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

The research, a collaboration between the Wyss Institute for Biologically Inspired Engineering at Harvard University, Harvard Medical School’s Department of Systems Biology, and the Stanford Doerr School of Sustainability, was led by Wyss Founding Core Faculty member Pamela Silver and Associate Faculty member Michael Springer. First author and chemical engineer Neil Dalvie, who spearheaded the project as a postdoctoral fellow in Silver’s laboratory, and his colleagues genetically engineered Alteromonas macleodii, a bacterium widespread in marine environments, to produce far greater quantities of molecules called siderophores. These compounds are the bacterial world’s iron-scavenging tools, and it turns out they are also remarkably effective at stripping iron from the surfaces of silicate minerals. In customized bioreactors flushed with a continuous flow of seawater, the engineered microbe accelerated the weathering of the silicate mineral olivine by 2.6-fold, measurably increasing the amount of atmospheric carbon dioxide drawn into the water. The findings were published in Nature Biotechnology.

To understand why bacteria can speed up rock dissolution, it helps to look closely at what actually happens on a weathering mineral surface. When olivine and similar silicates dissolve, they release magnesium, iron, and silicate, and the chemistry of that dissolution simultaneously traps atmospheric carbon dioxide in the surrounding water as bicarbonate. But the released iron presents a problem: exposed to oxygen in the atmosphere, it is not soluble and instead precipitates as rust, coating the mineral surface and slowing the entire weathering process to a crawl. Bacteria that produce siderophores can capture, solubilize, and import that oxidized iron to satisfy their own nutritional needs. In doing so, they effectively de-rust the mineral surface, exposing fresh reactive material to seawater and allowing dissolution to continue. It is a subtle biological intervention with outsized geochemical consequences, and it is precisely this natural mechanism the Harvard team set out to amplify.

The first obstacle the researchers encountered was regulatory rather than chemical. Using custom bioreactors to dissect when natural bacteria produce siderophores, they discovered that even a small amount of iron-containing mineral completely shut down siderophore production. Wild bacteria, it seems, are thrifty: once they have accumulated enough iron to support growth, they stop investing energy in making the scavenging molecules altogether. That built-in thriftiness is a disaster for anyone hoping to harness siderophores for industrial-scale carbon removal, because the whole point is to have the bacteria continuously attack mineral surfaces regardless of how much iron is already available. Once wild bacteria have enough iron to grow, they stop making siderophores completely, Dalvie explained. To enable enhanced weathering at scale, the team engineered A. macleodii to always produce siderophores, essentially decoupling production from environmental iron levels and converting a self-regulating survival mechanism into a relentless industrial workhorse.

Engineering the microbes took roughly a month, but the far harder task was proving that the modification actually translated into faster weathering and greater carbon uptake. For that validation, Dalvie teamed up with Amogh Jalihal, a postdoctoral fellow in Springer’s group at the Wyss Institute and Harvard Medical School. The two researchers concluded that the most rigorous measurement would be made at steady state, with seawater and bacteria continuously flowing over the minerals rather than sitting in batch cultures where conditions drift unpredictably. Fortunately, Springer’s group had recently acquired an entire room of eVOLVER bioreactors, small-scale devices originally designed by Ahmad Khalil, another Wyss Associate Faculty member and professor at Harvard University. The eVOLVER platform, with its modular, automated control of growth conditions, proved ideal for the small-scale studies that would establish whether the engineered strain genuinely outperformed its wild-type ancestor on real rock.

Those early experiments showed promise, and the team escalated to pilot-scale bioreactors loaded with several kilograms of green olivine sand submerged under gallons of raw seawater drawn from Boston Harbor. Working at pilot scale forced the researchers to confront the practical questions that separate laboratory demonstrations from deployable technology: how often cells needed to be added, how they should be fed, and how the system could be kept running continuously. Eventually the team was able to measure actual uptake of 0.5 grams of atmospheric carbon dioxide into the reactors each day, a modest absolute quantity but a compelling proof of principle for a process that could, in principle, be replicated across enormous basins. The result demonstrated that engineered bacteria could survive and function in unprocessed seawater, on unrefined mineral feedstock, under conditions far closer to the open environment than a sterile laboratory flask.

