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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"8 Synthesis." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

CHAPTER EIGHT Synthesis This chapter synthesizes the impact potential and research agendas for the various negative emissions technologies (NETs). It summarizes the committtee’s assessment of the potential rates of CO2 removal for both the United States and the globe, as well as the costs for the individual NETs. It also combines the research proposals for each NET into an integrated research proposal and a list of research priorities. The committee repeatedly encountered the view that NETs will primarily be deployed to reduce atmospheric CO2 after fossil emissions are reduced to near zero. In contrast, because it will likely be very expensive to decrease anthropogenic emissions once they reach low levels, methods for reduced and negative emissions will probably be competitors for an extended period, even during a sustained period of net negative global emissions. Conclusion 1: Negative emissions technologies are best viewed as a component of the mitigation portfolio, rather than a way to decrease atmospheric con- centrations of carbon dioxide only after anthropogenic emissions have been eliminated. CO2 IMPACTS In Chapters 2-7, the committee identified the potential rates of CO2 removal and sequestra­ ion that could be achieved safely and economically, given our current t knowledge and level of technological development. “Safe” means that deployment of the NET would, with high confidence, not cause the large adverse societal, economic, and environmental impacts that are described in those chapters and later in this chap- ter. “Economical” means that deployment would cost1 less than $100/t CO2 (and in some cases less than $20/t CO2). As noted earlier in the report, geologic sequestration is an enabling technology and not a NET in and of itself. Including combustion-based bioenergy with carbon capture and sequestration (BECCS) as being ready for large- scale deployment implies that the committee believes that geologic sequestration 1 The committee refers to direct costs of attaining negative emissions (e.g., operating costs, labor costs). All NETs have a full set of indirect costs (e.g., impact on land values) that may not be reflected in direct cost estimates. 351

N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N is ready for large-scale deployment. The following information provides context for these estimated costs of deployment: • the most recently published EPA estimates of the social cost of carbon are ~$10/t CO2 to ~$100/t CO2 in 2020 and ~$25/t CO2 to ~$200/t CO2in 2050, at discount rates of 2.5-5% (EPA, 2016b); • price of $19.66/t CO2 in the European Union carbon market as of July 19, 2018;2 • current U.S. tax credit of $50/t CO2 for carbon capture and sequestration known as the 45Q rule;3 • average 2018 price of ~$100/t CO2 under California’s Low Carbon Fuels Stan- dard (Aines and Mcoy, 2018); • ~$200/t CO2 combination of the 45Q rule and the recently announced changes in credits under California’s Low Carbon Fuels Standard, which would allow fuels made with CO2 from direct air capture;4 and • the carbon price of more than $1,000/t CO2 in year 2100 estimated by several integrated assessment models (IAMs) reviewed in the latest IPCC report (IPCC, 2014b). In addition, $100/t CO2 is also approximately equal to $1/gallon of gasoline, because combustion of a gallon of gasoline releases approximately 10 kg of CO2. The committee’s assessments of individual NETs and of technologies that sequester CO2 are presented in Tables 8.1 and 8.2, respectively. The NETs and sequestration ap- proaches in these tables exhibit a wide range of technical maturity. Some approaches to carbon removal, such as reforestation, have been developed over many decades and have already been deployed at large scale. Others, such as several types of en- hanced carbon mineralization, are at the early stages of exploration by academic researchers and have never been tried in the field. In general, the cost estimates for technologies that have not been demonstrated are more speculative than those for technologies that have been deployed at scale. However, even NETs that are relatively mature will benefit from additional research to reduce costs and negative impacts and to increase co-benefits. There are also fundamental differences among the primary factors that limit potential rates and capacities of NETs. Land-based NETs, especially afforestation/reforestation and BECCS, are ultimately constrained by land availability, because of the competing needs to produce food and preserve biodiversity and by the responses of landowners 2  See https://www.eex.com/en/market-data/environmental-markets/spot-market/european-emission -allowances#!/2018/07/19 (accessed January 29, 2019). 3  See https://www.law.cornell.edu/uscode/text/26/45Q (accessed January 29, 2019). 4  See https://www.arb.ca.gov/fuels/lcfs/lcfs.htm (accessed January 29, 2019). 352

Synthesis to incentives. Research on land-based options would help to ensure that the capaci- ties listed in Tables 8.1 and 8.2 can be increased. In contrast, the major barrier to large-scale direct air capture is the high current cost. If made less expensive, direct air capture technologies could be scaled up to remove very large amounts of carbon. Finally, carbon mineralization is currently constrained by many unknowns, including environmental impacts and likely cost. However, like direct air capture, carbon min- eralization technologies could generate very large capacity if their costs and environ- mental impacts could be sufficiently reduced. These tables provide the evidence to support the committee’s conclusions about the readiness of NETs: Conclusion 2: Four negative emissions technologies (NETs) are ready for large- scale deployment: afforestation/reforestation, changes in forest management, uptake and storage by agricultural soils, and bioenergy with carbon capture and sequestration (BECCS). The costs of these NETs can be low to medium ($100/t CO2 or less) and they have substantial potential to be safely scaled up from current deploy- ment. These options also have co-benefits including: • increased forest productivity (changes in forest management); • improved agricultural productivity, soil nitrogen retention, and soil water holding capacity (enhanced uptake and storage by agricultural soils); and • liquid fuel production and electricity generation (BECCS). Conclusion 3: Current negative emissions technologies with direct costs that do not exceed $100/t CO2 can be safely scaled up to capture and store substantial amounts of carbon, but significantly less than ~1 Gt/y CO2 in the United States and ~10 Gt/y CO2 globally. Nonetheless, the global total of substantially below 10 Gt/y CO2 is also substantially lower than the negative emissions that will likely be needed to adequately address the carbon and climate problem, according to virtu- ally every recent assessment (EASAC, 2018; Fuss et al., 2018; Griscom et al., 2017; IPCC, 2014b; Mulligan, 2018; NRC, 2015b; UNEP, 2017). These “safe” upper bounds represent substantial fractions of the total emissions of ~ 6.5 Gt CO2e in the United States and more than 50 Gt CO2e globally, but would be challenging to achieve, because they would require unprecedented rates of adoption of agricultural soil conservation practices, forestry management practices, and waste biomass capture. Many programs intended to induce landowners to change forest, grazing, and cropland management in the past have achieved low levels of adoption. Research may help improve these outcomes, but this is uncertain. Also, approximately half the 1 Gt/y CO2 in the United States and 10 Gt/y CO2 globally would be achieved with BECCS fueled exclusively with biomass waste, and would require the collection and delivery of all economically 353

TABLE 8.1  Synthesis of Key NET Attributes with Current Technology and Understanding (Committee Assessment) 354 Potential Rate of CO2 Removal with Current Technology and Potential Capacity with Current Tech- Land Required Estimated Understanding nology and Understanding (Mha) Cost of (Gt/y CO2) (Gt CO2) Implementa- United United tion at Scale Other NET States Globally United States Globally States Globally ($/t CO2) Impacts Coastal Blue Carbon: 0.024-0.050a 0.13b-0.80c 0.26– 4.0a 8b -65c 0 0 10d Multiple co- Annual Carbon Burial benefits; competition for land and submerged habitats Terrestrial Carbon 0.25e-0.6f 2.5 e-9f 015-38g 1125-570g (3-4)e - (70-90)e - 15-50 Warms at high Removal and (16-20)f (350-500)f latitudes; reduces Sequestration: streamflow in Afforestation/ areas with low Reforestation and rainfall Forest Management Terrestrial Carbon 0.250h 3h 7i 90i None None 0-50 Improved soil Removal and health, H2O Sequestration: retention, crop Agricultural Practices yields; sometimes to Enhance Soil may increase N2O Carbon Storage emission

Bioenergy with 0.5 j-1.5k (3.5-5.2)j – Limited by geologic Limited by 0j-78k 0 j- Electricity: 70 Biophysical Carbon Capture and (10-15)k storage capacity geologic (380- Fuels: 37-132 impacts of Sequestration (BECCS) (electricity) or storage capacity 700)k feedstock biomass availability (electricity) production (fuels) or biomass availability (fuels) Direct Air Capture: 0l 0l Limited by economic Limited by 0.5-5.8m 0.5-5.8m 90-600n Not assessed Solvent- and Sorbent- demand or by economic per per based Approaches practical barriers to demand or by Gt CO2 Gt CO2 pace of scale-up practical barriers to pace of scale- up Carbon Mineralization: 0.001 0.02-0.20 <1 10 NA <1 10-20 Possible water Surficial Existing and air contami- Tailingso nants Carbon Mineralization: Unknown Unknown Essentially unlimited Essentially Tailings: Tailings: 50-500 Possible water Surficial Mining and unlimited 0.1-1 3-30 and air contami- Grindingo mm/Gt microns/ nants CO2 /area Gt CO2/ of US area of oceans continued 355

TABLE 8.1 Continued 356 Potential Rate of CO2 Removal with Current Technology and Potential Capacity with Current Tech- Land Required Estimated Understanding nology and Understanding (Mha) Cost of (Gt/y CO2) (Gt CO2) Implementa- United United tion at Scale Other NET States Globally United States Globally States Globally ($/t CO2) Impacts Carbon Mineralization: NA NA NA NA NA NA <10 Possible concerns Produce Alkaline but no formal Water from Calciteo work published Carbon Mineralization: Unknown Unknown Essentially unlimited Essentially NA NA 20-5000 Possible concerns In Situ Basalt and unlimited but no formal Peridotiteo work published NOTES: The factors that impact the ranges provided for each of the attributes vary among each of the NETs. In general, the upper bounds in the rate and capacity ranges for terrestrial-based NETs represent more aggressive programs and would likely lead to adverse societal, economic, and environmental impacts. The number of significant digits reflects state of knowledge among different NETs and between U.S. and global estimates. a Low and high removal rate based on approximately 25 percent and 100 percent implementation for restoration and nature-based adaptation, respectively, active management of existing areas and managed wetland transgression. b Global removal rate based on coastal wetland area lost since approximately 1980 (Pendleton et al. 2012) and annual burial rate with restoration; does not include active management of existing areas or managed wetland transgression. c Based on recovering emissions from coastal wetland area lost since approximately 1980 minus estimated storage (stocking wetlands from carbon sourced from outside of coastal areas). d Assumes that carbon removal and storage objectives are added to projects undertaken for other purposes. Cost is all monitoring and verification. e Lower number has minimal impact on food and biodiversity. See Box 3.1 for rate and capacity estimates with frontier technologies. f Larger number has large impacts on food and biodiversity.

