Title: Direct Air Capture of CO2: A Key Technology for Ambitious Climate Change Mitigation
Abstract: Christian Breyer is Professor for Solar Economy at LUT University, Finland. His major expertise is research of technological and economic characteristics of renewable energy systems specializing for highly renewable energy systems, on a local but also global scale. Research includes integrated sector analyses with power, heat, transport, desalination, industry, NETs, CCU, and Power-to-X. He worked previously for Reiner Lemoine Institut, Berlin, and Q-Cells (now Hanwha Q Cells). He is a member of ETIP PV, IEA-PVPS, scientific committee of the EU PVSEC and IRES, chairman at the Energy Watch Group, and reviewer for the IPCC.Mahdi Fasihi, M.Sc., is Research Assistant at LUT University, Finland. His focus area is CO2 direct air capture and techno-economic assessment of renewable electricity-based Power-to-X fuels and chemicals production and global trading. Highly resolved energy system modeling is a key method for his potential assessments. He received his M.Sc. degree in Energy Technology at LUT University and B.Sc. in Mechanical Engineering at Guilan University, Iran.Cyril Bajamundi, PhD, is Chief Technology Officer of Soletair Power Oy, a Finnish start-up company focused on CO2 direct air capture and Power-to-X fuel conversion. He had been a Senior Scientist with VTT Technical Research Center of Finland, working in direct air capture of CO2 to support power-to-gas and power-to-liquid technologies for energy storage. Previously, he worked as Assistant Professor in the Department of Chemical Engineering at the University of the Philippines, where he received his M.Sc. in Chemical Engineering.Felix Creutzig leads a working group at the Mercator Research Institute on Global Commons and Climate Change, Berlin, and is Chair of Sustainability Economics of Human Settlements at Technical University Berlin. Educated as a physicist, he holds a PhD in Computational Neuroscience. He coordinates the chapter on “demand, services, and social aspects of mitigation” in the 6th assessment report of the IPCC. Research interests include data science and machine learning approaches for designing low-carbon cities, and demand-side solutions for climate change mitigation. Christian Breyer is Professor for Solar Economy at LUT University, Finland. His major expertise is research of technological and economic characteristics of renewable energy systems specializing for highly renewable energy systems, on a local but also global scale. Research includes integrated sector analyses with power, heat, transport, desalination, industry, NETs, CCU, and Power-to-X. He worked previously for Reiner Lemoine Institut, Berlin, and Q-Cells (now Hanwha Q Cells). He is a member of ETIP PV, IEA-PVPS, scientific committee of the EU PVSEC and IRES, chairman at the Energy Watch Group, and reviewer for the IPCC. Mahdi Fasihi, M.Sc., is Research Assistant at LUT University, Finland. His focus area is CO2 direct air capture and techno-economic assessment of renewable electricity-based Power-to-X fuels and chemicals production and global trading. Highly resolved energy system modeling is a key method for his potential assessments. He received his M.Sc. degree in Energy Technology at LUT University and B.Sc. in Mechanical Engineering at Guilan University, Iran. Cyril Bajamundi, PhD, is Chief Technology Officer of Soletair Power Oy, a Finnish start-up company focused on CO2 direct air capture and Power-to-X fuel conversion. He had been a Senior Scientist with VTT Technical Research Center of Finland, working in direct air capture of CO2 to support power-to-gas and power-to-liquid technologies for energy storage. Previously, he worked as Assistant Professor in the Department of Chemical Engineering at the University of the Philippines, where he received his M.Sc. in Chemical Engineering. Felix Creutzig leads a working group at the Mercator Research Institute on Global Commons and Climate Change, Berlin, and is Chair of Sustainability Economics of Human Settlements at Technical University Berlin. Educated as a physicist, he holds a PhD in Computational Neuroscience. He coordinates the chapter on “demand, services, and social aspects of mitigation” in the 6th assessment report of the IPCC. Research interests include data science and machine learning approaches for designing low-carbon cities, and demand-side solutions for climate change mitigation. The Paris Agreement and especially its indicative 1.5°C target pose a dramatic challenge for the energy system, requiring both unprecedented decarbonization and at least a limited amount of carbon dioxide removal (CDR).1Grubler A. Wilson C. Bento N. Boza-Kiss B. Krey V. McCollum D.L. Rao N.D. Riahi K. Rogelj J. De Stercke S. et al.A low energy demand scenario for meeting the 1.5 C target and sustainable development goals without negative emission technologies.Nat. Energy. 