Quantifying the climate value of any proposed carbon removal technology requires more than measuring uptake in a reactor, however. To that end, Dalvie and Jalihal collaborated with Abigail Fitzgibbon, a doctoral student working with Steven Davis, Professor of Earth System Science at the Stanford Doerr School of Sustainability, whose group develops models to quantify the carbon emissions of industrial and agricultural processes and their effects on air quality and human wellbeing. Together the teams carried out a Life Cycle Analysis, an accounting framework that captures all carbon emitted or sequestered by the entire system over time, including its living, geological, and chemical components. The collaboration enabled the researchers to calculate the net carbon balance of their system precisely and to identify which process parameters would be decisive in making the technology efficient at industrial scale. Such analyses are essential for distinguishing genuinely negative-emission technologies from those that merely shuffle carbon from one reservoir to another.

The path from pilot reactor to planetary impact still runs through substantial scale-up work. The team notes that further studies are needed to identify economically viable sources of feedstocks and silicate minerals, since the cost and carbon footprint of mining, crushing, and transporting rock could easily erode the climate benefit if chosen poorly. Intriguingly, the researchers are also investigating whether valuable metals could be extracted from the silicate minerals alongside carbon sequestration, potentially creating a co-product revenue stream that improves the economics of deployment. Dalvie recently received a fellowship from the Burroughs Wellcome Career Awards at the Scientific Interface program, which will fund continued work on microbial siderophore production and mineral processing, providing momentum for the next phase of development.

Springer’s vision for deployment is strikingly pragmatic. The most straightforward way to create environmental impact, he suggested, would be to grow the bacterial strains with adequate food sources in large basins resembling those found at sewage treatment plants, continuously pumping unprocessed seawater in and releasing alkaline seawater back into the ocean, where the bound carbon would be completely harmless and buffered away. Such a design would piggyback on existing industrial infrastructure and established engineering practices, avoiding the need to invent novel containment systems from scratch. Because the carbon ends up as bicarbonate dissolved in seawater, the approach avoids many of the permanence and monitoring concerns that complicate other carbon removal strategies, and the alkalinity released to the ocean may itself help counteract acidification, though the team’s published claims rest on the weathering and carbon uptake results rather than on ocean alkalinity benefits.

Silver framed the work as an embodiment of biologically inspired engineering, demonstrating how synthetic biology can enhance natural climate-regulating processes with potentially positive planetary impact. She and her colleagues believe the strategy is easily applicable and low-risk, and could be implemented in many locations with real-world decarbonization outcomes. Whether engineered bacteria can weather rock fast enough to matter for the global carbon balance remains to be proven at scale, and the jump from half a gram of carbon dioxide per day to gigatonne-relevant removal is enormous. But the study, supported by the Wyss Institute Director’s Fund, the Synthetic Biology Hive at Harvard Medical School, Harvard’s Climate and Sustainability Translational Fund, the Salata Institute for Climate and Sustainability, a Garden Grant from the Homeworld Collective, and a Schmidt Science Fellowship, establishes a credible new entry in the growing portfolio of ocean-based carbon removal approaches. Other authors on the study include Jan-Tobias Böhnke, Mohammed Hijaz, and Quincey Justman. If the numbers scale as hoped, the humble chemistry of rusting iron and dissolving stone, accelerated by reprogrammed microbes, could become one of the more elegant tools in humanity’s decarbonization arsenal.

Subject of Research: Synthetic biology enhancement of marine bacterial siderophore production to accelerate silicate rock weathering for atmospheric carbon dioxide removal

Article Title: Pulling carbon into seawater using engineered bacteria

Article References: Pulling carbon into seawater using engineered bacteria. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: carbon removal, rock weathering, synthetic biology, siderophores, Alteromonas macleodii, olivine, ocean alkalinity, enhanced weathering, climate change, bioreactors, life cycle analysis, marine bacteria

The underlying chemistry is elegant. Seawater’s capacity to store carbon dioxide is governed by its total alkalinity, essentially the charge balance of carbonate and bicarbonate ions dissolved in it. When alkaline minerals such as olivine, limestone, quicklime, hydrated lime, steel slag or magnesium hydroxide dissolve in seawater, they shift the carbonate equilibrium: carbon dioxide is converted into bicarbonate and carbonate ions, lowering the partial pressure of CO2 at the sea surface and drawing more of the gas in from the atmosphere. Because the added alkalinity is conservative, meaning it persists in the water until consumed by other reactions, the stored carbon can remain out of the atmosphere for tens of thousands of years. This durability is what makes OAE attractive compared with biological approaches such as tree planting, where stored carbon can be released by a single fire.