g Capacity estimates assume carbon stock increases over a duration of 80 years until the end of the century for afforestation/reforestation, and 30 years for forest management, at which time net increases in biomass stocks cease to be greater than a business as usual baseline. h CO removal rate and capacity that are feasible, with current technologies, without compromising food supply or biodiversity from large-scale land conversions. 2 See Box 3.1 for rate and capacity estimates with frontier technologies. i Capacity estimates assume that carbon gains occur over 30 year time period, after which time soil carbon stocks approach a new equilibrium with no further carbon stock increases. j Assumes only waste biomass used as a feedstock. k Assumes feedstocks include waste biomass and dedicated energy crops. l Future economic demand for $100/t CO direct air capture could be in the tens of gigatons per year. 2 m Depends on the size of the contactor, the spacing requirements of multiple contactors, and contactor configuration. n Upper bound is the current demonstrated cost of direct air capture (see Chapter 5). o There is a wide variety of carbon mineralization applications and a limited number of published analyses and demonstrations. See Tables 6.1 and 6.2 for ad- ditional detail. 357

TABLE 8.2  Synthesis of Key Attributes for CO2 Sequestration Only with Current Technology and Understanding 358 (Committee Assessment) NET Potential Rate of CO2 Potential Capacity with Current Estimated Cost of Other Removal with Current Technology and Understanding Implementation at Impacts Technology and (Gt CO2) Scale Understanding ($/t CO2) United States Global (Gt/y CO2) Coastal 0.008-0.034a 0.15–1.43a 12–18b NA Not assessed Sequestration (annual sequestration from (Augmentation augmentation techniques with Carbon based on area of projects from Other completed per year for other Areas) purposes) Ex Situ 0.012-0.04 ~0 0.6–2.0 10 [brucite] Permanence higher, Sequestration in risk of groundwater Existing Brucite, 100 [olivine] contamination similar, Olivine and leak risk lower, compared Serpentinec 200-500 [serpentine] to saline aquifer storage. Remediates asbestos risk. In Situ Up to 32 ~100,000 ~1,000,000 10-30 Permanence higher, Sequestration in risk of ground water Peridotite and contamination and Basaltc induced earthquakes similar, leak risk lower, compared to saline aquifer storage.

Sequestration 0.05–1.6 Not assessed 0.5–5.0 75->1,000 Remediates risk of water after Reactions contamination. With Municipal and Industrial Waste for Environmental Cleanupc Geologic 1 Gt/y CO2 in the US would 2600-26,000 5,000–25,000f 7–13g Permanence very high Sequestration: require an increase of 10% per with a median of (>99%). Surface leaks Saline Aquifer year given the current base of 3000e likely to be acute rather Storage 65 Mt/y CO2d than chronic and so can be remediated. Induced earthquakes if injection pressures too high. Some risk of groundwater contamination. a Based on approximately 25 percent and 100 percent implementation of areas augmented with carbon sourced from outside coastal areas b Based on estimated fraction of areas augmented with carbon in the United States. c There is a wide variety of carbon mineralization applications and a limited number of published analyses and demonstrations. See Tables 6.1 and 6.2 for additional detail. d Practical limits will be set by the availability of CO , pipelines, regulatory infrastructure, and public opinion 2 e DOE, 2015b; U.S. Geological Survey, 2013. f Benson et al., 2012; Benson et al., 2005. g The wide range reflects the highly site-specific nature of geologic sequestration projects. Primary variables include the depth of the formation, number of injection wells required, existing land uses, and ease of deploying monitoring programs. 359

N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N available agricultural, forestry and municipal waste to a BECCS facility able to use that type of waste. This would be logistically challenging anywhere, and especially in countries with limited organizational capacity. It is thus important to understand that “substantially less than 1 Gt/y CO2 in the United States and 10Gt/y CO2 globally” means that achievable limits could be smaller by a factor of two or more. The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (2014b) analyzed some paths that would limit global warming over preindustrial levels to less than 2.0°C, and Fuss et al. (2018) recently published a comprehensive review of scenarios that limit warming to 1.5°C and to less than 2.0°C. The breadth of the scenarios considered complicates the analysis, but, in aggregate, the message is clear and not very different for either target. Net anthropogenic emissions of all green- house gases must decline from more than 50 Gt CO2e today to approximately less than 20 Gt CO2e at midcentury and to approximately zero by 2100 (Figure 8.1). Ap- proximately 10-20 Gt CO2e of gross anthropogenic emissions come from sources that would be very difficult or expensive to eliminate, including a large fraction of agricul- tural methane and nitrous oxide. Feasible scenarios, such as the one in Figure 8.1, thus rely on 10 Gt CO2 of removal and storage approximately by midcentury and 20 Gt CO2 by the century’s end. Conclusion 4: If the goals for climate and economic growth are to be achieved, negative emissions technologies will likely need to play a large role in mitigating climate change by removing ~10 Gt/y CO2 globally by midcentury and ~20 Gt/y CO2 globally by the century’s end. At substantially less than 10 Gt/y CO2, the available safe and economical NETs are insufficient to limit warming to 2°C or less and are by no means guaranteed to achieve that level of abatement. Having more options is likely to reduce overall risk and costs and to increase the chances of success. Thus, existing options would need to im- prove, and new options would need to be developed—or both. This report proposes a research program that would reduce the costs of all NETs and expand the portfolio of safe and economical options. The case for new research on NETs does not rest solely on the adoption of a 2°C climate target. NETs would reduce the cost and the disruption of any program to limit climate change by reducing the need to eliminate emissions from the most recalcitrant or expensive sources of CO2, such as those from agriculture, land-use change, or aviation fuels. At less than $20/t CO2, some currently available NETs are less expensive than most mitigation methods (Table 8.1). For this reason, Nationally Determined Contributions submitted under the Paris agreement already include approximately 1 Gt/y CO2 of negative afforestation/reforestation emissions. 360

FIGURE 8.1  Scenario of the role of negative emissions technologies in reaching net zero emissions (UNEP, 2017). NOTES: Green represents mitigation, brown represents anthropogenic greenhouse gas emissions, and blue represents anthropogenic negative emissions. Negative emissions of 10 Gt CO2 are required by the late 2050s and of 20 Gt CO2 by the late 2090s because of ongoing positive emissions from essential activi- ties such as agriculture (mostly N2O and CH4) and activities that are very expensive to mitigate. The committee recognizes that the federal government has many other research priorities, including others in mitigation and adaptation to climate change. Multiple reasons exist to pursue research on NETs. First, states, local governments, corporations, and countries around the world are making substantial investments to reduce their net carbon emissions and plan to increase these investments. Some of these efforts already include negative emissions. This means that advances in NETs will benefit the U.S. economy if the intellectual property is held by U.S. companies. These advances would increase U.S. competitiveness, create new jobs, enhance exports, and poten- tially benefit agricultural and silvicultural yields and the stability of farm and forestry economies. Second, as damages mount, the United States will inevitably increase efforts to limit climate change in the future. Third, the United States is already making a substan- tial effort, including the new 45Q tax credit rule5 that provides $50/t CO2 for carbon 5  See https://www.law.cornell.edu/uscode/text/26/45Q (accessed January 29, 2019). 361

N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N capture and storage, including direct air capture as a source, which would leverage the value of new investments in NET research. Table 8.1 highlights the primary limiting factors for each of the NETs. For example, afforestation/reforestation and BECCS are primarily limited by competing needs for the land, removal and storage in agricultural soils by the low per-hectare rate of CO2 removal, direct air capture by its current high cost, and carbon mineralization and coastal/near-shore blue carbon approaches by a lack of fundamental understanding of future uptake rates. These constraints are also reflected in Table 8.1 by the large ranges for potential CO2 removal rates, capacities, and land requirements for forestry approaches and BECCS; by the large current costs for direct air capture; and by the large ranges in cost for the two high-capacity carbon mineralization options (ex situ mining and grinding of reactive rocks and in situ capture and sequestration in basalt or peridotite). If we could find a way to extend afforestation/reforestation and BECCS to hundreds of millions of hectares of arable land, without disrupting the food supply or causing the clearance of remaining tropical forests, then these options could supply more than 10 Gt/y CO2 of negative emissions globally, as shown by integrated assess- ment model (IAM) results reviewed in IPCC (2014b) (Table 8.1). Similarly, simply dis- posing of wood products in landfills designed to prevent decomposition could double the global capacity of forest management approaches. Inexpensive direct air capture or carbon mineralization would be revolutionary, because the potential capacity of each of these options is larger than the need (Table 8.1). FACTORS AFFECTING SCALE UP The committee considered a range of factors that affect the scale-up of NETs. These include the availability of land given the competing needs for food and biodiversity preservation, other environmental constraints, energy requirements, high cost, practi- cal barriers, permanence, monitoring and verification, governance, and insufficient scientific or technological understanding. These factors helped inform the recom- mended research program for each NET and are summarized here. The Land Constraint The land constraint is pivotal to the conclusion that fundamentally new CO2 removal options are needed. All recently published assessments of NETs highlight the dan- gers of competition for land among afforestation/reforestation, BECCS, food produc- tion, and biodiversity preservation, but also report large upper bounds for negative 362

