The required emissions trajectory is far steeper than the reductions expected from national climate pledges. Full implementation of nationally determined contributions, or NDCs, would lower emissions by only 5–8% from 2025 levels by 2030 and by 11–15% by 2035, according to the report. The IIASA-led Scenario Compass Initiative supplied the scenario data used in the analysis. These figures are policy-pathway estimates rather than observed reductions: they describe what would be required under the lowest-possible-overshoot pathway and how far current commitments fall short. The report also warns that the earlier starting point has deteriorated because of changes in participation in the Paris Agreement and revised estimates of historical emissions.

Current policies point toward particularly high warming, while stronger delivery of existing NDCs produces only a limited improvement. If current policies continue, warming could reach 2.8°C this century and continue increasing after 2100, compared with 2.6°C if all NDCs are delivered and comparable efforts continue. Even the achievement of additional net-zero targets would limit projected warming to 2.1°C. These results are worse than the projections in the previous year’s report, and the report’s authors state that new NDCs have made a negligible difference to that deterioration. They also calculate that every five years of carbon dioxide emissions at current levels adds approximately 0.1°C to peak warming.

The report’s lowest-possible-overshoot pathway is not simply a continuation of present trends. It requires rapid cuts across the economy, sustained implementation of climate policies and major changes in electricity production. By 2035, electricity generated by solar and wind would need to be at least three times its current level, while carbon dioxide emissions from energy systems would need to decline by at least 35%. Globally, coal-fired electricity generation would have to be effectively phased out by 2040, and solar and wind generation would need to grow at least five-and-a-half-fold. The scenario also calls for a transition away from fossil fuels in energy systems, reductions in non-carbon-dioxide greenhouse gas emissions, and measures to halt and reverse deforestation and forest degradation.

Some elements of the first Global Stocktake under the Paris Agreement are already showing progress. Countries agreed to triple renewable energy capacity, double the annual rate of energy-efficiency improvement by 2030, transition away from fossil fuels in energy systems, reduce non-CO2 emissions, and halt and reverse deforestation and forest degradation. Since the Paris Agreement was adopted, global renewable electricity capacity has expanded three times faster than anticipated. Yet the report finds insufficient progress in other areas. Sophie Boehm of the World Resources Institute said that renewables are already a game-changing element of climate action and the only area found to be on track for 2030, but their growth alone cannot close the emissions gap.

Fossil-fuel use remains a central obstacle. According to Louise Jeffery of the New Climate Institute, coal and oil consumption grew much more slowly over the past decade than expected in 2015, while gas use broadly followed the trajectory previously projected. Jeffery said this progress still requires a U-turn across all fossil fuels, with the most rapid change needed in electricity supply. The contrast illustrates why additions of renewable capacity are not by themselves sufficient: generation must also displace fossil-fuel sources at a pace capable of producing the deep emissions reductions required by the report’s pathway. Setu Pelz of IIASA said meeting the minimum effort levels for minimizing 1.5°C overshoot will require cooperation that reflects differences in responsibility and capability.

The report also finds growing evidence that climate policies can reduce emissions in developed and developing countries and can produce structural changes rather than merely short-term adjustments. Its review draws on more than 220 evaluations covering different sectors and national contexts. Evaluated electricity-sector policies were associated with average emissions reductions of 9%, while economic instruments such as carbon taxes and cap-and-trade schemes produced reductions of 5–13% over the periods examined. These outcomes are averages from a varied policy literature, not uniform effects, and the report cautions that successful interventions remain concentrated in particular countries, sectors and time periods. Their wider value depends on replication, extension and sustained implementation.

Even the lowest-possible-overshoot pathway would require removing and permanently storing roughly 320 gigatonnes of carbon dioxide over the century, an amount equivalent to about eight years of global CO2 emissions in 2024. The report describes the feasibility of this requirement as uncertain because of socioeconomic and technological challenges. Carbon dioxide removal therefore cannot substitute for near-term emissions cuts; the scenario depends on both sharply reducing emissions and deploying large-scale removal and permanent storage later in the century. Keywan Riahi of IIASA said the policy challenge is to scale up proven emissions reductions through fast, deep and sustained action while limiting reliance on large-scale carbon dioxide removal.

IIASA researchers involved in the report characterized the remaining window as narrow but not closed. Shonali Pachauri, who coauthored Chapter 1, said every additional fraction of a degree and every additional year above 1.5°C increases climate risks and narrows the options for a safe future. Joeri Rogelj, who served as a lead author for Chapter 4, emphasized the gap between the emissions reductions needed and those implied by current policies and national commitments. The report’s central conclusion is that the Paris Agreement goals remain reachable, but only with fast, deep and sustained emissions reductions and greater delivery of the first Global Stocktake commitments. The modeled return to 1.5°C remains uncertain, and the report’s low-overshoot pathway is designed to minimize the peak and duration of warming rather than guarantee a specific temperature in 2100.

Subject of Research: UN scenario analysis of emissions cuts, technology transitions and policy measures needed to limit and reverse global warming above 1.5°C.

Article Title: New UN report lays out emissions cuts needed for return to 1.5°C

Article References: New UN report lays out emissions cuts needed for return to 1.5°C. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: 1.5°C warming, greenhouse gas emissions, UNEP Emissions Gap Report, climate policy, nationally determined contributions, renewable electricity, fossil fuels, carbon dioxide removal, Scenario Compass Initiative, global warming, report, lays

Forests created through afforestation, the establishment of new forests, and reforestation, the restoration of lost forests, have already helped expand global forest cover by more than 300 million hectares. Over the past decade, these activities have been estimated to remove around 2.2 billion tonnes of carbon dioxide from the atmosphere each year, roughly equivalent to annual fossil-fuel carbon dioxide emissions across the European Union. These estimates describe the scale of forest-based removal to date, but they also underscore why the durability and broader feasibility of forest expansion matter for climate planning.

Wenkai Bao, an LMU geographer who led the study, and colleagues brought together evidence from real-world case studies with machine-learning analysis of extensive global datasets. Their global assessment compared the estimated carbon dioxide removal potential of afforestation and reforestation with social, institutional and economic conditions affecting those efforts. The analysis, published in the peer-reviewed journal One Earth, identifies poverty, food insecurity, insecure land rights and weak governance as major worldwide constraints, while limited forestry infrastructure and a lack of support from local stakeholders make it harder to establish and maintain forests over time. The research assesses potential and barriers rather than reporting outcomes from a new global tree-planting trial.

The geographic pattern differs substantially. The study finds fewer social and institutional barriers to afforestation and reforestation in Europe and China, while barriers are greater across Africa and in India and Brazil. This contrast does not establish that projects in lower-barrier areas will necessarily succeed or that higher-barrier regions lack ecological potential. Instead, it shows that estimated removal potential cannot be separated from the conditions in which trees are planted, land is managed and forests are maintained. Bao said credible climate strategies must pair afforestation and reforestation with efforts to strengthen livelihoods, rights and institutions, especially because much of the estimated potential lies in tropical countries facing these constraints. Co-author Julia Pongratz said reaching greenhouse gas neutrality will require at least tripling the global amount of carbon dioxide removed from the atmosphere by 2050, with additional forest cover playing a dominant role as technological removal options are scaled up. She cautioned that planting forests can complement, but not replace, broader climate action and sustainable development.

Subject of Research: Global socioeconomic barriers to afforestation- and reforestation-based carbon dioxide removal

Article Title: Climate protection: Where reforestation bears social risks

Article References: Climate protection: Where reforestation bears social risks. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: afforestation, reforestation, carbon dioxide removal, climate change, land rights, food security, poverty, governance, forestry infrastructure, sustainable development, Climate, protection

IAMs are the mapmakers of climate policy. They weave together energy systems, economics, technology, land use and emissions into quantitative pictures of the coming decades, allowing analysts to compare long-term decarbonization pathways and their trade-offs. When the IPCC’s Sixth Assessment Report presents scenarios compatible with limiting warming to 1.5 or 2 degrees Celsius, those pathways overwhelmingly come from IAMs. The problem, the authors contend, is that almost every scenario in that report assumes gross domestic product keeps rising until 2100, and that assumption cascades through everything the models produce.