2018; 3: 515-527Crossref Scopus (518) Google Scholar Direct air capture (DAC) of CO2 is increasingly expected to emerge as a key technology in the decades to come. As a result, start-ups back DAC with substantial investments and innovation,2Keith D.W. Holmes G. St Angelo D. Heidel K. A process for capturing CO2 from the atmosphere.Joule. 2018; 2: 1573-1594Abstract Full Text Full Text PDF Scopus (609) Google Scholar as cost reduction potential is substantial2Keith D.W. Holmes G. St Angelo D. Heidel K. A process for capturing CO2 from the atmosphere.Joule. 2018; 2: 1573-1594Abstract Full Text Full Text PDF Scopus (609) Google Scholar, 3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar and overall efficiency in extracting CO2 is comparably high.4Creutzig F. Breyer Ch. Hilaire J. Minx J. Peters G. Socolow R. The mutual dependence of negative emission technologies and energy systems.Energy Environ. Sci. 2019; 12: 1805-1817Crossref Google Scholar DAC is an enabling technology useful for, first, CDR as direct air carbon capture and storage (DACCS)5Fuss S. Lamb W.F. Callaghan M.W. Hilaire J. Creutzig F. Amann T. Beringer T. de Oliveira Garcia W. Hartmann J. Khanna T. et al.Negative emissions - Part 2: Costs, potentials and side effects.Environ. Res. Lett. 2018; 13: 063002Crossref Scopus (565) Google Scholar and second, as CO2 utilization (DACCU) for fuels in the transport sector, particularly in marine, aviation, and chemical industry, where sustainable options hardly exist.6Haegel N.M. Atwater Jr., H. Barnes T. Breyer C. Burrell A. Chiang Y.-M. De Wolf S. Dimmler B. Feldman D. Glunz S. et al.Terawatt-scale photovoltaics: Transform global energy.Science. 2019; 364: 836-838Crossref PubMed Scopus (229) Google Scholar DACCS has not yet been established as a major CDR option1Grubler A. Wilson C. Bento N. Boza-Kiss B. Krey V. McCollum D.L. Rao N.D. Riahi K. Rogelj J. De Stercke S. et al.A low energy demand scenario for meeting the 1.5 C target and sustainable development goals without negative emission technologies.Nat. Energy. 2018; 3: 515-527Crossref Scopus (518) Google Scholar for factors like perceived high costs and substantial energy input requirement,7Socolow R.H. Desmond M.J. Aines R. Blackstock J. Bolland O. Kaarsberg T. Lewis N. Mazzotti M. Pfeffer A. Sawyer K. et al.Direct Air Capture of CO2 with Chemicals: A Technology Assessment for the APS Panel on Public Affairs. American Physical Society, College Park, MD2011https://www.aps.org/policy/reports/assessments/upload/dac2011.pdfGoogle Scholar despite substantial benefits offered compared to the mainly considered bioenergy carbon capture and storage (BECCS), such as required land area, water demand, technology learning, scalability, and life-cycle aspects.4Creutzig F. Breyer Ch. Hilaire J. Minx J. Peters G. Socolow R. The mutual dependence of negative emission technologies and energy systems.Energy Environ. Sci. 2019; 12: 1805-1817Crossref Google Scholar DAC technology is in accordance with the sustainability guardrails for energy systems. The two main technology routes for DAC considered in this study are the high-temperature (HT) and the low-temperature (LT) desorption processes.2Keith D.W. Holmes G. St Angelo D. Heidel K. A process for capturing CO2 from the atmosphere.Joule. 