Synthesis emissions from BECCS and from afforestation/reforestation, which would require hundreds of millions of hectares of land (i.e., EASAC, 2018; Fuss et al., 2018; Griscom et al., 2017; IPCC, 2014b; Mulligan et al., 2018; UNEP, 2017). Until research proves other- wise, it is prudent to view as impractical upper bounds for afforestation/reforestation and BECCS deployment of more than 10 Gt/y CO2. The committee believes it is best to assume that every square meter of productive land on Earth is already used for some purpose (Smith et al., 2010). That is, every parcel not covered by ice or desert is already devoted to producing crops or meat, preserving remaining biodiversity, providing valued ecosystem services, producing wood fiber, or providing urban and suburban space for people (according to FAO [2008], Earth currently has approximately 3.7 billion hectares of forest, 1.6 billion hectares of crop- land, 3.5 billion hectares of pasture, and a trace that is urban or suburban). Although substantial amounts of land classified as “degraded” or “marginal” exist in national and international inventories, one person’s nonessential land is typically another person’s source of essential livelihood, refuge, or preserve. As mentioned in Chapter 3, one recent study’s estimate of 1,300 Mha6 of marginal land includes land that supports one-third of humanity with subsistence-level food and fuel (Kang et al., 2013).7 To complicate matters, two additional land-use problems of daunting global mag- nitude should be managed at the same time as climate change. Food demand is projected to double by midcentury because of increased meat consumption with increased wealth and population growth (Foley et al., 2011). Extinction rates are esti- mated to be 100-1,000 times the background rate from the fossil record, and 80 per- cent of threatened species are at risk because of habitat loss, with 90 percent of these threatened because of agricultural expansion (MEA, 2005b; Thornton, 2010; Tilman et al., 2011). The combination of climate change with food demand and continued habitat loss could cause a mass extinction (Barnosky et al., 2011; Tilman et al., 1994). Competition among land uses will only strengthen through the current century as the demand for food and fiber grows, and as ecosystems and agriculture contend with worsening climate change. Fortunately, most proposed solutions for the food problem suggest the possibility to meet midcentury food demand on roughly the current agri- cultural land (crop plus pasture) by increasing agricultural productivity and reducing food waste (Foley et al., 2011; Thornton, 2010; Tilman et al., 2011). Some studies also propose that diets need to become modestly less meat-rich (Foley et al., 2011), but the link between meat consumption and income has proven resistant to change. 6  Mega hectare (ha x 106). 7  Estimates of marginal land are uncertain due to inconsistencies in the definition. See Chapter 3 for a detailed discussion. 363

N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N The inescapable conclusion is that repurposing a substantial amount of current agri- cultural land to produce feedstocks for BECCS or for afforestation/reforestation, could significantly impact food availability and food prices (as predicted by IAMs in IPCC, 2014b). In addition to harming the world’s poor, food price shocks have substantial national security implications (see Bellemare, 2015; Carleton and Hsiang, 2016; Hsiang et al., 2013; Werrell and Femia, 2013). Because remaining biodiversity is already threat- ened by habitat loss exacerbated by climate change (Barnosky et al., 2011), devoting a substantial amount of nonagricultural land to land-hungry NETs would likely cause a substantial increase in extinction (Smith et al., 2008). Moreover, land taken for affores- tation/reforestation or BECCS from either agriculture or production forestry would cre- ate economic pressure to convert remaining primary forest to cropland and pasture to meet continued food demand, or to harvest it to meet continued fiber demand. Simi- larly, a forest management approach to increase the length of time between succes- sive forest harvests would increase the average biomass of carbon on fiber-producing lands, and also, at least temporarily, would increase economic pressure for increased harvest in other locations. The consequences would be additional biodiversity loss and additional CO2 emissions from deforestation (Fargione et al., 2008). This problem is unavoidable if a substantial amount of land is converted from one use to another. Although some IAMs and other models attempt to estimate costs of far-field effects associated with land-use change, including those described above, these estimates are highly uncertain (IPCC, 2014b; Popp et al., 2014; Riahi et al., 2017; Rose et al., 2014), and existing models may omit what could be the most important costs. For example, the security implications of land-use change that affects food production are not explicitly included in IAMs. In their recent assessment of land-use options for carbon mitigation, Griscom et al., 2017 attempted to minimize adverse consequences of land use transfers by excluding or limiting the most problematic, but it is not clear how well such restrictions could be maintained in the face of deliberate economic incentives for afforestation/reforestation and BECCS. Because this problem combines limited understanding with the most severe consequences if we get it wrong, the commit- tee believes that humanity should develop new high-capacity NETs such as low-cost direct air capture and carbon mineralization. The safe levels of afforestation/reforesta- tion, forest management approaches, and BECCS in Table 8.1 are set to minimize the risk of unintended consequences of land-use transitions. Other Environmental Constraints Other environmental constraints vary idiosyncratically among the various NETs. Be- cause forests established at high latitudes decrease albedo by, for example, reducing 364

Synthesis the reflectivity of snow cover, afforestation/reforestation at high latitudes would likely cause net warming despite the cooling caused by the forest’s CO2 uptake. In addition, forests established in regions with limited rainfall have adverse effects on streamflow, irrigation, and groundwater supplies (see Chapter 3). Ex situ methods of carbon miner- alization would create enormous volumes of waste rock that may contaminate water and/or air. Agricultural soils options generally have large positive side benefits, includ- ing increased productivity, water holding capacity, stability of yields, and nitrogen use efficiency, but sometimes cause increased N2O emissions. Afforestation/reforestation, BECCS, and potentially some direct air capture routes may have substantial water requirements. In particular, irrigated bioenergy crops may lead to a trade-off between land and water requirements, in addition to freshwater ecosystem degradation and biodiversity loss. Energy Requirement Direct air capture and some carbon mineralization options require a large energy input per ton of CO2 captured, which increases costs. Solvent-based direct air capture systems require roughly 10 GJ to capture a ton of atmospheric CO2 and sorbent-based systems require roughly 5 GJ. To put this into perspective, combustion of 100 gallons of gasoline releases about 13GJ of energy and emits about a ton of CO2. Gt-scale direct air capture thus necessitates an enormous increase in low- or zero-carbon energy to meet these energy demands, which would compete with use of such energy sources to mitigate emissions from other sectors. Table 8.1 includes the large land areas required to produce this energy from renewable sources, not including nuclear or natural gas with CCS options. High Cost The primary impediment to direct air capture is high cost. Climeworks, which has the only existing commercial direct air capture machine, captures CO2 at a reported cost of $600/t CO2 (Daniel Egger, personal communication, October 11, 2018). A recent paper by Keith et al., 2018 estimates costs between $200 and $300/t CO2 for CO2 captured from the atmosphere by a solvent-based system (although costs are lower if the CO2 captured from natural gas combustion used to produce heat in the system are included). The analysis in Chapter 5 suggests that the cost of sorbent-based direct air capture and sequestration might be reduced to approximately $90/t CO2. The chap- ter further states that it is too early to determine whether sorbent- or solvent-based systems will ultimately prove to be the least expensive. 365

N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N The estimated cost of capture and sequestration for BECCS systems that produce elec- tricity is $70/t CO2 (Table 8.2), largely because of the low thermal efficiency relative to fossil electricity. The costs for BECCS systems producing liquid fuels and char might be lower (Table 8.2) but depend on the uncertain economics of char. In addition, negative emissions from the liquid fuels/biochar pathway are smaller, per unit of biomass, than from the biomass electricity/carbon-capture pathway. The costs of carbon mineralization are difficult to determine because fundamental understanding of the processes is lacking. The costs of the two high-capacity options (ex situ mining and grinding of reactive rocks and in situ capture and sequestration in basalt or peridotite) may be as low as $20-$50/t CO2 or could be prohibitively expen- sive. Costs of terrestrial carbon removal and sequestration approaches are compara- tively well understood and are relatively low. Practical Barriers Practical barriers to scaling up deployment of NETs include shortages of materials, financing and human capital, robust and reliable financial incentives, as well as social acceptance of large-scale deployment. For example, a 10 percent per year increase from the 65 Mt/y CO2 that is currently injected underground for CO2-enhanced oil recovery and saline aquifer sequestration is needed in order to scale up underground injection for geological sequestration. If there is a serious attempt to limit warming to 2°C, then comparable or greater rates of growth will be required of every available NET. At these rates, scale-up could become limited by materials shortages, regulatory barriers, infrastructure development (i.e., CO2 pipelines and renewable electricity), the availability of trained workers, and many other barriers. However, afforestation/refor- estation, forest management, and agricultural soils activities in the United States are already supported by well-developed state and federal (U.S. Department of Agricul- ture [USDA]) extension services with decades of experience in facilitating changes in land-use practice, augmentable thorough additional technology transfer, training, and outreach. Furthermore, humans often resist actions that appear to be in their economic interest. For example, historical adoption rates of agricultural soil conservation and forestry management practices that would save farmers and forest landowners money have been surprisingly low, as have dietary changes, such as reduced meat consumption, that would increase health while freeing agricultural land for forestry NETs and BECCS. These behaviors could limit deployment of NETs, as could public resistance to new local infrastructure, but they are not well represented in IAMs. Although a general 366

Synthesis treatment is beyond the scope of its tasks, the committee did consider social science issues. In particular, the committee supports the need to better understand land- owner responses to incentives for forestry, agricultural soils, and coastal NETs, as well as general improvement in the ability of IAMs to predict responses to incentives (see, e.g., items 6, 8, 12, and 16 in Table 8.3). Permanence Carbon stock increases through terrestrial (afforestation/reforestation, forest manage- ment, and agricultural soils) and coastal blue carbon options are all reversible if the carbon sequestering practices are not maintained. Forested land can be cleared again for agriculture, liquidating the biomass carbon. Reverting to intensive tillage would reverse much or all of the soil carbon gains from reduced tillage practices in agricul- tural soils methods (Conant et al., 2007; Grandy and Robertson, 2007; Minasny et al., 2017). A restored coastal wetland could be drained again for development. Nonethe- less, appropriate policies and governance could reduce the frequency of any such reversals, and the reversals are themselves reversible. Moreover, NETs plus reversals for forest plantings (afforestation/reforestation) will eventually result in an age-structured mosaic of patches, where age measures the time since the most recent establishment of negative emissions practices in a patch. The total carbon stored by the mosaic of patches will increase with mean age, despite the presence of reversals. In contrast, car- bon lost from coastal wetlands because of too-rapid sea level rise cannot be recovered in the same site. Likewise, carbon lost from forest or soil carbon because of permanent changes in climate that decrease the equilibrium carbon content of ecosystems can- not be recovered at the same sites. Biochar soil amendment has been proposed as a promising path for long-term carbon removal strategy (for both agricultural soils and the biomass-to-fuel and biochar BECCS pathway); however, questions remain about the long-term stability of biochar in soil environments. The other BECCS pathways and direct air capture have comparatively minor issues of permanence. CO2 can leak from saline aquifers, but at rates low enough to remediate. Permanence would be very high in mineralization of basalt or peridotite. Of note, the high-capacity backstop of CO2 removal and sequestration that would be provided by reliable low-cost direct air capture and mineralization would reduce concerns of per- manence compared to not only other sequestration technologies, but also solar radia- tion management, which presents major concerns regarding its permanence (Jones et al., 2013a; NRC, 2015a). As discussed in Chapter 1, the scientific and economic issues associated with the length of time that CO2 remains in sequestration, and the value of that time, are daunting. 367

