Clarifying the overlap between carbon removal and CCUS

Authored by David Morrow, Director of Research, Institute for Carbon Removal Law and Policy

Prepared for the Institute for Carbon Removal Law and Policy

Ask ten people what role “carbon capture” should play in addressing climate change, and you will likely get a dozen different answers, in part because the term “carbon capture” gets used in so many ways. It sometimes refers only to technologies that capture carbon dioxide from large point-sources, such as power plants or steel factories; sometimes only to technologies that scrub carbon dioxide from the ambient air; and sometimes to both. This terminological confusion not only makes it harder to understand one another in important climate policy conversations, but it leads people to run together different technologies that could play very different roles in climate policy.

In a new working paper, Michael Thompson (Carnegie Climate Governance Initiative) and I try to cut through one of the thorniest knots in this confusing conversation: what is the relationship between carbon removal and carbon capture with utilization and storage (CCUS)?

The paper encourages people to stop worrying so much about technological categories and focus instead on two simple questions:

(1) Where does the captured carbon come from?

(2) Where does the captured carbon go?

We argue that answering these two questions makes it easy to see which pathways lead to carbon removal, which to carbon recycling, and which to emissions reductions. The final figure in the paper, shown here, summarizes the results of this analysis.

A matrix showing how answering two questions--where does captured carbon from, and where does it go?--reveals the role that a particular technology can play in climate policy.

For more details, download the working paper, “Reduce, Remove, Recycle: Clarifying the Overlap between Carbon Removal and CCUS.”

Negative Emissions and The Long History of Carbon Removal

Authors: Wim Carton, Adeniyi Asiyanbi, Silke Beck, Holly J. Buck, Jens F. Lund

Prepared for the Institute for Carbon Removal Law and Policy

Recent IPCC assessments highlight a key role for large-scale carbon removal in meeting the objectives of the Paris Agreement. This focus on removal, also referred to as negative emissions, is suggestive of novel opportunities, risks, and challenges in addressing climate change, but tends to build on the narrow techno-economic framings that characterize integrated assessment modeling. While the discussion on negative emissions bears important parallels to a wider and older literature on carbon sequestration and carbon sinks, this earlier scholarship—particularly from the critical social sciences—is seldom engaged with by the negative emissions research community. In this article, we survey this “long history” of carbon removal and seek to draw out lessons for ongoing research and the emerging public debate on negative emissions. We argue that research and policy on negative emissions should proceed not just from projections of the future, but also from an acknowledgment of past controversies, successes and failures. In particular, our review calls attention to the irreducibly political character of carbon removal imaginaries and accounting practices and urges acknowledgment of past experiences with the implementation of (small-scale) carbon sequestration projects. Our review in this way highlights the importance of seeing continuity in the carbon removal discussion and calls for more engagement with existing social science scholarship on the subject. Acknowledging continuity and embracing an interdisciplinary research agenda on carbon removal are important aspects in making climate change mitigation research more responsible, and a precondition to avoid repeating past mistakes and failures.

Ambient Weathering Magnesium Oxide For Co2 Removal From Air

Authors: Noah McQueen, Peter Kelemen, Greg Dipple, Phil Renforth, Jennifer Wilcox

Full Citation: McQueen, N., Kelemen, P., Dipple, G., Renforth, P., and Wilcox, J. Ambient weathering of magnesium oxide for CO2 removal from air. Nat Commun 11, 3299 (2020).

Updated Abstract: 

To combat the dangerous effects of climate change, new technologies are needed to remove billions of tonnes of carbon dioxide (CO2) from the atmosphere. This paper analyzes the cost of a land-based process that uses a magnesium carbonate (magnesite, MgCO3) feedstock to repeatedly capture CO2 from the atmosphere. 

In this process, the initial magnesium carbonate feedstock is fed into a high temperature reactor, called a calciner. In the calciner, the magnesium carbonate is heated to produce magnesium oxide (MgO) and CO2, which is subsequently captured. The produced MgO is highly reactive with the CO2 in air; at ambient conditions, the MgO and CO2 react to re-produce magnesium carbonate materials. This high reactivity means the MgO can be transported to plots of land and used to naturally uptake CO2 from the ambient air. At the end of one year, the MgO will have reacted with CO2 to form magnesium carbonates. From here, the magnesium carbonates are transported back to the calciner, where they are once again heated to re-produce the MgO and release the atmospheric CO2 as a high-purity CO2 stream which can then be captured and stored or utilized. The process can then continue cyclically, making up for any losses by adding new MgCO3 into the calciner. 

