The role and deployment timing of direct air capture in Saudi Arabia’s net-zero transition

The Kingdom of Saudi Arabia (KSA) has pledged to achieve net-zero greenhouse gas emissions by 2060. Direct air carbon capture and storage (DACCS) is critical for the country to meet its net-zero target given its reliance on fossil fuels and limited options for carbon dioxide removal (CDR). However, the role of DACCS in KSA’s national climate change mitigation has not been studied in the literature. In this study, we aim to understand the potential role of DACCS and the effect of its deployment timing in KSA’s transition toward its net-zero target using the Global Change Analysis Model (GCAM)-KSA, which is a version of GCAM with KSA split out as an individual region. We find that the annual DACCS CO2 sequestration in KSA reaches 0.28–0.33 Gt yr−1 by 2060 depending on its deployment timing. Early DACCS deployment, driven by its early and rapid cost reduction worldwide, could bring significant savings (∼420 billion USD during 2020–2060) in the cost of climate change mitigation in KSA, approximately 17% reduction relative to delayed DACCS deployment. Our study suggests a strong role for KSA to proactively invest in the R&D of DACCS, initiate early DACCS deployment, and explore a broad suite of CDR options.


Introduction
Achieving the ambitious climate targets under the Paris Agreement requires immediate actions to reduce carbon dioxide (CO 2 ) emission to net-zero by as early as mid-century.Such actions entail not only rapid decarbonization of energy, industrial, and land systems, but also large-scale deployments of carbon dioxide removal (CDR) measures at several to tens of gigatons CO 2 per year by the end of the century (Rogelj et al 2018, IPCC 2022).
Direct air carbon capture and storage (DACCS) is a CDR technology that removes CO 2 from atmosphere based on engineered processes and permanently stores it in deep geological formations.DACCS has gained increasing attention given its advantages (e.g.flexibility of deployment location, scalability potential, lower footprint in land use) compared bioenergy with carbon capture and storage (Smith et al 2016, Fuss et al 2018, Creutzig et al 2019).However, the technology has not yet reached fully commercial deployment, with only pilot-scale plants operating worldwide mainly due to high costs, substantial energy inputs, a lack of experience on large-scale operation, and public concerns on safety (Fuss et al 2018, Cox et al 2020, Ozkan et al 2022).Nowadays, there are 27 small-scale direct air capture (DAC) plants that have been commissioned globally, and these plants together capture a total of 10 kt CO 2 yr −1 .Six DAC projects are currently under construction, with the largest two expected to come online in 2024 in Iceland (37 kt CO 2 yr −1 ), and in 2025 in the United States (U.S.) (500 kt CO 2 yr −1 ) (IEA 2022).
The timing of mitigation action could have significant impact on the effectiveness, costs, and overall outcomes of addressing climate change (Jakob et al 2012, Luderer et al 2013, Obersteiner et al 2018, Victoria et al 2020).As an emerging mitigation option, the role of CDR technologies, including DACCS, in contributing to global and national climate change mitigation have not yet been widely studied in the literature.Available studies have mostly focused on the global level and several major regions Y Qiu et al (e.g.China, Europe, and the U.S.).These studies generally show that CDR plays an important role in offsetting emissions from the hard-to-abate sectors and therefore could significantly reduce mitigation costs for both national and sectoral decarbonization pathways (Realmonte et al 2019, Bistline and Blanford 2021, Fuhrman et al 2021b).However, postponing CDR deployment could otherwise increase the mitigation costs and limit the overall CO 2 removal potential, putting the global and national mitigation targets at risk (Galán-Martín et al 2021).As countries are beginning to implement their climate commitments and undertake domestic actions that will set the foundations for longer-term emissions reductions, it is important to understand the role of key CDR technologies, such as DACCS, in facilitating mitigation in various regional and national contexts.
Kingdom of Saudi Arabia (KSA) is the largest economy in the Middle East, and the Kingdom pledges to achieve net-zero greenhouse gas (GHG) emissions by 2060 (Saudi Green Initiative 2021).However, this ambitious climate target faces challenges given the fact that KSA's economy heavily relies on its oil industry-KSA's oil industry contributes to 41% of the country's GDP (in 2019) and its energy supply is predominately from oil and natural gas (Hasanov et al 2022, Energy Institute 2023).To achieve the netzero climate target while maintaining vibrant economy, key initiatives have been adopted to diversify its economy and encourage sustainable development.For example, the energy price reform aims to increase the domestic energy prices (which has long been incentivized to make energy affordable domestically) and link them with the international market.Studies have shown this initiative effectively curbed the KSA's gasoline and electricity consumption in 2018 (Aldubyan and Gasim 2021) and could contribute to significant expansion of renewable energy technologies in KSA's power sector (Groissböck andPickl 2018, Wogan et al 2019).Improving energy efficiency is another important effort KSA has undertaken under the Saudi Energy Efficiency Program (SEEP), which aims to rationalize energy consumption and improve energy efficiency across key sectors (including industry, buildings, and transportation) (Ministry of Energy 2022, Saudi Energy Efficiency Center 2023).This initiative could reduce carbon intensity of energy consumption, contributing substantially to overall carbon mitigation of KSA (Belaïd and Massié 2023).Additionally, a number of studies have further incorporated KSA's national decarbonization targets and current sectoral policy initiatives to evaluate the contributions of key economic sectors (industry, electricity, transportation, and building) to the KSA's carbon mitigation targets (Kamboj et al 2023a(Kamboj et al , 2023b)).
These previous studies cover a wide range of policy initiatives and mitigation strategies in KSA, and they provide important insights to assist relevant decision-making.However, studies that evaluate the role of CDR in KSA's climate change mitigation are limited in the literature.Alatiq et al, qualitatively suggests that Arabian Gulf Countries, including KSA, have abundant solar resources and CO 2 sequestration capacity, which make this region a good candidate for DACCS implementation (2021), and Kamboj et al further quantifies the DACCS capacity needed for KSA to achieve net-zero GHG emission targets (2023b).But these studies do not evaluate the implications of DACCS deployment and its timing on the cost of climate change mitigation and future transitions of different socio-economic sectors in KSA.Understanding these implications is important to inform KSA's policy decisions on the national decarbonization pathways and relevant policy supports to the innovation and deployment of DACCS in the Kingdom.Therefore, this study aims to investigate the effects of DACCS deployment and its timing on the policy cost of climate change mitigation and energy consumption of different socio-economic sectors in KSA.

