To get there, scientists and startups are working on ways to tweak natural processes that already suck up carbon to enhance their utility as a carbon sink.
Some dream that these techniques will form part of a giant new industry that pulls enough carbon dioxide from the air to dial down the planet’s temperature. But the proposals come with environmental risks, and measuring the benefits is a challenge.
One natural process that sequesters carbon is known as rock weathering. Rainwater, which is slightly acidic because it contains dissolved carbon dioxide from the atmosphere, slowly breaks down some rocks, such as volcanic basalt. The process traps CO2 as bicarbonate, which eventually flows to the sea to be stored for millennia. Seattle-based Lithos Carbon is one of several startups trying to fast-track that process by spreading ground-up basalt on the soil.
A Market for Dust
It will take plenty of dust. Lithos wants to remove a billion tons of carbon dioxide from the air by 2030, a target that it says could take 4 billion tons of basalt—roughly half the weight of all the coal burned worldwide in 2022.
Lithos expects to remove around 20,000 tons of CO2 this year, working with farmers in the U.S., Brazil, Europe and elsewhere. It pays quarry owners for basalt dust, a mining byproduct, then pays farmers to spread it. For them, basalt dust is an alternative to the lime used on acidic soil.
This is possible because of the carbon market. Frontier, an “advance market commitment” launched last year by payment-processing platform Stripe, Meta Platforms, Alphabet, Shopify and McKinsey to sponsor carbon-removal technologies, agreed to pay Lithos $500 a metric ton to remove 640 tons of carbon dioxide. Frontier’s founding companies, plus others that joined this year, say they plan to commit more than $1 billion by 2030 to buy permanent carbon removal from suppliers offering promising new solutions.
The high price—compared with carbon offsets from forestry projects, which typically fetch a few dollars a ton—reflects enhanced weathering’s potential to store carbon for very long periods.
Rick Bennett, a farmer in Keysville, Va., who has spread basalt from Lithos on 163 acres of acidic soil, says lime would cost $150 an acre or more. Lithos paid him $50an acre to use basalt.
“That’s a no-brainer, if it works,” Bennett says. Various field tests have shown basalt can improve crop yields, but his results won’t be known until harvest time.
Lithos is selling carbon credits to other companies based on the CO2 it removes. Lithos Chief Executive and co-founder Mary Yap says the company could potentially charge farmers for basalt but hopes the carbon-credit sales will allow Lithos to avoid that.
The company takes soil samples to measure the weathering process using tests and software developed by Lithos co-founders Noah Planavsky, a Yale University geochemist, and Chris Reinhard, an Earth scientist at the Georgia Institute of Technology, who no longer have stakes in the company. As yet, there’s no agreed methodology for measuring the rate of carbon removal, which depends on factors like soil chemistry and dust consistency. The CO2 in rainwater that doesn’t react with the basalt returns to the atmosphere.
Without rigorous standards, Yap sees a risk of the nascent industry “blowing up on the launchpad.”
Changing the Ocean’s Chemistry
As the weathering process dissolves rock, it creates an alkaline solution that eventually washes out to sea. That causes chemical reactions that convert CO2 already in the ocean into stable bicarbonate and carbonate molecules and allow the water to absorb more atmospheric CO2. Some researchers believe that cycle could be accelerated by adding alkalinity to the sea, or with an electrochemical process that removes acid from the water.
The Carbon to Sea Initiative, a nonprofit research program launched this month by Mike Schroepfer, former chief technology officer of Facebook and Meta, said it raised more than $50 million to fund laboratory work, field trials and the development of measurement techniques to discover whether modifying the ocean’s alkalinity could be an effective way to remove CO2.
“We’re trying to get to a point where we can hopefully have results in the order of years, not decades,” Schroepfer says.
The program, funded by Schroepfer and other philanthropic backers including the charitable initiative of Facebook founder Mark Zuckerberg and his wife Priscilla Chan, said it has so far committed $23 million.