The coupling between growth and environmental harm is the crux of the issue. Historically, economic growth has been tightly linked to rising greenhouse gas emissions, resource extraction and ecological degradation. The concept of green growth, championed by institutions like the World Bank, the OECD and the United Nations Environment Programme, holds that technological improvement can decouple GDP from environmental impact, allowing prosperity to rise while emissions fall. But the empirical record is sobering. Observed decoupling rates remain far too slow to deliver the required emissions cuts, and the only periods of declining absolute resource use have coincided with economic recessions. A widely cited review by Hickel and Kallis concluded that green growth theory lacks empirical support, and that sustained global green growth is incompatible with the 1.5 degrees Celsius carbon budget, fitting within the 2 degrees budget only with near-zero economic growth.

When models assume growth must continue regardless, they are forced into increasingly heroic compensating assumptions. Because GDP and energy demand rise together in these frameworks, the models lean on technology to slash emissions intensity instead. That means unprecedented deployment of negative emissions technologies, such as carbon dioxide removal, alongside extraordinary gains in energy efficiency. The numbers are stark: IPCC-aligned pathways assume an average of 6 gigatonnes of carbon dioxide removed per year by 2050 and 13 gigatonnes per year by 2100. Current intentional removal, excluding forestry, stands at roughly 2 megatonnes per year, primarily from biochar, bioenergy with carbon capture, enhanced weathering and direct air capture. Closing that gap would require growth rates several orders of magnitude beyond anything demonstrated, which experts have described as extremely challenging. If that deployment fails, the planet could be locked into a high-warming trajectory.

The authors dissect how this growth bias is embedded in model architecture. In the MESSAGE model, GDP is an exogenous input, typically calibrated to the shared socioeconomic pathways, all of which assume GDP increases through 2100. In the WITCH model, GDP is computed endogenously, but its key driver, total factor productivity, is calibrated to match those same external projections. Either way, growth is baked in. More fundamentally, the utility functions that IAMs optimize treat welfare as a monotonically increasing function of per capita consumption, so the models are structurally programmed to maximize consumption subject to emissions constraints. Following the classic IPAT framework, where environmental impact depends on population, affluence and technology, they hold population fixed, assume affluence rises, and leave technology to do all the work.

That structure produces two troubling consequences. First, it prioritizes aggregate economic output over equity and wellbeing, and technological fixes over sociopolitical ones. Second, it can lead to ethically fraught conclusions. Because population appears as a demand driver, some studies propose climate mitigation through incentivizing lower birth rates, adjusting the population term in the equation rather than questioning affluence or its distribution. The authors argue that making the math work by shrinking the number of people, while assuming perpetual growth and unequal resource distribution, should prompt serious introspection rather than acceptance.

The empirical case for rethinking the wellbeing-growth link is substantial. GDP correlates with life expectancy, health and subjective wellbeing only up to a point, beyond which returns become marginal. Social and political factors, including income distribution, democratic participation and high-quality public services, mediate that relationship and can matter more than consumption itself. In some high-income countries, wellbeing can actually increase when consumption decreases, a finding that aggregate models simply cannot capture. Meanwhile, growth remains strongly correlated with ecological degradation that directly harms human welfare, even when carbon emissions are accounted for.

Alternatives exist, and the paper surveys them. Degrowth frameworks reject the hegemony of economic growth as an organizing principle, prioritizing the downscaling of production and consumption and the redistribution of resources to improve wellbeing, social justice and environmental sustainability. Notably, degrowth does not require depopulation or reduced quality of life; its focus is not necessarily less, but different. Sufficiency approaches aim to improve wellbeing directly by prioritizing consumption that enhances it and avoiding the rest, recognizing that wellbeing gains stagnate beyond a certain level of energy and material use. Both draw support from movements such as Buen Vivir, commons-based communities and the global justice movement, and both are inherently pluralist, favoring socially and culturally appropriate solutions over a single global prescription.

The authors propose a concrete reframing: models should optimize for service provision and the material requirements of decent living standards, rather than economic proxies. Research by Rao and Min and by Millward-Hopkins and colleagues offers quantifiable benchmarks, including roughly 2,000 to 2,150 kilocalories of food per person per day, 60 square meters of floor space per household, 50 liters of water per person daily, 4 kilograms of new clothing per year, and 5,000 to 15,000 passenger-kilometers of mobility annually. Strikingly, meeting these standards for everyone on Earth would require substantially less per capita energy than most of the world currently uses, though inequality can double the energy needed to secure universal decent living. The authors argue these material wellbeing indicators should sit directly in IAM objective functions, with economic growth treated as a model output rather than an input or constraint, and with scenarios still compared across both growth and post-growth assumptions.

Early evidence suggests the shift is tractable. Li and colleagues modified the MESSAGE model by making GDP endogenous and replacing the logarithmic utility function with a non-monotonic one that peaks at a specified consumption level. Applied to Australia, the modified model showed that reducing consumption lowers greenhouse gas emissions, infrastructure requirements and dependence on negative emissions technologies. The broader implication is that the solution space for climate policy is far larger than current models admit. A robust transition pathway, the authors suggest, requires limited technological optimism and support across models with different foundational assumptions. Without widening the lens, the maps that guide policymakers remain incomplete, and humanity may be pursuing the most technologically perilous route to safety while feasible alternatives go unexplored.

Subject of Research: The role of perpetual economic growth assumptions in integrated assessment models and their effect on climate mitigation pathways

Article Title: Structural green growth assumptions in energy system models obscure alternative transition strategies

Article References: Kamana-Williams, B., & Grubert, E. (2026). Structural green growth assumptions in energy system models obscure alternative transition strategies. Frontiers in Energy Research, 14, Article 1984182. https://doi.org/10.3389/fenrg.2026.1984182

Image Credits: AI Generated

DOI: 10.3389/fenrg.2026.1984182

Keywords: integrated assessment models, climate change mitigation, economic growth, degrowth, green growth, GDP, decent living standards, negative emissions, carbon dioxide removal, IPCC, sufficiency, energy system modeling

The research, led by Keju An and colleagues at the National Laboratory of the Rockies in Golden, Colorado, tackles a stubborn computational bottleneck. Detailed models of adsorption systems—devices where solid sorbent materials grab CO2 molecules from air and then release them when heated and placed under vacuum—are so computationally expensive that simulating a full year of hour-by-hour operation was previously impractical. Without year-long simulations, engineers could not properly explore how machines should behave when weather and grid conditions change around them.

The team’s solution was a physics-informed reduced-order model: a stripped-down but physically faithful mathematical description of a temperature-vacuum swing adsorption (TVSA) cycle, the six-stage process of vacuum extraction, heating, desorption, cooling, pressurization, and adsorption. Crucially, the model retains the phenomena that matter most. It tracks CO2 and water co-adsorption on the sorbent, uses a two-pool formulation in which some CO2 binds quickly to accessible sites while a slower pool represents stubbornly retained molecules, and captures incomplete regeneration—the fact that each cycle never fully clears the sorbent, leaving residual loading that carries over as a memory into the next cycle.

That cycle-to-cycle memory is the heart of the study’s argument. Because the sorbent’s state at the start of each cycle depends on everything that happened before, performance cannot be predicted from any single steady-state snapshot. The loading states act as memory variables that determine the working capacity available in the next cycle, the humidity-dependent adsorption behavior, and the energy required for regeneration. The model tracks six coupled states—fast and slow CO2 pools, free and bound water, gas-phase CO2 concentration, and bed temperature—propagating them forward step by step through the year.