Methods
In this study, we use a modified version of the Global Change Analysis Model version 6 (GCAM 6.0) to investigate the role of DACCS and its deployment timing in KSA's transition toward net-zero GHG emissions by 2060.GCAM 6.0 is an open-source, multi-sector integrated assessment model, which is available in a public repository (Bond-Lamberty et al 2022).It represents the behavior and interactions among five systems which are economy, energy, agriculture and land use, water, and climate.These systems have different geographical resolutions, including 32 geopolitical regions, 384 land subregions, and 235 water basins across the globe.GCAM 6.0 operates in 5 year time-steps from 2015 (model calibration year) to 2100, and it is driven by exogenous assumptions about population growth, labor participation rates, and labor productivity in the 32 geopolitical regions, together with other assumptions of resources, technologies, and policy.GCAM 6.0 solves for the equilibrium prices to ensure that supplies and demands are equal for various energy, agricultural, water, land-use, and GHG markets in each time-step and region.Each system in GCAM 6.0 has technological detail.Individual technologies compete for market share based on their levelized costs.GCAM 6.0 also includes a representation of three CDR options that are deployed in scenarios with emission policies, namely, DACCS, bioenergy with carbon capture and storage (BECCS), and afforestation (Fuhrman et al 2021a).
A modified version of GCAM 6.0 (GCAM-KSA) has been developed by explicitly splitting out KSA from the Middle East (which is one of the existing 32 regions in GCAM 6.0) as one individual region (Kamboj et al 2023b).In GCAM-KSA, we use regionalized data inputs for KSA that capture key socioeconomic and technological developments in the country.Particularly, due to the arid and hot climate, the availability of dedicated biomass resources for energy generation is limited in KSA (Demirbas et al 2017), so BECCS is not considered as a CDR option in our current modeling efforts for KSA.Additional details about the modeling framework of GCAM and how KSA is split out as an individual region are provided in the supplementary note 1, and a list of modifications and regionalized data inputs used in this study is included in supplementary table 1.
Three central scenarios are considered in this study, namely, Reference, Net-Zero KSA w/early DACCS, and Net-Zero KSA w/ delay DACCS (table 1).The Reference is a counterfactual scenario that assumes no explicit climate policies and no CDR deployment.The two Net-Zero KSA scenarios include emissions constraints which assume that the KSA meets its nationally determined contribution (NDC) target (reducing GHG emissions by 278 Mt CO 2 eq by 2030) and achieves net-zero GHG emissions by 2060, and the rest of the world achieve their NDCs in addition to long-term strategies and net-zero pledges following the assumptions from a previous study (Iyer et al 2022).Under the two Net-Zero KSA scenarios, it is anticipated that the global surface temperature change will be limited to <2 • C warming in this century.Both of the Net-Zero KSA scenarios include DACCS deployment worldwide.Two types of DACCS technologies are considered in this study, namely high temperature solvent-based DACCS and low temperature solid-based DACCS.Depending on the heat source, the high temperature solvent-based DACCS can use heat from either natural gas combustion (HT-DACCS-NG) or heat supply by electric furnace (HT-DACCS-ELEC).As for the low temperature solid-based DACCS, the heat is supplied by heat pump (LT-DACCS-HP).Detailed information about the technology description can be found in supplementary note 2, and the parameter inputs (e.g.cost, energy use, etc) of DACCS used in the GCAM-KSA can be found in (Fuhrman et al 2021a).
The two Net-Zero KSA scenarios differ in the projections of the levelized costs of non-energy capture (LCOC) of DACCS (i.e.excluding the costs of electricity and/or fuels), which ultimately leads to different timings of DACCS deployment.The Net-Zero KSA w/early DACCS assumes that, with earlier investment in research and development (R&D), the LCOCs of DACCS worldwide (including KSA) starts to decline linearly in 2020 and reach floor costs in 2030, and it remains constant beyond that.By contrast, the Net-Zero KSA w/ delay DACCS scenario assumes delay in R&D investment which results in the LCOCs of DACCS remaining at its starting level until 2050, and then declining linearly to the same floor costs in 2080 (table 1).Fuhrman et al developed different cost trajectories for DACCS, which capture the changes in DACCS cost, performance, and deployment across a range of socio-economic future with different nearterm incentivizing policies.In these central scenarios, the minimum LCOCs of DACCS are adopted from the moderate-cost DACCS scenario (2021a).Note that cost projections under the two Net-Zero KSA central scenarios are intended as bounding assumption to test the effects of DACCS deployment timing (induced by its drastic different cost projection) on KSA's policy cost of climate change mitigation.
In addition to these central scenarios, we consider a suite of additional sensitivity scenarios to examine the sensitivity of our core findings and results to key assumptions (see supplementary note 3).
For all of our scenarios, we evaluate the implications of DACCS deployment timing and level on the cost of climate change mitigation in KSA using the estimated carbon prices and policy costs of climate change.Carbon price is a price on CO 2 emission which GCAM calculates endogenously based on emissions constraints.The carbon price is passed down to all the systems in GCAM and affects the costs and relative competitiveness of goods and services whose productions and uses emit CO 2 .The added carbon price also affects the supply and demand of these goods and services to ensure the system CO 2 emission meet the emission constraints in each model period.The policy costs of climate change mitigation is also estimated by GCAM as the area under the marginal abatement curve (MAC, representing the carbon price with respect to the CO 2 abatement level) (Calvin et al 2019).This method of calculationwhile not unique-is well-established in the literature particularly that is based on partial equilibrium economic models and represents the deadweight loss to the economy associated with emission reduction measures (Iyer et al 2015, IPCC 2022).Every policy cost metric has its own advantages and disadvantages.A detailed comparison with other methods of calculating policy costs (e.g.GDP loss) is beyond the scope of this study.In this study, we calculate the cumulative policy costs of climate change mitigation in KSA from 2020 to 2060 (present value based on 5% discount rate in the main results) under the two Net-Zero KSA scenarios, and they represent the total cost of climate change mitigation in the country over the 40 year period.