2018; 2: 1573-1594Abstract Full Text Full Text PDF Scopus (609) Google Scholar, 3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar Additionally, LT moisture swing adsorption is the third route for DAC, which has been excluded from this study due to lack of publicly accessible financial data for a real prototype or pilot plant. A vast majority of all known active companies in the field invest on the LT options.3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar The LT options may lead to lower cost for captured CO2 and allow the utilization of waste heat in the range of 70°C–100°C, which can further reduce the CO2 capture cost by about 40%, compared to lack of free waste heat.3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar It may even be possible to use lower-temperature levels, but that would require more heat for thermodynamic reasons. Waste heat might be available from combined heat and power plants, such as geothermal plants or solar thermal power plants, as well as from waste incinerators, electrolysers, or Fischer-Tropsch synthesis plants. A thermal energy storage as heat buffer may be needed, which is available for comparably low cost. While the HT route requires water as input, some LT DAC technologies produce water.3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar Water production could be an advantage for integrated systems with water demand but could increase energy demand for CO2 regeneration. The HT route could have faster industrial scaling due to use of more standard components, such as calcination. On the other hand, the new technologies used in the LT route could potentially have a higher learning rate, which may accelerate the industrial scaling. Keith et al.2Keith D.W. Holmes G. St Angelo D. Heidel K. A process for capturing CO2 from the atmosphere.Joule. 2018; 2: 1573-1594Abstract Full Text Full Text PDF Scopus (609) Google Scholar indicate that levelized cost of CO2 of 94–232 USD/tCO2 may be achievable in the near future. A common misperception is that excess electricity of a few hundreds of hours per year from solar or wind plants could be used for DAC, but detailed cost analyses show least cost of captured CO2 at 6,000–8,000 full load h per year,3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar which requires a constant energy supply incompatible with the previous notion of only excess electricity utilization. DAC could become a key technology for climate change mitigation. One study estimates a logistic growth of DAC reaching 1 GtCO2/a in 2050.4Creutzig F. Breyer Ch. Hilaire J. Minx J. Peters G. Socolow R. The mutual dependence of negative emission technologies and energy systems.Energy Environ. Sci. 2019; 12: 1805-1817Crossref Google Scholar Another study estimates the market potential for DAC at about 7 GtCO2/a in the energy system and about 8 GtCO2/a in CDR in 2050.3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar The first large-scale DACCS implementation study in integrated assessment models (IAMs) is not as optimistic, with about 0.3 GtCO2/a in 2050, while 30 GtCO2/a DACCS capacity is achieved in 2080 in a 1.5°C scenario.8Realmonte G. Drouet L. Gambhir A. Glynn J. Hawkes A. Köberle A.C. Tavoni M. An inter-model assessment of the role of direct air capture in deep mitigation pathways.Nat. Commun. 2019; 10: 3277Crossref PubMed Scopus (169) Google Scholar The DAC deployment level is still too early for market data on the learning rate of the technology; however, a 10%–15% learning rate seems to be realistic, when compared to similar technologies. Fasihi et al.3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar conclude that the realization of half of this capacity, i.e., 7.5 GtCO2/a, with a 10% learning rate can lead to DAC capital expenditures of 199–222 €/tCO2·a, which is equal to levelized cost of direct air capture (LCOD) of 54 €/tCO2 (LT), 32 €/tCO2 (LT, free waste heat), and 71 €/tCO2 (HT) in 2050 for weighted average cost of capital of 7% and the solar and wind condition in the Maghreb region. Such cost levels lead to CO2 DAC cost shares of about 20% or less for synthetic hydrocarbons3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar and could place DACCS as a major CDR option, also due to good compatibility to a solar-, wind-, and battery-dominated sustainable energy system.4Creutzig F. Breyer Ch. Hilaire J. Minx J. Peters G. Socolow R. The mutual dependence of negative emission technologies and energy systems.Energy Environ. Sci. 2019; 12: 1805-1817Crossref Google Scholar, 6Haegel N.M. Atwater Jr., H. Barnes T. Breyer C. Burrell A. Chiang Y.-M. De Wolf S. Dimmler B. Feldman D. Glunz S. et al.Terawatt-scale photovoltaics: Transform global energy.Science. 