To make the framework fast enough for serious optimization work, the researchers generated roughly 120,000 cycle-resolved simulations using Latin hypercube sampling across environmental conditions, operating strategies, system designs, and initial sorbent states. Each simulated cycle recorded its ambient conditions, control settings, internal sorbent states, and resulting performance. This dataset then trained a compact neural network—a single hidden layer of 39 neurons—that reproduces the physics model’s state transitions at a tiny fraction of the computational cost, creating a surrogate fast enough to embed inside a model predictive control framework.

Before trusting the surrogate, the team benchmarked the physics model against published experimental data from Sendi and colleagues. Across twelve benchmark cases spanning typical temperature and humidity conditions, the reduced-order model reproduced productivity with a mean absolute percentage error of 10.2 percent and electricity demand with an error of 11.4 percent. Deviations grew largest under extreme conditions—high temperature with low humidity, or very cold conditions—reflecting the simplifications inherent in a lumped, zero-dimensional formulation. But the model faithfully captured the direction and relative sensitivity of performance to environmental changes, which matters more for large-scale screening than exact point accuracy.

Sensitivity analysis revealed a starkly asymmetric performance landscape. Regeneration temperature dominated everything: raising it from 70 to 130 degrees Celsius cut annual productivity by roughly 10 tonnes of CO2 per cubic meter of bed while adding 0.7 to 0.8 megawatt-hours of electricity demand per tonne captured—a punishing double penalty from hotter, slower cycles. Humidity was the second most influential factor for energy, with relative humidity climbing from 0.1 to 0.9 adding roughly 0.5 megawatt-hours per tonne, a direct consequence of water co-adsorbing alongside CO2 and demanding extra thermal energy during regeneration.

The real payoff came when the neural-network surrogate was handed to the optimization controller and run against hourly 2025 weather, electricity price, and grid carbon intensity data for two contrasting American locations: humid Atoka, Texas and dry, cooler Madison, Wyoming. A baseline machine running fixed settings completed about 1,094 cycles per year. The adaptive controller pushed that to roughly 1,449 cycles in Atoka and 1,379 in Madison by shifting energy-hungry regeneration steps into hours when electricity was cheap and clean, and exploiting favorable humidity windows for capture.

The results were striking. In Atoka, electricity demand fell 18.8 percent while annual CO2 productivity rose 25.5 percent. In Madison, energy dropped 8.9 percent and productivity climbed 22.4 percent. The most dramatic gains appeared in carbon-adjusted net productivity—capture minus the emissions embedded in the electricity consumed—which nearly doubled at both sites, rising 95.2 percent in Texas and 94.4 percent in Wyoming. Notably, the economics did not always align with the climate math: electricity cost fell slightly in Atoka but rose 3.7 percent in Madison, showing that carbon-aware control sometimes accepts higher operating costs to harvest cleaner power.

The authors are careful about scope. Their model is a control-oriented screening tool, not a plant-specific predictor, and because the surrogate learns from the physics model, its uncertainties propagate into the optimization results—meaning the reported gains are relative, model-based estimates rather than guarantees. Still, the framework offers something the field has lacked: a scalable path from adsorption physics through fast dynamic simulation to real-world control, demonstrating that the biggest untapped efficiency reserve in direct air capture may not be new materials or bigger machines, but smarter timing.

Subject of Research: Dynamic modeling and neural-network-based optimization of solid-sorbent direct air capture systems under varying weather and electricity conditions

Article Title: Cycle-resolved dynamic modeling of atmospheric CO2 separation systems under time-varying ambient and electricity conditions

Article References: An, K., Wald, D., Chen, K., & King, R. (2026). Cycle-resolved dynamic modeling of atmospheric CO2 separation systems under time-varying ambient and electricity conditions. Frontiers in Environmental Engineering, 5, Article 1881554. https://doi.org/10.3389/fenve.2026.1881554

Image Credits: AI Generated

DOI: 10.3389/fenve.2026.1881554

Keywords: direct air capture, carbon dioxide removal, temperature-vacuum swing adsorption, reduced-order model, neural network surrogate, model predictive control, humidity, electricity carbon intensity, energy optimization, solid sorbents, climate engineering, Cycle-resolved

The new report, published in BMC Pediatrics, describes a retrospective single-center case series of seven children with pediatric acute respiratory distress syndrome, or PARDS, who also had acute kidney injury. In each case, the clinicians integrated extracorporeal carbon dioxide removal, known as ECCO₂R, into a CRRT circuit that had already been indicated for kidney support. Rather than adding a second large-bore extracorporeal circuit dedicated solely to lung support, the team adapted the existing blood purification circuit so that it could also strip carbon dioxide from the bloodstream. The study was retrospectively registered in the German Clinical Trials Register as DRKS00038799.

The physiological logic behind the technique is straightforward but demanding in practice. ECCO₂R works by passing blood through a gas exchanger, essentially an artificial membrane lung, where a controlled flow of oxygen sweeps carbon dioxide across the membrane and out of the blood. The removed CO₂ is then vented away, and the blood returns to the patient with a lower carbon dioxide tension. Because carbon dioxide diffuses through membranes far more readily than oxygen does, meaningful CO₂ clearance can be achieved at blood flows far lower than those required for full extracorporeal membrane oxygenation, or ECMO. In adults, this has made ECCO₂R attractive as a way to permit ultra-lung-protective ventilation, in which tidal volumes and airway pressures are driven down to minimize ventilator-induced lung injury while the artificial circuit takes over the burden of CO₂ elimination.

In children, however, the technique has remained largely unexplored territory. Pediatric patients have smaller blood volumes, lower cardiac outputs, and narrower vascular access, all of which complicate the extracorporeal circuits designed primarily for adults. The Freiburg team’s insight was that children who need both lung support and kidney support could, in principle, have both delivered through a single circuit. CRRT machines already circulate blood continuously through an extracorporeal loop; adding a gas exchanger in that loop converts the circuit into a dual-purpose organ support system without the need for additional large-bore cannulation.

To assess how this played out in practice, the researchers analyzed the first treatment episode for each of seven patients treated between November 2023 and November 2025, restricting the principal analysis to one episode per patient to avoid the statistical problems that arise when repeated observations from the same child are treated as independent. The children had a median age of 12 years, with an interquartile range of 6 to 14 years. ECCO₂R was delivered at a median blood flow of 270 milliliters per minute, with an interquartile range of 100 to 300 milliliters per minute. That flow corresponds to roughly 9 percent of the estimated cardiac output, with an interquartile range of 6 to 20 percent, a strikingly modest fraction compared with the much higher flows typical of ECMO.

The physiological results, analyzed with Friedman tests for longitudinal change, showed statistically significant improvements across all predefined principal outcomes. Median arterial carbon dioxide tension, or PaCO₂, fell by 10 millimeters of mercury within the first 24 hours, with an interquartile range of −27 to −3 millimeters of mercury. Peak inspiratory pressure dropped by a median of 11 millibars, driving pressure by 9 millibars, and tidal volume by 1.6 milliliters per kilogram of body weight. Each of these shifts points in the direction that lung-protective ventilation strategies aim for: less pressure, less stretch, less stress on injured lung tissue, achieved while carbon dioxide was being cleared extracorporeally rather than by aggressive ventilator settings.

On the safety front, the picture was cautiously reassuring but not unblemished. The investigators found no predefined major bleeding events, no clinically apparent hemolysis, no thromboembolic complications, and no device-related infections attributable to the integrated ECCO₂R-CRRT approach. The main complication observed was circuit clotting requiring circuit exchange, which occurred in two of the seven patients. Four of the seven children were successfully weaned from ECCO₂R during their treatment course. For a first-in-children application of an adapted circuit, these figures suggest that the approach can be delivered without an outsized burden of extracorporeal complications, though the small sample size and retrospective design make it impossible to draw firm conclusions about true event rates.

