Over the course of millions of years, the earth regularly removes carbon dioxide from the atmosphere through a natural process called weathering, when exposure to the elements wears down surface rocks and silicate minerals.
But at the rate humans have been producing and releasing carbon dioxide into the atmosphere since the Industrial Revolution, this process that happens on a geological time scale just isn’t fast enough to keep up.
A corn and soybean farm in the village of Buckingham, Illinois, 60 miles south of Chicago, is providing the testing grounds for an Irish startup attempting to “enhance” weathering, thus shortening the process from millenniums to decades.
The Illinois trial, the first of its kind in the United States, is one of many efforts to leverage the potential of different materials to combat global warming.
“The whole carbon removal concept exists because we have to backtrack — we’ve gone too far,” said Maurice Bryson, founder and CEO of Irish startup Silicate. “The idea of this solution is, we’re using what’s already there.”
Last week, Silicate began covering over 100 acres of farmland with 500 to 1,000 tons of fine dust from ready-mix concrete that has been returned. Researchers at the climate tech company hope the concrete dust can permanently remove up to 220 tons of carbon dioxide from the atmosphere and transfer it to the soil over the course of a year, the equivalent of CO2 emissions from almost 50 cars in one year.
Carbon dioxide removal is a technique by which carbon that is already in the atmosphere is removed through processes like enhanced weathering, reforestation and direct air capture, which uses engineered mechanical or chemical systems to capture carbon dioxide directly from the air. Earlier this month, The New York Times reported a California startup was the first to commercially market direct air capture in the United States.
But direct air capture is expensive. According to climate economist Danny Cullenward, it is also extremely energy-intensive and sometimes requires a lot of water.
And planting trees is not quick — older trees are more efficient at sequestering carbon than younger trees — or permanent — reforestation is a reversible solution because trees are not permanent reservoirs like rocks underground and they can release carbon again if cut down or destroyed in wildfires.
In theory, these pitfalls should not confront enhanced weathering, experts say.
“If it’s done well, it can result in very long-term, highly durable carbon storage,” Cullenward said. “And because you’re relying on essentially natural chemical processes without extremely energy-intensive production techniques, if you can figure out how to make this work, the pathway to scaling it is potentially a little bit easier and cheaper than it would be for some of the other competing carbon removal technologies.”
Decarbonization, or the reduction and removal of greenhouse gas emissions from the atmosphere, also encompasses other approaches like carbon capture and storage, where the gas is contained and stored before it can be released into the atmosphere.
This approach has become a point of contention in Illinois particularly over the past year after an Omaha company announced a project to build a pipeline that would transport millions of tons of liquid carbon dioxide from ethanol and fertilizer plants in South Dakota, Minnesota, Nebraska, Iowa and Illinois and store it deep underground in central Illinois.
Opposition from farmers, landowners and environmentalists eventually helped derail plans for the Heartland Greenway pipeline, a fight that encapsulates the myriad opinions on the most effective approach to decarbonization, which will likely be on display at the United Nations Climate Change Conference in Dubai, United Arab Emirates, later this month.
Scientists underscore the exploratory nature of decarbonization research: There is still much to understand and figure out.
“What I would emphasize is that it’s still early days for this,” said Frank McDermott, a professor in the Department of Earth Sciences at University College Dublin, who since 2021, has worked with Bryson as an independent scientific collaborator. “There’s a lot of efforts going on throughout the world at the moment, in Brazil and the United States and Europe adding various kinds of materials — rocks, basalt, steel slag, all sorts of materials — on soils. Concrete too.”
To meet their ambitious goal, researchers at Silicate are simply leveraging a process as old as the earth itself.
“Weathering is a natural phenomenon. It occurs all around us,” McDermott said. “Everything that’s exposed to the atmosphere eventually breaks down — whether it’s natural materials like rocks and soils, or man-made objects, like buildings or monuments — they all degrade over time. It’s mainly because of acid from rainfall.”
As rain falls and dissolves carbon dioxide in the atmosphere, it forms carbonic acid, a compound people may recognize from the sparkling water sold at restaurants and grocery stores. Through weathering, carbonic acid reacts with rocks and minerals and is converted into bicarbonate ions that store carbon.
“We’re just hoping that when the (concrete) dissolves you get more of that bicarbonate, which is soluble in water, and it percolates through the soil, eventually into the rivers and into the ocean, where it gets stored,” said Ruadhán Magee, a postdoctoral researcher at Silicate. The bicarbonate can stay there for well over 80,000 years, he said.
Cement — one of the two main components of concrete — has high concentrations of calcium, a mineral that speeds up the weathering process.
After concrete dust is spread onto a large area of agricultural land, enhanced weathering will occur, removing atmospheric carbon at a faster rate than natural weathering would.
