The publication highlights of this week cover a wide range of issues related to direct air capture, afforestation and biochar.
Advancing Geothermal Energy Utilization Opportunities: Potential and Strategies for Integrating Direct Air Capture
Abstract
Geothermal energy has been utilized for centuries. Prior to the industrial revolution, geothermal surface expressions were healing destinations in regions of Indigenous America, and geothermal energy was used to heat baths across the Roman empire and throughout Japan. Today, geothermal energy is harnessed for direct use in some industrial applications requiring low-grade heat as well as district heating systems, and for low-carbon electricity production, making up over 13 GW of worldwide electricity production. In the U.S., new legislation introduced incentives to promote geothermal energy as a baseload renewable electricity source. However, geothermal energy also has potential for CO2 abatement beyond electricity generation. For example, low temperature geothermal resources can be used directly for residential heating systems, industrial processes or to power direct air capture (DAC) systems. This study explores the potential of geothermal resources to meet the thermal and electrical demands of DAC systems through the development of a geothermal-DAC evaluation framework. The framework examines configurations where binary geothermal power plants and DAC units are engineered to optimize geothermal resource use. These configurations are evaluated based on their CO2 abatement potential, achieved by displacing carbon-intensive grid electricity and removing atmospheric CO2. The framework was applied to two hypothetical geothermal resources, representing low (86 °C) and high (225 °C) temperature regimes for binary geothermal power plants, considering various organic Rankine cycle (ORC) working fluids. It was also tested on the Raft River binary geothermal combined cycle power plant. Results show that integrating geothermal energy with DAC systems improves CO2 abatement potential compared to using geothermal resources solely for electricity. Improvements range from 5–757%, depending on the resource and configuration. Technoeconomic evaluations of each configuration determined the levelized cost of energy delivered to the DAC system (LCOEDAC), ranging from $101–8579 per tCO2. The geothermal-DAC evaluation framework highlights strategic decisions and constraints for integrating geothermal resources with DAC to maximize grid electricity production and CO2 abatement.
Pisciotta, M. et al. (2025) Advancing Geothermal Energy Utilization Opportunities: Potential and Strategies for Integrating Direct Air Capture. Energy & Environmental Science.
Read the full paper here: Advancing Geothermal Energy Utilization Opportunities: Potential and Strategies for Integrating Direct Air Capture I Energy & Environmental Science.
Effects of Planting Density on the Performance of Reforestation and Afforestation Plantings in Temperate and Boreal Forests: A Systematic Review
Abstract
Rising demand for forest products, climate mitigation, and ecosystem restoration has driven international pledges to expand forests, mostly on abandoned agricultural lands and areas of low conservation value. According to a recent survey among restoration practitioners across Europe, optimal planting designs and densities are key questions for reforestation efforts. We aimed to determine how planting density affects the performance of reforestation/afforestation plantings, how these effects vary by climate, species types, and stand age, and whether there are planting density thresholds triggering significant performance shifts. Using both descriptive statistics and meta-analyses, we systematically reviewed 120 studies from temperate and boreal forests to analyze planting density effects on the performance of tree plantings. Higher planting densities increase overall yield but also mortality. Negative effects on individual stem growth occur mainly at early ages, while negative impacts on individual stem growth and survival intensify over time. Benefits on stand yield are observed at both young and old ages, and there are no clear differences in the density response of shade-tolerant and shade-intolerant species. On average, an increase in planting density of 71 and 118% is needed to cause significant impacts on performance at stand-level and individual-tree level, respectively, though effects vary across studies and variables. Observed patterns aligned with expectations, as higher planting densities increased mortality and lowered individual growth while promoting overall yields. However, the timing and thresholds of positive and negative effects vary, presenting opportunities to optimize management through variable densities over time.
Kremer, K. et al. (2025) Effects of Planting Density on the Performance of Reforestation and Afforestation Plantings in Temperate and Boreal Forests: A Systematic Review. Restoration Ecology.
Read the full paper here: Effects of Planting Density on the Performance of Reforestation and Afforestation Plantings in Temperate and Boreal Forests: A Systematic Review I Restoration Ecology.
Quantitative Assessment of the Potential Benefits of Global Afforestation on Ecosystem Productivity
Abstract
Accurately estimating the contribution of afforestation/deforestation to gross primary productivity (GPP) of an ecosystem is necessary to develop future afforestation policies. However, there is currently a lack of quantitative assessments of the potential consequences of afforestation and deforestation on GPP at a global scale. In this study, we used a 30 m high-resolution forest raster map and a satellite-driven GPP product to assess GPP differences under various afforestation/deforestation scenarios, using spatial rather than temporal comparisons. Our results showed that (1) the simultaneous occurrence of high-intensity afforestation and deforestation was extremely low globally (4.64%). Under this hypothetical scenario, the potential GPP of afforestation could reach 734.13 g C m−2 yr−1, significantly higher than that in the other scenarios. While the percentage of concurrent medium- to low-intensity afforestation and deforestation was up to 41.37%, the potential value of afforestation to promote GPP increase was only 219.56 g C m−2 yr−1. (2) The potential of afforestation to boost GPP varied significantly across space and time. Proximity to equatorial forests, such as evergreen broad-leaved forests, generally facilitate GPP accumulation. However, as latitudinal zonality increased, the fixed GPP potential of high-latitude coniferous forests decreased significantly. Summer (particularly June) showed the highest potential for afforestation to enhance GPP, more than twice as much as in the other seasons, and this pattern was consistent globally. (3) Afforestation costs vary substantially depending on forest type and cover. Afforestation in rainforest areas with a better water-heat balance often requires a higher GPP to achieve the desired effect. Low-density forests dominated by temperate or cold zones yield significantly lower GPP benefits than afforestation in tropical rainforests. This study quantifies the potential impact of afforestation on GPP for the first time and provides guidelines for future afforestation planning across various regions.