The authors are careful to frame their findings as hypothesis-generating rather than as evidence of treatment efficacy or device safety. This is a retrospective, uncontrolled, single-center case series with seven patients in the principal analysis, and the observed improvements in PaCO₂ and ventilatory pressures are temporally associated with ECCO₂R initiation rather than causally attributable to it. Children with PARDS and AKI are a heterogeneous group, and natural disease evolution, changes in sedation, adjustments in ventilator strategy, and concurrent therapies could all contribute to the measured changes. Still, the consistency of the physiological signal across multiple outcomes, and the fact that it emerged in a real-world pediatric intensive care setting rather than a highly controlled research protocol, gives the findings practical weight.

The study also highlights the interdisciplinary machinery required to make such an approach work. The authors specifically acknowledge the dialysis nursing team, the Division of Pediatric Nephrology, and the nursing staff of the Pediatric Intensive Care Unit at the Medical Center – University of Freiburg, noting that their expertise and dedication were essential to successful implementation. They also thank the family of the first child treated with integrated ECCO₂R-CRRT at the institution for supporting publication of the experience. The research received no dedicated financial support, with open access funding organized through Projekt DEAL, and the authors declare no competing interests.

Looking ahead, the Freiburg team argues that prospective multicenter studies are needed to define patient selection criteria, anticoagulation strategies, weaning protocols, and the broader role of integrated ECCO₂R-CRRT within pediatric extracorporeal respiratory support. If those questions can be answered, the approach could offer a pragmatic middle ground for carefully selected children who need both kidney and lung support, avoiding the cannulation burden and complexity of full ECMO while still relieving the ventilator of some of its most dangerous demands. For now, the message is one of cautious optimism: a technique borrowed from adult critical care, adapted to the constraints of pediatric physiology and existing dialysis infrastructure, appears technically feasible and physiologically promising in a small, carefully selected cohort.

Subject of Research: Extracorporeal carbon dioxide removal integrated into continuous renal replacement therapy for pediatric acute respiratory distress syndrome

Article Title: Extracorporeal carbon dioxide removal integrated into continuous renal replacement therapy in pediatric patients with ARDS: a retrospective single-center case series

Article References: Kuntz, M., Matheisl, D., Schüle, I., Klotz, D., Fuchs, H., & Schneider, H. (2026). Extracorporeal carbon dioxide removal integrated into continuous renal replacement therapy in pediatric patients with ARDS: a retrospective single-center case series. BMC Pediatrics, 26(1), Article 860. https://doi.org/10.1186/s12887-026-07656-y

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07656-y

Keywords: ECCO2R, continuous renal replacement therapy, pediatric ARDS, acute kidney injury, lung-protective ventilation, pediatric critical care, extracorporeal membrane oxygenation, carbon dioxide removal, case series, pediatric intensive care, ventilator pressures, BMC Pediatrics

Enhanced rock weathering is not a new idea in principle; it is an acceleration of one of Earth’s oldest climate-regulating processes. Over geological time, rain and soil moisture react with silicate rocks in a chain of chemical reactions that pulls carbon dioxide out of the air and converts it into dissolved inorganic carbon, ultimately carried by rivers to the oceans and stored there. The natural process is far too slow to matter on human timescales, but grinding rock into fine powder dramatically increases the reactive surface area exposed to water and air. When that powder is scattered on agricultural fields, soil moisture, plant roots and soil acids attack the mineral grains, releasing cations such as calcium and magnesium that combine with dissolved CO2 to form bicarbonates. In effect, the field becomes a vast, passive chemical scrubber, and the farmer’s existing machinery and irrigation infrastructure do much of the work.

What has been missing, the authors argue, is a credible national-scale quantification for China, the country whose carbon-neutrality pledge by 2060 arguably depends more than any other on finding affordable negative-emissions options at enormous scale. Most carbon dioxide removal technologies face well-known constraints: direct air capture remains expensive and energy-intensive, afforestation competes for land and stores carbon in vulnerable biomass, and bioenergy with carbon capture requires both large biomass supplies and reliable geological storage. Enhanced rock weathering sidesteps some of these bottlenecks because it piggybacks on agriculture, uses abundant silicate rocks such as basalt, and in many cases delivers co-benefits to soils, including the release of plant nutrients and the potential to ameliorate soil acidity.

The Tsinghua-Cambridge team addressed the gap with a spatially explicit analysis across China’s croplands, meaning that rather than averaging the country into a single number, they resolved the relevant variables location by location. That matters because the effectiveness of enhanced rock weathering is exquisitely sensitive to geography. Weathering rates depend on climate, with warm, wet conditions accelerating the dissolution of silicate minerals, and on soil chemistry, which controls how quickly acids in the soil can attack the rock. They also depend on logistics: basalt must be crushed, transported and spread, and the energy and emissions embedded in that supply chain eat directly into the net climate benefit. A field in humid South China served by a nearby quarry is a very different proposition from a dry northern plain hundreds of kilometres from suitable rock.

By accounting for these factors across the national cropland base, the study arrives at its headline range of 0.44 to 0.79 billion tonnes of CO2 removed by 2100 from a single year of application. To put that in perspective, the upper end of the range is comparable to a substantial fraction of China’s annual emissions from a single year of rock, spread once and continuing to weather for decades as the grains dissolve. The cost estimate of 127 to 226 dollars per tonne of CO2 removed is a net, life-cycle-adjusted figure, meaning the authors subtracted the emissions and costs of grinding, transporting and spreading the rock before tallying the balance. That places enhanced rock weathering in a competitive band relative to many other carbon removal pathways, though still well above the levels needed for mass deployment without policy support.

One of the study’s most consequential technical findings concerns particle size. The researchers found that particles finer than those typically used commercially provide the most favorable balance between removal potential and cost. The logic follows directly from reaction kinetics: the rate at which a mineral grain dissolves scales with its exposed surface area, and grinding rock finer multiplies that area. Finer milling costs more energy up front, but the additional carbon removed over the decades that follow more than compensates in the study’s accounting. This is a practical insight for anyone hoping to design a real deployment program, because it suggests the industry should invest in finer grinding than current agricultural lime or rock-dust practice would suggest, and it gives quarry operators and equipment manufacturers a concrete engineering target.

The analysis also looked beyond a one-off application. Under multi-year application, repeated spreading across successive seasons, the authors estimate that enhanced rock weathering could contribute 5 to 30 percent of China’s negative emissions needs by 2060. That range is wide, reflecting genuine uncertainties in weathering kinetics, application rates and future costs, but even the low end represents a meaningful slice of the enormous carbon-removal burden implied by carbon neutrality. The study identifies priority areas in Northeast, Central-South and East China, regions where the combination of climate, soils, cropland extent and proximity to basalt resources makes the approach most favorable. Such spatial prioritization is exactly what policymakers need to move from a promising concept to a targeted pilot program.

The authors are careful to frame their work as an initial spatially resolved assessment rather than a final verdict, and they are explicit about what must happen next. They call for field trials and coupled soil-river geochemical modeling to constrain three critical unknowns: the actual rate of weathering under real field conditions, the fraction of the dissolved carbon that is retained as it travels downstream rather than being re-released, and the magnitude of losses along the pathway from field to ocean. These are not minor caveats. The carbon captured on a farm exists as dissolved bicarbonate in soil water, and its ultimate fate depends on hydrology and river chemistry at scales far beyond any single plot. Without that downstream accounting, removal estimates could be systematically optimistic or pessimistic.