“It’s supposed to be like a sponge, soaking it up,” Bryson said.
Low cost, no maintenance
Researchers acknowledge it might seem counterintuitive that a grayish, human-made construction material could be good for the environment. But, besides removing carbon from the atmosphere, concrete dusted on cropland could also work as a soil pH amendment, offering benefits such as improved soil health and crop productivity.
“It’s something different,” said Erich Schott, the farm owner. “Which is fine … it’s how we learn.”
Agricultural lime has long been applied to gardens, lawns and fields to make soil less acidic and more alkaline, adding nutrients such as phosphorus and zinc for good bacteria to grow, as well as improving water penetration.
Applying concrete to cropland would ideally also be low-cost, as the material requires no maintenance after being applied to fields. And its supply would be readily available from the construction industry: Local concrete and materials company Ozinga is providing the milled concrete for the trial at Schott Farms.
In a very rough estimate, approximately 400 million cubic yards of concrete are used in the United States every year, according to Rick Bohan, senior vice president of sustainability at the Portland Cement Association, a nonprofit that promotes the research and use of cement and concrete.
“There is a certain amount of concrete that will always be wasted,” Bohan said. “And it’s a small amount, it’s probably in the single digits.”
According to the National Ready Mixed Concrete Association, approximately 1% to 2% of concrete is returned to suppliers, but most of it is reused to make new concrete or other products like landscaping blocks and barriers. Some of it is crushed and made into aggregate for fill and base material or as recycled aggregate in new concrete.
For Schott Farms, Ozinga is crushing concrete that has been returned, which according to the company accounts for less than 1% of their production. But that small percentage still represents “quite a bit of material,” according to Ryan Cialdella, Ozinga’s vice president of research and development.
The company will also scoop up fine concrete particles that settle in treated ponds after equipment is cleaned. Cialdella said Silicate’s trial will give what would have been waste products a “much more valuable endgame.”
Because of its synthetic origin, there are always concerns that spreading materials like concrete can do more harm than good to the soil.
Bryson said the company’s trials in Ireland complied with European Union liming standards, which require products used to lime fields or change the pH of the soil meet limits for the presence of elements like chromium and nickel.
“We’re pretty confident the material is safe,” he said. “We wouldn’t be putting it out there if we weren’t.”
Bryson said Silicate analyzes the concrete dust before spreading it to make sure there is no “nasty stuff” such as coal ash, which is sometimes used in concrete — or if there is, that it falls below certain levels to ensure its safe use. And as the company continues to test water samples from the fields where concrete is spread, Bryson said, researchers will keep an eye on possibly harmful leaching or contaminated water.
On a recent overcast morning, Bryson, Magee and a third Silicate researcher, Leo Hickey, walked with Schott through one of the soybean fields in his 5,000-acre farm. Tractor tire marks were still fresh in the mud since the beans had been harvested only a week before.
Hickey stopped next to a water sampler, which sucks in water through a vacuum from the soil. Then the researchers measured the temperature and soil pH and later analyzed the sample in a lab for the chemical reaction that produces the bicarbonate ions which store the carbon dioxide.
At the edge of a field closer to Schott’s farmhouse, where the only evidence of the recent harvest was the ears of corn scattered around, Hickey crouched next to a circular machine. It whirred as the top swung closed.
“There’s a constant flux of gases coming off the soil, and it’s just capturing that flux,” he explained.
The aptly named flux chamber draws air up from the ground, feeding the gases through a tubing system into a yellow box that sends information to two analyzers: the first for methane, carbon dioxide and water, the second for nitrous oxide.
Besides testing water and air, the researchers will also test soil samples and compare them with readings from nearby control areas to get a better picture of just how much carbon is actually being pulled from the atmosphere and into the soil.
Founded in County Sligo in 2021, Silicate has conducted similar projects it says have shown “huge promise” across Ireland, including on barley, oat and cauliflower crops.
Silicate says it is able to remove almost 5 tons of carbon dioxide per acre each year.
For its projects in Ireland, Silicate has measured the carbon dioxide removed from the atmosphere and sold carbon credits to private companies.
Buying carbon credits is a way for companies and people to compensate for their greenhouse gas emissions. They can do so by purchasing credits in carbon markets from companies like Silicate, which reduce emissions or remove them from the atmosphere to combat climate change.
But skeptics say that carbon credits cannot replace actions such as transitioning energy production away from polluting fossil fuels to clean renewable sources. This is because quantifying how much carbon has been successfully removed is an intricate challenge, said Cullenward, who has often criticized the carbon offsets industry.
“It is very difficult to make a claim about either avoiding emissions or removing CO2 from the atmosphere,” he said. “And there’s lots of different ways that uncertainty in those claims can manifest and lots of different reasons why those claims can be suspect.”
