This week’s publication highlights cover a wide range of issues including the evaluation of CDR deployment in Saudi Arabia and other issues pertaining to DAC and enhanced weathering.
Applying Multi-criteria Decision Analysis in the Assessment of Carbon Dioxide Removal Technologies for Saudi Arabia
Abstract
This paper investigates the potential application of various carbon dioxide removal strategies within Saudi Arabia. It evaluates both traditional and innovative carbon dioxide removal solutions using a multi-criteria decision analysis approach. The study defines performance, economic, and environmental criteria, including factors such as technology readiness, CO2 permanence, costs, environmental impacts, and socio-economic co-benefits. Furthermore, it examines the policy and regulatory environment, as well as the feasibility and preparedness for monitoring, reporting, verification, and certification of different carbon dioxide removals. The analysis identifies five key groups of carbon dioxide removals for prioritization in Saudi Arabia: (i) energy-from-waste and biomethane production integrated with carbon capture, utilization, and storage, (ii) direct air capture, (iii) biomass pyrolysis producing biochar, (iv) conventional nature-based solutions, and (v) enhanced weathering. The study suggests that policies in the Kingdom should focus on diverting waste from landfills to ‘energy-from-waste with carbon capture, utilization, and storage’ facilities and on utilizing waste heat from industrial sites for direct air capture networks. By offering this detailed analysis, the paper seeks to provide valuable guidance for policymakers, researchers, and stakeholders in advancing carbon dioxide removal efforts in Saudi Arabia.
Odeh, N. et al. (2025) Applying Multi-criteria Decision Analysis in the Assessment of Carbon Dioxide Removal Technologies for Saudi Arabia 205 (144698) Energy Policy.
Read the full paper here: Applying Multi-criteria Decision Analysis in the Assessment of Carbon Dioxide Removal Technologies for Saudi Arabia I Energy Policy
Deep Uncertainty in Carbon Dioxide Removal Portfolios
Abstract
Deep uncertainty about the costs and resource limits of carbon dioxide removal (CDR) options challenges the design of robust portfolios. To address this, we here introduce the CDR sustainable portfolios with endogenous cost model, a mixed-integer linear optimization model for cost-optimal and time-dependent CDR portfolios including endogenous treatment of technology cost dynamics. We explore future uncertainty in three key dimensions: realisable mitigation potentials, cost dynamics, and resource constraints. Our results demonstrate that afforestation and reforestation, and soil carbon sequestration appear as robust options, deployed regardless of the removals required. Direct air carbon capture and storage emerges as the most deployed technology in 2100 at median value (6.7 GtCO2 yr−1), but with the widest range of possible outcomes (interquartile range from 4 to 8.7 GtCO2 yr−1) depending largely on future renewable energy capacity and annual geological storage injection rates. Bioenergy with CCS deployment remains severely constrained by available land, as the median falls from 1.8 to 0.3 GtCO2 yr−1 in land-constrained scenarios, but gains portfolio share when future energy availability is bounded. Our simulations also reveal that ocean alkalinisation could become a dominant solution in high removal scenarios. Evaluating the performance of portfolios beyond economic costs, we also provide a framework to explore trade-offs across different aspects relevant to planetary boundaries.
Mendez, Q. et al. (2025) Deep Uncertainty in Carbon Dioxide Removal Portfolios. 20 (054013) Environmental Research Letters.
Read the full paper here: Deep Uncertainty in Carbon Dioxide Removal Portfolios I Environmental Research Letters.
Passive Adsorptive Direct Air Capture (PADAC) Using a Nature-Assisted Temperature Swing Process: A Sustainable Solution for Residential CO2 Emissions
Abstract
Numerous regions worldwide experience abundant natural sunlight and significant temperature differentials between night and day. We propose a novel system called Passive Adsorptive Direct Air Capture (PADAC), which leverages a natural temperature gradient to facilitate CO2 adsorption and desorption cycles. Specifically, CO2 is adsorbed during the cooler nighttime temperatures and desorbed during the warmer daytime temperatures. Our conceptual prototype was designed, developed, and tested in Morocco with a single adsorptive-desorptive cycle. To assess its global applicability, we selected several regions worldwide, where our system could be installed and work optimally, characterized by significant temperature fluctuations between day and night. This paper aims to demonstrate proof of concept to validate the feasibility of the PADAC process. The design of a pilot-scale experimental setup is presented, along with supporting experiments in the field that validate the proof of concept. We have experimentally demonstrated that the PADAC system can reach desorption temperatures of up to 93 °C, while its overnight temperature can drop to as low as 13 °C. These temperature ranges obtained by the Nature-assisted Temperature Swing Adsorption (Na-TSA) process, are optimal for the desorption and adsorption processes of most solid adsorbents. We have found that the PADAC achieves an efficiency of approximately 52 % in delivering the required temperature range for desorption. This innovative approach addresses the high energy costs typically associated with DAC by utilizing free thermal energy from natural temperature variations between night and day, with the main purpose of offsetting up to 1 t of CO2 per person per residence.