For China’s climate planners, the study supports considering enhanced rock weathering in the national carbon-management portfolio, a conclusion with global resonance. The same modeling framework could be applied to other major agricultural economies, from India and Brazil to the United States, where basaltic rocks and extensive croplands coexist. The work was supported by the National Key R&D Program of China, and its open-access publication means the underlying assessment is available to researchers and policymakers worldwide. If field trials bear out the model’s assumptions, the vision that emerges is quietly revolutionary: a carbon removal technology that requires no exotic chemistry, no vast new industrial infrastructure, and no land taken out of food production, only rock, crushers, spreaders and the patient chemistry of water meeting stone. In a world desperately searching for affordable ways to draw carbon down, the answer may lie in the oldest scrubber of all, the weathering of rock, accelerated by human ingenuity and deployed across the fields that already feed a fifth of humanity.

Subject of Research: National-scale assessment of enhanced rock weathering as a carbon dioxide removal strategy on China's croplands

Article Title: Assessing the potential and cost of enhanced rock weathering in China

Article References: Wang, Z., Teng, F., & Reiner, D. M. (2026). Assessing the potential and cost of enhanced rock weathering in China. Communications Earth & Environment. https://doi.org/10.1038/s43247-026-04136-0

Image Credits: AI Generated

DOI: 10.1038/s43247-026-04136-0

Keywords: enhanced rock weathering, carbon dioxide removal, China, basalt, croplands, carbon neutrality, negative emissions, soil chemistry, climate mitigation, carbon costs, geochemical modeling, Tsinghua University

A team led by Abigail Swann of the University of Washington, together with Charles Koven of Lawrence Berkeley National Laboratory and colleagues across fifteen institutions, analyzed simulations from ten Earth system models run under the new flat10MIP experimental protocol, an idealized framework adopted for the Coupled Model Intercomparison Project Phase 7. Unlike earlier experiments that prescribed atmospheric carbon dioxide concentrations, flat10MIP specifies emissions directly, letting each model calculate how much carbon dioxide actually accumulates in the air as its land and ocean components absorb or release carbon. That design allows scientists to probe two crucial climate metrics, the transient climate response to cumulative emissions and the zero emissions commitment, while simultaneously tracking where carbon ends up on land.

The experimental architecture is elegantly simple. In the core flat10 experiment, carbon dioxide is emitted at a constant 10 petagrams of carbon per year, close to present-day rates, for at least a century, accumulating 1000 petagrams of cumulative emissions. From that point, two branches diverge. In the zero-emissions branch, emissions drop instantly to zero and the simulation runs for another 200 years. In the carbon-dioxide-removal branch, emissions decline steadily, turn negative, and eventually reach minus 10 petagrams per year, so that by year 300 the cumulative emissions over the whole experiment return to zero. Ten models, including ACCESS-ESM1-5, CESM2, NorESM2-LM, GFDL-ESM4, UKESM1.2, MPI-ESM1-2-LR, MIROC-ES2L, CNRM-ESM2-2, NASA-GISS-E2.1-G-CC2, and HadCM3LC-Bris, completed all three scenarios.

During the positive emissions phase, the models agreed on a broad pattern: land gained carbon, on average about 246 petagrams by year 100, and the majority of that gain, roughly 60 percent, landed in vegetation rather than soil. The mechanism is familiar. Elevated atmospheric carbon dioxide enhances photosynthesis, a process represented in every model, and the carbon flows first into leaves, wood, and roots before slowly leaking into litter and soil pools. The gains were largest in the tropics and mid-latitudes, and in most models carbon accumulated on land nearly linearly with cumulative emissions, at least through the first 1000 petagrams. A few models, notably ACCESS-ESM1-5, showed the accumulation rate tapering off earlier, as tropical gross primary productivity began to saturate under heat and moisture stress.

Then the picture darkened. When emissions were cut to zero, atmospheric carbon dioxide continued to fall as land and ocean sinks kept drawing it down, but the land’s internal accounting shifted dramatically. In seven of the ten models, tropical latitudes lost carbon during the net-zero phase, and in every single model, tropical vegetation carbon declined. Meanwhile, mid- and high-latitude regions kept gaining carbon, mostly in soils. The explanation is a cruel asymmetry. As carbon dioxide concentrations fall, the fertilization effect that boosted tropical growth partially reverses, yet temperatures remain high, accelerating respiration and stressing plants in the hottest regions. The tropics, which gained the most during the emissions phase, become the biggest losers once emissions stop.

The negative emissions branch told a similar story at a different baseline. By the point of cumulative zero emissions, when all the carbon ever emitted had hypothetically been removed, vegetation carbon had declined in most models and tropical carbon had fallen in all of them, relative to the pre-industrial starting state. Mid-latitude soils and high-latitude vegetation and soils, by contrast, often ended up above their initial stocks. The similarity between the net-zero and cumulative-zero responses suggests that the same processes, faster turnover of vegetation under heat stress and the reversal of carbon dioxide fertilization, operate in both cases, just from different starting points.

Perhaps the most striking result concerns timing. Peak atmospheric carbon dioxide arrived about 15 years before net-zero emissions, and global temperature peaked roughly 6 years after net-zero. Vegetation carbon peaked a remarkably consistent 10 years after net-zero, with a spread of only about 7 years across the ensemble, suggesting that the processes governing vegetation growth and decay are represented similarly across models. Soil carbon was another matter entirely. Its peak arrived on average 33 years after net-zero, but ranged from 9 years before to a staggering 126 years after, with GFDL-ESM4’s late peak reflecting its unusual soil model in which turnover slows as productivity rises. Because the zero emissions commitment depends on century-scale carbon sink behavior, this soil carbon disagreement directly undermines confidence in projecting how much warming will persist after emissions stop.

The study also exposed uncomfortable gaps in what the models actually contain. Pre-industrial land carbon stocks varied enormously, from 978 petagrams in GFDM-ESM4 to 3119 petagrams in NorESM2-LM, against an IPCC benchmark of about 3350 petagrams for the present day, and many models appear to hold too little soil carbon, particularly in high latitudes where permafrost processes are missing from most land components. Only three models resolve soil carbon by depth, and just two of those represent permafrost; both showed stagnation or losses of high-latitude soil carbon under zero emissions, consistent with warming-driven permafrost thaw. Even more puzzling, none of the structural differences the team examined, whether nutrient limitation, dynamic vegetation, fire, or soil complexity, correlated with model behavior. Models with and without nitrogen cycling, with one soil pool or eighty, spread across the full range of outcomes, implying that parametric uncertainty and unrepresented processes swamp the visible architecture.

That last point carries a warning for carbon dioxide removal efforts. The models in this study lack many mechanisms that would make tropical losses worse: heat damage to enzymes and reproduction, hydraulic failure and mortality, pests and pathogens, and some fire-related disturbances. The simulated tropical declines are therefore likely underestimates. And because most afforestation and reforestation projects are planned for low latitudes, precisely the regions where the models show carbon being gained and then lost, the study raises the prospect that tree-planting schemes could see their stored carbon evaporate under the sustained heat of a zero-emissions world. The idealized flat10MIP scenarios also impose removal as a boundary condition rather than modeling the physical side effects of specific removal methods, which could add further complications.

The takeaway is sobering but precise. Tropical carbon is the most likely to be gained during rising emissions and the most likely to be lost under zero, declining, and negative emissions, making it a fragile foundation for net-zero accounting. Mid- and high-latitude soils, meanwhile, behave more reliably but on timescales so uncertain and so model-dependent that they dominate the spread in the zero emissions commitment. As nations design removal portfolios and net-zero pledges, the message from this ten-model ensemble is clear: stopping emissions does not stop the carbon cycle from rearranging itself, and the places we most depend on to store carbon may be the places least able to keep it.

