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

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