The world's oceans stow vast amounts of carbon dioxide. Now, a growing group of scientists and companies say they've found a way to increase that storage capacity by tweaking ocean water chemistry.
The technique, known as ocean alkalinity enhancement, usually involves dissolving acid-neutralizing rocks in the ocean, allowing it to absorb more carbon dioxide.
Researchers have been exploring this technology for the last five years, but over the last two months, at least a couple of start-ups have begun operation along the Atlantic and Pacific coasts. Planetary, a start-up based in Nova Scotia, removed 138 metric tons of carbon last month for Shopify and Stripe. The start-up Ebb Carbon is running a small site in Washington that can remove up to 100 carbon metric tons per year and committed in October to remove 350,000 metric tons of carbon from the atmosphere over the next decade for Microsoft.
Proponents of the technology say it's one of the most promising forms of carbon removal, which experts say will be necessary to meet climate goals even as the world cuts emissions.
But in order for this to make a dent, it will need to be scaled up toremove billions, not hundreds of thousands, of metric tons of carbon per year, Yale associate professor of earth and planetary sciences Matthew Eisaman said.
HOW IT WORKS
At its core, ocean alkalinity enhancement is a chemical reaction, one that is already happening in the ocean all the time.
"The ocean is the greatest carbon vault on the planet and its ability to permanently store CO2 resides not only on its immense size, but actually on the natural alkalinity of seawater," said Antonius Gagern, executive director of Carbon to Sea, an initiative that funds ocean alkalinity projects.
Today's ocean is slightly alkaline at a pH of 8.2, in part due to the chemical weathering of limestone, basalt and other rocks throughout Earth's history.
Dissolved carbon dioxide in the water reacts with these alkaline substances to form bicarbonate ions, a stable form of carbon that can trap the element for millennia, thereby reducing carbon dioxide in the atmosphere without acidifying the ocean. Then, to restore equilibrium, the ocean absorbs more carbon from the atmosphere. This chemical reaction makes the ocean the planet's largest carbon sink, a term referring to a natural or man-made reservoir that absorbs more carbon than it releases.
The new technology aims to enhance this natural process by adding alkaline minerals to the water, either in a crushed or dissolved form. After studying the potential of marine carbon removal technologies, the National Oceanic and Atmospheric Association found ocean alkalinity enhancement was the most effective at capturing carbon long-term and among the cheapest options.
Removing carbon could also helpprevent ocean acidification. Although the ocean's chemistry has varied through geologic time, it has become more acidic as it has absorbed more carbon from human-generated emissions, said Andy Jacobson, a geochemist at Northwestern University. The increased acidity makes it difficult for some marine organisms to build their skeletons and shells.
"In theory, [ocean alkalinity enhancement] has a lot going for it," Jacobson said. "But more research is needed to determine how effective it is and how permanent the carbon removal is."
WILL IT TAKE OFF?
Climate ventures and philanthropic funders are spending millions of dollars to fund ocean alkalinity enhancement.
Researchers are still investigating the best strategy to implement the method. Ebb Carbon, for example, takes existing saltwater waste streams from treatment and desalination plants and uses electricity to alkalize it before returning it to the ocean, said Eisaman, who is the start-up's co-founder and chief scientist.
Another method is depositing alkaline minerals or solution into the ocean using a ship; others want to enhance the rock weathering that already occurs on the coast.
One of the biggest challenges is measuring how much carbon this can sequester. Alkaline minerals quickly dissipate in a large body of water, and it's difficult to quantify the carbon removed, said Dariia Atamanchuk, senior research scientist at Dalhousie University in Nova Scotia who advises Planetary on measuring carbon.
Because questions remain about its impact on the ocean's ecosystems, any project would likely face opposition from the fishing industry.Communities on the East Coast have pushed back against proposals, saying the effects are not well understood.
"They should not be dumping anything into the ocean," said Beth Casoni, executive director of the Massachusetts Lobstermen's Association, adding that she is skeptical of "the notion that you can alkalize the ocean like the pool in your backyard."
The growing evidence from early studies in labs and controlled outdoor settings suggest no serious impacts on plankton, which are at the bottom of the food web.
Regulations from the Environmental Protection Agency would limit some impacts because, for some types of ocean alkalinity enhancement, it caps the seawater pH change that results from the addition of materials to a pH of nine, said Grace Andrews, executive director and founder of the nonprofit Hourglass Climate, which researches ocean alkalinity and its environmental impacts.
"Right now, most people are hesitant to say, 'This is definitely going to be helpful for marine life,' simply because of the scale required to change entire oceans," she said. "But it certainly has the potential."