Using an exploratory economic analysis, we estimate that this process could cost approximately 45 to 193 USD per tonne of CO2 captured from the air, considering the use of grid or solar electricity. The thermal energy for this process is provided by natural gas, which is combusted inside the calciner in pure oxygen, allowing for the co-capture of combustion-related CO2. The cost range presented here is large mainly on account of varying process parameters and uncertainty in the capital expenses.

This cyclical technology may achieve lower costs than optimistic projections for other direct air capture methods and has the scalable potential to remove 2 to 3 billion tonnes of CO2 per year, and thus may make a meaningful contribution to mitigate global warming.

California Announces New Actions to Fight Climate Change and Protect Biodiversity

Authored by Sydney J. Chamberlin, Ph.D. Climate Policy Associate, The Nature Conservancy in California

Record breaking heat waves. Massive mega-fires. Hurricane after hurricane. In a year wrought with disaster on global scales, these fingerprints of climate change serve as a poignant reminder that the time for climate action is now. With a recent Executive Order, California Governor Gavin Newsom lays out a new possible path for action – focusing on the role that natural and working lands can play in mitigating climate change and protecting biodiversity.

When sustainably managed, our natural and working lands – our forests, wetlands, grasslands, farmlands, rangeland, deserts and urban green spaces – provide a multitude of services that support thriving communities and habitat: they provide food, fiber, and recreational space; store and transport water; bolster local economies; support wildlife; buffer communities against floods, storms, and other disasters; and capture and store carbon. 

In the same way that our lands can act as a carbon sink, changes that impact soil organic matter and ecosystem health – including land-use modifications, deforestation, wildfires, and more – can result in stored carbon being released to the atmosphere. Ultimately, the dance between carbon stored and carbon released determines whether our lands function as a net sink of carbon or net source of carbon – and consequently, whether they serve as an asset or a liability in the fight against climate change. 

In the United States, managed forests and other lands have traditionally acted as net carbon sinks (EPA, 2020). However, over the past 150 years, land-use changes have added almost half as much carbon to the atmosphere as fossil fuel emissions (Houghton & Nassikas, 2017; Le Quéré et al., 2017) – and climate stressors are further driving changes in ecosystem carbon stocks, threatening to turn some of our lands into a net source of emissions (Sleeter et al., 2019). 

In light of this threat, decision-makers and governments are increasingly recognizing the role that strategic land management, conservation, and restoration activities (also known as nature-based climate solutions) can play in removing carbon from the atmosphere and sequestering it in soil and vegetation. 

These nature-based strategies provide climate mitigation benefits while they deliver a suite of additional environmental, economic and social benefits – enhancing both ecosystem and community resilience. Protecting people and nature from the worsening impacts of climate change will require swift and decisive action that recognizes the importance of natural and working lands and intact ecosystems. 

In 2020, California legislators led efforts to integrate nature into the State’s climate strategy. Assemblymember Kalra’s (aptly named) Assembly Bill 3030 aimed to protect 30% of the state’s land areas and water by 2030, aligning with an international “30 by 30” campaign that strives to avoid a point of no return for many of Earth’s species and ecosystems. Assembly Bill 2954, authored by Assemblymember Robert Rivas, would have required the State to set an overall climate goal for California’s natural and working lands and to identify methods to help the State utilize the natural and working lands sector in achieving its goal of carbon neutrality by 2045.

California’s new Executive Order, signed in October 2020, builds on the leadership of Assemblymembers Kalra and Rivas and advances some of the outcomes that Assembly Bills 3030 and 2954 strove to achieve. The Order calls for the State to protect 30% of the state’s water and land by 2030, and directs the California Natural Resources Agency to form a California Biodiversity Collaborative to help achieve this goal. 

The Order also acknowledges the critical role that the stewardship of natural and working lands must play in achieving the State’s climate change, air quality, water quality, equity, and biodiversity goals. It tasks California agencies with establishing a climate target for the natural and working lands sector and firmly establishes carbon sequestration as a part of the State’s climate strategy. The Order further directs State agencies to identify and implement strategies that will accelerate the removal of carbon with nature – while building climate resilience in California communities.