Yet the authors argue that the field’s obsession with gigatonne-scale potential has distorted research priorities and public expectations. Instead, they propose a portfolio approach: many different OAE pathways, each matched to the local environment where it makes sense. Spreading crushed olivine on sandy beaches might suit one coastline; discharging alkalinity from wastewater treatment plants or desalination facilities might suit another; electrochemical methods that split seawater or accelerate carbonate dissolution on ships could serve shipping lanes; and adding alkaline minerals to organic-rich sediments, as experiments in the Baltic Sea suggest, could tap into benthic weathering processes. The diversity of pathways, the team writes, favours implementation across heterogeneous coastal environments, with upscaling achieved through widespread bottom-up adoption rather than centralized rollout.

A central claim of the Perspective is that the intended increase in seawater bicarbonate and carbonate shows no tendency to be inherently harmful within plausible limits. This is a striking statement, because the ocean is already suffering from the opposite problem: acidification. By raising alkalinity, OAE would partially reverse the pH decline that threatens corals, shellfish and calcifying plankton. Indeed, historical precedent exists. Lime has been used in aquaculture ponds for decades to manage pH, control pests such as starfish, and improve conditions for farmed shellfish and abalone, providing a long, largely overlooked record of alkalinity addition to coastal waters.

But harmless bicarbonate is not the whole story. The authors emphasize that collateral perturbations tend to drive the real environmental risk. Dissolving certain minerals can cause transient pH and CO2 excursions in the immediate vicinity of deployment. Mineral powders add suspended solids that can smother or abrade organisms. Some alkaline materials, notably steel slag and olivine, release trace metals such as nickel, chromium and copper, and several recent experiments have shown that these can influence plankton communities in pathway-specific ways. Land-based life-cycle impacts matter too: mining, grinding, transporting and dispersing minerals consumes energy and generates emissions, and life-cycle assessments show that a poorly designed OAE operation could erode or even negate its own carbon benefit. Environmental assessment, the team argues, should therefore focus on these pathway-specific local effects rather than on the added carbonate chemistry itself.

One of the most technically intriguing sections of the paper concerns sediments. Because most practical OAE deployments will occur near heterogeneous coastal sediments, their effectiveness will depend heavily on what happens at the seafloor. Sediments are not inert. They host natural alkalinity production through carbonate dissolution, silicate weathering, sulfate reduction and pyrite burial. Added alkaline minerals can interact with these processes in complicated ways: secondary minerals may precipitate and consume the very alkalinity that was added, a phenomenon known as runaway carbonate precipitation that laboratory studies have shown can be triggered when aragonite supersaturation exceeds critical thresholds. Conversely, alkaline additions may stimulate natural benthic weathering, amplifying the carbon removal beyond what the added mineral alone would deliver. There is also an additionality problem: anthropogenic alkalinity can suppress natural alkalinity-generating processes, so the net removal is smaller than the gross addition. Recent work on anthropogenic seafloor disturbances, such as bottom trawling, has even revealed that alkalinity destruction in disturbed sediments generates hidden CO2 emissions, underscoring how sensitive the coastal alkalinity budget is.

Verifying that a local OAE project actually removed the carbon it claims is perhaps the hardest problem of all. The added alkalinity draws down atmospheric CO2 only gradually, as air-sea equilibration takes months to years and depends on wind, temperature and mixing. Meanwhile, the ocean’s background carbonate chemistry varies enormously with season, currents and biological activity. The authors call for integrated, site-specific observation programs and high-resolution models that can distinguish a project-scale carbon removal signal from this natural variability and quantify uncertainty transparently. Nested coastal models, such as one recently developed for Halifax Harbour, illustrate the kind of local simulation that will be needed. Emerging carbon-removal registries and the first OAE credits have already highlighted how contested verification methodologies remain, and the paper argues that accounting rules must be locally grounded and openly documented to support trust.

Governance is the third pillar of the rethink. The authors argue that global geoengineering frameworks, centred on the London Convention and Protocol and the United Nations Convention on the Law of the Sea, are poorly suited to regulating thousands of small coastal deployments. Instead, they envision locally grounded regulation, community co-design and transparent carbon accounting, with projects shaped by the governments, Indigenous communities, aquaculturists and coastal residents who will live alongside them. Social science research shows that public acceptance hinges on exactly this kind of local involvement; surveys and scenario studies across several countries indicate that communities evaluate marine carbon removal not only on environmental risk but on procedural fairness, economic benefit and who controls the technology. The authors also stress humility: research suggests OAE could contribute to climate mitigation, but major uncertainties persist, and rigorous assessment must continue as deployments grow.

