recently, much of the scientific focus has been on biological methods that use photosynthetic organisms to pull carbon dioxide out of the atmosphere. The biomass accumulated during the removal process would then be burned, and the resulting biochar would be stored along with any residual carbon dioxide produced during the combustion process. Biomass capture is certainly feasible and very often affordable. Unfortunately, growing enough biomass to affect the world’s carbon balance would require vast amounts of agricultural land. Biological processes are simply not carbon-intensive enough to balance out industrial carbon emissions, but they can help start the process.
Chemical engineering approaches focused on capturing carbon dioxide directly from the air and then disposing of it by various means will make it possible to stop littering the air with carbon dioxide. Direct air capture (DAC) has been demonstrated in the laboratory and by several small start-up companies in small pilot plants. Collectors absorb carbon dioxide from air on filter surfaces, much like leaves on a tree. Several DAC methods have been proposed. In our own design, collectors stand passively in the wind like trees. Such synthetic trees are one thousand times faster in collecting carbon dioxide from the air than natural trees of similar size. The wind blows over the leaves of the synthetic trees and carbon dioxide sticks to them. Once loaded with carbon dioxide, the leaves need to be regenerated; the carbon dioxide that has been stripped off then needs to be processed further. Regeneration may involve heating the sorbent or exposing it to a vacuum.
Through our own research we discovered a sorbent that absorbs carbon dioxide when dry and releases it when exposed to moisture. Our leaves absorb carbon dioxide in the dry wind, and then release the carbon dioxide when wetted in a closed chamber. The raw product stream then needs to be cleaned, dried, and compressed. In our version, the initial product is a gas stream that contains one hundred times more carbon dioxide than in ambient air. If the regeneration chamber where we strip off the gas is evacuated prior to wetting, the carbon dioxide product is quite pure. If the chamber is filled with air when regeneration starts, then we produce a stream of carbon dioxide-enriched air. Further processing will depend on what is to be done with the carbon dioxide. Although some storage technologies can handle our carbon dioxide with little or no additional processing, if it is to be stored in geologic features, the carbon dioxide must be converted into a concentrated form under higher pressure. Technologies to upgrade the purity of carbon dioxide are already commonly used during flue gas scrubbing in what are called carbon capture and sequestration operations, and they are also used in various other commercial applications ranging from the production of carbonated beverages to the filling of fire extinguishers.
DAC and direct air capture with carbon storage (DACCS) can reach the scale of current carbon dioxide emissions without excessive land use and without the environmental impact of biomass growth. A collector the size of a trailer truck could pull a ton of carbon dioxide per day out of the air. Thousands of mass-produced units could be aggregated into air capture farms collecting a few million tons of carbon dioxide per year on a square mile of land, before the amount of air passing over the land limits carbon dioxide collection. Moving from a single tree farm to the global scale, a hundred million collector units would keep up with current world emissions. Befitting the size of the problem, this scale is huge but in no way unimaginable for a complex yet essential industrial product; the number of cars and trucks on the road globally amounts to about a billion. Moreover, our initial estimates suggest that a synthetic tree farm would be much more compact, perhaps hundreds of times more so, than a wind farm that would prevent an equivalent amount of carbon dioxide emissions.
With these technologies, a picture of a possible carbon-neutral future emerges. Companies, communities, and environmentally conscious individuals are already looking for ways to reduce their carbon footprints. Forests of DAC trees could be installed in remote locations where carbon disposal problems will be minimal. Devices could also be installed near industrial sites that use carbon dioxide as a raw material, such as in the production of synthetic fuels, thus eliminating costs of shipping liquid carbon dioxide for commercial applications. As the market for disposal grows, more such units could be deployed. In such scenarios, the cost of closing the carbon cycle will define the carbon price. In cases where it is cheaper to capture carbon at the source (such as a coal- or gas-fired power plant) or eliminate the use of fossil carbon, the markets will move in this direction. Wherever biomass capture turns out to be cheaper, it will also be incentivized. At the very least, DAC can take back emissions that are difficult to avoid, such as from aircraft, heavy trucks, and ships. DACCS even makes it possible to collect and dispose of carbon dioxide that has been emitted in the past; indeed, it may be the only feasible option for removing the old waste that still litters the atmosphere.
But is it affordable?
