This week’s publication highlights cover various issues related to direct air capture, biochar, afforestation, enhanced weathering and ocean CDR.
Polymers in Direct Air Capture: A Mini Review
Abstract
The urgent need to mitigate climate change has intensified interest in direct air capture (DAC) technology, which targets extracting carbon dioxide (CO2) directly from the atmosphere. Among the various sorbents used in DAC, polymers have emerged as a promising solution, either as active sorbents or as structural supports for active DAC materials, due to their customizable properties, scalability and low cost. This mini-review investigates the latest trends in polymer-based materials for DAC and identifies critical research gaps, such as the need for thorough lifecycle assessments and in-depth studies on the degradation of polymeric materials. It also outlines future directions, emphasizing the importance of developing cost-effective, scalable and durable polymers that can perform efficiently across diverse climatic conditions, including the unique challenges presented by cold weather regions abundant in renewable energy. This mini-review aims to inform ongoing efforts in the design and utilization of polymeric sorbents, providing insights that could guide the development of economically viable and environmentally sustainable DAC technologies.
Behbahani, H. and Green, M. (2025) Polymers in Direct Air Capture: A Mini Review. Polymer International.
Read the full paper here: Polymers in Direct Air Capture: A Mini Review I Polymer International.
The H/C Molar Ratio and Its Potential Pitfalls for Determining Biochar’s Permanence
Abstract
Biochar carbon removal (BCR) is widely recognized as a globally feasible technique for removing CO2 from the atmosphere and storing carbon in a stable form within the environment. The hydrogen-to-carbon (H/C) molar ratio serves as the primary proxy for classifying biochar into different quality categories and is a key parameter in decay models used to estimate its long-term stability. In the context of climate credit systems that rely on biochar for carbon sequestration, an accurate assessment of biochar’s carbon pools and permanence is crucial. The results of this study confirm that the H/C molar ratio is a robust bulk geochemical proxy for biochar carbonization. However, its use as a standalone benchmark for biochar permanence should be approached with caution. To ensure a more comprehensive assessment, the H/C molar ratio should be combined with the random reflectance (Ro) method, which provides spatially resolved insights into the degree of carbonization within a biochar sample. Relying exclusively on a single bulk H/C molar ratio may, in some cases, lead to inaccurate determinations of biochar’s carbon storage security. Such limitations could undermine the credibility of climate credit systems that depend on biochar for permanent carbon dioxide removal. Therefore, integrating both H/C ratio and Ro analysis is essential for accurately evaluating biochar stability and its long-term carbon sequestration potential.
Petersen, H. and Sanei, H. (2025) The H/C Molar Ratio and Its Potential Pitfalls for Determining Biochar’s Permanence 17 (6) GCB Bioenergy.
Read the full paper here: The H/C Molar Ratio and Its Potential Pitfalls for Determining Biochar’s Permanence I GCB Bioenergy.
Assessing the Climate Benefits of Afforestation in the Canadian Northern Boreal and Southern Arctic
Abstract
Afforestation greatly influences several earth system processes, making it essential to understand these effects to accurately assess its potential for climate change mitigation. Although our understanding of forest-climate system interactions has improved, significant knowledge gaps remain, preventing definitive assessments of afforestation’s net climate benefits. In this review, focusing on the Canadian northern boreal and southern arctic, we identify these gaps and synthesize existing knowledge. The review highlights regional realities, Earth’s climatic history, uncertainties in biogeochemical (BGC) and biogeophysical (BGP) changes following afforestation, and limitations in current assessment methodologies, emphasizing the need to reconcile these uncertainties before drawing firm conclusions about the climate benefits of afforestation. Finally, we propose an assessment framework which considers multiple forcing components, temporal analysis, future climatic contexts, and implementation details. We hope that the research gaps and assessment framework discussed in this review inform afforestation policy in Canada and other circumpolar nations.
Dsouza, K. et al. (2025) Assessing the Climate Benefits of Afforestation in the Canadian Northern Boreal and Southern Arctic 16 (1964) Nature Communications.
Read the full paper here: Assessing the Climate Benefits of Afforestation in the Canadian Northern Boreal and Southern Arctic I Nature Communications.
Soil Cation Storage is a Key Control on the Carbon Removal Dynamics of Enhanced Weathering
Abstract
Significant interest and resources are currently being channeled into techniques for durable carbon dioxide removal (CDR) from Earth’s atmosphere. A particular class of these approaches — referred to as enhanced weathering — seeks to modify the surface alkalinity budget to store CO2 as dissolved inorganic carbon species. Here, we use a reaction-transport model designed to simulate enhanced weathering in managed lands to evaluate the throughput and storage timescales of anthropogenic alkalinity in agricultural soils in the coterminous U.S. We find that lag times between alkalinity modification and carbon removal can span from years to many decades depending on region. Background soil cation exchange capacity, agronomic target pH, and fluid infiltration all impact the timescales of CDR relative to the timing of alkalinity input, suggesting there is scope for optimization of alkalinity transport through variation in land management practice. However, shifting practices to reduce lag times may decrease total CDR from weathering and lead to non-optimal nutrient use efficiencies and soil nitrous oxide (N2O) fluxes. Our results indicate that there may be a large temporal disconnect between deployment of enhanced weathering and climate-relevant CDR, with important implications for monitoring, reporting, and verifying carbon removal through enhanced weathering.
Kanzaki, Y. et al. (2025) Soil Cation Storage is a Key Control on the Carbon Removal Dynamics of Enhanced Weathering. Environmental Research Letters.
Read the full paper here: Soil Cation Storage is a Key Control on the Carbon Removal Dynamics of Enhanced Weathering. Environmental Research Letters.
Hidden Acidification Challenges in Electrochemical Ocean Decarbonization
Abstract
Electrochemical direct ocean capture (eDOC) is an emerging methodology for carbon capture. However, our comprehensive thermodynamic and initial kinetic analyses reveal critical challenges inherent in the electrochemical pH-swing process. Specifically, the mixture of treated ocean water post-eDOC fails to achieve complete neutralization, resulting in unintended ocean acidification. This issue stems from the disproportionate impacts of acidification and alkalinization on dissolved inorganic carbon dynamics and hydroxide precipitation. Our findings underscore the necessity for innovative process designs that effectively balance pH shifts and manage precipitate formation, thereby ensuring the environmental sustainability of eDOC technologies.
Zhang, W. et al. (2025) Hidden Acidification Challenges in Electrochemical Ocean Decarbonization. 10 (XXX) ACS Energy Letters.
Read the full paper here: Hidden Acidification Challenges in Electrochemical Ocean Decarbonization I ACS Energy Letters