The practical vision sketched in the Perspective is, notably, consistent with what is already happening in the real world. Early commercial deployments have been small, coastal and locally negotiated, from shoreline mineral dispersal trials to ship-based experiments in the North Atlantic, and buyers have purchased modest volumes of removal credits rather than betting on gigatonne promises. Whether this bottom-up mosaic can deliver meaningful climate impact remains an open question, and the authors are careful not to overpromise. But their message is clear: the future of ocean alkalinity enhancement will be written not in one sweeping global treaty or one planetary intervention, but in hundreds of carefully monitored, environmentally responsible, demonstrably carbon-negative projects, each designed for the particular stretch of coast where it operates. For a field that has oscillated between utopian hype and reflexive dismissal, that shift from planetary dream to local practice may be the most important recalibration yet.

Subject of Research: Ocean alkalinity enhancement as a localized marine carbon dioxide removal strategy

Article Title: Rethinking ocean alkalinity enhancement

Article References: Bach, L. T., Atamanchuk, D., Britton, D., Fuhr, M., Hylén, A., Nawaz, S., & Rohr, T. (2026). Rethinking ocean alkalinity enhancement. Nature Reviews Earth & Environment, 7(10), 725-742. https://doi.org/10.1038/s43017-026-00828-5

Image Credits: AI Generated

DOI: 10.1038/s43017-026-00828-5

Keywords: ocean alkalinity enhancement, carbon dioxide removal, marine biogeochemistry, coastal ecosystems, enhanced weathering, carbon verification, ocean acidification, sediment chemistry, climate governance, geoengineering, carbon markets, marine carbon dioxide removal

The Mississippi River Basin covers approximately 41% of the contiguous United States and encompasses roughly 65% of U.S. croplands. For generations, farmers in this area have utilized liming to manage soil pH, reduce acidity, and improve crop yields. The practice involves spreading crushed limestone over agricultural fields. While the primary goal has historically been agricultural productivity, the new study reveals that this activity also has significant implications for climate change mitigation by removing carbon dioxide from the atmosphere.

Tim Jesper Suhrhoff, a geochemist at Yale and the first author of the study, noted that the results align climate action with practices that are already beneficial for farmers. Suhrhoff, a postdoctoral associate at the Yale Center for Natural Carbon Capture, explained that the study provides a more complete picture of the liming process. The research team analyzed more than 120 years of historical records to trace the long-term effects of adding crushed carbonate rock to agricultural soil. This extensive dataset allowed the researchers to evaluate the net carbon impact of liming over a significant period.

The mechanism by which liming stores carbon is similar to a related practice known as enhanced weathering. In this process, adding crushed rock to soil reacts with carbon dioxide to form stable bicarbonate ions. These ions can be transported through soils, groundwater, and rivers, eventually reaching the ocean where the associated carbon can remain stored for long periods. While enhanced weathering has often focused on silicate rocks, the new study demonstrates that carbonate-based liming also contributes to net carbon removal when evaluated against a realistic baseline.

A key advance of the study is its accounting for what would have occurred without liming. The researchers noted that even in the absence of lime, acidity generated by fertilizer use and air pollution would cause chemical reactions in the soil and water that release carbon dioxide. By comparing the liming scenario to this more complex baseline, the study finds that liming results in long-term net carbon removal. This approach provides a more accurate assessment of the practice’s climate benefits than previous methods that did not account for these background emissions.

The findings challenge the way agricultural liming is currently treated in conventional greenhouse gas accounting. The default methodology of the Intergovernmental Panel on Climate Change treats the carbon contained in applied lime as emitted carbon dioxide. However, the study suggests that a more complete framework could recognize situations where liming benefits both farmers and the climate. Suhrhoff and his colleagues emphasized that they support the IPCC’s efforts to document emissions but argued that accounting for liming’s net carbon removal would better align climate and agricultural incentives.

Christopher Reinhard, a professor at the Georgia Institute of Technology and co-corresponding author of the study, stated that better soil pH management can improve yields and soil health while also benefiting the climate. He suggested that this provides another reason to expand access to liming where it is sensible. The study’s results indicate that carbonate-based enhanced weathering may deserve renewed attention as a strategy for scaling up climate change mitigation. The researchers highlighted the potential for this practice to contribute significantly to global carbon removal efforts if adopted more broadly.