Ren, J. et al. (2025) Quantitative Assessment of the Potential Benefits of Global Afforestation on Ecosystem Productivity. 20 (034055) Environmental Research Letters.
Read the full paper here: Quantitative Assessment of the Potential Benefits of Global Afforestation on Ecosystem Productivity I Environmental Research Letters.
Characterizing the Effects of Policy Instruments on Cost and Deployment Trajectories of Direct Air Capture in the U.S. Energy System
Abstract
Capturing and sequestering carbon dioxide (CO2) from the atmosphere via large-scale direct air capture (DAC) deployment is critical for achieving net-zero emissions. Large-scale DAC deployment, though, will require significant cost reductions in part through policy and investment support. This study evaluates the impact of policy interventions on DAC cost reduction by integrating energy system optimization and learning curve models. We examine how three policy instruments—incremental deployment, accelerated deployment, and R&D-driven innovation—impact DAC learning investment, which is the total investment required until the technology achieves cost parity with conventional alternatives or target cost. Our findings show that while incremental deployment demands significant learning investment, R&D-driven innovation is considerably cheaper at cost reduction. Under a baseline 8% learning rate, incremental deployment may require up to $998 billion to reduce costs from $1,154 to $400/tCO2, while accelerated deployment support could save approximately $7 billion on that investment. In contrast, R&D support achieves equivalent cost reductions at less than half the investment of incremental deployment. However, the effectiveness of R&D intervention varies with learning rates and R&D breakthroughs. R&D yields net benefits in all cases except at extremely low breakthroughs (5%) and very high learning rates (20%), where they are slightly more expensive. For learning rates below 20%, R&D provides net benefits even at minimal breakthroughs. These findings underscore the need for comprehensive public policy strategies that balance near-term deployment incentives with long-term innovation investments if we are to ensure DACS becomes a viable technology for mitigating climate change.
Kanyako, F. and Craig, M. (2025) Characterizing the Effects of Policy Instruments on Cost and Deployment Trajectories of Direct Air Capture in the U.S. Energy System. 13 (6) Earth’s Future.
Read the full paper here: Characterizing the Effects of Policy Instruments on Cost and Deployment Trajectories of Direct Air Capture in the U.S. Energy System I Earth’s Future.
Advancing Sustainable Concrete Using Biochar: Experimental and Modelling Study for Mechanical Strength Evaluation
Abstract
Innovative and creative solutions are needed to reduce the substantial carbon footprint of the concrete industry using low-carbon materials. Biochar has been recognised as an environmentally efficient material for concrete production. Also, it is required to build interpretable predictive models to advance modelling-based mix design optimisation. This study uses biochar as a cement substitute in concrete and assesses the mechanical strength using lab tests followed by predictive modelling approaches. Two types of biochar derived from olive pits and wood were used in 2.5 and 5 wt.% of cement. Cubes, cylinders, and beams were cast to test biochar concrete’s compressive, tensile, and flexural strength. The test data were used to develop and validate prediction models for the compressive strength (CS) using linear regression and gene expression programming (GEP) techniques. Moreover, SHapley Additive exPlanation (SHAP) analysis was performed to evaluate the influence of parameters on the CS. The results showed that olive pit biochar was more effective in enhancing the concrete strength than wood biochar due to the reduced particle size. The optimal replacement levels for olive pit biochar were 2.5 wt.% for the CS and 5 wt.% for the split tensile and flexural strength. The GEP model effectively captured the non-linear behaviour of biochar concrete and was more accurate than the linear regression model for the CS. The approach adopted in this study can be used to optimise mix design formulations for biochar concrete. These findings highlight the potential of biochar as a sustainable and effective cement substitute, contributing to the development of greener concrete with improved mechanical performance. Integrating biochar into concrete production can significantly lower the industry’s carbon footprint, promoting environmentally responsible construction practices while maintaining structural integrity.
Ahmad, W. et al. (2025) Advancing Sustainable Concrete Using Biochar: Experimental and Modelling Study for Mechanical Strength Evaluation 17(6) Sustainability.
Read the full paper here: Advancing Sustainable Concrete Using Biochar: Experimental and Modelling Study for Mechanical Strength Evaluation I Sustainability.