DAC deployment level and timing
DACCS deployment shows different timings and levels in both the globe and several world regions (KSA, China, and the USA) with different underlying   Scaling up DACCS deployment in KSA also requires significant amount of energy consumption for DACCS operation.The total energy consumption of DACCS in KSA is projected to reach 1.88 and 1.85 EJ yr −1 in 2060 under the Net-Zero KSA w/early and delay DACCS scenarios.These figures account for about 13% of the total primary energy consumption in KSA under both two scenarios (supplementary figure 7).The total energy consumption of DACCS consists of electricity and heat consumption (from natural gas combustion).In the Net-Zero KSA w/early DACCS scenario, the electricity and heat consumptions of operating DACCS in 2060 are estimated at 0.62 EJ yr −1 (equivalent to 172 TWh yr −1 , about 12% of KSA's estimated electricity generation in 2060) and 1.26 EJ yr −1 .With delayed DACCS, the electricity and heat consumptions are 0.39 EJ yr −1 (equivalent to 108 TWh yr −1 ) and 1.46 EJ yr −1 in 2060.These findings emphasize the necessity for KSA to develop additional energy capacity to cater to the growing demand from DACCS technologies.Ideally, this energy supply should predominantly come from clean energy sources to ensure the high CO 2 sequestration efficiency of DACCS.