Subject of Research: Land carbon sink responses to positive, zero, and negative CO2 emissions across Earth system models

Article Title: Land carbon response to positive, zero, and negative CO2 emissions across Earth system models

Article References: Swann, A. L. S., Koven, C. D., Proistosecu, C., Fisher, R. A., Sanderson, B. M., Brovkin, V., Hajima, T., Jones, C. D., Kiang, N. Y., Lawrence, D. M., Liddicoat, S., Liddy, H., Romanou, A., Séférian, R., Sentman, L. T., Steinert, N. J., Tjiputra, J., & Ziehn, T. (2026). Land carbon response to positive, zero, and negative CO 2 emissions across Earth system models. Earth System Dynamics, 17(5), 1237-1275. https://doi.org/10.5194/esd-17-1237-2026

Image Credits: AI Generated

DOI: 10.5194/esd-17-1237-2026

Keywords: land carbon sink, Earth system models, net-zero emissions, negative emissions, tropical forests, soil carbon, CO2 fertilization, flat10MIP, zero emissions commitment, carbon dioxide removal, permafrost, climate modeling

The study focused on three of the most prominent engineered carbon removal methods now moving from laboratory to real-world deployment. Direct air carbon capture and storage, or DACCS, strips carbon dioxide from ambient air using chemical sorbents and locks it underground. Bioenergy carbon capture and storage, known as BECCS, grows biomass that absorbs carbon, burns it for energy and captures the resulting emissions. Enhanced rock weathering, or ERW, spreads crushed silicate minerals on land, accelerating natural chemical reactions that pull carbon dioxide from the atmosphere and eventually lock it away in oceans and soils. Each carries a distinct risk and cost profile, from land-use conflicts and energy demands to mining and transport burdens, yet the researchers discovered something remarkable: the technology itself mattered far less than the way it was implemented.

To isolate what actually drives public acceptance, the team ran a multifactorial vignette experiment embedded in surveys conducted in Brazil, Malaysia, Saudi Arabia, Italy, Norway and the United Kingdom. Roughly 1,800 respondents per country were assigned to one of the three technologies and then evaluated five hypothetical projects out of 36 possible variants. Each project description differed along four attributes grounded in a multidimensional conception of justice: who implemented the project, whether the decision-making process involved consultation, how profits were distributed, and how much carbon the project could remove. Respondents rated each project on a ten-point scale from strong opposition to strong support, generating more than 54,000 individual evaluations for statistical analysis.

The headline result is unambiguous. Across every country and every technology, procedural fairness exerted the strongest effect on support. Compared with projects approved by authorities without any consultation, opening the decision-making process to local communities or scientific experts increased support by roughly 1.0 to 1.7 points on the ten-point scale. The effect was largest in Brazil, where consulting the affected population raised support by 1.68 points, and smallest but still substantial in Saudi Arabia, at just over 1.0 point. Notably, consulting local communities and consulting scientific experts produced nearly identical gains, suggesting that what matters to the public is the principle of being heard, not the specific identity of who is asked.

Distributive fairness came a close second. When developers retained all profits, projects fared worst. Redistributing revenues to affected local communities increased support by between roughly 0.5 and 1.25 scale points, with the largest effect again in Brazil, followed by the United Kingdom and Italy. Not-for-profit arrangements, in which carbon removal operates as a public service without generating profit, also raised support everywhere, though less dramatically in Saudi Arabia. By contrast, whether a company or a regional government carried out the project made little difference in most countries, with only a modest penalty for corporate implementation in the United Kingdom, Italy, Norway and Malaysia. The lesson for the emerging carbon removal industry is uncomfortable: the public appears far more interested in how benefits flow than in who owns the machinery.

Perhaps the most striking finding concerns trade-offs. The researchers tested whether a project promising high removal capacity could compensate for unfair governance, and the answer was a clear no. Across nearly all countries, the effect of increasing carbon removal was remarkably similar regardless of whether projects consulted anyone or shared profits. Respondents rewarded projects that were both effective and fairly governed, but these two considerations operated independently. A high-capacity project run without consultation and with privatized profits still lost the support that fairness would have generated. The reverse also held: progressive governance could not rescue a project with meager removal performance. From the perspective of public legitimacy, neither technical excellence nor ethical design alone is sufficient.

Support levels themselves varied across countries in ways the authors interpret cautiously. Brazil and Saudi Arabia showed the highest average support, with means between roughly 7.1 and 7.3, while European respondents were more moderate, with Norway recording the lowest scores, averaging around 5.1 to 5.4 depending on the technology. The researchers warn that cross-cultural differences in survey response styles, such as tendencies toward acquiescence or avoiding extreme answers, may partly explain these gaps, and they emphasize the experimentally varied attributes over absolute levels. Within Europe, DACCS consistently received lower support than the other two methods, while in Malaysia no significant differences emerged among the technologies at all.

When asked directly what level of public involvement would be fair, respondents revealed a strong appetite for engagement. Allocating decision-making authority to local communities was judged the fairest option for permitting projects by around 44 percent of respondents in the United Kingdom and Italy, 43 percent in Norway, and between 34 and 39 percent in Brazil, Saudi Arabia and Malaysia. Only a tiny fraction, between 2 and 9 percent, thought local communities should have no involvement at all. Strikingly, political orientation played almost no role in shaping support, a sharp contrast with the well-documented polarization of climate attitudes more broadly. Carbon removal, the data suggest, has not yet been absorbed into partisan identity, and public judgments rest instead on risk perceptions, trust and effectiveness.

Even self-described opponents of hosting carbon removal near their homes responded to fairness cues. Dividing respondents into opponents, moderates and supporters of local projects, the researchers found similar preference structures across all three groups, with opponents reacting as strongly or more strongly to governance attributes than anyone else. Opponents, in other words, do not categorically reject carbon removal; they remain open to projects developed through consultation and benefit sharing. This conditional openness offers developers a genuine path forward, but also a narrow one, since perceived injustice can trigger the protests, litigation and delays that have stalled energy infrastructure around the world.

The authors caution that today’s moderate support and weak polarization reflect the novelty of these technologies and low public familiarity, not a stable consensus. As real projects take shape and costs, trade-offs and distributional questions become tangible, controversies are likely to intensify, and spillovers from adjacent debates over biofuels, carbon storage, fracking or nuclear waste could reshape perceptions rapidly. Their prescriptions are correspondingly structural: open decision processes to public and expert scrutiny, treat carbon removal as a public good rather than a profit engine, and experiment with regional, upstream engagement at the planning stage rather than leaving participation to developer-led consultations after key choices are made. With national carbon removal governance still nascent in most of the world, the window for embedding justice into deployment pathways remains open, but the study’s message is that it will not stay that way for long.

Subject of Research: Public support for novel carbon dioxide removal technologies and the role of procedural and distributive fairness in their governance

Article Title: Public support for novel carbon removal hinges on procedural and distributive fairness

Article References: Fritz, L., Losi, L., Merk, C., Boldrini, M., Bosetti, V., Baum, C. M., & Sovacool, B. K. (2026). Public support for novel carbon removal hinges on procedural and distributive fairness. Nature Climate Change, 16(10), 1152-1161. https://doi.org/10.1038/s41558-026-02741-7

Image Credits: AI Generated

DOI: 10.1038/s41558-026-02741-7

Keywords: carbon dioxide removal, public perception, procedural fairness, distributive fairness, direct air capture, BECCS, enhanced rock weathering, climate governance, survey experiment, social acceptance, climate policy, benefit sharing

The core of the problem lies in a mismatch between two very different modeling worlds. Integrated assessment models, or IAMs, simulate the global economy, energy systems, agriculture, and land use, and they decide where and when carbon removal technologies should be deployed based on costs, resource demands, and policy assumptions. Earth system models, or ESMs, simulate the physics, chemistry, and biology of the atmosphere, ocean, and land surface in fully coupled detail. In the current state-of-the-art setup, used for the fifth and sixth phases of the Coupled Model Intercomparison Project and planned again for the seventh, the IAM simply hands the ESM a net emissions number in which the carbon removed by technologies like bioenergy with carbon capture and storage is folded in as a prescribed negative flux. The Earth system model never sees the bioenergy crops growing, never simulates the forests being planted, and never computes the ocean chemistry changes caused by dumping alkaline material into the sea. Everything the model does in response to that removal is therefore invisible.

