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 concentrations 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 sequestration that could be achieved safely and economically, given our current 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 chapter. “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

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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.

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 Standard (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 approaches 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 enhanced 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

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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).

to incentives. Research on land-based options would help to ensure that the capacities 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 mineralization technologies could generate very large capacity if their costs and environmental 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 deployment. 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 virtually 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

TABLE 8.1 Synthesis of Key NET Attributes with Current Technology and Understanding (Committee Assessment)

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.

^fLarger 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 CO₂ removal rate and capacity that are feasible, with current technologies, without compromising food supply or biodiversity from large-scale land conversions. 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 CO₂ direct air capture could be in the tens of gigatons per year.

^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 additional detail.

TABLE 8.2 Synthesis of Key Attributes for CO₂ Sequestration Only with Current Technology and Understanding (Committee Assessment)

^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 CO₂, pipelines, regulatory infrastructure, and public opinion

^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.

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 greenhouse 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). Approximately 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 agricultural 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 improve, 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.

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 potentially 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 substantial effort, including the new 45Q tax credit rule⁵ that provides $50/t CO₂ for carbon

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⁵ See https://www.law.cornell.edu/uscode/text/26/45Q (accessed January 29, 2019).

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 assessment model (IAM) results reviewed in IPCC (2014b) (Table 8.1). Similarly, simply disposing 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, practical barriers, permanence, monitoring and verification, governance, and insufficient scientific or technological understanding. These factors helped inform the recommended 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 dangers of competition for land among afforestation/reforestation, BECCS, food production, and biodiversity preservation, but also report large upper bounds for negative

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 otherwise, 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 cropland, 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 magnitude 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 estimated to be 100-1,000 times the background rate from the fossil record, and 80 percent 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 agricultural 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.

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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.

The inescapable conclusion is that repurposing a substantial amount of current agricultural 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 threatened 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 afforestation/reforestation or BECCS from either agriculture or production forestry would create 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. Similarly, a forest management approach to increase the length of time between successive 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 committee believes that humanity should develop new high-capacity NETs such as low-cost direct air capture and carbon mineralization. The safe levels of afforestation/reforestation, 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. Because forests established at high latitudes decrease albedo by, for example, reducing

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 mineralization would create enormous volumes of waste rock that may contaminate water and/or air. Agricultural soils options generally have large positive side benefits, including 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 chapter further states that it is too early to determine whether sorbent- or solvent-based systems will ultimately prove to be the least expensive.

The estimated cost of capture and sequestration for BECCS systems that produce electricity 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 expensive. Costs of terrestrial carbon removal and sequestration approaches are comparatively 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/reforestation, forest management, and agricultural soils activities in the United States are already supported by well-developed state and federal (U.S. Department of Agriculture [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

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 landowner 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 management, 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 agricultural soils methods (Conant et al., 2007; Grandy and Robertson, 2007; Minasny et al., 2017). A restored coastal wetland could be drained again for development. Nonetheless, 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, carbon 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 cannot 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 permanence compared to not only other sequestration technologies, but also solar radiation 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.

TABLE 8.3 Research Plan and Budget for Negative Emissions Technologies (abbreviated from research tables in Chapters 2-7).

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 Technology, 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.

Monitoring and Verification

Monitoring and verification will be critical components of any large-scale deployment 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 fundamental 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 processing 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 monitoring 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 management, agricultural soils, and BECCS. Because of landscape and shoreline evolution, intensive coastal verification might have to continue indefinitely.

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 agricultural 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 sectors covered by a national or international agreement, including afforestation/reforestation (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 experience 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 increasing 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 understanding. 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 effectively 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 reaction products—cannot be predicted. In addition, positive feedbacks, such as increasing permeability and reactive surface area via “reaction-driven cracking,” are not well

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 development, 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 impacts 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 adaptation) 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 biochar 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 expertise 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 afforestation/reforestation and forest management is lower than that for other NETs because these approaches are more mature. In contrast, the estimated research budgets for

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 unanswered 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 biodiversity—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 biodiversity 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

TABLE 8.4 Research Plan and Budget for NET-Enabling Research

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.

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 continued 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 impacts 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 storage 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 protecting 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 development of unconventional gas and oil. In these cases, costs dropped dramatically, in part because of decades of subsidies that incentivized private companies to compete 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

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 generated 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 emissions 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 mineralization 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 protection) at zero or low cost. The potential rate of U.S. coastal blue carbon is only about

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 engineering 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 engineering 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 incentives (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 institutions 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–academia–nongovernmental organization–industry program work group would also be useful, particularly for the development of a comprehensive coastal blue carbon projects 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 relatively 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 tropical 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

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 expenditure 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 science 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 intermediate 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 systems 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 reduce 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 capability at low cost. Collectively, the three “frontier” items (17,18, and 19) might double

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 evaluation 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 behavioral 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 negative 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 possibility 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 complex, 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 technology 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

capabilities and the investigation of institutional structures that will have the capabilities 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 developing ~$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/reforestation, agricultural soils, BECCS-to-fuels, and coastal blue carbon). For this reason, the development of a practical direct air capture option will require sustained government 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 technology 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 research (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 distribution 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

professional engineering design. A centralized facility/national testbed similar to the NETL’s National Carbon Capture would be appropriate for development and demonstration testing of direct air capture components and systems. Moreover, contracting mechanisms, such as fixed-fee or cost-plus contracts, would prove useful for developing 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 applications ($17M/y for 10 years, item 31). It includes an effort to map near-surface formations 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 includes $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 domains 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, Development, & Demonstration [SubTER] initiative) hold the potential for funding research on the overall topic of kinetics and other aspects of carbon mineralization. University research in the theoretical aspects of carbon mineralization research will be key, and an

explicit NSF partnership to fund greenhouse gas mitigation research would be useful. Such a partnership could resemble several successful initiatives within NSF’s Directorate 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 subsidized 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 selection (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 methods 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 research and development needs in DOE’s purview include research on trapping mechanisms 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 contamination 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 negative 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 afforestation/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

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 reasonable cost, without substantial unintended harm to the global food supply and environment. 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 mineralization 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 sequestration that should be undertaken anyway as part of an emissions mitigation research portfolio.

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