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CCS is one strategy which could help to control greenhouse gas emissions that contribute to climate change and ocean acidification. CO₂, captured from sources – such as fossil fuel-burning power plants or industry - is relocated beneath the ocean floor in suitable geological formations. There it is permanently stored, well away from the planet’s atmosphere. Storage beneath the sea floor is not without challenges, however, and the integrity of the geological storage sites must be demonstrated to ensure confidence that no CO₂ will leak into the atmosphere.

To be confident that leaks are not occurring potential leakage needs to be detected accurately and promptly. Storage monitoring uses seismic techniques to produce images of geologically stored CO₂, which is an expensive method. Instead, a chemical way of checking for emissions at the sea floor could be more suitable. But this process in itself is complex, and what to measure remains open to debate. CO₂ levels in seawater are naturally variable and increases in CO₂ could be a result of other factors, such as rivers, circulation patterns, changes in temperature, biological activity and ocean acidification.

A group of PML scientists have developed an effective strategy for assuring the absence of leaks by first characterising natural variability of CO₂ in their North Sea study area using sophisticated computer models of the marine system. They have shown that by taking measurements of seawater acidity (pH) several times an hour, they can be certain that changes as small as 0.01pH unit (representing a tiny amount of additional CO₂) would indicate an anomaly – or possible leak - rather than natural variability. As a result monitoring strategies can be recommended that will give assurance that stored CO₂ is secure, and in the very unlikely event of leakage, enable rapid detection and management.

Detecting anomalies – and potential CO₂ leaks - in this way is cost-effective, practical and highly sensitive. Thus PML’s modelling expertise will contribute to an increase in confidence for carbon capture and storage.

“Climate change remains an existential crisis, and it is important that society invests in a range of methods of reducing CO₂ emissions, including renewable energy, energy efficiency and techniques like CCS,” said Jerry Blackford, Head of Science for Marine Ecosystems Models and Predictions at PML. “Our work demonstrates that we could monitor the integrity of subsea CO₂ storage with confidence, as well as develop bespoke monitoring strategies for subsea CCS storage around the globe.”