Schwinger and colleagues argue that this prescribed approach must give way to what they call activity-driven simulation of carbon dioxide removal. Instead of prescribing a negative emission, the ESM explicitly represents the activity that draws down atmospheric CO2. For bioenergy with carbon capture and storage, that means growing the crops inside the model, harvesting the biomass, and routing a scenario-dependent fraction of the harvested carbon into geological storage. For ocean alkalinity enhancement, it means adding an alkaline agent such as slaked lime to the surface ocean and letting the model’s carbonate chemistry, circulation, and biology determine how much CO2 is actually sequestered, and how quickly. Only afforestation and reforestation have always been simulated this way, because the land-use patterns passed from IAMs to ESMs implicitly contain the forest transitions. Extending the same philosophy to other methods harnesses the full power of Earth system models: climate change effects on removal efficiency, from drought stress on bioenergy crops to ocean circulation changes, are computed rather than assumed.

But simulating the activity is only half the challenge. To measure what carbon removal actually achieves, scientists need a reference against which to compare, and this is where the study makes its most consequential conceptual contribution. The team defines two distinct metrics. The first is Process Carbon Removal, the gross amount of carbon a removal process takes up minus its own positive emissions, without any feedback effects. This is essentially what IAMs estimate, and it is the quantity relevant for carbon accounting, in the same way that emissions are priced per tonne regardless of how natural sinks respond. The second is Net Atmospheric Removal, the true difference in atmospheric carbon content between a world with the removal technology and a world without it, including every carbon-cycle and biogeophysical feedback the Earth system can muster. Crucially, the authors show that these two numbers can diverge substantially, because the planet’s carbon sinks respond to removal in ways that partially undo the benefit.

The reason for that divergence is the buffering nature of the carbon cycle. Today, terrestrial and oceanic sinks absorb more than half of every tonne of CO2 humanity emits. Models project that under declining emissions these sinks will take up less carbon, and under net-zero or net-negative emissions they can even flip into carbon sources, releasing CO2 back to the atmosphere as the reversed feedbacks operate in reverse. The practical consequence is stark: the net atmospheric reduction achieved by any carbon removal portfolio will always be less than the gross amount removed. How much less is a question the new framework is designed to answer quantitatively, scenario by scenario and model by model.

Constructing the necessary no-CDR baseline turns out to be anything but trivial. The authors distinguish two fundamentally different approaches. The first is an ex-post adjustment: take an existing IAM mitigation scenario and surgically remove the carbon removal, for instance by freezing the land-use transitions associated with afforestation or by omitting the alkalinity flux to the ocean. This preserves the original scenario’s geography and allows regional attribution of effects, but it produces a socio-economically inconsistent world, one where land earmarked for bioenergy simply sits idle rather than being reallocated to food production. The second is a counterfactual IAM scenario: re-run the economic model in a world where carbon removal was never an option, letting the energy system, land use, and emissions evolve consistently without it. This counterfactual world is socio-economically coherent but so different in its land-use and emissions geography that regional biogeophysical effects of the original removal deployment cannot be isolated. The two approaches are complementary, and the authors recommend that IAM teams begin producing counterfactual no-CDR baselines for selected scenarios, something that, to their knowledge, does not yet exist in the scenario literature.

To demonstrate the framework in action, the team turned to the Norwegian Earth System Model NorESM2-LM and a deep mitigation scenario generated by the REMIND-MAgPIE integrated assessment model, expanded to include ocean liming as a removal method. The scenario reaches an end-of-century carbon budget of 500 gigatonnes of CO2 from 2020, corresponding to 1.5 degrees Celsius of warming in 2100 after a substantial overshoot, with a peak cumulative budget exceeding 1000 gigatonnes around 2060 before massive upscaling of removals pulls it back down. In the Earth system model, ocean alkalinity enhancement was simulated activity-driven, with alkalinity deployed within exclusive economic zones excluding polar regions, while bioenergy removals remained prescribed. Three ensemble members were run for each of the required simulations.

The results are striking and, for anyone banking on ocean-based removal, sobering. For a deployment of 4.93 petamoles of alkalinity between 2050 and 2100, equivalent to 182.5 gigatonnes of calcium hydroxide, the model simulated a Process Carbon Removal of 28.2 petagrams of carbon by 2100. Carbon-cycle feedbacks from both land and ocean then clawed back 7.9 petagrams, roughly 28 percent, leaving a Net Atmospheric Removal of just 20.3 petagrams of carbon, equivalent to a 9.7 parts-per-million reduction in atmospheric CO2. The ocean and terrestrial biosphere contributed roughly equally to the feedback losses, at 4.8 and 3.1 petagrams respectively, though the authors caution that the land feedback in particular may vary greatly between models. Equally revealing was the comparison with the IAM’s own estimate: REMIND-MAgPIE, which assumes a constant efficiency of 0.57 moles of CO2 per mole of alkalinity and instantaneous uptake, overestimated the removal by about 7.4 petagrams, roughly 20 percent, partly because real ocean chemistry takes ten to fifteen years to fully equilibrate an alkalinity addition.

Perhaps the most humbling finding concerns the noise floor of the climate system itself. Even a tiny initial difference in carbon removal deployment acts as a perturbation that causes the scenario and baseline simulations to diverge chaotically, exactly as separate ensemble members with different initial conditions do. Within a few years of the alkalinity deployment beginning around 2040, the El Niño-Southern Oscillation states of the two simulations had become completely uncorrelated. The resulting internal variability in calculated removals and feedback fluxes remained comparable in magnitude to the global annual mean signal, and even decadal averages carried a noise level exceeding 0.25 petagrams of carbon per year. The implication is uncomfortable: detecting the small signals associated with carbon removal and its feedbacks in emission-driven simulations requires either sufficiently large initial-condition ensembles or averaging over long periods, and for some applications, such as quantifying regional biogeophysical effects, stylized modeling approaches may simply remain preferable.

The timing of this work could hardly be better. The upcoming seventh phase of the Coupled Model Intercomparison Project has adopted emission-driven scenario simulations as a priority, yet its ScenarioMIP protocol still foresees only prescribed carbon removal and no no-CDR baselines, limiting what those simulations can say about removal effectiveness. The authors argue that the next phase of the Carbon Dioxide Removal Model Intercomparison Project should adopt their framework, and they issue concrete recommendations to the modeling community: IAMs should provide gross positive and negative emissions separately for each removal method, deliver spatially explicit information on bioenergy with carbon capture in future land-use datasets, and flag the difference between passive forest regrowth and deliberate afforestation. As nations and companies commit billions to carbon removal portfolios whose real-world performance remains deeply uncertain, this framework offers something the field has lacked: a transparent, physically consistent way to separate what a removal technology promises from what the Earth system actually delivers.