Accomplishing these ambitious goals will require the State to reexamine its current priorities and funding commitments – though there are also a number of non-monetary policy pathways that the State can use to elevate the role of natural and working lands in its climate action. 

The potential rewards of this action are substantial; a newly released report by The Nature Conservancy shows that implementing a suite of nature-based climate solutions could reduce more than 514 million metric tons of carbon dioxide cumulatively by 2050, with economic savings from avoided damages of more than $2.4 billion (The Nature Conservancy, 2020). The report shows that, in many cases, nature-based strategies can be dramatically scaled up by better aligning existing California policies and programs – and at a fraction of the cost of other methods such as industrial carbon capture. The many additional multiple benefits that accompany nature-based climate solutions provide another incentive to achieve the goals laid out by the Executive Order. 

In the post-COVID-19 world, restoring the vibrancy of California communities will require the State to balance climate action against other competing priorities. Nature is a powerful and cost-effective tool that the State can and should deploy to remove carbon. Implementing this tool will require shifting priorities and funding to match the urgency of the climate crisis. The time to act is now – and in acting to protect nature, California ensures that nature can help to protect us. 



EPA. (2020). Inventory of US Greenhouse Gas Emissions and Sinks. 

Houghton, R., & Nassikas, A. A. (2017). Global and regional fluxes of carbon from land use and land cover change 1850–2015. Global Biogeochemical Cycles, 31(3), 456–472.     

Le Quéré, C., Andrew, R. M., Friedlingstein, P., Sitch, S., Pongratz, J., Manning, A. C., …, Zhu, D. (2017). Global carbon budget 2017. Earth System Science Data Discussions, 10, 405–448.‐2017‐123   

Sleeter, B. M. , D. C. Marvin, D. R. Cameron, P. C. Selmants, A. L. Westerling, J. Kreitler, C. J. Daniel, J. Liu, and T. S. Wilson. (2019). Effects of 21st‐century climate, land use, and disturbances on ecosystem carbon balance in California. Global Change Biology 25(10):3334-3353. 

The Nature Conservancy. (2020). Nature-based Climate Solutions: A Roadmap to Accelerate Action in California. 

Managing Land‐based CDR: BECCS, Forests and Carbon Sequestration

Duncan Brack, Richard King

doi: 10.1111/1758-5899.12827


Decisions about when, where and how to achieve widespread carbon dioxide removal (CDR) are urgently required. Delays in developing the requisite policy and regulatory frameworks increase the risks of overshooting climate goals and will necessitate much larger negative emissions initiatives in the future. Yet the deployment of bioenergy with carbon capture and storage (BECCS) at the scales assumed under most ParisAgreementcompliant emissionreduction pathways is unlikely. More generally, the sustainability of largescale BECCS is questionable given its extensive land, water, and energy requirements for feedstocks and the competing necessity of these resources for the provision of ecosystem services and attainment of multiple Sustainable Development Goals. BECCS on a more limited scale, however, could have more benign impacts if feedstocks were restricted to wastes and residues. There is also widespread recognition that extensive afforestation, reforestation and forest restoration have critical roles in reducing greenhouse gas emissions to net zero. To date there has been little focus on the optimum strategies for integrating landbased CDR approaches – under which circumstances forest areas are best left undisturbed, managed for conservation, and/or managed for harvested wood products, and how these options affect the availability of residual feedstocks for BECCS. This paper reviews this debate and suggests appropriate policy measures.

Three principal policy implications emerge:

First, the necessity of abandoning the assumption, common in integrated assessment models, that BECCS is the preeminent carbon removal solution. Rather it needs to be analysed alongside all other negative emissions technologies (NETs), on the basis of full lifecycle carbon balances (including dropping the assumption that biomass feedstock is inherently carbonneutral), as well as other ecosystem and sustainability cobenefits and tradeoffs.

Second, urgent action is required to scale up the development and deployment of sustainable NETs. No single NET – whether BECCS, naturebased, or otherwise – will achieve the scale of CDR required in the vast majority of 1.5°C and 2°C mitigation scenarios, let alone do so sustainably. But portfolios of multiple NETs, deployed sensitively at modest scales, will be invaluable for achieving climate security. This requires designing policy and financial mechanisms that are sufficiently attuned to the contextual specificities of each potential deployment, but which are sufficiently catalytic to galvanise appropriate and complementary actions at adequate scales and with enough urgency.

