Geological carbon capture and storage may be an effective climate mitigation tool, reports a study published in Nature Communications. Modelling shows that under appropriate regulation, there is a 50% probability that 98% of injected CO₂ is retained in the subsurface for over 10,000 years. Under poor regulation, 78% of injected CO₂ is retained in the subsurface.

Carbon capture and storage involves the injection into the subsurface of CO₂ emitted from using fossil fuels in industrial processes. Despite the potential of this technology to reduce global CO₂ emissions and help in achieving the Paris Agreement targets, there are concerns that the injected CO₂ could leak into the atmosphere in future.

Juan Alcalde and colleagues develop a numerical program, the Storage Security Calculator, to assess the effectiveness of geological CO₂ storage for climate mitigation. The calculator quantifies the immobilisation of CO₂ injected into the subsurface between 2020 and 2050, and the total CO₂ leakage to the atmosphere over 10,000 years. The authors perform this calculation for two scenarios, one where injection site density is modest and sites are regulated using current best practices, and another where sites are poorly regulated.

They find that if sites are appropriately regulated, yearly leak rates are lower than 0.01% per year, considered by many to be the acceptable limit for effective climate mitigation. For inadequately regulated sites, although leakage exceeds this limit for the first 100 years, after 1,000 years it is reduced to acceptable levels.

The authors caution that an incomplete understanding of CO₂ behaviour in the subsurface over the thousands of years timescale is a key uncertainty in their model, which could result in an overestimation of CO₂ storage.