Carbon Capture Snake Oil
(Adapted from The Climate Pandemic: How Climate Disruption Threatens Human Survival)

Carbon capture and storage (CCS) is another supposed savior that will help rescue the world from soaring CO2 levels. Indeed, CCS is integral to the Paris Agreement’s assumptions in its plans to limit emissions (see Paris Agreement: Blind and Toothless).

CCS’s major current technology involves extracting CO2 from fossil fuel power plant exhaust and pumping it deep underground. The broader field of carbon dioxide removal (CDR) encompasses not only CCS, but also sequestering carbon in forests, soils, minerals, and other reservoirs.[1]

The Climate Pandemic cover

The Petra Nova CCS plant in Texas exemplifies the huge scale of such projects, as well as their just-as-huge drawbacks. Petra Nova aimed to capture carbon dioxide (CO2) from a coal-powered generating station. The plant cost $1 billion to build, including $190 million in federal support. Far from energy-efficient, the plant required a large natural-gas-fired generating station to supply heat and power to capture the low concentration of CO2 in the exhaust stream. The captured CO2 was pumped to a nearby oilfield to boost oil production.

The Petra Nova plant was closed in 2021, the victim of low oil prices and poor performance. The plant missed its carbon-capture targets—which amounted to only a small fraction of the coal plant emissions—and was only operational two-thirds of the time.[2] [3]

Another abandoned CCS facility was a “clean coal” project, the Kemper County plant in Mississippi, in 2017. The plant, built at a cost of $7.5 billion, was planned to turn coal from a nearby strip mine into gas for power generation. The CO2 in the exhaust was to have been captured and piped to a nearby oilfield to use in extracting oil. However, the CO2 extraction technology failed to perform as planned, so natural gas will be used in the generators.[4]

Other CCS projects have suffered significant performance shortfalls. In 2021, a Canadian coal power carbon capture plant captured less than half the CO2 it was meant to because of mechanical problems.[5] And as of 2021, an Australian CCS project—the Gorgon facility described as the world’s largest—captured only a fraction of the five-year target of CO2 it was designed for.[6]

So-called CCS successes have come with major caveats. For example, Shell Canada’s $1.3-billion Quest CCS project advertised that it met its five-year goal of capturing five million metric tons of CO2 emitted from processing Alberta tar sands into oil.[7] Such processing emits CO2 in generating the hydrogen needed to upgrade the thick bitumen from the sands. However, an investigation by the human rights organization Global Witness found that the plant emitted 7.7 million metric tons of greenhouse gases over the same period.[8]

“Waste of money”

Despite these failures, the US Inflation Reduction Act of 2022 includes billions of dollars in tax credits for CCS projects—dubbed a “counterproductive waste of money, backed by the fossil fuel industry” by environmental engineer Charles Harvey and business executive Kurt House. Writing in The New York Times, they said of their own early CCS project “it’s clear that we were wrong, and that every dollar invested in renewable energy—instead of CCS power—will eliminate far more carbon emissions.” They pointed out that, since almost all the captured CO2 is used in producing oil or gas, “we consider these ventures oil or natural gas projects, or both, masquerading as climate change solutions.”[9]

In any case, it will take many expensive CCS projects to discover which technologies are viable, concluded political scientist David Reiner.[10] He said that:

There's an inherent tension in developing CCS—it is not a single technology, but a whole suite and if there are six CCS paths we can go down, it's almost impossible to know . . . which is the right path.[11]

Indeed, the US Department of Energy invested hundreds of millions of dollars in CCS plants that were never built because they were uneconomic, according to a report by the Government Accountability Office (GAO). The GAO charged that the Department had used a “high-risk selection and negotiation process” in selecting the projects.[12]

Such technological gambles would need to be made at a breakneck pace because the 2°C limit would demand construction of large-scale CCS facilities on an extremely short timescale. In fact, the International Energy Agency (IEA) concluded that the technology is “well off track” to meet its Net Zero Emissions by 2050 Scenario.[13]