Third, we need to be absolutely clear that all CDR efforts have to be additional to – not substituting for, or detracting from – urgent acceleration of conventional abatement actions. This means we need to accelerate conventional abatement action as rapidly as possible. There are too many drawbacks and uncertainties associated with BECCS and other NETs to place excessive reliance on them – though carbon removal solutions will undoubtedly be needed.

ICRLP Co-Director Dr. Wil Burns Explores Ocean Alkalinization’s Potential

ICRLP Co-director Wil Burns and co-author Charles R. Corbett recently published an important article in One Earth titled “Antacids for the Sea? Artificial Ocean Alkalinization and Climate Change.” This important article explores ways in which artificial ocean alkalinization (AOA) could serve as an important component of a large-scale carbon removal strategy. It includes an analysis of the risks and benefits of AOA, as well as governance considerations. 

Despite the world community coming together in 2015 and signing the Paris agreement, it has since become clear that the reality of meeting the 2.0/1.5°C temperature targets are becoming increasingly unrealistic, as countries continue to lag on meeting even the already lackluster pledges they have made. Furthermore, 87% of the scenarios run in the IPCC Fifth Assessment Report that meets the Paris Agreements targets incorporate large-scale adoption of carbon dioxide removal strategies.

Thus far, the majority of the focus on carbon dioxide removal (CDR) has been on terrestrially based technologies such as bioenergy and carbon capture (BECCS), afforestation and reforestation, and direct air capture. Although these are all methods deserving of consideration and assessment, there are also many associated shortfalls and risks, providing a compelling rationale for assessing the potential role of ocean-based carbon removal approaches. 

Ocean-based approaches to CDR are under-developed, under-funded, and under-tested. This is despite the fact that the ocean comprises 71% of Earth’s surface and is already passively absorbing 10 gigatons of carbon every year, with the great potential to store more. In light of the climate crisis, this potential is something the global community cannot afford to overlook.

Thus far, most of the ocean-based CDR has focused on ocean iron fertilization (OIF). However, recent research has concluded that OIF’s sequestration potential may be low, and it could pose serious risks to ocean ecosystems. As a consequence, it has largely been abandoned as the most viable ocean-based CDR method.  

 However, despite the shortcomings of OIF, the method does provide some incentive to look into other ocean-based methods of CDR. AOA may provide some of the greatest potentials in that regard. 

AOA is the method of adding alkalinity to ocean systems, increasing pH levels, which in turn leads to greater carbon absorption and a reduction in acidification. AOA has the potential to represent meaningful contributions to the battle against climate change and carbon sequestration, even at the low end of its potential. Several methods have been proposed:

  • Addition of powdered olivine (highly reactive lime)
  • Addition of calcium hydroxide, produced by the calcination of limestone, applied to ocean surfaces or into deep currents that end in upwelling regions
  • Utilization of local marine energy sources to manufacture alkalinity
  • Combining waste CO2 with minerals for reaction, which result in dissolved alkaline material, and pumping it into the ocean

AOA also has the added benefit of potentially combating another detrimental side effect of climate change: ocean acidification. Acidification of the ocean:

  • Reduces levels of carbonate, compromising the formation of calcium carbonate shells among coral, bivalve, and crustaceans
  • Harms finfish species, which has a detrimental impact on habitat, food source and larval survival

Ocean Acidification has increased 30% since the beginning stages of our current anthropogenic CO2 emissions, and pH levels are the lowest they have been in 2 million years.

However, AOA is not without its own potential risks, including:

  • Inhibiting photosynthesis in phytoplankton communities;
  • Threatening species that may not be able to easily adjust to increasing levels of alkalinity;
  • Introducing new and heavy toxic materials to ocean ecosystems

When facing both the uncertainties and the potential benefits of AOA deployment, good governance is critical. It enables the facilitation of research by providing clear guidelines and assessment protocols. Additionally, it identifies risks, creates rules and guidelines, and enforces them. Lastly. it provides the research legitimacy by establishing responsibility and helping to build societal support.

