Carbon does not disappear—it gets locked into different forms
Humanity has long looked to nature's own rhythms for guidance, and now two technologies — enhanced weathering and ocean alkalinity enhancement — attempt to borrow and accelerate those rhythms to draw carbon from the sky. Backed by major investors and beginning to generate tradeable carbon credits, these approaches carry real promise. Yet a new assessment in Science quietly asks the harder question: not whether the chemistry works, but whether the carbon actually stays removed — or simply wanders through soil, rivers, and coastal waters before slipping back into the cycle it was meant to escape. The integrity of an entire class of climate solutions may rest on how honestly that question is answered.
- Startups funded by Google and Microsoft are already spreading crushed rock across farmland and adjusting ocean chemistry, with carbon credit markets beginning to price the results as if the science were settled.
- A peer-reviewed assessment in Science now warns that the journey captured carbon must take — through soil, rivers, estuaries, and coastal zones — is far messier than current models assume, with significant losses possible along the way.
- A subtler threat compounds the first: artificially boosting alkalinity in one place may simply displace carbon removal that nature would have performed elsewhere, making the intervention redistributive rather than truly additional.
- Field trials have largely measured success at the point of application, leaving the downstream fate of captured carbon — across entire watersheds and into the open ocean — poorly understood and largely untracked.
- Researchers point to New Zealand's volcanic geology, high rainfall, and land-sea connectivity as a potential proving ground for whether these technologies deliver durable, additional removal or merely a promising illusion at scale.
Two technologies designed to accelerate nature's own carbon-removal processes are moving quickly from concept to commercial deployment. Enhanced weathering grinds rock into fine powder and spreads it across agricultural land, speeding up the slow chemical dissolution that ordinarily unfolds over millennia. Ocean alkalinity enhancement applies a parallel logic to seawater, amplifying the ocean's innate capacity to absorb atmospheric carbon dioxide. With investment rising and voluntary carbon credit markets beginning to trade on their outputs, the premise seems straightforward: harness what nature already does, only faster.
A new assessment published in Science complicates that picture. The underlying chemistry is not in dispute. What is in dispute is the journey — the winding path that captured carbon must travel through soils, rivers, estuaries, and coastal waters before reaching the open ocean and genuine long-term storage. Current models tend to treat this journey as reliable. The research suggests it is not. Dissolved minerals can recombine into clays and other compounds as they move through soil, locking carbon away from the ocean rather than delivering it there. In coastal waters, alkalinity can cycle back into solid form before contributing to permanent storage. The losses vary with climate, rainfall, soil chemistry, and biology — factors that differ dramatically across geographies.
A second problem is more conceptual. Artificially raising alkalinity in one part of the Earth system may suppress natural weathering that would have occurred elsewhere anyway. If that is the case, the intervention is not removing additional carbon from the atmosphere — it is simply relocating carbon removal that nature had already scheduled. For climate strategy, the distinction between additive and redistributive action is not a technicality; it is the entire point.
Most field trials have measured what happens at the application site, where results look encouraging. But the durability of storage is determined downstream — across catchments, river systems, and coastal zones far removed from where the technology operates. Neither enhanced weathering nor ocean alkalinity enhancement is dismissed by the research; both may yet contribute meaningfully to mitigation. The urgent question, as these approaches scale toward global carbon credit markets, is whether they contribute as much and as durably as current estimates claim. New Zealand, with its volcanic soils, high rainfall, and tight land-sea connectivity, has been identified as an ideal environment for tracking how alkalinity and carbon actually move through the Earth system — and whether removal, once achieved, truly holds.
Two technologies that speed up nature's own carbon-removal processes are moving rapidly from laboratory concept into the real world. Enhanced weathering crushes rock into fine powder and spreads it across farmland, mimicking—but vastly accelerating—the slow chemical breakdown that happens when rainwater dissolves minerals from stone. Ocean alkalinity enhancement takes a similar approach in seawater, boosting the ocean's natural capacity to absorb carbon dioxide from the air. Startups backed by Google and Microsoft are already running field trials. Investment is climbing. Carbon credits are beginning to trade on voluntary markets. The premise is straightforward: if you speed up what nature does anyway, you can pull carbon from the atmosphere faster and store it safely in the ocean for centuries.
