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Why is leakage a concern for underground carbon storage?

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Illustration of various geoengineering techniques to address climate change, including carbon capture and storage methods like artificial trees, industrial scrubbers, and deep ocean CO2 storage, as well as solar reflectance strategies such as sulfur aerosols, reflective crops, cloud whitening, and orbital mirrors. The scene shows these interventions applied to land, sea, and atmosphere, with labeled features explaining each process. — Geoengineering Various geoengineering proposals designed to increase solar reflectance or capture and store carbon.

Leakage is a primary concern for underground carbon storage because the fundamental goal of carbon capture and storage (CCS) is to isolate carbon dioxide from the atmosphere to mitigate global warming.12

If stored gas escapes, it undermines the effectiveness of the sequestration process, as the carbon dioxide would return to the atmosphere and continue to contribute to the greenhouse effect. In the context of geologic storage, such as in depleted oil and gas reservoirs, leakage can occur if the storage site is not properly sealed by layers of rock free from faults that could provide pathways for the gas to migrate upward.21

While leakage remains a technical challenge, experts emphasize that the ethical imperative to address climate change necessitates rigorous management of these sites. Current estimates suggest that properly managed geological storage has a high probability (66–90 percent) of retaining 99 percent of sequestered carbon dioxide for over 1,000 years.2