In the carbon offsets market, people often say they are doing something new when in reality they’re just taking credit for something that’s already happening, Cullenward said.
Another problem with the carbon credit market is that it doesn’t take into account how long carbon will be removed from the atmosphere. If it is rereleased within a short period of time, the benefit is minuscule.
“There’s this disconnect,” Cullenward said. “And when you justify permanent pollution with temporary benefits, eventually the bill comes due and the atmosphere gets screwed over.”
Enhanced weathering potentially offers permanent storage of the carbon it removes. But measuring how much is actually removed from the atmosphere will not be an easy feat.
“I’m not trying to say this is a bad idea,” Cullenward said. “But what I’m getting at is how hard it is to quantify the climate outcome, even if you think you’re actually correct. You know this is good, you just don’t know how good it is.”
Despite its promise, enhanced weathering raises a lot of big questions, said Freya Chay, program lead at the nonprofit Carbon Plan, which uses open data to analyze the scientific integrity of climate solutions such as carbon offsets and removal.
At Carbon Plan, Chay led the development of a tool that offers around 30 methods to estimate the net carbon removal of enhanced weathering at various stages.
The complexity of this tool alone encapsulates some of the challenges with quantification.
“We’re talking about processes related to soils, waters, biology, chemistry and environment. These are geochemical systems that are variable through time and space,” Chay said. “We’re also talking about a carbon removal approach that can have really large delays — both spatial and temporal delays — between putting that (concrete) down and actually removing carbon from the atmosphere. So it’s just a really complex system.”
The brains behind the trials at Schott Farms are acutely aware of the challenges associated with quantifying enhanced weathering results, especially given the researchers’ limitations of only being able to measure carbon removal at the farm.
“Then, what happens to the carbon?” said McDermott, Bryson’s research collaborator. “Does it all eventually make its way into the oceans, which we hope? Or do we lose some of the CO2 back into the air during transport, in rivers and streams? … I think all of us, all the companies involved and the researchers, are pretty much at the stage of focusing on the initial part, and most of us haven’t had a chance to look at more downstream stuff.”
A win-win for air and soil
Bryson said the carbon credit practice at Silicate might soon become an old model if the concrete dust proves to be beneficial for cropland.
“We might try and do all of that without selling carbon credits,” he said. “We’re providing with such value to the soil with this material, that maybe the carbon that we remove then leads to incredibly beneficial changes in pH. So we wouldn’t have to sell the carbon we removed, we’d just let that happen.”
If Silicate changed its business model from selling carbon credits to selling a service to farmers with carbon removal as a co-benefit, Cullenward said, that would be an innovative approach to carbon offsetting.
“This is music to my ears,” he said. “Because it has proven extremely difficult for even the most well-intentioned carbon (crediting) applications to appropriately quantify the climate benefits of interventions. And one of the things about enhanced weathering that is potentially so appealing, is that it is one of the few areas of carbon removal where there’s a very clear private benefit to landowners.”
If all goes well at the Schott Farms trial — considering the new crop types, soil composition and moisture levels the group of Irish researchers is working with — Silicate hopes to expand operations across Illinois and the region next season in late September and October, when farmers apply lime to their fields.
Their goal is to be able to eventually remove 50 million to 100 million tons of carbon dioxide from the atmosphere in the Midwest each year.
“It’s really important that we don’t say it’s all solved,” Bryson said. “It’s important for all of us in this space to be honest with each other. And the honesty is, there’s this huge potential here. But there’s work to be done that we’re getting on with doing.”
Cullenward emphasized that efforts to remove carbon from the atmosphere are still in the early stages, and the benefits have not been proven. People often say carbon removal is a central part of the climate mitigation story, he said. “It is not.”
These new approaches should not be equated, he said, with tangible, near-term opportunities to reduce pollution like using clean energy to reduce greenhouse gas emissions, “which need to be the vast majority of our focus.” That doesn’t mean carbon removal won’t become important in the long term, especially when it comes to stabilizing planetary temperatures.
“This is a civilizational-scale exercise we’re going through,” Cullenward said. “There are things that are at the beginning of the journey; there are things that are mature and ready to go.”
Climate experts believe it will take many different approaches in concert to slow global warming and stabilize the climate.
“We see a lot of innovative ideas that bubble to the top, and I always encourage people — it’s worth looking at these things. But for so many of them, you really have open questions about scalability, energy, feasibility, the economics,” said Bohan of the cement association. “I don’t ever want to dismiss any of them because I’m a big believer that it’s an ‘all of the above’ approach. That’s how I look at this. Is this going to change the world? Probably not. But that doesn’t mean it’s not worth looking at and researching.”