The provision of guidelines and structure around the international laws pertaining to oceans is also another important component of AOA implementation. Coastal countries have sovereignty over bodies of water within 12 nautical miles of their shore, and AOA would need to comply with the national permitting process of each nation. When the practice expands into a country’s exclusive economic zone (EEZ), which is the area about 200 nautical miles from the coast, things begin to get more complicated. However, the coastal country still has the authority to regulate activities that affect the marine ecosystem, so research protocols should remain similar to those being conducted in the waters just beyond the territory. Beyond the EEZ, AOA research would be permitted, but subject to principles of state responsibility should harm occur to the interests of other States under the UN Convention on the Law of the Sea. Moreover, principles of the Biodiversity Beyond National Jurisdiction, an agreement being developed under the Convention on the Law of the Sea, could be apposite, including the requirement that the parties establish conservation areas and environmental assessments pertaining to the marine biological diversity of areas beyond their national jurisdiction.

In order to ensure that a standard of compliance with acceptable environmental standards is set, looking at this matter with regard to OIF is a good starting point. In 2013 the London Protocol passed an amendment prohibiting ocean iron fertilization scientific research without a national permit and engagement in a stringent risk-assessment procedure.

Despite its potential AOA still comes with uncertainty around potential risks, questions about who has control over deployment decisions, and who bears the burden of liability. Local AOA treatments could serve as a good starting point for a gradual understanding of its impacts, and a means to allow government structures to mature alongside advances in technical understanding.

The Potential of Carbon Capture and Sequestration in the Northeast and Mid-Atlantic regions

The International Panel on Climate Change cites the widespread deployment of carbon capture and sequestration (CCS), bioenergy, and/or their combination (BECCS) as critical to the effort to limit 21st century warming due to CO2 release. The removal of CO2 from industrial effluent streams and storage in geological formations (CCS), is an established mitigation strategy that has the potential to decrease the rate at which CO2 is emitted into the atmosphere. More importantly, it is a technology that can progress towards achieving negative emissions through coupling CCS with CO2 capture from electricity generation processes driven by the combustion of biomass (BECCS). BECCS is particularly appealing because it addresses how electricity could be produced in a carbon negative future.

In “Total Cost of Carbon Capture and Storage Implemented at a Regional Scale: Northeastern and Midwestern United States” (Schmetz, Hochman & Miller, 2020), the authors show that CO2 emissions may be stored at the Northeast and Mid-Atlantic regions of the US at $52 per ton, sourced from coal-fired plants and stored onshore in depleted oil and gas fields, and that the region also has the opportunities to store CO2 in onshore saline reservoirs for less than $60 per ton. Offshore storage is also an option, where the lowest total costs of CCS with storage in offshore saline reservoirs are just over $60 per ton. Storage offshore carries less risk and inconvenience and less potential for interference from populations than onshore storage. Offshore storage could also be required if formation pressures pose geological risk issues when injecting gigatons of supercritical CO2 into onshore formations. Emissions from natural-gas-fired plants are more expensive to capture per ton of CO2, making the lowest total costs over $80 per ton. This analysis suggests that a relatively small (15%) reduction in the total cost of CCS, would make CCS economically viable at a large-scale (~8 Gt CO2 over 30 years). Large-scale carbon storage may be additionally justified when coupled with BECCS technology. Similarly, demonstrating the feasibility of CCS could ultimately facilitate a pathway to BECCS.

Enacted in 2018 by the 115th United States Congress, the Section 45Q tax credits allot $50 per ton CO2 in tax credits for the permanent sequestration of CO2 in saline geological formations, as well as $35 per ton CO2 for EOR applications of CCS. To this end, the difference between representative total costs of CCS in the northeastern and midwestern United States and the threshold for profit motivated adoption is relatively small with the Section 45Q credits. With some technological improvement, adoption of CCS on a meaningful scale is possible in this region. With EOR and 45Q, CCS is viable, and has been undertaken on commercial scales at the Petra Nova-WA Parish Generating Station in Texas and the Boundary Dam plant in Canada. CO2 captured at both of these locations is transported to nearby oil fields and sold to enhance recovery. Governments can and should support these initiatives as sound environmental policy, like the U.S. and Canadian federal governments did for Petra Nova and Boundary Dam, providing $190 million and $240 million for those projects, respectively. Grant funding supporting the construction of commercial scale CCS projects, like the $190 million DOE supplied for the Petra Nova plant, incentivize first-of-a-kind construction that allows for learning, feasibility testing, and risk reduction for future commercial implementations. The 45Q tax credit incentive is a promising environmental policy initiative that encourages the adoption of CCS, the reduction of its cost over time because of learning-by-doing and could ultimately result in reduction of CO2 in the atmosphere.