2019; 364: 836-838Crossref PubMed Scopus (229) Google Scholar The growth rates required to scale DAC beyond 10 GtCO2/a in 2050 would translate into a compound annual growth rate of the cumulative DAC capacity of around 26% from 2030 to 2050, if 100 MtCO2/a are installed by 2030. To put this in perspective, a cumulative DAC capacity of 100 MtCO2/a necessitates investments of around 32–42 b€ for a learning rate of 10%–15%, based on the insights of Fasihi et al.3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar This investment is comparable to about 34 b€ investment on solar photovoltaics in the 10 years from 1996 to 2005. Later, the solar photovoltaic capacity grew from 5.2 GW in 2005 to 500 GW in 2018, i.e., by a factor of 95 in 13 years, comparable to the growth requirement of DAC from 2030 to 2050. The envisaged industrial scaling is hence possible, given clear and ambitious policy targets and policies that bring investment security at least in the first decade. CDR demand may grow fast beyond 2050 on a level of 10–20 GtCO2/a,9Lawrence M.G. Schäfer S. Promises and perils of the Paris Agreement.Science. 2019; 364: 829-830Crossref PubMed Scopus (27) Google Scholar as it is already too late to avoid massive CDR activities.1Grubler A. Wilson C. Bento N. Boza-Kiss B. Krey V. McCollum D.L. Rao N.D. Riahi K. Rogelj J. De Stercke S. et al.A low energy demand scenario for meeting the 1.5 C target and sustainable development goals without negative emission technologies.Nat. Energy. 2018; 3: 515-527Crossref Scopus (518) Google Scholar A DAC system including full renewable energy supply on the scale of 1 GtCO2/a may lead to an annual cost of 55 b€ in 2050 according to Breyer et al.,10Breyer C. Fasihi M. Aghahosseini A. Carbon Dioxide Direct Air Capture for effective Climate Change Mitigation based on Renewable Electricity: A new Type of Energy System Sector Coupling.Mitig. Adapt. Strategies Glob. Change. 2019; (Published online February 13, 2019)https://doi.org/10.1007/s11027-019-9847-yCrossref Scopus (61) Google Scholar with the DAC units contributing 45% of the annual cost, while other components contribute to the rest: solar photovoltaics (16%), batteries (15%), heat pumps (16%), thermal energy storage (7%), and others (2%). Using the latest cost considerations based on Fasihi et al.3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar and Breyer et al.10Breyer C. Fasihi M. Aghahosseini A. Carbon Dioxide Direct Air Capture for effective Climate Change Mitigation based on Renewable Electricity: A new Type of Energy System Sector Coupling.Mitig. Adapt. Strategies Glob. Change. 2019; (Published online February 13, 2019)https://doi.org/10.1007/s11027-019-9847-yCrossref Scopus (61) Google Scholar and for solar photovoltaics,11Vartiainen E. Masson G. Breyer C. Moser D. Medina E.R. Impact of Weighted Average Cost of Capital, Capital Expenditure, and Other Parameters on Future Utility-Scale PV Levelised Cost of Electricity.Prog. Photovolt. Res. Appl. 2019; (Published online August 29, 2019)https://doi.org/10.1002/pip.3189Crossref Scopus (171) Google Scholar a global CO2 DAC cost map for 2050 can be derived (Figure 1), optimized in full hourly resolution according to Breyer et al.10Breyer C. Fasihi M. Aghahosseini A. Carbon Dioxide Direct Air Capture for effective Climate Change Mitigation based on Renewable Electricity: A new Type of Energy System Sector Coupling.Mitig. Adapt. Strategies Glob. Change. 2019; (Published online February 13, 2019)https://doi.org/10.1007/s11027-019-9847-yCrossref Scopus (61) Google Scholar The model includes solar photovoltaics, wind energy, batteries, heat pumps, thermal energy storage, and DAC units. Low-cost storage helps to reduce the LCOD. Figure 1 highlights the cost potential of DAC for 50 €/tCO2 or below in major parts of the word. Since 1 GtCO2 removal may cost around 45–55 b€ annually for year 2050 considerations, as depicted in Figure 1, it is important to rapidly defossilize the global energy system so that massive cost burden for future generations can be avoided. Using the same assumptions, based on Fasihi et al.3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar and Vartiainen et al.11Vartiainen E. Masson G. Breyer C. Moser D. Medina E.R. Impact of Weighted Average Cost of Capital, Capital Expenditure, and Other Parameters on Future Utility-Scale PV Levelised Cost of Electricity.Prog. Photovolt. Res. Appl. 2019; (Published online August 29, 2019)https://doi.org/10.1002/pip.3189Crossref