TABLE 8.3  Research Plan and Budget for Negative Emissions Technologies (abbreviated from research tables in 368 Chapters 2-7). Potential Sponsors and Barrier(s) Research Cost Duration Performers of Addressed or Item NET Title $M/y Years Summary Research Frontier 1 Coastal Basic 6 5-10 5 projects at $2M/y for 10 years to address NSF Scientific/ research in fate of organic carbon produced and USACE Technical understanding buried in soils/sediments of coastal DOE Understanding and using ecosystems; 5 projects at $2M/y for 10 Industry Permanence coastal years to address change in area coastal ecosystems as blue carbon ecosystems in response to a NET change in major climate change or sea level rise and management drivers; 5 projects at $2M/y for 5 years to address selection of materials and coastal plants/phenotypes producing high organic carbon density materials with slow decay rates buried in coastal sediments carbon. 2 Coastal Mapping 2 20 $2M/y (tidal wetland: $1.5M; seagrass: NASA Scientific/ current and $500K) for 20 years. DOE Technical future (i.e., NOAA Understanding after sea level USFS Permanence rise) coastal EPA Monitoring and wetlands. Verification

3 Coastal Integrated 40 20 15 engineered sites at a cost of $1M/y NSF Scientific/ network of per site (approx. LTER); 20 augmented NOAA Technical coastal sites for managed and engineered sites at a cost of Understanding scientific and $500K/y; 8 new managed sites at $500K/y Cost experimental (i.e., wetland transgression – 0-2 ft and Other work on carbon seagrass); 5 U.S.-scale synthesis activities Environmental removal and (wetland: 3; seagrass: 2) at a cost of $200K/y Constraints storage. per activity. 4 Coastal National 2 20 The center would make the mapping NOAA Scientific/ Coastal data (above) public and would overlay USACE Technical Wetland information about all coastal restoration Understanding Data Center, and engineering projects, including carbon Monitoring and including removal and storage projects. One center Verification data on all at $2M/y. Governance restoration and carbon removal projects. 369 continued

TABLE 8.3 Continued 370 Potential Sponsors and Barrier(s) Research Cost Duration Performers of Addressed or Item NET Title $M/y Years Summary Research Frontier 5 Coastal Carbon- 10 20 Carbon-rich NET demonstration projects NSF Scientific/ rich NET and field experiment network (15 sites NOAA Technical demonstration funded at $670K/site/y). USACE Understanding projects & field DOE Cost experiment Industry Monitoring and network Verification Permanence Other Environmental Constraints 6 Coastal Coastal blue 5 10 Social science research on cost effective NSF Practical carbon project adaptive management of coastal blue NOAA Barriers deployment. carbon, and on the response of coastal land Governance owners and managers to carbon removal and storage incentives. $5M/y. 7 Afforesta- Monitoring of 5 ≥3 Develop ($1M) and operate ($4M/y) a USFS and Monitoring and tion/ forest stock national monitoring system for forest partners Verification Reforesta- enhancement carbon that would complement the USFS Governance tion, Forest projects forest inventory (currently funded at $70 Manage- M/y). This would monitor afforestation/ ment reforestation and forest management

activities remotely and measure carbon in a statistical sample of locations. A system capable of measuring international far-field effects (i.e. enhanced harvest elsewhere in response to reduced harvest in U.S.) would cost 10 to 20 times more. 8 Afforesta- IAM and 3.7-14 10 Economic and behavioral studies and DOE Land tion/ regional modeling to estimate how much land NSF Other Reforesta- life cycle use change will occur elsewhere in USDA Environmental tion, Forest assessment the world in response to diversion of EPA Constraints Manage- of BECCS land to afforestation/reforestation or Universities Monitoring and ment, BECCS mitigation BECCS dedicated energy crops, or in and national Verification potential and response to reduced wood harvest (forest labs Permanence secondary management). Attempt to improve Governance impacts understanding of impacts of land diversion to afforestation/reforestation and energy crops on food prices, food security, ecosystem services, biodiversity, albedo, and hydrology. Increase spatial resolution of models. 371 continued

TABLE 8.3 Continued 372 Potential Sponsors and Barrier(s) Research Cost Duration Performers of Addressed or Item NET Title $M/y Years Summary Research Frontier 9 Afforesta- Forest 4.5 3 Demonstration projects to improve USDA Practical tion/ demonstration collection and disposal of wood products and NSF Barriers Reforesta- projects: after use (3 3-year projects at 500K/y USFS and Other tion, Forest increasing each); 3 multiyear projects for preserving partners Environmental Manage- collection, harvested wood in different environments Constraints ment disposal, and (500K/y each); and 3 multiyear projects Governance preservation to demonstrate carbon benefits of forest of harvested restoration in different geographic regions wood; ($500K/y each). and forest restoration 10 Forest Man- Preservation 2.4 3 Landfill designs for achieving the lowest EPA Frontier agement of harvested possible rate of wood decomposition (3 USFS wood multiyear projects, each $800K). IAM and LCA (see item 8). 11 Forest Man- Research on 1 3 Research on greenhouse gases and USDA Other agement greenhouse social impacts of reducing traditional NSF Environmental gases and uses of biomass for fuel, which involves Constraints social impacts households and small entities using wood Energy Use of reducing biomass for heating and cooking. Funding Governance traditional uses for initiation of 1 multiyear project. of biomass for fuel

12 Forest Man- Social sciences 1 3 Extension and outreach educational USDA Practical agement research on programs for transferring research NSF Barriers improving findings and technologies to farmers and Governance landowner practitioners. Funding for initiation of 3 responses to multiyear projects. incentives and equity among landowner classes 13 Agricultural National 5 Ongoing Augmentation of USDA’s existing NRI USDA Monitoring and Soils agricultural system. Full buildout to approximately Verification soils 5,000-7,000 NRI locations with soil Permanence monitoring sampling and analysis carried out at Governance system intervals of 5-7 years (on an annual rotating basis similar to the USFS FIA system). Monitor adoption and permanence of agricultural soils on U.S. agricultural lands. 14 Agricultural Experimental 6-9 ≥12 Field experiments to rigorously evaluate USDA Scientific/ Soils network and further develop region-specific best Land grant Technical Un- improving management practices for soil carbon universities derstanding agricultural sequestration (and net greenhouse gas Other Envi- soil carbon reductions). 10-15 sites at $600K/site. ronmental processes. Constraints Cost Governance 373 continued

TABLE 8.3 Continued 374 Potential Sponsors and Barrier(s) Research Cost Duration Performers of Addressed or Item NET Title $M/y Years Summary Research Frontier 15 Agricultural Data-model 5 5 Develop improved tool for predicting and USDA Science/ Soils platform for quantifying soil carbon storage accurately NSF Technical predicting and and cost effectively. Initial development Understanding quantifying should focus on systems integration, Monitoring and agricultural soil including of existing data sources and Verification carbon removal models. Other and storage Environmental Constraints Cost Governance 16 Agricultural Scaling up of 2 3 Support for initiation of 4-5 regional USDA Practical Soils agricultural projects per year to identify solutions to NSF Barriers soils overcome barriers to adoption. Ideally Governance sequestration coupled to programs in Items 14-15. 4 activities projects at $500K/y. 17 Agricultural High carbon 40-50 20 Screen and develop crop varieties and DOE Frontier Soils input crop species specifically to enhance storage in USDA phenotypes agricultural soils. The DOE/ARPA-E ROOTS NSF program is currently funded for $35M total.

18 Agricultural Soil carbon 3-4 5 Develop and test methods of deep USDA Frontier Soils dynamics at inversion of soils, which may increase NSF depth sequestration by ~1 tCO2/y for decades. 4-6 projects per year at $750K/project. 19 Agricultural Biochar studies 3 5-10 Assess biochar’s effects on agricultural DOE Scientific/ Soils, BECCS productivity, soil carbon, nutrient use, USDA Technical water use, and albedo. Assess longevity NSF Understanding of biochar in soils. Determine the carbon storage limits that can be achieved with biochar. 3-5 projects per year. 20 Agricul- Reactive 3 10 Assess weathering rates of reactive DOE Frontier tural Soils, mineral minerals (i.e. olivine) added to agricultural USDA Carbon additions to soils and effects on agricultural NSF Mineraliza- soils productivity, soil carbon, nutrient use, tion water use, and albedo. Determine the carbon storage limits that can be achieved with mineral addition. 21 BECCS Biomass-to-fuel 40-103 10 Assess the carbon removal potential of all DOE Scientific/ with biochar biomass conversion to fuel pathways and USDA Technical develop negative carbon fuel pathways Industry Understanding that are cost-competitive. Cost 375 continued

TABLE 8.3 Continued 376 Potential Sponsors and Barrier(s) Research Cost Duration Performers of Addressed or Item NET Title $M/y Years Summary Research Frontier 22 Direct Air Basic research 20-30 10 Research on low-cost sorbents, ways to DOE Scientific/ Capture and early phase reduce large thermal energy requirements, Technical technology new materials with better sorption capacity Understanding development and reaction and diffusion kinetics, Cost advances in solvent and sorbent contactor Energy Use design, identify any environmental Other contaminants released, increase gas Environmental throughput and reduce pressure drop. ~30 Constraints projects per year at $1M/project, each ~3 years in length. 23 Direct Air Independent 3-5 10 Independent techno-economic analysis of Industry Scientific/ Capture techno- products of basic research (Item 22) and a Technical economic public database to facilitate rapid progress. Understanding analysis, third- Cost party materials Energy Use testing and evaluation, and public materials database 24 Direct Air Scaling up 10-15 10 Scale materials synthesis to >100 kg, design DOE Scientific/ Capture and testing novel system components and equipment Technical of air capture for a pilot-scale effort, test integrated lab- Understanding materials and scale air capture system (>100 kg/d CO2). Cost components Energy Use

