Efforts to help the ocean absorb more carbon dioxide should focus on small projects tailored to local conditions, scientists say, with applications potentially ranging from wastewater management to the use of surplus wind power.

A paper published in Nature Reviews Earth & Environment on October 6, argues that ocean alkalinity enhancement (OAE) could help communities meet climate targets, provided projects demonstrate a net carbon benefit and acceptable environmental impacts.

The technique increases seawater's alkalinity, or its ability to neutralize acid, allowing it to absorb and store more CO2. It has drawn interest as a potential means of removing billions of tonnes of the gas from the atmosphere each year.

But turning that potential into practical projects requires a better understanding of local waters, ecosystems and available resources, the researchers say.

Lead author Lennart Bach, an associate professor at Australia's University of Tasmania, Institute for Marine and Antarctic Studies, pointed to possible uses alongside existing infrastructure.

A city could use alkalinity derived from silicate minerals to help offset emissions associated with domestic wastewater. A wind farm could use surplus electricity to drive chemical processes that increase seawater alkalinity.

The underlying chemistry builds on a natural process. Rivers carry alkalinity into the sea, helping regulate ocean chemistry. Increasing it shifts dissolved CO2 mainly into bicarbonate – a form of carbon that can remain stored in the ocean for thousands of years – while allowing seawater to absorb more CO2 from the atmosphere.

Environmental effects, however, vary with the method used. Co-author Damon Britton noted that some approaches could make seawater cloudier or introduce trace metals. Their effects on marine life must be assessed locally to determine whether the benefits outweigh the risks.

Delivering and dispersing alkaline material presents another difficulty. Additions would be concentrated at particular locations, and the seawater must remain in contact with the atmosphere long enough to absorb the intended amount of CO2.

Co-author Tyler Rohr said early modeling had focused on alkalinity already diluted across the ocean, without establishing how that distribution would occur.

The team calls for better measurements and models to distinguish carbon removed by individual projects from natural ocean variability. Wider adoption would depend on evidence that projects remove more CO2 than they emit, are environmentally responsible and have public trust.

"Incentivizing small-scale projects is key to building the uptake of OAE, without an implied obligation to scale up to unrealistic targets," Bach said in a university statement.