Subject of Research: Earth system modeling of carbon dioxide removal efficiency and feedbacks in mitigation scenarios

Article Title: Assessing Earth system responses in mitigation scenarios with activity-driven simulation of carbon dioxide removal

Article References: Schwinger, J., Merfort, L., Bauer, N., Bernardello, R., Butenschön, M., Bourgeois, T., Gidden, M. J., Gupta, S., Lee, H., Mengis, N., Moustakis, Y., Muri, H., Nieradzik, L., Peano, D., Pongratz, J., Sauer, P., Tourigny, E., & Wårlind, D. (2026). Assessing Earth system responses in mitigation scenarios with activity-driven simulation of carbon dioxide removal. Earth System Dynamics, 17(5), 1341-1363. https://doi.org/10.5194/esd-17-1341-2026

Image Credits: AI Generated

DOI: 10.5194/esd-17-1341-2026

Keywords: carbon dioxide removal, Earth system models, integrated assessment models, ocean alkalinity enhancement, BECCS, afforestation, carbon cycle feedbacks, no-CDR baseline, CMIP7, net-zero emissions, NorESM2, climate mitigation scenarios

The experiment took place at the Sleepers River Research Watershed in Danville, Vermont, a long-studied 59-hectare agricultural catchment known as W-2, where hayfields and pasture cover roughly three-quarters of the land. After a full year of baseline monitoring, the team spread basalt powder at a rate of 20 tonnes per hectare over 8.9 hectares of the downstream portion of the catchment in June 2023, amounting to about 15 percent of the total watershed area. The basalt, sourced from the Holyoke Basalt formation of the Newark Supergroup, was rich in the calcium-bearing minerals that make silicate weathering an effective carbon sink. When silicate minerals dissolve, they consume atmospheric carbon dioxide and convert it into bicarbonate alkalinity, a form of carbon that can remain safely stored in the ocean for tens of thousands of years once it arrives there.

What happened next surprised even the researchers. Streamwater alkalinity and calcium concentrations in the treated catchment rose above counterfactual estimates within a single month of application. In the first three months, alkalinity exceeded the no-basalt baseline by an average of 267 microequivalents per liter, peaking at 557 microequivalents per liter above the counterfactual in September, while calcium climbed by as much as 696 microequivalents per liter. Because a nearby forested reference watershed, W-9, showed no such changes, the team could attribute the shifts directly to the basalt. The concentration-discharge relationships in the stream also changed character, weakening the natural dilution pattern that had been established during the baseline year, a sign that a new, persistent source of solutes had entered the system.

The evidence went well beyond alkalinity. Concentrations of silica and lithium, both far more abundant in basalt than in the carbonate rocks that could otherwise explain the chemistry, rose in parallel with the base cations. The isotopic composition of lithium shifted as well: the ratio of lithium-7 to lithium-6 in streamwater declined from an average of 19.0 per mil before treatment to 17.5 per mil within three months, moving toward the isotopically light signature of the applied basalt itself, which measured just 2.34 per mil. Rubidium, which substitutes for potassium in the feldspars and micas of the basalt, also increased at equivalent stream discharges. Together, these geochemical tracers painted a coherent picture of freshly applied silicate rock dissolving and its dissolution products racing to the stream.

One curious detail was the preferential export of calcium over sodium and magnesium, with the calcium increase more than twenty times larger than the corresponding rises in the other cations. The researchers attribute this to a combination of mechanisms. The soils at the site are dominated by calcium on their exchange complex, with roughly 85 percent calcium saturation, meaning other basalt-derived cations can displace calcium from exchange sites and flush it downstream early. Non-stoichiometric mineral dissolution plays a role too, since clinopyroxene and calcium-rich plagioclase, both abundant in the feedstock, release calcium preferentially. A small carbonate content in the basalt, about 0.14 percent by weight, likely contributed a minor share as well.

Perhaps the most consequential finding is that the treatment effect was strongly seasonal. Using a generalized additive model coupled with a difference-in-differences framework that leveraged data from the reference watershed, the team found that enhanced weathering accounted for 14 to 18 percent of streamwater alkalinity, calcium, magnesium, sodium and silica during the summer of 2023, but the effect weakened in autumn, became statistically indistinguishable from zero in winter, and rebounded in spring with snowmelt. The same pattern repeated, slightly attenuated, in the second year. Export of basalt-derived alkalinity, expressed as removed carbon dioxide, plunged from a summertime high of about 102 tonnes of CO2 per square kilometer per year to less than 3 tonnes in winter.

The seasonal rhythm reflects two intertwined controls. Temperature governs the kinetics of basalt dissolution, and the researchers quantified this with an Arrhenius analysis of discharge-normalized alkalinity export, deriving an apparent activation energy of 58.5 kilojoules per mole, squarely within the expected range for basalt weathering and actually exceeding laboratory values for calcium-bearing plagioclase. That excess likely reflects additional temperature-dependent processes in the field, such as seasonal swings in soil carbon dioxide from microbial and root respiration, which acidify soil water and accelerate dissolution. Hydrology supplies the second control: an endmember mixing analysis showed that basalt-derived solutes traveled to the stream mainly through quick-flow pathways fed by shallow, near-stream soils, whose solute concentrations jumped by up to 1,200 microequivalents per liter in summer and autumn, while slow-flow water originating upslope showed no detectable weathering signal at all.

Over the full 22-month monitoring window, the exported alkalinity amounted to 63.8 tonnes of CO2 per square kilometer, equivalent to 34.7 tonnes per square kilometer per year, which is among the highest rates reported for any field-based enhanced weathering study and roughly matches the median carbon consumption rate of natural basaltic rivers worldwide. Yet that figure represents only 9.5 to 11 percent of the theoretical maximum carbon removal potential of the applied basalt. The gap is not necessarily a failure. Water isotope analysis showed that only about 23 percent of streamflow was younger than roughly two months, meaning most water lingers in catchment storage, and weathering products traveling along slower, deeper paths may simply not have emerged yet. The mean residence time of water in the catchment is about 1.3 years, so a substantial fraction of the carbon removal signal may still be in transit.

The implications for the booming carbon removal industry are significant. Monitoring schemes that rely on streamwater chemistry will need to account for seasonal variability, or they risk badly misestimating removal, particularly if measurements cluster in winter when the signal vanishes. Deployments that target moist, near-stream corridors will be most responsive to stream-based verification, while upslope applications may require extended monitoring windows stretching well beyond two years to capture the delayed tail of the weathering signal. There are also limits to watch: repeated applications could push streamwater toward calcite saturation in summertime, triggering carbonate precipitation that would claw back alkalinity and reduce net removal.

What the Vermont trial ultimately demonstrates is that a watershed can serve as a natural integrator of enhanced weathering signals, capturing the combined effects of dissolution kinetics, hydrologic transport and climate variability in a single, measurable output at the stream gauge. Despite the cold northern climate that should slow weathering, the high calcium saturation of the soils and favorable hydrologic connections allowed signals to emerge quickly and repeatably across two years. As enhanced weathering scales from experimental plots toward the gigatonne ambitions projected for global croplands, studies like this one provide the template for knowing what to measure, when to measure it, and how to read the seasonal heartbeat of a landscape quietly eating carbon dioxide.

Subject of Research: Watershed-scale monitoring of carbon dioxide removal via enhanced weathering with crushed basalt

Article Title: Multiple lines of evidence reveal rapid, seasonal watershed responses to enhanced weathering

Article References: Sun, F., Rioux, R. A., Suhrhoff, T. J., Tatge, W., Kalderon-Asael, B., Zacharias, Q., Miller-Brown, W. A., MacDonald, A. A., Garcia, E., Shanley, J. B., Raymond, P. A., Planavsky, N. J., & Saiers, J. E. (2026). Multiple lines of evidence reveal rapid, seasonal watershed responses to enhanced weathering. Nature Water. https://doi.org/10.1038/s44221-026-00716-8

Image Credits: AI Generated

DOI: 10.1038/s44221-026-00716-8

Keywords: enhanced weathering, carbon dioxide removal, basalt, alkalinity, streamwater chemistry, hydrology, seasonality, silicate dissolution, carbon sequestration, watershed monitoring, lithium isotopes, climate mitigation