Scopus (171) Google Scholar for the projected cost levels and efficiencies in the year 2040, leads to a cost range of about 55–70 b€ annually to capture 1 GtCO2, and specific cost in 2030 may be around 85–100 €/tCO2, based on an industrial scaling substantially below 1 GtCO2/a. The weighted average cost of capital (WACC) is assumed to be 7%, which may be too high for a common public effort and almost risk-free investments due to governmental decisions. WACC of 5% would reduce the LCOD by a further 15%. Sustainable long-term CO2 storage requires further financial means.12Gunnarsson I. Aradóttir E.S. Oelkers E.H. Clark D.E. Arnarson M.I. Sigfusson B. Snæbjornsdottir S.O. Matter J.M. Stute M. Juliusson B.M. et al.The rapid and cost-effective capture and subsurface mineral storage of carbon and sulfur at the CarbFix2 site.Int. J. Greenh. Gas Control. 2018; 79: 117-126Crossref Scopus (59) Google Scholar Gaseous CO2 storage raises concerns about the long-term sustainability, which can be overcome in an additional synthesis step, fulfilling the following criteria: CO2 converted and stored as a solid compound, which is chemically inert with a very high combustion point, since these requirements avoid the risk of gaseous CO2 leakages and later reuse or technical accidents involving combustion. Enhanced weathering (EW) as practiced in Iceland12Gunnarsson I. Aradóttir E.S. Oelkers E.H. Clark D.E. Arnarson M.I. Sigfusson B. Snæbjornsdottir S.O. Matter J.M. Stute M. Juliusson B.M. et al.The rapid and cost-effective capture and subsurface mineral storage of carbon and sulfur at the CarbFix2 site.Int. J. Greenh. Gas Control. 2018; 79: 117-126Crossref Scopus (59) Google Scholar such as enhanced rock weathering in the form of permanent geological CO2 mineralization in the subsurface fulfills such sustainability constraints for carbon capture and storage (CCS). The CarbFix2 project on Iceland demonstrates that DACCS-EW is a viable option. The two main applications of DAC are carbon capture and utilization (CCU), which is typically discussed as Power-to-X (PtX),6Haegel N.M. Atwater Jr., H. Barnes T. Breyer C. Burrell A. Chiang Y.-M. De Wolf S. Dimmler B. Feldman D. Glunz S. et al.Terawatt-scale photovoltaics: Transform global energy.Science. 2019; 364: 836-838Crossref PubMed Scopus (229) Google Scholar and CDR as CCS, which can be summarized as DACCU and DACCS. A challenge for DACCU and DACCS may be the amount of energy required. To avoid problematic life-cycle GHG emissions from gas-powered DACCU and DACCS, low-cost solar and wind electricity powering DACCU and DACCS will be essential to provide affordable and effective synthetic hydrocarbons and carbon sequestration.6Haegel N.M. Atwater Jr., H. Barnes T. Breyer C. Burrell A. Chiang Y.-M. De Wolf S. Dimmler B. Feldman D. Glunz S. et al.Terawatt-scale photovoltaics: Transform global energy.Science. 2019; 364: 836-838Crossref PubMed Scopus (229) Google Scholar An alternative would be bioenergy-based routes with CCU and CCS, leading to the much-discussed BECCS and more recently discussed BECCU. This route is preferred in most scenarios because of its lower perceived costs. Key challenges of the bioenergy route are high cost, limited area availability (and thus limited resource potential of energy crops), low efficiency of the photosynthesis process, and additional water demand,13Creutzig F. Economic and ecological views on climate change mitigation with bioenergy and negative emissions.Glob. Change Biol. Bioenergy. 2016; 8: 4-10Crossref Scopus (44) Google Scholar to be summarized as limited compatibility with sustainability guardrails. Biomass-based residues and wastes are better suited for BECCU (e.g., waste incinerators with carbon capture and utilization, or biogas plants with hydrogen-based upgrade to biomethane for CO2 composition in output gas) due to subsequent CO2 utilization for production of synthetic hydrocarbons. The anticipated point source capture costs are competitive with those by DAC. Substantial negative CO2 emissions in the Gt/a scale require large volume streams of biomass, which cannot be provided by bio-waste and residues and would require energy crops on large scale. Fossil-fuel-based CCU and CCS options are in massive conflict with the targets of the Paris Agreement and sustainability guardrails, since only point sources can be used, such