25 Direct Air Third-party 3-10 10 Professional help with a project’s DOE Scientific/ Capture professional engineering design, including mass and Industry Technical engineering energy balances, process flowsheets, Understanding design firm preliminary piping and instrument Cost assistance diagrams, main equipment definitions Energy Use for the above and sizing, preliminary bill of materials, effort, including risk assessment, and process economics independent analysis. Independent testing of materials testing, and a and components on standardized public database hardware at national test center (Item 27). Maintenance of a public database of tested materials and their performance. 26 Direct Air Design, build, 20-40 10 $20M/project, each with 3 years duration, DOE Scientific/ Capture and test pilot and 1-2 projects/year. Technical air capture Understanding system (>1,000 Cost tCO2/y) Energy Use 27 Direct Air National Air 10-20 10 Establish National Air Capture Test Center DOE Scientific/ Capture Capture Test to support pilot efforts, including 3rd- NIST Technical Center support party front-end engineering design and Industry Understanding of pilots economic analysis, and creation and Cost maintenance of a public database on plant Energy Use performance. 377 continued

TABLE 8.3 Continued 378 Potential Sponsors and Barrier(s) Research Cost Duration Performers of Addressed or Item NET Title $M/y Years Summary Research Frontier 28 Direct Air Design, build, 100 10 $100M/project, 1 project/year each with DOE Scientific/ Capture and test 3-5 years duration Technical air capture Understanding demonstration Cost system of Energy Use >10,000 t CO2/y 29 Direct Air National 15-20 10 Engage national test center to support DOE Scientific/ Capture air capture demonstration projects and maintain NIST Technical test center public record of full-scale plant Industry Understanding support of performance and economics. Cost demonstrations Energy Use 30 Carbon Min- Basic 5.5 10 5 projects at $500K-$1.5M for 10 years. USGS Scientific/ eralization research on DOE Technical mineralization NSF Understanding kinetics 31 Carbon Min- Basic research 17 10 Exploration of positive and negative USGS Frontier eralization on rock feedbacks between reaction and fluid flow, DOE mechanics, for in situ carbon mineralization, in situ NSF numerical mining, geothermal power generation, modeling, and extraction of oil and gas from tight field studies reservoirs, ensuring integrity of reservoir

caprock and wellbore cement. $6M/y for rock mechanics, $5M/y numerical modeling, and $5M/y for field studies. 22 projects at $0.5-$1.5M for 10 years. 32 Carbon Min- Mapping of 7.5 5 Minerals and rocks include all that react USGS Science/ eralization reactive mineral rapidly and exothermically with CO2, DOE Technical deposits and including brucite, olivine, peridotite, basalt NSF Understanding existing tailings etc. 5 projects at $1.5M for 5 years. Other (scoping for Environmental pilot studies) Constraints Governance 33 Carbon Min- Surficial (ex 3.5 10 Ex situ mine tailings, broadcast of reactive USGS Cost eralization situ) carbon minerals and rocks on soils, beaches, DOE Energy Use removal pilot shallow ocean. 5 projects at $0.25- $1.0M NSF Other Envi- studies for 10 years. ronmental Constraints Governance Monitoring and Verification Practical Bar- riers 379 continued

TABLE 8.3 Continued 380 Potential Sponsors and Barrier(s) Research Cost Duration Performers of Addressed or Item NET Title $M/y Years Summary Research Frontier 34 Carbon Min- Medium-scale 10 10 No prior experiments on field scale, initial USGS Frontier eralization in situ field low porosity requires stimulation and/or DOE experiment in practical knowledge of positive feedbacks NSF peridotite rock such as “reaction-driven cracking,” $10M/y for 10 years, constant annual cost for phased project with increasing annual expenses for successive phases. 35 Carbon Min- Development 2 5 Database that would allow the results of USGS Scientific and eralization of a resource carbon mineralization research activities Technical database are disseminated broadly to the research Understanding for carbon community. 4 projects at $500K for 5 years. Practical mineralization barriers to scale up 36 Carbon min- Study of the 10 10 12 projects at ~ $800K/y. NSF Scientific and eralization environmental USGS Technical impact of DOE Understanding mineral Costs addition to Other terrestrial, Environmental coastal, Constraints and marine Governance environments Practical barriers to scale up

37 Carbon Min- Examination of 5 10 10 projects at $500k for 10 years. NSF Cost eralization the social and Other environmental Environmental impact of an Constraints expanded Practical extraction barriers to scale industry for the up purpose of CO2 removal NOTE: ARPA-E=Advanced Research Projects Agency-Energy, CCUS=Carbon Capture, Utilization and Storage, DOE=Department of Energy, EPA=Environmental Protection Agency, FIA=Forest Inventory and Analysis, FTE=Full-Time Equivalent, IAM=Integrated Assessment Model, LCA=Life Cycle Assessment, LTER=Long-Term Ecological Research, NET=Negative Emissions Technology, NIST=National Institute of Standards and Technol- ogy, NRI=National Resource Inventory, NSF=National Science Foundation, ROOTS=Rhizosphere Observations Optimizing Terrestrial Sequestration, USACE=US Army Corps of Engineers, USDA=US Department of Agriculture, USFS=US Forest Service, USGS=US Geological Survey. 381

N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N Monitoring and Verification Monitoring and verification will be critical components of any large-scale deploy- ment of NETs. It is important to distinguish between the monitoring and verification required in a private transaction to determine whether a single project has delivered the promised negative emissions, and that required by a nation to determine, for example, the effectiveness of its overall mitigation efforts. The former requires direct measurement of the carbon stored on site, while the latter could rely on low-cost monitoring of an activity, such as reforestation or improved crop rotations, together with more limited higher-cost direct measurements of a statistical sample. Of course, direct measurements everywhere would be preferable but may not always be worth the added expense. Afforestation/reforestation, forest management, and agricultural soils are sufficiently well understood that, in most cases, they could be deployed in the United States with remote monitoring and verification backed up by onsite measurements in a statistical sample. Effective monitoring and verification here will not require additional fun- damental research into carbon dynamics. Rather it will require improved systems to monitor forest carbon and soil carbon on agricultural lands, expanded remote sensing of land use and management practices, better integration of existing data sets and models, and selected improvements in global monitoring to help address leakage (i.e., land-use changes in one location inducing land-use changes in other locations). This also applies to BECCS, with the proviso that emissions from transport and process- ing of biomass should also be verified. BECCS-to-fuels with biochar has the separate complication that emissions from char decomposition are not fully understood. Again, implementation of afforestation/reforestation, forest management, and BECCS above the levels in the second and third columns in Table 8.1 would probably cause far-field changes, such as increased deforestation elsewhere, and thus require global moni- toring and verification. See the National Academies report Verifying Greenhouse Gas Emissions: Methods to Support International Climate Agreements (NRC, 2010) for a full treatment of this issue. Coastal blue carbon and storage could be monitored and verified with inexpensive remote methods backed up by onsite measurements of a statistical sample. However, fine-scale spatial heterogeneity in coastal wetlands will likely require finer spatial resolution than monitoring and verification of afforestation/reforestation, forest man- agement, agricultural soils, and BECCS. Because of landscape and shoreline evolution, intensive coastal verification might have to continue indefinitely. 382

Synthesis Some forms of in situ and ex situ mineralization that store CO2 in inert and essentially permanent solid form might have lower monitoring and verification costs than any of the other NETs. However, dispersal of reactive rock material in soil, along beaches, or into the shallow ocean could be as difficult, or more difficult, to verify than agricul- tural soils. Monitoring and verification of direct air capture would be straightforward. Monitoring and verification of sequestration in saline aquifers requires sophisticated methods such as seismic imaging, measuring pressure in and above the sequestration reservoir, and routine measurements of well integrity. Governance Appropriate governance of NETs is obviously critical because overly lax oversight would lead to ineffective CO2 removal and loss of public confidence, while overly strict oversight would limit deployment. Governance is especially critical when large-scale deployment is imminent. Currently, governance is well established only in those sec- tors covered by a national or international agreement, including afforestation/refor- estation (under the United Nations Framework Convention on Climate Change) and saline aquifer storage (under the Underground Injection Protocol of the Safe Water Drinking Act). In addition, the United States and other countries have ample experi- ence regulating agriculture and forestry for non-NET purposes. One way to maintain public confidence during rapid deployment of NETs is to invest in a substantial effort to educate the public during the research and development phase. Further, a recent commentary within Nature (Lenzi et al., 2018) called for in- creasing the use of social science to develop assumptions used in models that assess the role of NETs in climate mitigation. Insufficient Scientific/Technical Understanding Virtually all approaches to carbon mineralization are limited by insufficient under- standing. For example, there is (1) no comprehensive public inventory of appropriate geologic deposits and existing tailings of reactive but unreacted rock, (2) a lack of understanding of the kinetics of CO2 uptake both at the laboratory scale and in the field, and (3) insufficient technical expertise to manage tailings piles so that they effec- tively take up CO2. Negative feedbacks—such as decreases in porosity because of the clogging of pores by carbonate minerals or the coating of reactive surfaces by reac- tion products—cannot be predicted. In addition, positive feedbacks, such as increas- ing permeability and reactive surface area via “reaction-driven cracking,” are not well 383