Major capture creates major impacts

The million-ton removal scale of current demonstration plants is trivial compared to the 0.5 billion to 3 billion metric tons of carbon each year that will have to be sequestered to meet the 2°C limit, according to study by Thomas Gasser and colleagues.[14]

That limit will require thousands of CCS plants to deliver a total of 94 billion metric tons of CO2 reductions just by 2050, according to an IEA report. Even avoiding a higher 4°C limit would require capturing 19 billion metric tons by 2050, said the report. And in any case, CCS would not likely make fossil plants completely carbon-free, the report noted.[15]

Almost half of the CO2 needed to be captured by 2050 would be from industrial processes, not power generation, another IEA report pointed out. Industrial sources are far more difficult to fit with carbon capture systems.[16]

An ambitious 1.5°C limit would require even greater capture, according to a 2018 IPCC report. The limit would require capturing from 100 billion to a trillion metric tons of CO2 during this century.[17]

By 2050, a CCS infrastructure of facilities and pipelines some two to four times larger than the current global oil industry would be required to absorb a significant amount of CO2, calculated a team of engineers.[18]

Since CCS would not be­­ profitable, “the taxpayers of rich countries would have to pay for huge capital costs and significant operating burdens of any massive CCS,” wrote energy policy analyst Vaclav Smil.[19]

A massive CCS infrastructure in itself would have major environmental impact, asserted a report by the Center for International Environmental Law.[20] The report pointed out that a large CO2 pipeline network poses risks similar to those of fossil fuel pipelines:

To date, the heavy environmental footprint and safety and health hazards associated with CCS infrastructure have been largely overlooked. . . . Effective transport through pipelines requires that CO2 be shipped at very high pressure and extremely low temperatures, demanding pipelines capable of withstanding those conditions. The presence of moisture or contaminants can make this condensed CO2 corrosive to the steel in those pipelines, increasing the risk of leaks, ruptures, and potentially catastrophic running fractures.

CCS’s “unmet expectations”

The IEA has asserted that without CCS, “reaching net-zero [emissions] will be virtually impossible.” However, the agency has concluded that “the story of [CCS] has largely been one of unmet expectations: its potential to mitigate climate change has been recognized for decades, but deployment has been slow and so has had only a limited impact on global CO2 emissions.”[21]

Relatively few CCS projects are planned or underway. As of 2022, there were 30 projects in operation, with 11 under construction and 153 in development, according to the Global CCS Institute, which advocates for CCS.[22] Even this group has conceded that current CCS development is inadequate. Limiting temperature rise to 2°C would require capturing and storing more than 5.6 billion metric tons of CO2 a year by 2050—compared to the 40 million metric tons being captured today, according to the Institute. Meeting the IEA sustainable development scenario would require deploying 2,000 large-scale facilities by 2050, costing up to $1.3 trillion in investment.

The timeline is incredibly short for large-scale deployment of CO2-removal technologies in general, concluded environmental scientists Christopher Field and Katharine Mach. Decarbonizing scenarios “bet the future on CDR technologies operating effectively at vast scales within only a few decades,” they wrote. The economics of such efforts are “crude for such scales,” and “the risks are high.”[23]

Half-baked bioenergy

Field and Mach’s analysis included “bioenergy with carbon capture and storage” (BECCS). This process involves growing massive acreage of biomass—trees and crops—burning it for energy, and capturing and storing the CO2 underground.

BECCS is just as burdened with shortcomings as CCS, they wrote. For one thing, the IPCC peak-and-decline scenarios assume that BECCS could store some 12 billion tons of CO2 a year by 2100, more than a quarter of current emissions.

Field and Mach called the assumption a “truly massive use of a technology with little real-world experience and poorly known economics.”

Such BECCS deployment would require vast amounts of land, they calculated—ranging from 25% to 80% of the total global cropland, or up to 8% of the entire land area of Earth.

“Converting land on this staggering scale would pit climate change responses against food security and biodiversity protection,” they wrote. “Massively expanding managed land for [CO2 removal] could crash through the planetary boundary for sustainable land use.”

