Can the sea soak up our excess carbon dioxide? These scientists are finding out

Beneath the smokestacks of the power plant that tower over Halifax harbour, Will Burt, chief ocean scientist at Planetary Technologies, leads a tour around Planetary’s site.

The site — which consists of a shipping container housing an array of sensors, a mixing tank, and dozens of metres of tubes snaking in and out of the harbour — is where the company hopes it will begin to change the trajectory of climate change. 

The process uses ocean alkalinity enhancement — a way of accelerating the natural process that occurs when alkaline (or chemically basic) rock washes into the sea — to draw carbon dioxide out of the atmosphere.

As human-caused carbon emissions have increased, the ocean has absorbed more of the gas; roughly 25 percent of those human-caused carbon emissions get sucked up by the ocean. Once dissolved in seawater, that CO2 forms an acid, acidifying the ocean.

Adding alkaline rock — which Burt says can be thought of as an antacid — neutralizes that acid, converting the CO2 into harmless bicarbonate. But reducing the amount of CO2 in the water doesn’t only do that. 

“Now you’ve essentially created a vacuum where the CO2 in the water is less than the CO2 in the air. And so naturally the ocean will take up CO2 from the air to fill that void.” 

Planetary began testing their version of this idea last year. They adding powdered magnesium oxide (an industrial by-product) to the seawater used in the cooling loops of the power plant, in trials starting last year. 

As the pace of climate change has accelerated, more companies are exploring marine carbon dioxide removal. It’s a form of climate change mitigation that could be enormously profitable through the sale of carbon removal credits. 

There’s no guarantee, and no one’s assuming that this will work. We just want to see if it’s possible.– Ruth Musgrave, Dalhousie University

Marine carbon dioxide removal is also the focus of growing scientific attention, and a $15-million international academic collaboration, called Ocean Alk-Align, headquartered in Halifax, is researching the effectiveness and the safety of tweaking the ocean’s chemistry — a kind of independent oversight scientists say is essential. 

“There is a lot of work to be done to determine whether any [carbon dioxide removal] technology, but [ocean alkalinity enhancement], in particular, can work and be scaled up and can be safe and effective,” says Ocean Alk-Align investigator and Dalhousie professor Katja Fennel. “We’re not at the point where this is off-the-shelf ready technology. There’s still many open questions.”

WATCH: Planetary Technology’s Halifax Carbon Removal Pilot Results:https://www.youtube.com/watch?v=si=AU5er5u9GRvOSSMo

Fennel says the project focuses on three main areas: the efficacy and permanence of carbon dioxide removal using this approach; the environmental costs and potential positive effects, and the quantification of the carbon taken out of the atmosphere — with the last part an essential part of forming a valid basis for the sale of carbon credits.

Fennel says she hasn’t always been receptive to marine carbon dioxide removal. The idea has been around, in different forms, for decades.

But one strength of ocean alkalinity enhancement is that it accelerates a natural process in the world’s oceans, and Fennel says she’s confident its effects can be measured. As the predictions about climate change have grown increasingly dire, Fennel says she felt she had to get involved.

“Even the IPCC [Intergovernmental Panel on Climate Change] … now say that it’s clear that in addition to emission reductions, we need to research technologies that could take CO2 out of the atmosphere,” she says. “It’s just too late now to prevent the worst negative consequences from global warming by emission reductions alone.”

On the other side of the Atlantic, at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, on the Baltic Sea, scientists involved in Ocean Alk-Align are investigating the potential impact on ecosystems.

Researchers there are attempting to assess the effect on marine life, as well as ocean chemistry. 

Ocean biogeochemist Kai Schulz says the work, which involves adding different alkaline materials to floating containment vessels filled with water in the Kiel fjord, allows scientists to assess their impact on water chemistry and how this, in turn, affects microscopic plants and animals in the water.

So far, Schulz says that work suggests a potential difference in effects based on how alkalinity is delivered, and on the time of year it’s applied.

“One interesting question is, maybe there are seasons that should be avoided for alkalinity enhancement and others in which it might be more safe.”

Either way, as scientists attempt to fill in more of the gaps, Schulz says it’s important to note that the researchers involved in the Ocean Alk-Align study aren’t advocating for this approach.

“What we’re advocating [for] is the research on it, to figure out, is it environmentally safe? What is the safe operating range? And then there needs to be, obviously, a public, open discussion on whether we want to employ this on a bigger scale.”

In Halifax harbour, researchers have been taking monthly measurements to establish the background conditions in the harbour and the adjoining Bedford Basin, in order to understand the environment’s natural physics and chemistry.

Ruth Musgrave, assistant professor at Dalhousie University and a Canada Research Chair in physical oceanography, says this data is fed into models that compare a harbour where alkalinity isn’t added, to a harbour where it is.

This allows researchers to quantify how much CO2 is taken up; it also grants researchers a better understanding of the complex processes that could affect the efficacy and impact of adding alkalinity. 

Musgrave says the only way to truly assess those impacts is in an ocean setting, because the ocean is too complex to represent in a lab. In other places, similar proposed tests have prompted public concern, and Musgrave says she is sympathetic to those worries. 

“I would also be skeptical if I was on the outside of this, and I think that skepticism is fair, and we have to address it,” she says. “But this is the only way we’re going to be able to assess whether this is a good idea or not.”

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If it is a good idea, the payoff could be massive. Some estimates have placed the carbon removal potential at 30 billion tonnes per year (by contrast, global emissions in 2023 were 37.4 billion tonnes). 

Fulfilling that potential requires not only resolving questions about efficacy and safety, but also navigating the logistical hurdles associated with sourcing and dispersing sufficient alkaline material, and developing regulations for a brand new industry.

But with the ocean already undergoing severe shifts as a result of climate change, the scientists participating in this work say they are finding hope in the idea that there may be a way to steer that change for the better. 

“So much of my life I felt like I’m just watching this train wreck in progress, and I have no control over it; there’s nothing I can do,” says Musgrave. “It’s motivating to work on something where there is a promise, perhaps, or a hope — but there’s no guarantee, and no one’s assuming that this will work. We just want to see if it’s possible.”