N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N understood. The long-term consequences of depositing crushed reactive minerals in agricultural soils, along beaches, or into the shallow ocean is unknown. The scientific understanding of coastal blue carbon is at a similar state of develop- ment, albeit more advanced for tidal wetlands than for seagrass meadows. The carbon removal caused by restoration and creation of tidal wetlands can be predicted with some confidence. However, the field lacks a mechanistic understanding of the number of critical processes that govern carbon burial and sequestration in coastal ecosystems that may change under high rates of sea level rise and other direct and indirect im- pacts of climate change, and few studies on transgression of coastal wetlands inland have been conducted. Finally, there are few empirically verified methods to augment carbon removal and sequestration as part of coastal engineering (i.e., coastal adapta- tion) projects. Although better understood than the mineralization and coastal options, the other NETs present some knowledge gaps. For example, the field does not fully understand (1) induced seismicity from subsurface injection of CO2 and (2) the co-benefits of bio- char beyond storage, especially whether biochar additions increase the rate of carbon storage in agricultural lands. Agricultural soils methods do not exist for some cropping systems and many grazing systems, particularly in semi-arid rangelands, and it is not obvious that established methods of agricultural soils are optimized in any system. PROPOSED RESEARCH AGENDA Scaling the capacity of NETs to address the expected needs for carbon removal will require a concerted research effort to address the constraints that currently limit deployment. The research agenda must address not only potential research gaps, but also other needs for scale-up of NETs, including cost reductions, deployment, and monitoring and verification. The proposed research is divided between (1) projects that would exclusively advance NETs (Table 8.3) and (2) research on biofuels and CO2 sequestration that would not only advance NETs, but should also be undertaken as part of an emissions mitigation research portfolio (Table 8.4). Drawing on the exper- tise of certain members, the committee estimated the budget for each research effort. Of course, these budget estimates contain some uncertainty, but there is value in assessing the relative levels of investment needed to advance each of the NETs and sequestration approaches. For example, the estimated research budget for afforesta- tion/reforestation and forest management is lower than that for other NETs because these approaches are more mature. In contrast, the estimated research budgets for 384

Synthesis carbon mineralization and direct air capture are larger because these technologies are relatively new and underexplored. The first task in the committee’s Statement of Task is “Identify the most urgent un- answered scientific and technical questions needed to assess the benefits, risks, and sustainable scale potential for carbon dioxide removal and sequestration approaches in the terrestrial and nearshore/coastal environment; and increase the commercial viability of carbon dioxide removal and sequestration.” The committee used this guidance to strike a balance between research that would provide answers within a decade and those that would take longer to do so. Most of the research will likely pay off fully within 10 years. In contrast, “frontier” research, such as breeding plants whose roots enhance agricultural soil carbon removal and storage or enhanced weathering in situ in ultramafic rock, may not pay off fully for two decades. The committee did not consider very long-term solutions such as increasing the fundamental efficiency of photosynthesis. The committee’s conclusion that afforestation/reforestation, forest management, agricultural soils, and BECCS will be insufficient to achieve the CO2 removal needed within a generation—because of competing demands for land with food and biodi- versity—led to a heavy emphasis on advancing new high-capacity alternatives. Thus, the research plan calls for a large investment in direct air capture, despite its current high cost and expected future cost of not far from $100/t CO2, and mineralization as a second option with significant potential. The research plan also includes a substantial investment to increase carbon removal and to understand and perhaps soften the land constraint facing afforestation/reforestation, forest management, agricultural soils, and BECCS. For example, the plan provides $6-9M/y to further understanding of ways to extend carbon removal to agricultural lands without disrupting food security, as well as $92-216M/y to reduce both the required land area and cost of BECCS. Based on its review of the factors that will influence scale-up of NETs, the committee drew the following conclusions that motivate the selection of research priorities: Conclusion 5: Afforestation/reforestation, agricultural soils, forest management, and BECCS can already be deployed at significant levels, but limited per-hectare rates of carbon uptake by agricultural soils and competition with food and biodi- versity for land (for afforestation/reforestation, forest management, and BECCS) will likely limit negative emissions from these options to significantly less than 10 Gt/y CO2, globally. Research could identify ways to soften the land constraint, for example by developing crop plants that take up and sequester carbon more efficiently in soils, or by reducing demand for meat or food waste. However, crop 385

TABLE 8.4  Research Plan and Budget for NET-Enabling Research 386 Potential Sponsors and Performers Barrier(s) Research Cost Duration of Addressed or Item NET Title $M/y Years Summary Research Frontier 38 BECCS Biomass-to-power 53-123 5 Improve (1) pretreatment technology DOE Cost with CCS: Biomass for converting biomass into a drop-in USDA supply and replacement for coal and (2) logistics National logistics research to address biomass supply chain labs issues (production, storage, handling, and Industry transportation). 39 BECCS Biomass-to-power 39-94 10 Increase the conversion efficiency of NETL Cost with CCS: High biomass to electricity by developing Industry efficiency biomass advanced conversion processes and by power pretreatment of biomass. 40 BECCS Biomass-to-fuel Ongoing research Advance cellulosic ethanol. DOE Cost with CCS efforts are sufficient Energy Use 41 Carbon Min- Mine tailings and 1 10 Kiloton to megaton per year field DOE Science/ eralization industrial wastes experiments, together with extensive NSF Technical field inventories and laboratory USGS Understanding characterization of the reactivity of Cost various potential solid reactants. 4 Energy Use projects at $250K/y for 10 years. Other Environmental

Constraints Governance Monitoring and Verification Practical Barriers 42 Carbon Min- Medium-scale 10 10 Optimization of injection strategies, DOE Science/ eralization field in-situ particularly for shallow reservoirs. Longer NSF Technical experiment in a duration, higher flux experiments should USGS Understanding basalt formation. examine evolution of subsurface reaction Cost fronts, determine the nature of local Energy Use carbon mineralization reactions, and Other feedbacks affecting permeability and Environmental reactive surface area. $10M/y for 10 years. Constraints Governance Monitoring and Verification Practical Barriers 387 continued

TABLE 8.4 Continued 388 Potential Sponsors and Performers Barrier(s) Research Cost Duration of Addressed or Item NET Title $M/y Years Summary Research Frontier 43 Geologic Se- Reduction of 50 10 The proposed budget would allow for DOE Science/ questration: seismic risk 3 experiments in different geographic NSF Technical Saline Aquifer regions of the United States each at a cost EPA Understanding Storage of about $15M/y for 10 years. The region- DOI Other specific projects would be supported by Environmental $5M/y of model development, laboratory Constraints studies, and analysis of new and existing Practical data sets. This research would improve Barriers understanding of and reduce the risks of induced seismicity at geological sequestration sites, develop methods for assessing and mitigating risks of seismicity, improve capacity estimates by screening sites that are high risk for induced seismicity, and help quantify the risk of leakage from fault slippage. 44 Geologic Se- Increasing the 45 10 Partner with industry to develop and test DOE Science/ questration: efficiency and innovative approaches for characterizing NSF Technical Saline Aquifer accuracy of site greenfield sites, which usually require on EPA Understanding Storage characterization the order of $100M to assess whether a DOI Cost and selection site is suitable. Industry Governance Practical Barriers

The program could be carried out by expanding the CarbonSAFE program to include 2 sites with sequestration quantities of 200+ Mt CO2 to assist states and commercial entities in qualifying sites for large-scale deployment (4 projects over a 10-year period). $5M/y of the proposed budget would be used to support academic, national laboratory, and industrial research developing innovative approaches that could be tested in the above-mentioned field programs. 45 Geologic Se- Improving 50 10 The proposed research program would DOE Monitoring questration: monitoring and provide for 4-6 projects at a cost of $5- NSF and Saline Aquifer lowering costs for 10M/y. The collaborative projects would EPA Verification Storage monitoring and develop and demonstrate approaches to DOI Cost verification optimize integrated monitoring programs Practical that reduce costs while increasing quality Barriers and access to real-time information about the status of stored CO2. In addition to the field experiments, $10M/year would be used to support fundamental research to develop and test new approaches for quantifying mass balances, measuring CO2 saturations, and quantifying leakage. 389 continued

TABLE 8.4 Continued 390 Potential Sponsors and Performers Barrier(s) Research Cost Duration of Addressed or Item NET Title $M/y Years Summary Research Frontier 46 Geologic Se- Improving 25 10 This research program would support DOE Science/ questration: secondary a 10-year multi-investigator team to NSF Technical Saline Aquifer trapping perform a large-scale experiment EPA Understanding Storage prediction designed to quantify the effectiveness DOI Permanence and methods of natural and accelerated trapping for Practical to accelerate immobilizing CO2 in the post-injection Barriers secondary period. The experiment would require a trapping combination of field experiments, multi- scale laboratory experiments, numerical modeling, and monitoring. 47 Geologic Se- Improving 10 10 This program would support 2-3 teams DOE Science/ questration: simulation models of researchers to develop improved NSF Technical Saline Aquifer for performance simulation models for predicting the fate EPA Understanding Storage prediction and and transport of CO2 in the subsurface, DOI Permanence confirmation particularly with regards to the effects of geological heterogeneity, secondary trapping mechanisms, geochemical reactions, geomechanical responses to CO2 injection, and the coupling between them over thousands of years.

48 Geologic Se- Assessing and 20 10 Improve understanding of the impact DOE Science/ questration: managing risk of leakage on groundwater systems and NSF Technical Saline Aquifer in compromised the vadose zone. Quantify the extent to EPA Understanding Storage storage systems which these interactions attenuate CO2 DOI Practical migration and mitigate risks of leakage to Barriers, the atmosphere. Permanence 49 Geologic Se- Developing 50 10 Develop and demonstrate reservoir DOE Science/ questration: reservoir management practices to co-optimize NSF Technical Oil and Gas engineering CO2-EOR and CO2 sequestration to EPA Understanding Field Seques- approaches for achieve negative emissions during DOI Practical tration co-optimizing oilfield operations. Quantify the extent Industry Barriers CO2-EOR and of negative emissions that can be sequestration achieved by co-optimization. Two field-scale experiments in partnership with industry are proposed, each with a budget of $20M/y for 10 years. $10M/y will support academic, national laboratory and industry research to develop new approaches for co-optimization. 391 continued

TABLE 8.4 Continued 392 Potential Sponsors and Performers Barrier(s) Research Cost Duration of Addressed or Item NET Title $M/y Years Summary Research Frontier 50 Geologic Social sciences re- 1 10 Establish best practice for community DOE Practical Sequestration search to improve engagement, rules of practice, and NSF Barriers public engage- regulation guidelines. Provide educational EPA ment effectiveness materials for increasing awareness of the DOI with local com- need, opportunity, risks, and benefits of munities and the geological sequestration for negative general public emissions. NOTES: All projects not only should be part of any comprehensive research effort on carbon mitigation, but also would support the advancement of negative emissions methods. BECCS=Bioenergy with Carbon Capture and Storage, CCS=Carbon Capture and Storage, DOE=Department of Energy, DOI=Department of the Interior, EOR=Enhanced Oil Recovery, EPA=Environmental Protection Agency, NSF=National Science Foundation.