Managing waste is never free. As a cost of good governance, we pay for sewage removal and treatment, for garbage collection, and for the production of clean water—and we make these payments willingly because we recognize both the public good that results and the consequences that would ensue if we did not deal with these matters. But we also make them willingly because they are not overly burdensome. What cost will be tolerated for carbon disposal may ultimately depend on a shared understanding of the pain that climate change will inflict. But even amidst continuing disagreement about the seriousness of the climate risk, some people will be open to paying some level of clean-up costs simply because they dislike the mess, just as many individuals were willing to voluntarily recycle their trash even before policies were put in place to incentivize recycling.
DACCS is likely to set the upper limit on the cost of carbon waste management. Since it can deal with any emission, it would displace more expensive technologies but would not stand in the way of cheaper methods where they are applicable. In the energy sector, the cost of carbon management must not dominate or even come close to the cost of using energy. This threshold is likely less than $100 per ton of carbon dioxide, which would add 85 cents to a gallon of gasoline. The American Physical Society in 2011 analyzed an early approach to air capture relying on off-the-shelf technology, and pegged the cost at $600 per ton of carbon dioxide. This would raise the cost of a gallon of gasoline by roughly $5. Newer technologies have greatly reduced this number, in some cases to below $100 per ton.
Although these numbers can be verified only through public demonstrations or in a market environment, production costs of most technologies go down as more is learned about how to produce and use them, and costs will likely go down for direct air capture as well. Energy and water, the raw materials for our DAC design, set a cost floor for the technology of $10 to $20 per ton. Other back-of-the-envelope engineering estimates we have made (for example, based on the weight of the collectors) point toward the possibility of similar numbers. Cost reductions come with experience and cumulative production, and just as we’ve seen such reductions for renewable energy technologies, we should expect to see them for DAC.
Direct air capture is still in its infancy, but has been proven in the laboratory and on small pilot scales. Critics initially claimed thermodynamic constraints would prevent DAC from ever being affordable. When the low thermodynamic energy requirements of DAC were demonstrated, critics next borrowed economic lessons of producing metal from low-quality ore to claim that the costs of extracting carbon dioxide from air would be prohibitive. But DAC economics is dominated by the cost of sorbent regeneration, not gas extraction, and while those costs are still high, they have the potential to come down dramatically.
But the necessary learning-by-doing reductions in production costs will not happen without doing. Unless the technology is supported and promoted, as renewable energy has been promoted in the past, it cannot reach affordable costs. A shift to a waste paradigm provides the policy rationale for such promotion by articulating carbon dioxide disposal as a public good, like sewage disposal or even national defense and public health. And just as government has supported technologies (for example, aircraft carriers and vaccines) to advance other public goods, it could use waste reduction as the public-goods focal point for developing the necessary carbon disposal technologies. Government support can create technical options and buy down the costs of these novel technologies until they become so affordable that their wide application is acceptable to people who are willing to pay only for litter removal. Alternatively, or in parallel fashion, philanthropists could fund demonstrations for proof of concept at scale and thereby advance social acceptability and stimulate voluntary efforts.
Transitioning to a carbon-neutral world
Costs are important, but equally important is trust in the waste management service. The process of carbon disposal or carbon recycling must be transparent and simple. Future service providers could either be trusted institutions or be audited by trusted institutions. They could be public entities, such as state or local governments, or even large corporations whose reputations would be severely damaged if they cheat (as in the case of Volkswagen).
Such trust can be established. For example, people usually do not question that gasoline pumps dispense different fuels for different octane ratings. High-end coffee shops can charge a premium for fair trade coffee. An important part of a waste management approach to excess carbon would be a transparent, generally accepted auditing methodology that results in certificates of negative emissions for the disposal of carbon. Certificates would be issued whenever carbon is stored; they would have to be relinquished when carbon is lost or purposefully mobilized. Many different methods of storage could be certified and contribute to the reduction of excess carbon in the mobile carbon pool. Consumers could simply purchase certificates that match their emissions. These certificates would offer a much more direct and satisfying alternative for individual action than carbon offsets, where individuals produce emissions but pay for others not to emit. In the waste management paradigm, you simply pay to remove your own emissions from the atmosphere, just as you pay to have your sewage processed. It would look odd to pay for someone else’s sewage treatment, while dumping one’s own into the river.
An important part of a waste management approach to excess carbon would be a transparent, generally accepted auditing methodology that results in certificates of negative emissions for the disposal of carbon.