The implication of DACCS deployment timing on the cost of climate change mitigation
The different levels and timings of DACCS deployment in KSA under the two Net-Zero KSA scenarios result in widely divergent cost implications.The carbon prices in KSA under both scenarios increase from 2020 to 2060 due to the progressively stringent mitigation targets which necessitate the adoption of mitigation options with higher costs.In 2060, the KSA carbon price under the Net-Zero KSA w/delay DACCS scenario reaches $732/t CO 2 , while, with early cost reduction and deployment of DACCS, the 2060 KSA carbon price can be reduced by 28% to $530/t CO 2 (figure 2(a)).Similarly, a stark difference is also observed in the cumulative policy cost of achieving net-zero GHG emissions in KSA.Early DACCS cost reduction and deployment can reduce the policy cost by about 17% to $2050 billion compared to the Additional sensitivity analysis is conducted to further explore the responses of the policy cost to two key factors-the decline rate and minimum level of DACCS LCOC.The results from the sensitivity analysis are consistent with our core findings: that early cost reduction and deployment of DACCS could substantially reduce the policy cost of climate change mitigation in KSA (supplementary note 3).
The higher carbon price and policy cost in KSA under the Net-Zero KSA w/delay DACCS scenario is driven by two separate yet related factors.First, due to limited CDR options considered in this study (modeling a full portfolio of CDR options is beyond the scope of this study, but might be explored in future endeavors), KSA relies on DACCS to achieve the netzero GHG emissions target.This inelastic demand for DACCS, together with delayed cost reduction of DACCS, contribute to higher carbon price in the carbon emitting sources and therefore higher cumulative policy cost for the country.Second, delaying DACCS deployment results in reduced oil and gas consumption in industry and transportation (only oil) sectors, increased deployment of nuclear and renewable solar and wind in the power sector, and higher electrification (figure 3).Due to KSA's high reliance on oil and gas and associated path dependence, displacing even small amounts of these fossil fuels and replacing them with alternative fuels result in an significant increase in the cost of achieving net-zero emissions.

The effect of DACCS deployment timing on sectoral energy consumption in KSA
Early DACCS deployment (compared to the delayed case) reduces the need for other mitigation options, such as less electrification (mainly in transportation), hydrogen use (mainly in industry sector), demand for nuclear and renewable electricity in the power sector.Overall, these changes are relatively small, accounting for at most 8% annual energy consumption and generation in these sectors of the Net-Zero KSA w/delay DACCS scenario.On the other hand, earlier and faster cost reduction of DACCS slows down the displacement of oil consumption in KSA (due to lower carbon price imposed on the fossil fuel energy sources) and allows more oil and gas consumption in the industry, transportation (oil only), and power (mostly gas) sectors.However, the additional amounts of these two fuel types together also remain relatively small, accounting for no more than 8% of the annual energy consumption of the three sectors combined under the Net-Zero KSA w/delay DACCS scenario.As a major oil producing and exporting country, KSA has higher oil production with early DACCS deployment.In 2060, the annual oil production under Net-Zero KSA w/early DACCS scenario is 0.52 EJ (16%) higher than that under the Net-Zero KSA w/delay DACCS scenario (3.25 EJ).This difference is roughly 18% of the oil production loss (−2.84 EJ) in 2060 due to the need for achieving the net-zero target (difference of oil production between the Reference and Net-Zero KSA w/delay DACCS scenario).Overall, due to KSA's high reliance on fossil-based energy sources and associated path dependence, early DACCS deployment in KSA, facilitated by rapid and early cost reduction, could help avoid a smaller amount displacement of fossil fuel (mainly oil) with alternative clean energy sources, but it could contribute to significant savings in the costs of achieving net-zero CO 2 emissions in the country.