Synthesis improvement is a slow process, while meat consumption and food waste remain high despite health and economic drivers to reduce them. Conclusion 6: Direct air capture and carbon mineralization have high potential capacity for removing carbon, but direct air capture is currently limited by high cost and carbon mineralization by a lack of fundamental understanding. Conclusion 7: Although their potential for removing carbon is lower than other negative emissions technologies, coastal blue carbon approaches warrant con- tinued exploration and support. The cost of the carbon removal is low or zero because investments in many coastal blue carbon projects target other benefits such as ecosystem services and coastal adaptation. Understanding of the im- pacts of sea-level rise, coastal management, and other climate impacts on future uptake rates should be improved. Conclusion 8: Several carbon mitigation research efforts would also support the advancement of negative emissions technologies. Research on geologic stor- age of carbon dioxide is critical to improve decarbonization of fossil fuel power plants, and also critical for advancing direct air capture and BECCS. Similarly, research on biofuels would also advance BECCS. The research recommendations in Tables 8.3 and 8.4 were developed to align with the types of funding currently offered by federal agencies. Exceptions include items 23, 25, 27, and 29, which describe public-private partnerships designed to ensure that the public realizes benefits from its funding of direct air capture start-ups, while protect- ing the intellectual property that makes those start-ups possible. However, it is worth considering the history of federal incentives for wind and solar electricity and the de- velopment of unconventional gas and oil. In these cases, costs dropped dramatically, in part because of decades of subsidies that incentivized private companies to com- pete on price, before their technologies were competitive in the open marketplace. The benefits to the United States have been extraordinary. Wind and solar are now the cheapest forms of energy in many locations, natural gas is abundant and inexpensive, and the United States is poised to be a major oil exporter. Thus, a historically effective way to reduce the cost of a technology has been to create a competitive market for it by offering financial incentives that make the technology profitable at its current price. This is the theory behind the 45Q tax credit rule. Which NETs might be ready for such a program? The obvious examples are the NETs with an existing knowledge base to develop a regulatory regime capable of verifying capture and a desired permanence of storage. Examples include most methods of 393

N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N afforestation/reforestation and forest management, some kinds of agricultural soils, such as the use of cover crops and reduced tillage in many cropping systems, electric power BECCS, and direct air capture. Perhaps some forms of mineralization, such as the management of reactive mine tailings, and some coastal options could also be quickly brought to readiness. RESEARCH BUDGET SUMMARY The scale of the research budget reflects the size of the carbon and climate problem. A solution such as the one presented in Figure 8.1 is likely to require electricity gener- ated by wind, solar, biomass, nuclear, and natural gas with CCS; biofuels and electricity for transportation; and some form of energy storage. Each of these technologies has received large government investment. For example, Sissine (2014) estimates that the federal government spent more than $22 billion dollars on renewable energy research and development from 1978 to 2013. These investments have paid off spectacularly, with the levelized cost of utility-scale solar and wind electricity now at 3-6¢/kWh (EIA, 2017b). A zero-emitting energy system that costs about what consumers pay today is now technologically feasible because of decades of government investment. NETs have not yet received comparable public investment despite expectations that they will provide ~30 percent of the net emissions reductions required this century (i.e., maxima of 20 Gt/y CO2 of negative emissions and 50 Gt/y CO2 of mitigation in Figure 8.1). NETs are essential to offset emissions that cannot be eliminated, such as a large fraction of agricultural emissions. Low-cost NETs are already less expensive than most forms of mitigation. Direct air capture at a cost of $100/t CO2 would offset emis- sions from fossil aviation fuels without affecting food and biodiversity and at a cost comparable to or less than biofuels. Inexpensive direct air capture or carbon mineral- ization could allow for indefinite use of fossil fuels without climate impacts. The scale of the recommended research budget is consistent both with the need for NETs that can solve a substantial fraction of the climate problem and the possible magnitude of the return to the U.S. economy. Coastal Blue Carbon Although coastal blue carbon would be prohibitively expensive if undertaken solely to manage carbon, it is likely that CO2 removal and/or storage could be added to coastal engineering projects that are undertaken for other reasons (such as storm protec- tion) at zero or low cost. The potential rate of U.S. coastal blue carbon is only about 394

Synthesis 0.02 Gt/y CO2, with another 0.01-0.03 Gt/y CO2 of storage that could be achieved by using organic materials in coastal engineering projects (but the carbon would need to be captured elsewhere). Even at a low average carbon removal and storage cost of $20/t CO2, achieving 0.06 Gt/y CO2 at zero cost would represent a savings of $200M/y. This calculation justifies the research expenditures proposed in Table 8.3. The core of the proposal for coastal blue carbon is item 3, which calls for $40M/y for 20 years to establish and operate a network of research sites. These would straddle edaphic gradients and include both natural systems and those undergoing coastal engineer- ing projects. A common set of measurements across the network would advance our understanding of carbon removal and storage in coastal ecosystems, and experiments would determine how best to add carbon removal and storage to coastal engineer- ing projects at the lowest cost. The plan also calls for $6M/y for 5-10 years for basic research (item 1), $2M/y for 20 years to map and monitor coastal wetlands (item 2), $2M/y for 20 years for a data center (item 4), and $5M/y for 10 years for social science research on cost-effective adaptive management of coastal blue carbon and on the response of coastal land owners and managers to carbon removal and storage incen- tives (item 6). The social science research would also investigate policies to manage responsibility for carbon lost to inundation or erosion. A broad range of federal, state, and local government agencies and academic insti- tutions comprise potential funding opportunities for coastal blue carbon research. These include, for example, the National Science Foundation (NSF), Department of Energy (DOE), EPA, National Aeronautics and Space Administration, U.S. Army Corps of Engineers, and National Oceanic and Atmospheric Administration. An interagency–ac- ademia–nongovernmental organization–industry program work group would also be useful, particularly for the development of a comprehensive coastal blue carbon proj- ects database. In addition, foundations and the private sector have important roles to play in research related to demonstration and deployment of coastal blue carbon and storage projects. Afforestation/Reforestation and Forest Management The research budget for afforestation/reforestation and forest management is rela- tively low because this is a relatively mature area. The field holds great promise for carbon removal and sequestration because (1) for more than a century, foresters have researched how to maximize wood production, including developing tree varieties that grow quickly; (2) wood is about 50 percent carbon; and (3) most temperate and tropi- cal forests store most of their carbon in wood. The total research effort to accomplish something very close to forest carbon removal and sequestration has already been 395

N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N very large. To cite just one example, the U.S. Forest Service (USFS) Forest Inventory and Analysis (FIA) Program spends $70M/y measuring U.S. wood biomass and changes in biomass in ~100,000 repeatedly censused plots. The largest forest-related expendi- ture in Table 8.3 (item 8, $3.7-14M/y for 10 years) is shared with BECCS. The effort to improve humanity’s understanding of the land-area constraint facing afforestation/­ reforestation, forest management approaches, and BECCS might allow increased carbon removal in all of these categories, and if not, might still reduce the probability of making a grave policy error. The proposed expenditure on IAM of land-use change is not larger because the committee believes that genuine understanding in this area is likely to improve only slowly. This also explains the 10-year proposed duration of the funding. Items 7 and 12 in Table 8.3 leverage substantial other investments by USFS. Item 10, if successful, could provide a very large benefit at very low cost (see Chapter 3). USFS has a central role in furthering research and funding for afforestation and forest management, while USDA and NSF are well suited to carry out research on social sci- ence topics and other environmental and societal impacts. Uptake and Storage by Agricultural Soils The cost of the research on carbon removal and storage by agricultural soils is inter- mediate relative to the research budget for other NETs. Unlike foresters, agricultural plant breeders have not focused specifically on aspects of plant productivity that would increase carbon removal and storage (i.e., above-ground biomass for trees, but deep and difficult to decompose roots for agricultural crops). Thus, $40-50M/y of the budget is for development of new agricultural varieties (item 17 in Table 8.3). The 20-year duration in the plan reflects the need for a sustained effort. This would expand the considerable investment in this area by the Advanced Research Projects Agency- Energy (ARPA-E). Despite the lack of breeding to enhance carbon removal and storage, agricultural scientists still know how to accomplish these goals in most cropping sys- tems and some grazing systems because soil carbon is a measure of soil health, which they have worked to improve for decades. The second largest portion of the plan, items 13 and 14 ($11-14M/y), is critical to extend carbon storage practices to cropping systems where previous work has been insufficient, and to increase efficiency and re- duce costs in all areas. This expenditure will also improve agricultural productivity and nitrogen- and water-use efficiency and could be justified because of these benefits alone. Item 19 is critical to develop both cost-competitive biofuels and biofuels with net negative emissions (fuels-BECCS). Finally, item 18 might provide large new capa- bility at low cost. Collectively, the three “frontier” items (17,18, and 19) might double 396

Synthesis the potential for storage in agricultural soils or more. Item 20 is discussed with the carbon mineralization options below. Programs within USDA, NSF, and/or DOE have the most appropriate infrastructure to conduct research on topics pertaining to agricultural soils. Land-grant universities also have an important role to play, for example, by conducting experiments for the evalu- ation of region-specific best management practices for soil carbon sequestration. In addition, the USDA/Natural Resource Conservation Service’s Conservation Innovation Grants can provide needed empirical knowledge on topics in economic and behav- ioral research along with the continuation and expansion of pilot emission reduction and carbon removal and storage projects. Bioenergy with Carbon Capture and Storage BECCS-to-fuels offers (1) the greatest opportunity for the development of new cost- competitive biofuels, (2) the possibility that these could be produced with net nega- tive emissions, and (3) a possible benefit for agricultural productivity (through the application of biochar). These are the reasons for the recommended investment in a comprehensive development push in this area for 10 years (item 21). The economic and energy security benefits from this investment might be speculative, while the CO2 removal and storage benefits are likely to be material, but still constrained by available waste biomass. Table 8.4 also proposes research for improving the productivity and density of energy crops used in electricity generation, and for research to increase the conversion efficiency of biofuels to electric power. Although this should be considered as part of the nation’s biofuels research budget, it is included here because the possi- bility of improved BECCS provides another justification for it. The BECCS research agenda also includes the development of a life cycle analysis- based framework to compare NETs in the United States. Although it is applicable to all NETs, it was included as part of the BECCS research agenda because BECCS is so com- plex, which makes it very difficult to determine net CO2 removal. This is much more straightforward for afforestation/reforestation, agricultural soils, coastal blue carbon, direct air capture, and even carbon mineralization. Several agencies within USDA, DOE, and EPA are active in and capable of effectively carrying out most of the proposed basic and applied research components and tasks for BECCS. However, they may not be currently equipped to effectively run a tech- nology demonstration program. Public-private partnership entities have historically played substantial roles in the demonstration and deployment of new technology. As such, the evaluation of existing government agency technology demonstration 397