Carbon disposal offers many different models. For example, a city could run its own carbon disposal site, or an oil company could offer carbon-neutral fuels at the pump. Oil companies should have a particular incentive to market carbon-neutral fuels. As electric vehicles and renewable technologies grab more clean-energy market share, oil companies’ entire business model will fall apart if carbon dioxide cannot be recovered from the atmosphere and environmental carbon constraints become more severe. As a result, the industry should be motivated to push carbon removal technologies down the cost-reduction learning curve as soon as possible. Car companies could offer cars that are branded as carbon-neutral and include in their purchase price a pre-emptive carbon disposal of the expected lifetime emissions, which would be about 100 tons of carbon dioxide. Or imagine a button at the gasoline pump where individuals can choose to pay to have the 20 pounds of carbon dioxide that are released from a gallon of gasoline recovered and properly disposed of. If 1% of all fuel buyers in the United States could be convinced to buy back their carbon, this would build a disposal business of 12 million tons per year, dwarfing all other attempts at carbon capture and storage and exceeding the market for merchant carbon dioxide. This would create business opportunities and with it many new models for financing carbon waste management.
Waste can often be recycled, and the biggest opportunity for carbon recycling lies in the production of synthetic fuels from carbon dioxide, water, and renewable energy. Ramping up and down the production of such fuels could be used to balance the intermittencies created by the large-scale move to renewable energy for electricity grids. Carbon mined from the atmosphere could also produce materials for the human-built environment. Examples include plastics and high-strength carbon compounds, as well as carbonate-based cements. Using such materials in the built infrastructure would effectively store carbon for the lifetime of the structure, and thus has the potential to tie up some fraction of the world’s excess carbon that has been already produced. To get a sense of the scale of this potential, consider that in the United States concrete in the infrastructure amounts to maybe 90 tons per person. We have calculated that if the infrastructure relying on recycled carbon reduced the concentration of carbon dioxide in the atmosphere by 100 parts per million, then a future world population of 10 billion people would have to tie up 40 tons of carbon per person. Such back-of-the envelope estimates are simply meant to show that there are many possible options that can be mobilized to advance a waste management paradigm.
Direct air capture will not be a silver bullet that all by itself stops climate change, but it has many assets that can directly address some of the key obstacles to technical, political, and economic progress on climate change. It can scale up nearly without limit, and thus can provide a backstop technology that if necessary could balance the carbon cycle, assuring that whatever goes into the atmosphere also comes out, no matter how difficult it is to reduce emissions from particular technologies or sectors, such as transportation. Direct air capture with carbon storage can also, if necessary, lower the carbon dioxide concentration in the atmosphere much faster than natural processes would. Without negative emissions, the warming impact of carbon dioxide will linger for the next millennium.
Direct air capture will not be a silver bullet that all by itself stops climate change, but it has many assets that can directly address some of the key obstacles to technical, political, and economic progress on climate change.
The waste management paradigm can be adopted without waiting for the energy system to transform. Adoption of DAC technologies does not depend on phasing out or out-competing incumbent energy technologies, and thus adoption is not held hostage to those who create the carbon problem and see no immediate gain from solving it. Nor must DAC replace existing energy infrastructure or social and cultural arrangements that depend on that infrastructure. When technologies provide functions and services not previously available, they can scale up rapidly. The introduction of cars, jet airplanes, and computers worldwide, or the introduction and speedy adoption of nuclear energy in France, show that new technologies can conquer markets in a couple of decades. New businesses can take on the task of carbon disposal, and so can existing ones that see new opportunities in the waste disposal business, even if they are not producing carbon dioxide.
A waste management approach introduces a disposal cost for carbon. As a result, it would often be more cost-effective to avoid emissions entirely. Efficiency, conservation, and carbon recycling will therefore be incentivized. Point-source carbon capture at power plants with associated disposal will often be more economic than air capture. But DACCS will make it possible to regulate all emissions no matter where they originate. Perhaps most important, the waste management approach, unlike efforts to reduce emissions by managing large-scale energy systems, does not require top-down coordination and management. Various government agencies and private companies have spent billions of dollars on new energy technologies aimed at reducing emissions, but, for many complex reasons, emissions continue to climb. For air capture of carbon dioxide, the story will be different. Each independent effort to capture and dispose of waste will always move us, however incrementally, in the right direction. That, in the end, is the power of the waste management paradigm.
Klaus S. Lackner is the director of the Center for Negative Carbon Emissions in the School of Sustainable Engineering and the Built Environment at Arizona State University. Christophe Jospe is Lackner’s former colleague and founder of Carbon A List, a consultancy specializing in marketing and fundraising for carbon management solutions.
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