as thermal plants or industrial sites, but the CO2 capture efficiency of 80%–90% is not sufficient for a zero and net negative GHG emission economy, and additional air pollution and emissions still harm peoples’ health and environment. The compatibility of the main energy sources (fossil fuels, bioenergy, solar, and wind energy) and the CCU and CCS routes with sustainability criteria is visualized in Figure 2. An essential precondition for a continued development and cost-scaling of DAC is sustained investments into the technology, from today onward. This requires substantial research and development efforts and, in particular, a stable market ramp-up for DAC for both CCU/PtX applications and CCS/CDR solutions. The past has shown that stable market conditions often coincide with respective regulations. The fundamental learning from the solar photovoltaics case in the 2000s and 2010s is that forward-looking policies, in particular the Feed-in Tariff legislation in Germany, a form of regulation, and substantial manufacturing scale-up backed with guarantees, as practiced in China, can accelerate technology deployment and diffusion by decades.14Nemet G.F. How Solar Energy Became Cheap: A Model for Low-Carbon Innovation. Routledge, 2019Crossref Scopus (76) Google Scholar Global scenarios of climate change mitigation only reluctantly model DACCS (e.g., Chen and Tavoni15Chen C. Tavoni M. Direct air capture of CO 2 and climate stabilization: a model based assessment.Clim. Change. 2013; 118: 59-72Crossref Scopus (76) Google Scholar and Realmonte et al.8Realmonte G. Drouet L. Gambhir A. Glynn J. Hawkes A. Köberle A.C. Tavoni M. An inter-model assessment of the role of direct air capture in deep mitigation pathways.Nat. Commun. 2019; 10: 3277Crossref PubMed Scopus (169) Google Scholar). Instead, IAMs prefer BECCS as negative emission technologies. This choice is based on the perceived lower costs of BECCS, its ability to generate rather consume energy, and its flexibility to provide fuels for different sectors. It may also be caused by inertia to adopt new options in IAMs, since BECCS has been introduced there much earlier than DACCS. Cost assumptions of DACCS originate in the influential report of the National Academy of Science.7Socolow R.H. Desmond M.J. Aines R. Blackstock J. Bolland O. Kaarsberg T. Lewis N. Mazzotti M. Pfeffer A. Sawyer K. et al.Direct Air Capture of CO2 with Chemicals: A Technology Assessment for the APS Panel on Public Affairs. American Physical Society, College Park, MD2011https://www.aps.org/policy/reports/assessments/upload/dac2011.pdfGoogle Scholar While these arguments are valid, we here suggest that other dynamics, insufficiently reflected in these models, lead to vastly different outcomes. These involve life-cycle emissions and land-use costs making BECCS more expensive than estimated, that the LT route of DACCS is less expensive than the HT route originally modeled,7Socolow R.H. Desmond M.J. Aines R. Blackstock J. Bolland O. Kaarsberg T. Lewis N. Mazzotti M. Pfeffer A. Sawyer K. et al.Direct Air Capture of CO2 with Chemicals: A Technology Assessment for the APS Panel on Public Affairs. American Physical Society, College Park, MD2011https://www.aps.org/policy/reports/assessments/upload/dac2011.pdfGoogle Scholar and that technological learning of modular technologies is mostly ignored. For example, in these models solar photovoltaic cost assumptions in the year 205016Krey V. Guo F. Kolp P. Zhou W. Schaeffer R. Awasthy A. Bertram C. de Boer H.-S. Fragkos P. Fujimori S. et al.Looking under the hood: A comparison of techno-economic assumptions across national and global integrated assessment models.Energy. 2019; 172: 1254-1267Crossref Scopus (78) Google Scholar have not been updated much in recent years and are about twice the real present cost.11Vartiainen E. Masson G. Breyer C. Moser D. Medina E.R. Impact of Weighted Average Cost of Capital, Capital Expenditure, and Other Parameters on Future Utility-Scale PV Levelised Cost of Electricity.Prog. Photovolt. Res. Appl. 2019; (Published online August 29, 2019)https://doi.org/10.1002/pip.3189Crossref Scopus (171) Google Scholar Such higher electricity cost is a further burden for DACCS. The IAMs still reflect technology development, only insufficiently reflecting technological learning by modular and granular technologies. The