In another analysis, climatologists Kevin Anderson and Glen Peters wrote:

The scale of biomass assumed in [the IPCC computer models]—typically, one to two times the area of India—raises profound questions about . . . carbon neutrality, land availability, competition with food production, and competing demands for bioenergy from the transport, heating, and industrial sectors.[24]

They noted that the quantities of biomass required would be “equivalent to up to half of the total global primary energy consumption.” They concluded: “Despite BECCS continuing to stumble through its infancy, many scenarios assessed by the IPCC propose its mature and large-scale rollout as soon as 2030.” They called such technologies “not an insurance policy, but rather an unjust and high-stakes gamble.”

Biomass production also uses immense amounts of water. Global water stress could greatly increase from irrigation of large-scale biomass plantations, concluded bioenergy researchers.[25] Their modeling of water needed for plantations large enough to significantly limit global heating “suggest that both the global area and population living under severe water stress . . . would double compared to today and even exceed the impact of climate change.”

Similarly, an IPCC report concluded that large-scale BECCS would threaten global food production, water supplies, and natural biodiversity.[26] [27]

Growing enough biomass to supply BECCS to counteract the current CO2 trajectory would require “eliminating virtually all natural ecosystems,” calculated researchers in another analysis.[28]

In the US, a limited 30% of potential biomass could be used for BECCS, given the lack of underground CO2 storage sites and long-distance transportation networks, calculated environmental engineers in another analysis.[29]

Expensive direct capture

Direct air carbon capture and storage (DACCS) of CO2 using absorbing chemicals has also been proposed as a removal technology. However, this approach would be stunningly expensive, given the low atmospheric concentration of CO2.

The Global CCS Institute has calculated that the cost of DACCS, including transport and storage, would range from $137 to $412 per metric ton. The Institute noted that “Because DACCS is a pre-commercial technology, the cost is highly uncertain.”[30]

Thus, for even the lowest estimate, sucking the billions of metric tons out of the air required to meet CO2 limits would cost trillions of dollars.

The company Carbon Engineering, funded by fossil fuel companies, has claimed an estimate of $94 to $232 per metric ton, based on a pilot project.[31]

However, that estimate comes with so many caveats as to render it meaningless. The process involves trapping CO2 as calcium carbonate, then heating it to 900°C to release the gas. The heat would come from burning natural gas; and the process itself would create half a ton of CO2 for each ton captured, found energy analyst Michael Barnard.[32] What’s more, asserted Barnard:

The total CO2 load for the energy required for capture, processing, compression, storage, distribution, and sequestration is almost certain to be greater than the CO2 removed from the atmosphere.

Carbon Engineering has proposed that the captured CO2 could be used to produce fuel. But Barnard calculated that such fuel would be at best 25 times the cost and create 35 times the emissions of an electric vehicle.[33] Nor would the company’s proposal to use the CO2 as an industrial feedstock be viable. Barnard concluded:

Carbon Engineering’s solution is only useful in tapped-out oil wells and as greenwashing for fossil fuel companies. No wonder three fossil fuel companies invested an infinitesimal fraction of their annual revenue in it.[34]

Environmental engineer Mark Jacobson told US News: “CO2 negative—yeah, right. It's a big sham. . . . I've looked at their published data and their own numbers.”[35]

Another analysis by Barnard pointed out that any direct capture would require a gargantuan air circulation system.

“If we wanted to just deal with 10% of our annual increase in CO2, we’d need to filter the air out of 44 billion Houston Astrodomes or 32 million Grand Canyons,” he wrote. Barnard has dubbed DAC as a “fig leaf funded by fossil fuel money.”[36]

It would cost up to $1 trillion annually for direct air capture of billions of tons of CO2 per year, found one analysis.[37] And that cost does not even account for the need for huge amounts of renewable energy necessary to make the industry truly carbon negative.

