Can we alter ocean chemistry to absorb carbon? Here are the pros and cons

As the planet warms, countries around the world are racing to meet their net zero targets set out in the 2015 Paris Agreement. To achieve this, we must collectively curb our net greenhouse gas emissions. These gases – the largest contributor being carbon dioxide (CO₂) – act as a cosmic blanket by trapping heat in Earth’s atmosphere. Scientists are investigating ways to lock up more atmospheric carbon in our oceans, forests and soils. One of the proposed methods is ocean alkalinity enhancement. This aims to boost the ocean’s natural ability to absorb and store atmospheric carbon dioxide by changing the chemistry of seawater. So how does this process work, and what are the risks? Let’s unpack the research. A lesson in ocean chemistry The ocean is one of the largest carbon stores on the planet. About 30% of the CO₂ we emit annually – through burning fossil fuels such as coal, oil and gas – are absorbed by our seas. The ocean’s ability to absorb CO₂ is largely determined by how alkaline it is. Seawater is naturally alkaline. This is because over millions of years, the ocean has absorbed alkaline minerals from the weathering and breakdown of rocks Read more: From laggard to leader? Why Australia must phase out fossil fuel exports, starting now What is ocean alkalinity enhancement? By taking up atmospheric carbon, the ocean has helped regulate Earth’s climate over long periods. However, this natural process is far too slow to combat climate change. That’s where ocean alkalinity enhancement comes in. Alkalinity enhancement accelerates this carbon capture process by increasing the ocean’s alkalinity. This allows seawater to convert more dissolved CO₂ into stable forms. As a result, the ocean absorbs more CO₂ overall and keeps more carbon out of our atmosphere. In practice, increasing the ocean’s alkalinity involves adding materials such as dissolved sodium hydroxide or ground-up silicate and carbonate rocks to seawater. So far, it has been tested through several small-scale projects. These typically involve researchers releasing alkaline materials at coastal locations, using ships or special facilities and equipment. Questions remain While this method seems promising, there are still some unknowns. Scale We don’t know whether it’s possible to roll it out at scale, which is key to reaching global net zero targets. Scientists are also investigating how well ocean alkalinity enhancement works in different regions and marine ecosystems. This means projects must be tailored to specific locations. Our research shows even seemingly minor differences in ocean currents, wind, water depth and seasonal conditions all affect how much CO₂ can be absorbed. CSIRO researchers conduct an ocean alkalinity enhancement field test. Harris Anderson Safety Early field trials and modelling suggest removing CO₂ through small-scale alkalinity enhancement projects had few measurable impacts on nearby protected areas. Several lab-based studies also suggest small increases in alkalinity have little to no effect on some Australian kelp and algae species. Meanwhile, other research identifies limitations on the amount that can be added and ecosystem effects from different alkaline materials. Scientists are working to add to this evidence base through proposed field tests in the Bass Strait, conducted aboard the RV Investigator. These tests, which will bring together experts and students from across Australia, will help us identify any environmental impacts and hone our skills in measuring changes caused by ocean alkalinity enhancement. Community support Without public support, alkalinity enhancement projects are unlikely to be successful. Research suggests communities are somewhat wary. Research from Tasmania shows people prefer to be involved in decision-making processes and not just consulted. Communities also want clear information about the environmental impacts of future projects. In Australia, we must also engage with First Nations communities when designing field tests and proposed projects. Only then can we draw on their deep knowledge and enduring connection to Sea Country. Read more: Plans to stabilise Earth’s climate rely on emerging carbon removal technology – we need to get moving Where to from here Our climate is rapidly changing. And unless we curb our carbon emissions, this trend will only get worse. Locking up atmospheric carbon dioxide through ocean alkalinity enhancement is one way to do this. However, changing the chemistry of our oceans comes with certain risks and limitations. So any future attempts must balance the urgent need for atmospheric carbon removal with robust research and meaningful community engagement. This ensures that any ocean alkalinity enhancement is both environmentally responsible and socially supported. Getting this balance right is essential for Australia and other nations, informing how we steward our seas and other natural resources to reach our ambitious climate targets.