Catch and lock for cleaner air

Sequestering carbon in geological sediments is considered an effective method for the large-scale removal of carbon dioxide (CO₂) from the atmosphere. A recent analysis, however, notes that this method can prudently capture no more than 1,460 billion tonnes of carbon, much below optimistic values of 40,000 billion tonnes. Furthermore, a warming reversal of only 0.7°C is possible, as opposed to the projected figures of up to 6°C (bit.ly/geologic-carbon).

The analysis, led by Austria's International Institute for Applied Systems Analysis, is based on a country's emissions and carbon storage capabilities. It notes that the potential for sedimentary carbon storage varies from country to country. The U.S., Russia, and Canada, which are responsible for historical CO₂ emissions, are best suited, geologically, for carbon sequestration. Brazil, Indonesia, and African countries have high storage potential but low historical emissions, and may be less incentivised for such storage.

India, the third-largest emitter of greenhouse gases today, has a relatively low historical emission record and limited potential to sequester carbon in geological sediments due to geographic and demographic constraints. A large part of India's onshore potential is lost, as it lies below the earthquake-prone Himalayan belt. Other significant basins are lost either because they are located along the border with Pakistan or in densely populated areas of Uttar Pradesh and Bihar. Exclusive economic zone and water depth restrictions in the Bay of Bengal limit storage capacities offshore.

India has some pilot and operational projects for Carbon Capture and Storage (CCS), mainly at refineries. A policy framework was drafted in 2022, but the policy is still developing. India plans to offset its coal dependence with CCS (https://reut.rs/4nQlNsf). The recent paper, therefore, is significant in citing the technically feasible limit.

Carbon storage measures in geological sediments sediments include injecting recovered CO₂ into deep saline aquifers, depleted or unmineable coal deposits, and in depleted oil fields in a liquefied form. Sometimes the carbon is converted into a crystalline form for storage.

While locking in carbon in sedimentary basins has so far the greatest and proven storage potential, ongoing research is investigating the injection of CO₂ and water into basalt rocks for "mineral storage". Siddharth Joshi, a co-author of the study, says that India's basalt-rich Deccan Plateau could be a potential storage site when the technology matures.