Using fossil fuels, DACCS would emit more CO2 than it removed, calculated economists.[38] They found that fossil-fuel-powered DACCS would emit from 1.46 to 3.44 metric tons of CO2 for every ton removed. They also calculated that using the CO2 for oil production would cause emissions of 1.42 to 4.7 metric tons of CO2 for every ton removed. They pointed out that the analyses claiming that such capture processes would reduce CO2 has neglected the full life cycle of the processes or contained other flaws.

Other proposed technologies to capture carbon are either in the laboratory or demonstration stage. None offers the prospect of scaling up soon enough to help capture the massive amounts of CO2 needed to blunt climate disruption. Nor have their economic or environmental validity been established. Those technologies include:

Capturing carbon in forests and soils

Growing forests to capture massive amounts of carbon seems a promising idea. One analysis found that allowing tropical forests to regrow could absorb huge amounts of carbon. Calculations showed that allowing abandoned farms and pastures in Latin America to regrow over 40 years could sequester some 31 billion tons of CO2. This amount would be the equivalent of all the carbon emissions in Latin America and the Caribbean from 1993 to 2014.[46]

However, this plan is unworkable, given continuing tropical deforestation and the irreversible decline in tropical forests due to climate disruption.

Sequestering large quantities of carbon in soils by improving farming techniques has been another proposed carbon-capture technique but presents its own major obstacles.

Subterranean injection hazards

Most sequestration technologies involve injecting vast amounts of CO2 into underground formations such as depleted oil fields. If the experience with fracking is any guide, such injection could cause leakage into aquifers that supply drinking water. Such CO2 groundwater infiltration could increase metal concentrations by more than a 100-fold—including potentially hazardous uranium and barium—found laboratory experiments by environmental engineers.[47]

CO2 is by no means an inert gas when injected into oil reservoirs, found a study of a Louisiana injection site. The researchers discovered that a significant fraction of the injected CO2 was transformed by bacteria into CH4, which is less soluble and more mobile than CO2. An even larger fraction was dissolved in the groundwater, found the researchers.[48]

As is the case with fracking, injecting vast amounts of CO2 could trigger earthquakes, pointed out geophysicists, who wrote:

Because even small- to moderate-sized earthquakes threaten the seal integrity of CO2 repositories, in this context, large-scale CCS is a risky, and likely unsuccessful, strategy for significantly reducing greenhouse gas emissions.[49]

Another proposed sequestration plan is to inject captured CO2 into deep-ocean sediments, where the immense pressure and low temperatures would transform it into a frozen form called a hydrate.[50] Scientists studying the plan’s potential concluded that the process appears viable. However, substantive mysteries remain about the subsea behavior of the frozen hydrates and whether changes in the marine environment might release stored deposits.

Deployment time crunch

Multiple independent analyses have found that the need to meet temperature limits make the time frame for massive deployment of CDR technologies unrealistically short.

A UN report concluded that keeping below the 2°C limit would require achieving net zero greenhouse gas emissions by 2070.[51] Achieving net zero by 2085 would require a long-term removal of carbon of at least 26 billion tons a year, climatologists have calculated.[52] Meeting the more stringent 1.5°C increase target would require net zero emissions by 2060, and a long-term carbon removal of almost 15 billion tons a year, the study found.

The Paris Agreement’s dependence on negative emissions poses a “climate risk for society,” argued one group of climate policy analysts.[53] They said that the 2°C limit is “infeasible” because of the failure of the major emitting countries to rapidly transform their energy systems.

Similarly, the European Academies’ Science Advisory Council concluded that negative emissions technologies “offer only limited realistic potential to remove carbon from the atmosphere and not at the scale envisaged in some climate scenarios.” The Council said that the IPCC’s dependence on them “has yet to take fully into account these limitations.”[54]

The time scale for CDR technologies to be effective will stretch far into the future, found another analysis:

Most methods are relatively slow acting and might take many decades to centuries to reduce atmospheric CO2 to some desired level. The few methods that have the theoretical potential to rapidly remove more CO2 remain technologically immature and would likely take decades to be fully developed and deployed at climatically relevant scales.[55]

Research in its infancy

In fact, significant basic research on negative emissions technologies has not even begun. The US Department of Energy has launched the Carbon Negative Shot program that aims to bring all types of carbon-sequestering technologies down to less than $100 per ton.[56] However, that goal is far from the current cost, and as of this writing, there has been no budget allocated to the effort.