case of solar photovoltaics, also relevant as low-cost energy input for DACCS, shows that such policies can accelerate the development by more than three decades. This analogy may show how responsible and forward-looking policies for DAC may offer a powerful climate mitigation technology faster than expected by most experts in the field. The relatively young research field of DAC technology still exhibits several research questions, which have not yet been well addressed. Sorbents with high CO2 capacity, easily regenerable, favorable kinetics, and long lifetime need more development. In addition, the DAC performance under different weather conditions and integration of DAC to systems with abundant waste heat needs to be demonstrated. Life-cycle assessment studies for DAC17van der Giesen C. Meinrenken C.J. Kleijn R. Sprecher B. Lackner K.S. Kramer G.J. A Life Cycle Assessment Case Study of Coal-Fired Electricity Generation with Humidity Swing Direct Air Capture of CO2 versus MEA-Based Postcombustion Capture.Environ. Sci. Technol. 2017; 51: 1024-1034Crossref PubMed Scopus (40) Google Scholar are still very limited and require more attention. A detailed global inventory of all CO2 point sources, which would still be available under strict sustainability criteria, such as cement mills, pulp and paper plants, and waste incinerators, is required, since such sources can be used first for CCU processes. The remaining CO2 raw material demand for hydrocarbon-based fuels and chemicals can be covered by DAC. The learning rate of DAC is not yet understood well but has a substantial impact on DAC cost projections.3Fasihi M. Efimova O. Breyer Ch. Techno-economic assessment of CO2 direct air capture plants.J. Clean. Prod. 2019; 224: 957-980Crossref Scopus (355) Google Scholar Technologically detailed and temporally and geo-spatially highly resolved studies for the impact of BECCS and DACCS on the energy system are missing. More research is needed for the feasibility and economics of large-scale carbon storage in solid form, in particular fulfilling the constraints of being chemically inert and a high combustion point. The 1.5°C target of the Paris Agreement may not be ambitious enough for a true sustainable re-balancing within the limits of our planet, which may lead to a revised target of 1.0°C equivalent to 350 ppm CO2 in the atmosphere.18Hansen J. Sata M. Kharecha P. von Schuckmann K. Beerling D.J. Cao J. Marcott S. Masson-Delmotte V. Prather M.J. Rohling E.J. et al.Young people’s burden: requirement of negative CO2 emissions.Earth System Dynamics. 2017; 8: 577-616Crossref Scopus (158) Google Scholar Latest research results indicate that an energy transition toward a highly renewable energy system could be achieved in a cost-neutral pathway, which will enable a broadly available sustainable power supply for DACCS. In case humankind would like to advance the targets of the Paris Agreement, DAC technology would become even more important. Importantly, a low-energy-demand scenario is modeled in accordance with stabilizing temperatures at 1.5°C.1Grubler A. Wilson C. Bento N. Boza-Kiss B. Krey V. McCollum D.L. Rao N.D. Riahi K. Rogelj J. De Stercke S. et al.A low energy demand scenario for meeting the 1.5 C target and sustainable development goals without negative emission technologies.Nat. Energy. 2018; 3: 515-527Crossref Scopus (518) Google Scholar If in addition a scalable negative emission technology can deliver CO2 sequestration at costs of less than 100 USD/tCO2, it becomes feasible to imagine trajectories that reduce temperatures to 1°C until 2100–2150. Such a highly ambitious target is in line with the global Fridays for Future movement of the youth all around the world, based on scientific insights. However, as there is no guarantee that DACCU and DACCS will be deployed, and without considerable environmental risks, all other mitigation levels, including demand-side solutions, still require strong policy support and are indeed a precondition for such ambitious targets. DAC technology is identified as a central technology for ambitious climate change mitigation, comparable to solar photovoltaics, wind energy, batteries, and electrolysers. Immediate and continued market ramp up is key for a fast, comprehensive, and beneficial impact of DAC on the energy transition and climate change mitigation ahead.