N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N capabilities and the investigation of institutional structures that will have the capabili- ties needed to effectively develop and demonstrate new biomass energy technology is critical to successful scale-up and deployment of new technologies. Direct Air Capture The direct air capture budget was formulated to provide a substantial chance of de- veloping ~$100/tCO2 direct air capture and sequestration within one or two decades. The challenge of direct air capture development is that no commercial driver for the activity exists in the absence of a high carbon price (unlike afforestation/reforesta- tion, agricultural soils, BECCS-to-fuels, and coastal blue carbon). For this reason, the development of a practical direct air capture option will require sustained govern- ment investment. However, the committee also concluded that progress would be most likely if a cooperating and competing ecosystem of researchers and start-ups could explore the many options for direct air capture and advance many dimensions of the technology at once. The plan and budget cover four separate stages of technol- ogy development. The effort by multiple researchers and companies at each stage is paired with work by a National Direct Air Capture Test Center, that would facilitate re- search (i.e., provide techno-economic analysis and engineering design help), conduct measurements of each entity’s technology using a common basis for comparison, and disseminate public information while protecting intellectual property. The first stage (items 22 and 23 and $23-35M/y for 10 years) would search for better materials and component designs with many $1 million efforts. The second (items 24 and 25 and $13-25M/y for 10 years) would scale up new materials and components so that they could be produced at the scale necessary for a pilot plant (>1,000 t CO2/y). The third (items 26 and 27 and $30-60M/y for 10 years), would build and evaluate $20M/project pilot plants. The fourth (items 28 and 29 and $115-120M/y for 10 years) would provide the final scale-up to >10,000 t CO2/y at $100M/project. Obviously, stages 1-4 would not run either entirely in parallel or entirely sequentially. Most groups would enter the program at stage 1, some at stage 2, and maybe one or two at stage 3. If successful, the effort would deliver commercial-scale direct air capture at greatly reduced price within 10-20 years. DOE’s Office of Fossil Energy and National Energy Technology Laboratory (NETL) have the appropriate infrastructure to manage direct air capture research, development, and demonstration projects through typical proposal and grant processes for distribu- tion of funding to universities, nonprofit research organizations, start-up companies, and large companies. DOE’s existing infrastructure can also manage contractors for independent materials testing, component testing, techno-economic analysis, and 398

Synthesis professional engineering design. A centralized facility/national testbed similar to the NETL’s National Carbon Capture would be appropriate for development and demon- stration testing of direct air capture components and systems. Moreover, contracting mechanisms, such as fixed-fee or cost-plus contracts, would prove useful for develop- ing direct air capture technology. However, no public investments should be made without first identifying a clear market incentive for carbon removal; in the absence of a market incentive for carbon removal, industry will not invest in the commercial deployment of direct air capture systems. Carbon Mineralization The committee recommends a substantial investment in new carbon mineralization research because carbon mineralization would have effectively unlimited capacity if cost-effective methods could be found, and because early work is encouraging. The plan calls for basic research on the kinetics of carbon capture by minerals ($5.5M/y for 10 years, item 30) and on feedbacks between reaction and fluid flow for in situ appli- cations ($17M/y for 10 years, item 31). It includes an effort to map near-surface for- mations and existing tailings piles of reactive minerals by the U.S. Geological Service (USGS) at $7.5M/y (item 32) and $3.5M/y for 10 years (item 33) to explore enhanced weathering of reactive surficial deposits in mine tailings and other locations. It in- cludes $3M/y for 10 years for experimental studies of the addition of reactive minerals to agricultural soils (item 20). The most ambitious project is to explore the possibility of in situ CO2 removal and sequestration in formations of near-surface ultramafic rock (averaging $10M/y for 10 years, item 34). Table 8.4 also contains two sequestration- only mitigation projects. The first is to attempt to store captured CO2 in reactive mine tailings ($1M/y for 10 years, item 41). Although the mass of existing tailings and their annual rate of production are relatively small (enough to store tens of Mt CO2), the costs could be as low as $10/t CO2. Item 42 proposes a medium-scale injection of CO2 into a basalt formation to provide an alternative to saline aquifer storage (averaging $10M/y for 10 years). This is the next step, given previous efforts in Washington State (~1,000 t CO2) and Iceland (order of 10,000 t/y CO2 for several years). Much of the recommended research for carbon mineralization falls within the do- mains of the NSF Directorate for Geosciences, USGS, and DOE. Several programs within DOE (e.g., Basic Energy Sciences Program and Office of Fossil Energy, combined with the Crosscutting Subsurface Technology and Engineering Research, Develop- ment, & Demonstration [SubTER] initiative) hold the potential for funding research on the overall topic of kinetics and other aspects of carbon mineralization. University re- search in the theoretical aspects of carbon mineralization research will be key, and an 399

N E G AT I V E E M I S S I O N S T E C H N O LO G I E S A N D R E L I A B L E S E Q U E S T R AT I O N explicit NSF partnership to fund greenhouse gas mitigation research would be useful. Such a partnership could resemble several successful initiatives within NSF’s Director- ate for Geosciences, such as the RIDGE, MARGINS, and GeoPRISMS Programs. Geologic Sequestration in Saline Aquifers Table 8.4 proposes new research on safe and cost-effective sequestration of CO2 in saline aquifers. This is a national budget to support a relatively mature field that is already practiced at large scale (approaching 100 Mt/y CO2) and that is now subsi- dized by the U.S. government at $50/t CO2. Saline aquifer storage is vital to mitigate fossil power emissions and to make direct air capture and BECCS carbon negative. The proposed research plan includes $50M/y to reduce risks of induced seismicity (item 43), $45M/y to increase the efficiency and accuracy of site characterization and selec- tion (item 44), $50M/y to improve and reduce the cost of monitoring and verification (item 45), $25M/y to improve secondary trapping of CO2 (item 46), $10M/y to improve simulation modeling (item 47), $20M/y to research ways to manage the risk of leakage of CO2 to the atmosphere and groundwater (item 48), and $50M/y to develop meth- ods that co-optimize enhanced oil recovery and carbon sequestration (item 49). DOE, NSF, EPA, and the Department of the Interior (DOI) all have important roles in continued funding and research on geological sequestration. For example, new re- search and development needs in DOE’s purview include research on trapping mecha- nisms as well as multiscale, multiphysics modeling of the fate and transport of CO2 in the subsurface. NSF plays an important role in engaging and leveraging university research on Earth processes that are relevant to sequestration. EPA could collaborate with DOE and DOI to support the development of reliable approaches regarding con- tamination sequestration sites. Both USGS and the Bureau of Land Management (BLM) are well suited to further the scale-up of geological sequestration. CONCLUSION Every recent analysis of solutions to the climate problem has concluded that NETs should play as large a role as any mitigation technology, with 10 Gt/y CO2 of nega- tive emissions needed by midcentury and 20 Gt/y CO2 by the century’s end. Several Gt/y CO2 of negative emissions at less than $20/t CO2 are already available, and a ­ fforestation/reforestation negative emissions have been part of the United Nations Framework Convention on Climate Change (UNFCCC) for more than a decade. Existing agricultural soils methods have large co-benefits that would improve the productivity 400

Synthesis and economic resilience of U.S. farms, even without the carbon benefit. Nonetheless, existing options (coastal blue carbon, afforestation/reforestation, forest management, agricultural soils, and BECCS) cannot yet provide enough negative emissions at rea- sonable cost, without substantial unintended harm to the global food supply and en- vironment. A substantial research investment is needed to improve existing NETs and to reduce their costs. In addition, two options with essentially unlimited capacity have remained substantially less explored than the other NETs. An investment in direct air capture and carbon mineralization research by the United States has the potential to revolutionize the future evolution of our energy system. Recommendation: The nation should launch a substantial research initiative to advance negative emissions technologies (NETs) as soon as practicable. A substantial investment would (1) improve existing NETs (i.e., coastal blue carbon, afforestation/reforestation, changes in forest management, uptake and storage by agricultural soils, and bioenergy with carbon capture and sequestration) to increase the capacity and to reduce their negative impacts and costs; (2) make rapid progress on direct air capture and carbon mineral- ization technologies, which are underexplored, but would have essentially unlimited capacity if the high costs and many unknowns could be overcome; and (3) advance NET-enabling research on biofuels and carbon sequestra- tion that should be undertaken anyway as part of an emissions mitigation research portfolio. 401

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To achieve goals for climate and economic growth, “negative emissions technologies” (NETs) that remove and sequester carbon dioxide from the air will need to play a significant role in mitigating climate change. Unlike carbon capture and storage technologies that remove carbon dioxide emissions directly from large point sources such as coal power plants, NETs remove carbon dioxide directly from the atmosphere or enhance natural carbon sinks. Storing the carbon dioxide from NETs has the same impact on the atmosphere and climate as simultaneously preventing an equal amount of carbon dioxide from being emitted. Recent analyses found that deploying NETs may be less expensive and less disruptive than reducing some emissions, such as a substantial portion of agricultural and land-use emissions and some transportation emissions.

In 2015, the National Academies published Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration, which described and initially assessed NETs and sequestration technologies. This report acknowledged the relative paucity of research on NETs and recommended development of a research agenda that covers all aspects of NETs from fundamental science to full-scale deployment. To address this need, Negative Emissions Technologies and Reliable Sequestration: A Research Agenda assesses the benefits, risks, and “sustainable scale potential” for NETs and sequestration. This report also defines the essential components of a research and development program, including its estimated costs and potential impact.

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