In one of the nine projects that have been funded, a team led by Adam Subhas, a scientist at the Woods Hole Oceanographic Institution, aims to start experiments off the Massachusetts coast in August. At first they will add dye to the water, using drones, satellites and aquatic sensors to observe its spread. The time water spends in contact with air influences the rate of CO2 removal, so assessing the effectiveness of ocean alkalinity enhancement, or OAE, depends on learning how the less-acidic water circulates.
Any added alkalinity—the Woods Hole team will add sodium hydroxide to the water in later tests—will rapidly disperse. That makes measurement tricky. Gauging the impact on CO2 is even harder, and must be estimated from changes in alkalinity, combined with laboratory data and knowledge of ocean currents. Taxpayers or corporations funding the effort would have to trust researchers’ models.
If successful, this approach to carbon removal could help counteract an impact of climate change—ocean acidification that threatens shellfish and other species.
Butscientists say ocean alkalinity enhancement also brings risks for wildlife in the waters. Excessive alkalinity swings could harm phytoplankton that support the food chain. Crushed rock added to the water could harbor toxic metals and could make it cloudy, potentially reducing photosynthesis.
In April on a beach in Cornwall, England, people protested plans by Planetary Technologies, another recipient of Carbon to Sea funding, to release highly diluted magnesium hydroxide via a wastewater pipe for testing purposes. Mike Kelland, chief executive of the Canadian startup, says the chemical, already used in water treatment, would be added in quantities well within legal limits. Planetary doesn’t yet have permission for the trial and is in talks with regulators, according to Kelland and a representative of the U.K.’s Environment Agency.
Planetary has sold carbon credits in advance of its removal operations to Shopify, and Kelland says the company is talking with other potential buyers that he declined to name.
OAE could change the Earth’s temperature only if it happens on a huge scale, so more fights are likely. As maritime laws weren’t written with carbon removal in mind, it’s a governance gray zone.
“This is going to be a big and messy industry, if and when it scales,” said Antonius Gagern, Carbon to Sea’s executive director. He says approaches that turn out to be too risky should be abandoned.
But Gagern, a marine scientist, says the unknowns should be considered alongside the impacts of climate change. Scientists say hotter, more acidic waters caused by carbon emissions could threaten much marine life.
Carbon-Hungry Trees
Living Carbon, a Hayward, Calif.-based biotech company, is approaching carbon removal on a micro scale. It has genetically engineered poplar trees that it says grow at a supercharged speed, absorbing CO2 and turning it into wood at an increased rate.
Some plants including pumpkins and green algae have genes that make the process of photosynthesis—the process by which plants use carbon dioxide and sunlight to grow—more efficient. The faster they grow, the faster they pull carbon from the air and store it in their living cells. Living Carbon co-founder Maddie Hall says the company added genes from those plants to its poplars.
The startup planted its seedlings in a managed forest in Georgia early this year, and recently planted two tracts on former coal mines in Ohio and Pennsylvania. Hall says Living Carbon has received commitments from companies to buy carbon credits in future.
In the greenhouse the super-poplars grew up to 53% faster than their non-GMO counterparts, according to a study by the company, but how they fare in the wild remains to be seen.
Lawren Sack, a professor of plant ecology at the University of California, Los Angeles, calls Living Carbon’s results “a very small first step.” The effectiveness of the company’s trees as a carbon-removal tool depends on complexities that require more study, including how their growth affects other plants and how long they last, he says.
Living Carbon’s poplars aren’t a permanent solution—they could succumb to pests, wildfire or logging. Fine-tuning trees for carbon removal could also come at the expense of biodiversity, if the result is homogeneous forests planted for carbon credits, experts say.
Hall says Living Carbon’s trees will only be planted in a diverse mix of local species. The poplars are female and don’t produce pollen, she adds, making them unlikely to reproduce.Still, there’s a small chance that wild trees could be fertilized and pass on the altered gene, she says.
Living Carbon is also experimenting with algae species that produce a highly durable biological polymer. If the algae could be genetically modified to make much more of it, it could store carbon for far longer periods than trees, the company says.
But for now, a more diverse range of souped-up trees is the priority. Already, Hall says, loblolly pines are sprouting in Living Carbon’s greenhouse—but it’s too early to say whether they’re outgrowing their all-natural cousins.
Write to Ed Ballard at ed.ballard@wsj.com