Discussion
This study provides several key implications for KSA in terms of deploying DACCS for climate change mitigation.Firstly, DACCS is an important CO 2 mitigation option in KSA.The cost reduction projection Additionally, it is also important for KSA to support the development of upstream and downstream infrastructures related DACCS, including energy supply, CO 2 transport and storage (or utilization) infrastructures.Under the Net-Zero KSA central scenarios, the projected CO 2 captured by DACCS in KSA will reach roughly 0.3 Gt by 2060.This would require equivalent scale of CO 2 transport and storage (or utilization) facilities to be built in the Kingdom as well.Given the importance of oil industry in KSA, CO 2 captured by DAC could also be utilized to extract oil through enhanced oil recovery (EOR).The potential feasibility and implication of combining DAC with EOR could be evaluated in future studies.The total energy (electricity and natural gas) consumption of DACCS could also be substantial by 2060 (13% of the total primary energy consumption in KSA).Ideally, the electricity consumption of DACCS should be generated by renewable or low-carbon sources to achieve high CO 2 sequestration efficiency.This result suggests that future planning of energy system expansion in KSA need to also account for the potential energy demands from DACCS.Future planning on DACCS and energy system in KSA may also consider the climate impacts.Climate change could have substantial impacts on both supply and demand of the energy system as well as the potential induced adaptation mechanisms (Yalew et al 2020, Khan et al 2021, Santos da Silva et al 2021).A recent study has revealed that ambient temperature and humidity could affect the electricity consumption and productivity of solidbased DAC plants (Sendi et al 2022).Therefore, these impacts could be incorporated into future studies to better guide KSA's decision making on energy system planning and DACCS deployment.
In addition to DACCS, it is essential for KSA to explore other CDR options that are suitable to the country's geographical and environmental conditions, and study the feasibility and implication of deploying these CDR options.KSA announced the Saudi Green Initiatives in 2021 to steer the country to a green and sustainable future.As an important part of the initiatives, the country plans to plant 10 billion trees to improve air quality, reduce sandstorms, and rehabilitate degraded land (Saudi Green Initiative 2021).Future studies may evaluate the contribution of this afforestation effort to the overall CO 2 sequestration in the Kingdom and the potential sensitivity to various key aspects, including the required water demand, plant species, and the implications on regional ecosystem and environment.Another potential CDR option that KSA could consider is the direct ocean carbon capture and storage (DOCCS), which takes advantage of the higher CO 2 concentration of sea water than that of atmosphere (by an approximate factor of 120) (DeVries et al 2017).One DOCCS approach involves the electrochemical processes to change the pH of the ocean water and off-gas the CO 2 which is then captured and sequestered.An advantage of this technology is its potential integration with desalination plants which use the seawater discharged from the CO 2 capture plant to produce freshwater, thereby creating costsaving opportunities and the co-benefit of carbon mitigation and freshwater production (Digdaya et al 2020).This co-benefit holds significant meaning for KSA, which aims to achieve net-zero GHG emission by 2060 (Saudi Green Initiative 2021) and currently possesses the world's largest capacity of desalination plants (Mahmoudi et al 2023).A recent study has also indicated that the DOCCS, paired with desalination plant, has substantial potential in the Middle East region (Fuhrman et al 2023).Future research needs to further investigate the feasibility of deploying DOCCS in KSA and quantify the potential capacity associated with the demand for desalination water to materialize the benefits of this technology.Furthermore, several other emerging CDR options, such as enhanced weathering, biochar, could also be explored in future studies to better understand their feasibility and potential implications for deployment in KSA.