 Considering the risk and long-term planning and capital commitment associated with constructing or renovating electricity generating infrastructure to serve CCS, the initiative to incentivize early CCS applications should also be coupled with a long-term commitment to the section 45Q credits. If the political support for CCS and the section 45Q credits appears fragile or short-lived, the potential repeal or expiration of these credits will become a hazard that adds to the risk prospective CCS adopters will need to account for. This short-term commitment coupled with the energy infrastructure risk paradigm could nullify the incentives for adoption of carbon capture technology that the Section 45Q tax credits were written to provide.

While the establishment of CCS must precede full-scale implementation of BECCS from a logical/technological perspective, concurrent pilot projects that demonstrate the feasibility of BECCS would represent significant advances. One such opportunity for CCS and BECCS could come in the form of power plants that are facing pressure to refuel or repower with more environmentally sound technology, such as the to-be-shuttered coal-fired B.L. England Generating Station in southern New Jersey. The plant was scheduled for a conversion to natural gas, but successful opposition to a pipeline link resulted in the cancellation of the project. A conversion to biomass, perhaps co-firing with coal, coupled with carbon capture could presumably ameliorate the environmental concerns that comprised the original basis for shuttering the plant. Additionally, this plant, and other legacy coal-fired locations, is served by a railroad infrastructure that would make transporting biomaterials to the plant for co-firing with coal a simple transition that does not require traversing the complexities of constructing new pipeline. This particular location, as well as a couple others on the U.S. East Coast, is well-suited for carbon storage with reservoirs available both below the power-plant and in nearby regions offshore that would encounter less citizen opposition. A project of this nature could represent an example of a catalytic “tangible, near-term success” for CCS, biomass, and/or BECCS. Application of BECCS technology in a state like New Jersey that lacks an oil and gas culture and history and is strongly opposed to further industrialization including pipelines might provide a viable test for addressing concerns about BECCS and aid in the transformation from coal to renewable, carbon negative BECCS technology.


Schmelz, William J., Gal Hochman, and Kenneth G. Miller. “Total cost of carbon capture and storage implemented at a regional scale: northeastern and midwestern United States.” Interface Focus 10.5 (2020):


A critical overview of solar assisted carbon capture systems: Is solar always the solution?

Mohammad Saghafifar, Samuel Gabra                                                                  International Journal of Greenhouse Gas Control, 2020

This paper focuses on possible integration schemes between solar thermal collectors and carbon capture systems. In its entirety, solar assisted carbon capture systems can be categorized into direct and indirect systems. Key factor in designing solar assisted carbon capture systems
is to match the thermal-grade between the collector and gas separation process.

For post-combustion systems, in particular, amine based systems have been widely considered for integration with solar thermal collectors using either direct or indirect schemes. Comparing direct and indirect integration schemes, results are overwhelmingly in favour of indirect solar integrations. The key merits of indirect integration include its additional flexibility in system operation and the high solar energy utilization factor it offers. For direct systems, solar thermal energy utilization is limited to the reboiler heat duty. Moreover, higher temperature concentrating solar thermal collectors with higher optical efficiencies can be used in indirect systems. These conclusions can be extended to the case of using any other low temperature gas separation technique including other chemical absorption and chemical/physical temperature swing adsorption. Direct integration may only be suitable when high grade heat is required for gas separation, as in calcium looping.

For pre-combustion systems, all the available studies focused on utilizing solar thermal energy for fuel reforming/gasification stage. It is more feasible to supply the H2/CO2 separation energy from other low-grade sources. The advantage of these systems is the inherent ability of storing solar energy chemically in form of the upgraded fuel. In addition, high-grade heat needed for reforming/gasification stage makes solar assisted systems more feasible.

For oxyfuel combustion, both direct and indirect schemes were studied. In direct systems, solar energy is used to derive an endothermic reduction reaction for chemical looping processes. Solar hybrid chemical looping systems have two advantages: first, the inherent carbon dioxide sequestration and second, storing solar thermal energy both chemically and sensibly. For indirect systems, solar energy is utilized within the power cycles whilst air separation systems were used for pure oxygen production. In terms of merits, these systems are similar to indirect systems using low temperature gas separation methods. Possible future research direction for solar assisted carbon capture systems can be classified into solar collectors cost reduction research and innovative integration scheme research. Firstly, the cost of collectors, irrespective of technology, must be reduced. In addition, more research must be carried out on high temperature solar collector integration within high-temperature carbon capture and storage (CCS) systems. For post-combustion systems, ongoing research on solar assisted calcium looping systems is promising. Integrating high-grade solar energy for fuel reforming and gasification in pre-combustion CCS is another potential research route.