Filahi, I. et al. (2025) Passive Adsorptive Direct Air Capture (PADAC) Using a Nature-Assisted Temperature Swing Process: A Sustainable Solution for Residential CO2 Emissions. 338 (119925) Energy Conversion and Management.
Read the full paper here: Passive Adsorptive Direct Air Capture (PADAC) Using a Nature-Assisted Temperature Swing Process: A Sustainable Solution for Residential CO2 Emissions I Energy Conversion and Management.
Enhanced Weathering May Benefit from Co-Application with Organic Amendments
Abstract
Enhanced weathering has emerged as a promising natural climate solution that has the potential to remove billions of tons of carbon from the atmosphere if widely adopted in agricultural settings. Despite this potential, few field trials have been published that verify the carbon dioxide removal (CDR) potential of enhanced weathering in croplands and, until now, none had been published in grazing lands. Anthony et al. (2025, https://doi.org/10.1029/2024AV001480) conducted the first trial of enhanced weathering in a California rangeland and showed weathering of ground silicate rocks despite drought conditions in an already dry climate. Co-application of inorganic (silicate rocks) with organic (biochar and compost) amendments revealed not just additive, but synergistic effects whereby organic amendments increased rates of weathering. This is important because field CDR rates were <10% of the theoretical maximum (i.e., the rate if basalt was completely weathered); thus, methods to improve weathering rates will be necessary for this practice to scale in a meaningful way. Multi-carbon pool measurements revealed not only how co-application of soil amendments heightened net carbon benefits, but also how soil amendments complemented each other to produce net benefits for soil carbon, biomass growth, and greenhouse gas emission reductions. Anthony et al. (2025, https://doi.org/10.1029/2024AV001480) produce new insights toward our understanding of enhanced weathering as well as introduce paths for future research concerning combined amendment applications, synergistic mechanisms for carbon storage, and deployment in various agricultural contexts. While questions remain about the fate of weathering products in arid regions, Anthony et al. (2025, https://doi.org/10.1029/2024AV001480) present novel findings on the potential for significant weathering to occur even under suboptimal conditions.
Almaraz, M. (2025) Enhanced Weathering May Benefit from Co-Application with Organic Amendments. 6 (2) Advancing Earth and Space Sciences.
Read the full paper here: Enhanced Weathering May Benefit from Co-Application with Organic Amendments I Advancing Earth and Space Sciences.
Direct Air Capture of CO2 for Solar Fuel Production in Flow
Abstract
Direct air capture is an emerging technology to decrease atmospheric CO2 levels, but it is currently costly and the long-term consequences of CO2 storage are uncertain. An alternative approach is to utilize atmospheric CO2 on-site to produce value-added renewable fuels, but current CO2 utilization technologies predominantly require a concentrated CO2 feed or high temperature. Here we report a gas-phase dual-bed direct air carbon capture and utilization flow reactor that produces syngas (CO + H2) through on-site utilization of air-captured CO2 using light without requiring high temperature or pressure. The reactor consists of a bed of solid silica-amine adsorbent to capture aerobic CO2 and produce CO2-free air; concentrated light is used to release the captured CO2 and convert it to syngas over a bed of a silica/alumina-titania-cobalt bis(terpyridine) molecular–semiconductor photocatalyst. We use the oxidation of depolymerized poly(ethylene terephthalate) plastics as the counter-reaction. We envision this technology to operate in a diurnal fashion where CO2 is captured during night-time and converted to syngas under concentrated sunlight during the day.
Kar, S. et al. (2025) Direct Air Capture of C02 for Solar Fuel Production in Flow 10 Nature Energy.
Read the full paper here: Direct Air Capture of C02 for Solar Fuel Production in Flow I Nature Energy.