A US National Academies report concluded that the US would need to spend many billions of dollars over a decade for such fundamental research. This research would be needed even before large-scale pilot plants and ultimately commercial facilities could be built, which would take even longer.[57] Even then, the report concluded:

Negative emissions technologies are best viewed as a component of the mitigation portfolio, rather than a way to decrease atmospheric concentrations of carbon dioxide only after anthropogenic emissions have been eliminated.

One nasty wrinkle is that, even if negative emissions did work, they might not effectively reduce atmospheric CO2 levels. For one thing, CO2 removal would be opposed by natural outgassing from the ocean and rocks, found modeling studies. They revealed a decreasing effectiveness of removal with the amount removed.[58] [59]

Negative emissions might weaken or even reverse the natural CO2 absorption by land and ocean, found another analysis of future emissions scenarios. The researchers’ modeling raises the possibility that negative emissions would have to be even greater to stabilize levels, much less reduce them.[60]

The predictable failure of negative emissions technologies is thus one more reason that humans seem doomed to suffer a rise toward a 6°C temperature increase and possible extinction.


[1] Wilcox, J., B. Kolosz, and J. Freeman, eds. CDR Primer (2021).

[2] Taft, Molly. “The Only Carbon Capture Plant in the US Just Closed.” Gizmodo (February 2021).

[3] US Department of Energy/National Energy Technology Laboratory. Final Scientific/Technical Report, Petra Nova (March 31, 2020).

[4] Fountain, Henry. “In Blow to ‘Clean Coal,’ Flawed Plant Will Burn Gas Instead.” The New York Times (June 28, 2017).

[5] Anchondo, Carlos. “CCS ‘Red Flag?’ World’s Sole Coal Project Hits Snag.” E&E News (January 10, 2022).

[6] Morton, Adam. “‘A Shocking Failure’: Chevron Criticised for Missing Carbon Capture Target At WA Gas Project.” The Guardian (July 19, 2021).

[7] Bakx, Kyle. “Alberta Carbon Capture Project Hits Another Milestone Ahead of Schedule and Below Cost.” CBC (July 10, 2020).

[8] Global Witness. Hydrogen’s Hidden Emissions (January 20, 2022).

[9] Harvey, Charles and Kurt House. “Every Dollar Spent on This Climate Technology Is a Waste.” The New York Times (August 16, 2022).

[10] Reiner, David M. “Learning through a Portfolio of Carbon Capture and Storage Demonstration Projects Nature Energy 1 (January 11, 2016).

[11] University of Cambridge. “Global Learning Is Needed to Save Carbon Capture and Storage from Being Abandoned.” (January 11, 2016).

[12] US Government Accountability Office. Carbon Capture and Storage: Actions Needed to Improve DOE Management of Demonstration Projects (December 20, 2021).

[13] International Energy Agency. “Tracking Clean Energy Progress: CCUS in Power” (November 2021).

[14] Gasser, T., C. Guivarch, K. Tachiiri, C. D. Jones, and P. Ciais. “Negative Emissions Physically Needed to Keep Global Warming Below 2 °C.” Nature Communications 6 (August 3, 2015).

[15] International Energy Agency. 20 Years of Carbon Capture and Storage Accelerating Future Deployment (2016).

[16] International Energy Agency. Technology Roadmap: Carbon Capture and Storage 2013 (2013).

[17] IPCC. Global Warming of 1.5o C, Chapter 2 From: Global Warming of 1.5 ºC (October 6, 2018).