An interesting aspect of solar assisted CCS systems is the possibility of its utilization as an energy storage scheme coupled with CO2 capture. In these schemes, extra available solar energy during high insolation periods is employed to further run the endothermic part of the CCS
process and store the product for usage during instances of low solar insolation. The products from these processes can be simply stored.

Integrated assessment modeling of carbon removal at ICRLP

Authored by David Morrow, Director of Research, Institute for Carbon Removal Law and Policy

Bioenergy with carbon capture and storage (BECCS) is sometimes described as the only technology ever invented by modelers. There’s a grain of truth to this: the idea of combining bioenergy with CCS to produce a negative emissions technology rose to prominence because of its adoption by integrated assessment modelers in the early 2000s. Since then, these models have provided one important tool for thinking about how carbon removal might play a role in climate policy. The Institute for Carbon Removal Law and Policy is helping to push the boundaries of integrated assessment modeling of carbon removal with two ongoing projects.

What are integrated assessment models?

Before we get to ICRLP’s modeling projects, let’s back up a bit. What are integrated assessment models (IAMs)? Basically, IAMs are computer models that combine a model of the climate system with models of the economy, the energy sector, and land use to help researchers think rigorously about possible climate futures. For instance, researchers can use these models to ask questions like, “What would happen to the energy sector and the climate if coal were phased out worldwide by 2050?” or, “How would the energy sector change over time if the whole world put a gradually rising price on carbon beginning in 2040?” Researchers can also use these models to identify decarbonization pathways by which the world could meet various climate policy goals, such as the Paris Agreement’s goal of limiting global warming “well below 2°C.” When you read headlines saying that the world needs to cut its emissions in half by 2030 in order to limit global warming to 1.5°C, you’re reading a conclusion based in large part on integrated assessment modeling.

CarbonBrief offers an excellent introduction to IAMs and their role in studying climate policy. If you prefer to learn by doing, check out Climate Interactive’s EnROADS model, an IAM that’s fast enough to run in your web browser.

How are IAMs used to study carbon removal?

Integrated assessment modelers realized almost twenty years ago that they could combine two technologies that were already represented in their models—bioenergy and CCS—to model a technology that actively removes carbon dioxide from the atmosphere. Research over the past two decades suggests that developing and scaling negative emissions technologies makes it much likely that the world can keep warming below 2°C or 1.5°C. In fact, modeling studies suggest that unless the world reduces its greenhouse gas emissions extremely rapidly over the next two or three decades, it may not be possible to limit warming below 1.5C without large-scale carbon removal

Until recently, however, few integrated assessment modelers had incorporated any kind of carbon removal into their model besides BECCS and reforestation. (For some notable exceptions, see recent papers led by Jessica Strefler, Giulia Realmonte, and Jay Fuhrman.) As a result, BECCS has long operated as a kind of stand-in for the wide variety of approaches to carbon removal that have been proposed. Actually implementing BECCS at the scales projected in many IAM scenarios would likely be disastrous because it would require devoting such vast tracts of land to bioenergy. Overcoming the conceptual and technical hurdles to modeling other approaches to carbon removal would be an important step in understanding what role carbon removal can realistically play in just and sustainable climate policy.

Integrated assessment modeling at ICRLP

Earlier this year, ICRLP launched a project to produce a variant of the Global Change Analysis Model (GCAM), a major IAM developed by the Joint Global Change Research Institute. I’m working with Postdoctoral Researcher Raphael Apeaning to extend GCAM’s ability to model carbon removal. That involves both incorporating additional approaches to carbon removal, starting with direct air capture, enhanced weathering, ocean alkalinization, and soil carbon sequestration; and giving GCAM the capacity to model various policies for incentivizing and supporting carbon removal. We gratefully acknowledge the financial support of the Alfred P. Sloan Foundation for this project.

I’m also supervising an undergraduate in American University’s School of International Service, Garrett Guard, as he uses GCAM to write his senior thesis on the role of BECCS in climate policy. His thesis grew out of a research project he did for a course I taught last year on using integrated assessment models for climate policy analysis. Garrett’s research looks at what happens when the world tries to meet various climate targets if we exclude fossil fuel CCS, BECCS, or both from the climate policy portfolio, as well as how that varies across different socioeconomic pathways.