But a new assessment published in Science suggests the math may not work as cleanly as the headlines promise. The problem is not with the basic chemistry—that part is sound. The problem is with what happens in between: the messy, complex journey that captured carbon must take through soil, rivers, estuaries, and coastal waters before it reaches the open ocean and long-term storage. Current models tend to assume this journey is straightforward. In reality, it is not.
When minerals dissolve during enhanced weathering, the dissolved elements can become trapped again as they move through the environment. Water seeping through soil, for instance, can cause those elements to recombine into new minerals—clays and other compounds—that lock the carbon away from the ocean. The same thing happens in coastal waters during ocean alkalinity enhancement. Dissolved materials interact with sediments and seawater chemistry, recycling alkalinity back into solid form before it ever contributes to permanent storage. The net effect is that some of the carbon that was supposedly captured gets lost along the way. How much? That depends on climate, rainfall, soil chemistry, and biological activity—all variables that differ wildly from place to place.
There is a second, subtler problem. When you artificially increase alkalinity in one part of the Earth system, you may inadvertently suppress the natural weathering and carbon removal that would have happened anyway elsewhere. The carbon you think you are removing might simply be carbon that nature would have removed on its own, just relocated in time and space. That distinction matters enormously for climate strategy. If the goal is to pull additional carbon from the atmosphere—not just shuffle existing carbon around—then you need to know whether your intervention is truly additive or merely redistributive.
Most field trials to date have focused on what happens at the application site itself: the rocks dissolve, the alkalinity increases, the measurements look good. But the real test of durability plays out downstream, across entire river systems and coastal zones. A single farm trial tells you little about what happens when that alkalinity travels through a catchment, down a river, and into the ocean. The long-term storage question—whether carbon remains locked away for decades or centuries—depends on processes that occur far from where the technology is deployed.
None of this means enhanced weathering or ocean alkalinity enhancement are worthless. Both could contribute meaningfully to climate mitigation. The question is whether they contribute as much as current estimates suggest, and whether they contribute durably. As these technologies move toward large-scale deployment and begin generating carbon credits at a global scale, that distinction becomes critical. New Zealand may offer a useful testing ground: its volcanic rocks, high rainfall, and strong connectivity between land and sea create ideal conditions for tracking how alkalinity and carbon actually move through the Earth system over time. If these approaches are going to play a major role in future climate strategy, we need to understand not just how fast minerals dissolve, but whether the carbon stays removed—and whether the removal is truly additional.
Notable Quotes
The true additional carbon removed from the atmosphere may be smaller than headline estimates suggest— Science assessment on enhanced weathering and ocean alkalinity enhancement
The central question is how much carbon remains removed from the atmosphere over decades to centuries—and whether that removal is truly additional— Research findings on carbon durability
The Hearth Conversation Another angle on the story
So these technologies are just speeding up what nature already does. Why wouldn't that work?
It works in principle. The chemistry is real. The problem is that nature's carbon cycle is not a simple pipeline. It is a web of interconnected processes, and when you accelerate one part of it, you create side effects in other parts.
Like what?
Like carbon getting trapped in new minerals as it moves through soil and water. Or natural weathering in one place being suppressed because you artificially increased alkalinity somewhere else. The carbon does not disappear—it just gets locked into different forms, or it never leaves the atmosphere in the first place.
So the companies claiming they are removing carbon might be overstating it?
Possibly. Current models assume the carbon will reliably reach the ocean and stay there. But those models do not account for all the ways the carbon can be lost or recycled back into solid form along the way.
How much carbon are we talking about?
That is the problem. Nobody knows yet. It depends on rainfall, soil chemistry, where you deploy the technology. A farm in New Zealand might see very different results than a farm in California. The field trials are too small and too focused on the application site itself to answer the durability question.
What would it take to know for sure?
You would need to track the carbon through entire river systems and coastal zones over decades. You would need to understand whether the removal is truly additional or just displacing carbon that nature would have removed anyway. That is expensive and slow work, and it is not what most trials are designed to measure.