[18] Mac Dowell, Niall, Paul S. Fennell, Nilay Shah, and Geoffrey C. Maitland. “The Role of CO2 Capture and Utilization in Mitigating Climate Change.” Nature Climate Change 7 (April 5, 2017).

[19] Smil, Vaclav. “Global Energy: The Latest Infatuations.” American Scientist 99 (May-June 2011).

[20] Center for International Environmental Law. Confronting the Myth of Carbon-Free Fossil Fuels: Why Carbon Capture Is Not a Climate Solution (July 2021).

[21] International Energy Agency. CCUS in Clean Energy Transitions (September 2020).

[22] Global CCS Institute. Global Status of CCS Report 2022 (2022).

[23] Field, Christopher B. and Katharine J. Mach. “Rightsizing Carbon Dioxide Removal.” Science 356, no. 6339 (May 19, 2017).

[24] Anderson, Kevin and Glen Peters. “The Trouble with Negative Emissions.” Science 354, no. 6309 (October 14, 2016).

[25] Stenzel, Fabian, Peter Greve, Wolfgang Lucht, Sylvia Tramberend, Yoshihide Wada, and Dieter Gerten. “Irrigation of Biomass Plantations May Globally Increase Water Stress More Than Climate Change.” Nature Communications 12 (March 8, 2021).

[26] IPCC. Climate Change and Land (August, 2019).

[27] Stokstad, Erik. “Bioenergy Not a Climate Cure-All, Panel Warns.” Science Vol 365, no. 6453 (August 9, 2019).

[28] Boysen, Lena R., Wolfgang Lucht, Dieter Gerten, Vera Heck, Timothy M. Lenton, and Hans Joachim Schellnhube. “The Limits to Global-Warming Mitigation by Terrestrial Carbon Removal.” Earth’s Future 5, no. 5 (May 17, 2017).

[29] Baik, Ejeong, Daniel L. Sanchez, Peter A. Turner, Katharine J. Mach, Christopher B. Field, and Sally M. Benson. “Geospatial Analysis of Near-Term Potential for Carbon-Negative Bioenergy in the United States.” Proceedings of the National Academy of Sciences 115, no. 13 (March 27, 2018).

[30] Williams, Eric. The Economics of Direct Air Carbon Capture and Storage. Global CCS Institute (July 26, 2022).

[31] Keith, David W., Geoffrey Holmes, David St. Angelo, and Kenton Heidel. “A Process for Capturing CO2 from the Atmosphere.” Joule 2, no. 8 (June 7, 2018).

[32] Barnard, Michael. “Chevron’s Fig Leaf Part 5: Who Is behind Carbon Engineering, & What Do Experts Say?Clean Technica (April 20, 2019).

[33] Barnard, Michael. “Chevron’s Fig Leaf Part 7: Carbon Engineering’s Fuel Is At Best 25x The Cost, 35x The CO2 Emissions Compared To an EV.” Clean Technica (April 27, 2019).

[34] Barnard, Michael. “Chevron’s Fig Leaf Part 4: Carbon Engineering’s Only Market Is Pumping More Oil,” Clean Technica (April 19, 2019).

[35] Neuhauseer, Alan. “Carbon Capture: Boon or Boondoggle?US News (July 26, 2019).

[36] Barnard, Michael. “Air Carbon Capture’s Scale Problem: 11 Astrodomes for a Ton of CO2.” Clean Technica (March 11, 2019).

[37] Hanna, Ryan, Ahmed Abdulla, Yangyang Xu, and David G. Victor “Emergency Deployment of Direct Air Capture as a Response to the Climate Crisis.” Nature Communications 12 (January 14, 2021).

[38] Sekera, June and Andreas Lichtenberger. “Assessing Carbon Capture: Public Policy, Science and Societal Need.” Biophysical Economics and Sustainability 5 (October 6, 2020).

[39] Carbfix. CarbFix Project website.

[40] Renforth, P., B. G. Jenkins, and T. Kruger. “Engineering Challenges of Ocean Liming,” Energy 60 (October 1, 2013).