Fuel out of Thin Air: CO2 Capture from Air and Conversion to Methanol

Authors: Raktim Sen, Alain Goeppert, Sayan Kar, G. K. Surya Prakash*Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, California, United States.

Full citation: Sen, R.; Goeppert, A.; Kar, S.; Prakash, G. K. S., Hydroxide Based Integrated CO2 Capture from Air and Conversion to Methanol. Journal of the American Chemical Society 2020, 142, 4544-4549.

Over the past two centuries, surging greenhouse gas emissions have led to an enormous rise in atmospheric CO2 levels, causing a significant increase in the average global temperature and ocean acidification. Humankind is now releasing every year > 36 billion tons of CO2 to the environment! Among various solutions explored to mitigate this problem, direct air capture (DAC) of CO2 is highly promising. DAC has significant advantages. It enables the point of capture to be independent from the emission sources. It also targets CO2 emissions from dispersed point sources, which are responsible for about half of total anthropogenic emissions but would otherwise be difficult to address. Furthermore, utilization of the captured CO2 (Carbon Capture and Utilization, CCU) as a carbon source for various chemical feedstocks and polymeric materials is very promising. In this context, CO2 is combined with hydrogen obtained by electrolysis of water using renewable energy sources such as solar and wind. Among various CO2 hydrogenation products, methanol is one of the most attractive and versatile alcohol. Methanol is a feedstock for a multitude of chemicals and products, already used on a scale of over 100 billion liters per year. Additionally, methanol, which is a liquid with a boiling point of 64.7 °C, is a superior fuel for internal combustion engines and fuel cells, as well as a convenient high density liquid hydrogen carrier. Methanol can be converted to ethylene and propylene through the MTO (methanol to olefins) process. Hence, the production of renewable methanol and the associated methanol economy holds significant potential to replace current fossil fuel-based economies.

Following the legacy of their late colleague Nobel Laureate George Olah, a major proponent of the methanol economy, G. K. Surya Prakash, professor and director at Loker Hydrocarbon Institute and his team including senior research scientist, Alain Goeppert have successfully combined the two steps of CO2 capture and hydrogenation to methanol into a seamless reaction sequence to transform the greenhouse gas into its combustible cousin. Until now, the integrated capture and conversion processes relied on organic bases called amines to capture CO2. While amines are easily regenerable, they are prone to oxidative degradation and suffer from notable toxicity and volatility. Hence, in order to improve the system, Prakash and his team turned to inorganic bases like sodium/potassium hydroxides which are superior CO2 capturing agents forming their respective bicarbonates/carbonates. Conventionally, however, recycling of the base by thermally decomposing bicarbonates/carbonates requires extreme temperatures above 700 °C making the process highly energy intensive. In initial efforts by the group, CO2 captured from air by a solution of hydroxide in water was converted to formate salts. However; further hydrogenation to methanol was ineffective. 

In their current study, the authors discovered that switching water with alcohols like ethylene glycol as a reaction medium could mediate effectively the process to methanol. When air was bubbled through potassium hydroxide dissolved in ethylene glycol and the CO2-loaded solution subsequently hydrogenated in the presence of H2 and a metal catalyst, complete conversion to methanol was observed at 140 °C. Moreover, regeneration of the hydroxide base occurred at mild temperatures of 100-140 °C. Notably, a fraction of the base was deactivated in an unwanted side reaction. Currently, the researchers are aiming to minimize the side reactions to efficiently recycle the potassium hydroxide. This system offers easy integration of existing hydroxide-based CO2 scrubbing industries to utilize the captured CO2 to produce methanol, paving a way for a sustainable and carbon neutral future. As Prakash says, “All living things are primarily made of carbon and therefore carbon has to be managed. Humankind requires carbon based fuels and chemical feedstocks currently obtained from fossil fuels. Renewable methanol can easily replace fossil fuels without requiring major changes to our current chemical and transportation infrastructures.   If CO2 is a one-carbon problem, then methanol is a one-carbon solution.”

The study authored by Prakash, Goeppert and graduate assistants Raktim Sen and Sayan Kar was recently published in Journal of the American Chemical Society (DOI: 10.1021/jacs.9b12711) and also featured in C&E News (