We’ve all heard about DACS. But while the world is holding its breath for news from the Orca removal plant in Iceland, others are venturing into much less chartered waters. Ocean carbon dioxide removal is still a new topic in climate circles, yet it already has strong proponents and critics on both sides. What does it mean for us, the ecosystems, and the future of our warming planet?

The ultimate buffer

Since we started emitting unprecedented amounts of carbon dioxide around the time of the industrial revolution, the oceans have been doing the majority of the heavy lifting to keep us afloat. Only between 1994 and 2007, oceans absorbed 34 gigatonnes of carbon dioxide, or roughly 1/3rd of what humans put into the atmosphere during that period, according to a Science study. Ocean ecosystems act as an ultimate buffer by permanently sequestering carbon in coastal soils and seabeds via primary producers such as mangroves, phytoplankton, and seaweed.

However, the growing concentration of CO2 means the pace with which they can continuously absorb it is slowing down. It also means the water is becoming increasingly acidic, which in turn threatens marine ecosystems such as coral reefs and shellfish.

Ocean’s natural capacity fizzing out

This is where ocean carbon dioxide removal (CDR) comes in. The emerging technology relies on the principle called Henry’s Law - the very reason why a bottle of a fizzy drink turns flat if left unattended. In line with Henry’s law, the gas has a natural affinity to flow from higher concentrations to lower concentrations to achieve equilibrium. Up until now, the oceans absorbed CO2 as its concentration was lower than in the atmosphere - but as the recent ocean data is telling us - this is not something we can rely on much for longer.

The science behind ocean CDR works by applying a voltage across a stack of membranes to split the seawater. This converts bicarbonates in the water to molecules of CO2, which can then be removed under a vacuum. A recent breakthrough method evolved by a team at MIT omits the use of costly membranes altogether and alternatively uses electrochemical cells to acidify and then alkalize the water molecules in a cyclic process. The output is valuable hydrogen or concentrated CO2 for industrial use or storage. 

Localised silver bullet

According to Allan Hatton, a Ralph Landau Professor of MIT Chemical Engineering, a reinjection of the treated water could slowly counteract ocean acidification - at least locally. This could find its application in places like fish farms that acidify the nearby waters. When done in a controlled and dispersed manner, it would also pose minimal risks to the ecosystems. 

As with all emerging CDR solutions, applications remain within the theoretical realm until they can breach the financing barrier. One of the front runners in the race is a  Caltech startup Captura founded in 2021. The company is utilizing the  $1 million from Elon Musk’s XPrize competition to promote its most recent pilot project, AltaSea. Based on the Los Angeles Port,  the pilot is 10 times bigger than the most recent prototype and should be able to take about 100 tons of CO2 out of the ocean a year.  To put it in perspective, the tech is still in its infancy - a successful operation would be sucking out the equivalent of removing 22 cars off the road. And even that remains incredibly expensive. 

The dark side of CDR

While some are drawing exponential graphs following the rapid scaling up of the technology to the Nth magnitude, others openly raise their concerns. The biggest qualm is around making sure that the massive floating recovery facility is in no way harmful to the ocean. The water filtering system can pose a risk to smaller but vital plankton particles that form the basics of deep water ecosystems. Further up the food chain, the machinery and noise can further disrupt fish and marine life. 

There are other reasons to be sceptical. The most generous backer behind the Captura project is Southern California Gas, the biggest gas utility in the US. Aramco and Equinor - oil and gas giants - are also among Captura’s supporters. 

“Across the board, the biggest backers [of carbon removal] are the fossil fuel industry and partners. It ends up being an industry scam or an industry distraction from real climate action, which is rapidly reducing fossil fuel extraction and use,” says Shaye Wolf, a climate science director at the Center for Biological Diversity.

Whether ocean carbon dioxide removal proves a valuable asset in the portfolio of projects that have an actual chance of moving the needle is yet to be determined. What is certain though is that carbon removal should not be treated as a viable mitigation solution for climate change - but only relied upon in the case of industries that are hard to decarbonise completely. Regardless, boosting the ocean’s ability to naturally absorb carbon dioxide can be further explored through solutions such as enhanced rock weathering and/or ocean alkalinity management. In the face of the regenerative capacity of nature-based CDR approaches, Captura’s early efforts remain a drop in the ocean.