Conclusion
This study highlights that DACCS can play a critical role for the KSA to reach its net-zero GHG emission by 2060.Due to KSA's high reliance on fossil-based energy sources and associated path dependence, the early deployment of DACCS in KSA could help to avoid displacing a small amount of oil consumption with other clean energy sources, but it could significantly reduce the cost of achieving net-zero goal.Our study suggests a strong role for KSA to proactively invest in research, development, demonstration, and deployment (RDD&D) of DACCS, providing favorable policy support to reduce the cost of DACCS as low and early as possible, which could contribute to early scale-up of DACCS and lead to substantial lower cost of climate change mitigation in KSA.Our study also suggests KSA build the relevant upstream and downstream energy and CO 2 transport and storage infrastructures that are needed for the increasing deployment of DACCS.KSA could further diversify its CDR portfolio by exploring other options that are suitable for the geographical and environmental conditions in the country, such as afforestation (which is already part of the Saudi Green Initiatives) and DOCCS.
A critical component of policy actions to facilitate RDD&D of CDR in KSA will be to thoroughly evaluate the feasibility of deploying various CDR options, their implications on the coupled energyland-water-climate system, and the optimal integration of these CDR options in contributing to the KSA's national climate change mitigation target.In that sense, our study and the GCAM-KSA model set the stage for future analytical research on potential CDR options within an integrated assessment framework.Such research could help decisionmakers identify the optimal portfolio of CDR technologies and understand their broader implications for human and earth systems.These insights could then facilitate informed decisions on CDR deployment and the design of climate change mitigation strategies.
emissions results under these climate policies of different central scenarios can be found in supplementary figure 6. c Fuhrman et al developed different cost trajectories for DACCS, which capture the changes in DACCS cost, performance, and deployment across a range of socio-economic future with different near-term incentivizing policies.In the central scenarios, the minimum LCOCs of DACCS are adopted from the moderate-cost DACCS scenario (2021a).The LCOC trajectories of DACCS of the two Net-Zero KSA central scenarios used in this study are displayed in supplementary figure 3.

Figure 1 .
Figure 1.Annual CO2 sequestration of DACCS in the world (total) and three other world regions (Saudi Arabia, China, and the USA).

Figure 2 .
Figure 2. Carbon prices trajectories (a) and cumulative policy costs (from 2020 to 2060, 5% discount rate) of achieving KSA's net-zero target (b) under Net-Zero KSA w/early and w/delay DACCS scenarios.The policy cost result under 3% discount rate is provided in supplementary figure 8.

Figure 3 .
Figure 3. Fuel composition of KSA's energy system by sector under the Reference, Net-Zero KSA w/early DACCS, Net-Zero KSA w/ delay DACCS central scenarios, and the difference between the two Net-Zero KSA central scenarios (last column, zoom-in panels are added to showing the differences with different y-axis scale).
Environ.Res.Lett.19 (2024)  064042 Y Qiu et al of DACCS, which affects the technology deployment timing and level, could lead to substantial changes in the policy cost of climate change mitigation in the Kingdom.Therefore, actively investing in the R&D of DACCS and deploying the technology in a timely manner are important measures for the climate change mitigation in KSA.Historically, learning-bydoing (experience gained through increased production or technology deployment) and learning-byresearching (technology improvement due to R&D activities) have contributed to the cost reduction of energy technologies (Sagar and van der Zwaan 2006, Rubin et al 2015).Similar cost reductions in DACCS could also be achieved through significant R&D investments and the scaling up the deployment.In a R&D agenda laid out by the National Academies of Sciences, an average of $150 million yr −1 federal funding is recommended in the U.S. over the next decade to deliver commercialscale DACCS at substantially lower cost-$100/tCO 2 (National Academies of Sciences 2018, Mulligan et al 2020).Regions and countries worldwide are also making notable progress in adopting policy support for the R&D and scaling up of DACCS deployment (Smith et al 2023), including the direct funding supports and tax credit for investment in the U.S. (United States Department of Energy 2021, United States Internal Revenue Service 2021), Europe (European Commission 2021, 2022), Canada (Government of Canada 2021), and the UK (His Majesty's Treasury 2023) and so on.Hence, KSA could also proactively adopt favorable policy and financial support to DACCS and initiate its early deployment within the country.

Table 1 .
The design of central scenarios in this study.