Noah Planavsky, a professor of Earth and planetary science at Yale and a corresponding author, described the study as a unique opportunity to trace historical records that demonstrate the effectiveness of enhanced weathering. He noted that the process already provides benefits to farmers and is now shown to be beneficial for the climate by removing carbon dioxide from the atmosphere. Planavsky, who is also a faculty member of the Yale Center for Natural Carbon Capture, emphasized the importance of understanding the long-term impacts of agricultural practices on the global carbon cycle.

The study estimates that since 1900, liming in the Mississippi River Basin has removed between 300 and 400 million metric tons of carbon dioxide. This substantial amount of carbon removal suggests an opportunity to scale up enhanced weathering by helping more farmers conduct agricultural liming. However, the researchers noted that the climate impact of liming will vary depending on local factors such as existing soil acidity, soil buffering capacity, and hydrology. The magnitude and duration of any upfront carbon dioxide emissions, as well as the efficiency of carbon removal, depend on these specific conditions.

Despite the promising findings, the researchers cautioned that the results from the Mississippi River Basin will not always transfer directly to every agricultural setting. Planavhoff noted that many farmers currently cannot afford optimal soil pH management and suggested that funding mechanisms could be developed to support this process by taking into account the carbon removals. The study was supported by funding from the Yale Center for Natural Carbon Capture, the Swiss National Science Foundation, the Environmental Defense Fund, the Foundation for Science and Technology, and the U.S. Department of Energy. Co-authors of the study include researchers from Yale, the Georgia Institute of Technology, Newcastle University, and Texas A&M University.

Subject of Research: Climate Change

Article Title: Adding limestone to Mississippi River Basin farmlands acts as a major carbon sink, study finds

Article References: Adding limestone to Mississippi River Basin farmlands acts as a major carbon sink, study finds. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: carbon sink, agricultural liming, Mississippi River Basin, enhanced weathering, soil management, climate mitigation, Yale University, Nature journal, Adding, limestone, Mississippi, River

The classic view of weathering as a stabilizing feedback traces back to influential work in the 1980s and 1990s. Robert Berner and colleagues formalized how silicate weathering responds to atmospheric carbon dioxide and temperature, creating a negative feedback loop: more carbon dioxide warms the planet and acidifies rain, which accelerates weathering, which in turn removes carbon dioxide from the atmosphere. Later, Maureen Raymo and William Ruddiman proposed that the uplift of mountain ranges such as the Himalaya may have cooled the Cenozoic Earth by exposing fresh rock to erosion. Francis Macdonald and colleagues later connected arc volcanism and associated weathering to major climatic transitions. These frameworks cemented the idea that mountain building and rock exposure are, in broad strokes, allies of a cool climate.

But as Bufe emphasizes, drawing down carbon dioxide is only one side of the ledger. Weathering and erosion also release carbon. The oxidation of fossil organic carbon buried in sedimentary rocks, and the oxidation of sulfide minerals such as pyrite, both deliver carbon dioxide to the atmosphere, in some landscapes at rates that rival or exceed the silicate weathering sink. Recent work by Bufe, Jeremy Rugenstein and Niels Hovius, published in Science in 2024, compiled global evidence that mountain ranges act not merely as carbon sinks but as carbon sources as well, with the balance between drawdown and release depending on what the rocks are made of, how fast they erode, and how water moves through them. In the Southern Alps of New Zealand, for example, rapid erosion of carbon-rich sedimentary rock can push the net carbon balance toward emission, whereas volcanic arcs dominated by fresh basalt tend to favor drawdown.

The picture grows still more complicated when biology and hydrology enter the equation. Susan Brantley and colleagues showed in 2023 that the depth and structure of the critical zone, the weathered skin of Earth where rock, soil, water and life interact, exert fundamental control on how much mineral surface area is available for reactions. Vegetation, microbial communities and soil organic matter can both accelerate mineral dissolution and shield it from infiltrating water. Meanwhile, organic carbon itself is constantly being eroded from soils, transported by rivers, buried in floodplains and deltas, or oxidized back to carbon dioxide. Studies led by Robert Hilton and A. J. West have mapped this biospheric carbon loop, and work by Guillaume Soulet and colleagues has quantified how efficiently the biosphere exchanges carbon with the atmosphere through erosion, complicating any simple accounting of weathering as a one-way carbon pump. Sue Tank and colleagues have further shown that in high-latitude permafrost landscapes, the fate of weathering-derived carbon in streams and lakes can shift dramatically as climates warm.