[41] Paquay, François S. and Richard E. Zeebe. “Assessing Possible Consequences of Ocean Liming on Ocean pH, Atmospheric CO2 Concentration and Associated Costs.” International Journal of Greenhouse Gas Control 17 (September 2013).

[42] Fuel Cell Energy. Fuel Cell Energy website.

[43] Schwartz, John. “Exxon Mobil Backs Fuel Cell Effort to Advance Carbon Capture Technology.” The New York Times (May 5, 2016).

[44] NET Power. NET Power website.

[45] McMahon, Jeff. “NET Power CEO Announces Four New Zero-Emission Gas Plants Underway.” Forbes (January 8, 2021).

[46] Chazdon, Robin L., Eben N. Broadbent, Danaë M. A. Rozendaal, Frans Bongers, Angélica María Almeyda, T. Mitchell Aide, Patricia Balvanera et al. “Carbon Sequestration Potential of Second-Growth Forest Regeneration in the Latin American Tropics Science Advances 2, no. 5 (May13, 2016).

[47] Little, Mark G. and Robert B. Jackson. “Potential Impacts of Leakage from Deep CO2 Geosequestration on Overlying Freshwater Aquifers.” Environmental Science & Technology 44, no. 23 (October 26, 2010).

[48] Tyne, R. L., P. H. Barry, M. Lawson, D. J. Byrne, O. Warr, H. Xie, D. J. Hillegonds et al. “Rapid Microbial Methanogenesis during CO2 Storage in Hydrocarbon Reservoirs.” Nature 600 (December 22, 2021).

[49] Zoback, Mark D. and Steven M. Gorelick. “Earthquake Triggering and Large-Scale Geologic Storage of Carbon Dioxide.” Proceedings of the National Academy of Sciences 109, No 26 (June 26, 2012).

[50] Teng, Yihua and Dongxiao Zhang. Long-Term Viability of Carbon Sequestration in Deep-Sea Sediments.” Science Advances 4, no. 7 (July 4, 2018).

[51] UN Environment Programme. Global Environment Outlook. Cambridge University Press, 2019.

[52] Sanderson, Benjamin M., Brian C. O’Neill, and Claudia Tebaldi. “What Would it Take to Achieve the Paris Temperature Targets? Geophysical Research Letters 43, no. 13 (July 16, 2016).

[53] Larkin, Alice, Jaise Kuriakose, Maria Sharmina, and Kevin Anderson. “What If Negative Emission Technologies Fail at Scale? Implications of the Paris Agreement for Big Emitting Nations.” Climate Policy (August 3, 2017).

[54] European Academies’ Science Advisory Council. Negative Emission Technologies: What Role in Meeting Paris Agreement Targets? (February 2018).

[55] Keller, David P., Andrew Lenton, Emma W. Littleton, Andreas Oschlies, Vivian Scott, and Naomi E. Vaughan. “The Effects of Carbon Dioxide Removal on the Carbon Cycle.” Current Climate Change Reports (June 14, 2018).

[56] US Department of Energy Office of Fossil Energy and Carbon Management. Carbon Negative Shot.

[57] The National Academies of Sciences, Engineering, and Medicine. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. National Academies Press, 2019.

[58] Tokarska, Katarzyna, and Kirsten Zickfeld. “The Effectiveness of Net Negative Carbon Dioxide Emissions in Reversing Anthropogenic Climate Change.” Environmental Research Letters 10, no. 9 (September 10, 2015).

[59] Zickfeld, Kirsten, and Deven Azevedo. “Effectiveness of Carbon Dioxide Removal in Lowering Atmospheric CO2 and Reversing Global Warming in the Context of 1.5 Degrees.” American Geophysical Union Fall Meeting (2017).

[60] Jones, C. D., P. Ciais, S. J. Davis, P. Friedlingstein, T. Gasser, G. P. Peters, J. Rogelj et al. “Simulating the Earth System Response to Negative Emissions.” Environmental Research Letters 11, no. 9 (September 20, 2016).