Spatial scale matters profoundly. A weathering flux measured on a single hillslope may not scale linearly to a whole catchment, and catchment-scale estimates may not extrapolate to mountain belts or continents. Supply of fresh mineral surface, runoff, temperature and lithology each impose their own dependencies, and these dependencies can switch sign across environments. In hot, wet tropical basaltic terrains, weathering rates can be extraordinarily high and largely supply-limited. In cold, arid or transport-limited settings, the same mineralogy may weather sluggishly. Time introduces its own twists: pulses of tectonic uplift or glacial grinding expose fresh rock that weathers rapidly at first, then slows as easily dissolved minerals are exhausted. Over million-year timescales, these transients mean that today’s weathering fluxes partly reflect climate and tectonics from deep in the past, making it treacherous to read modern weathering rates as a simple response to modern conditions.

Disciplinary boundaries compound the challenge. Geochemists who trace dissolved ions in rivers, geomorphologists who measure erosion and sediment transport, soil scientists who study profile development, ecologists who quantify vegetation dynamics and carbon cycling, and climate modelers who simulate global feedbacks each hold pieces of the puzzle. Bufe argues that only research spanning spatial scales, temporal scales and disciplines can resolve how weathering modulates the carbon cycle in a warming world. As the climate changes, weathering itself will change: rising temperatures and altered hydrology will accelerate some reactions, thawing permafrost will expose new mineral surfaces and release ancient organic carbon, and intensifying storms will mobilize sediment in ways that models are only beginning to capture. Whether the geological thermostat will help blunt anthropogenic warming, and on what timescale, remains an open and consequential question.

It is against this backdrop of genuine scientific uncertainty that Bufe levels his sharpest critique. Enhanced rock weathering, the practice of spreading crushed silicate rock such as basalt on farmland to accelerate carbon dioxide drawdown, has surged in popularity as a carbon removal strategy. A growing industry now sells carbon credits based on the assumption that a quantifiable and permanent fraction of the applied rock dissolves, and that the resulting bicarbonate represents durable carbon sequestration. Commercial rankings of the best enhanced weathering credit projects have proliferated, and the market is expanding faster than the underlying science can constrain it. In a companion review in Nature Reviews Earth & Environment, Maximilian Schiedung and colleagues catalogued the substantial uncertainties in measuring, reporting and verifying enhanced weathering outcomes, from dissolution kinetics in real soils to secondary carbonate formation that can return carbon to the atmosphere.

Bufe contends that issuing carbon credits for enhanced weathering at the present stage is premature. The very complexities that make natural weathering hard to quantify, the competing sources and sinks, the dependence on lithology, hydrology, biology and timescale, apply with full force to engineered deployments. Crushed rock applied to one field may behave very differently from the same material in another, and the net climate benefit must account for the carbon cost of mining, grinding and transporting rock, as well as for nitrous oxide and other greenhouse gas effects that soil amendments can trigger. Without robust, context-specific measurement of how much carbon is actually drawn down and for how long, credits risk monetizing an assumption rather than a verified outcome, potentially undermining confidence in carbon removal as a whole.

None of this argues that enhanced weathering should be abandoned, Bufe stresses. Rock weathering remains one of the most promising and scalable negative-emissions pathways, rooted in a process that has regulated Earth’s climate for eons. But realizing that promise responsibly demands investment in the fundamental science: long-term field experiments across climates and soil types, improved tracers of mineral dissolution and carbon fate in rivers and oceans, and models that honor the tangled interplay of tectonics, erosion, hydrology and life. The geological thermostat is real, but it is not a simple dial. Understanding its gears, and the directions in which some of them spin backward, is a prerequisite for turning rock weathering into a trustworthy tool against climate change rather than a cautionary tale about moving faster than the science.

Subject of Research: The complex role of rock weathering in Earth's carbon cycle and the risks of premature carbon crediting for enhanced weathering

Article Title: Rock weathering’s tangled role in Earth’s carbon cycle

Article References: Bufe, A. (2026). Rock weathering’s tangled role in Earth’s carbon cycle. Nature Water. https://doi.org/10.1038/s44221-026-00707-9

Image Credits: AI Generated

DOI: 10.1038/s44221-026-00707-9

Keywords: rock weathering, carbon cycle, enhanced weathering, carbon credits, chemical weathering, silicate minerals, carbon dioxide removal, geomorphology, biogeochemistry, erosion, climate mitigation, Nature Water