Carbon sequestration (CS) refers to the long term storage of carbon (usually that carbon that has the immediate potential to become CO2 gas) in plants, soils, oceans and other geological formations. It can be natural or artificial.

Process of natural carbon sequestration

• Natural CS is a continuous cycle of absorption of atmospheric CO2 such that a balance of CO2 is maintained in the atmosphere for sustaining life.
• Animals, plants (at night), forest fires, volcanic eruptions etc. release CO2 while the forests, oceans, oil/ gas reservoirs and biomass are the carbon sinks that absorb/ store it. Photosynthesis is the most important mechanism of natural CS.

Of the carbon emitted to the atmosphere by human activities, only 45% remains in the atmosphere; about 30% is taken up by the oceans, and the remainder is incorporated into terrestrial ecosystems.

Artificial Carbon Capture and Storage involves capturing waste carbon dioxide (CO2) from large point sources, such as fossil fuel power plants, transporting it to a storage site, and depositing the CO2 to atmospherically-isolated locations, usually an underground reservoir for long term storage.

Artificial CCS has been gaining prominence due to the following factors:

• Using natural CS ways is a slower process and also competes with other land-use purposes.
• It is a potential means of mitigating the contribution of fossil fuel emissions to global warming and rectifying ocean acidification.
• It has also attracted the attention of private players and is currently being seen as profitable business venture by some of the venture capitalists.
• Artificial CCS has immense potential to increase the agricultural yield and enhanced oil recovery.
• Supply chain for CCS will create large variety of jobs. Jobs will be created in core engineering, manufacturing, design, management and operation and other skills related to CO2 storage.

However, following risks are associated with artificial CCS

• IPCC has estimated that carbon capture and storage would increase the cost of electricity generation by about one to five cents per kilowatt-hour, depending on the fuel, technology, and location.
• It is relatively unexamined and its side effects are still unknown. For instance, Lake Nyos (Cameroon, Africa) disaster, where limnic eruption (dissolved carbon dioxide (CO2) suddenly erupting from deep lake waters) produced huge amount of CO2 killing hundreds of people and livestock.
• Since it deals with compression and transportation of CO2, therefore, it is costly and energy intensive.
• Process of ocean sequestration will make oceans acidic, thus affecting the marine life in unknown ways.

Overall, direct air capture combined with natural carbon sequestration will serve as the insurance against the effects of excess atmospheric CO2. Alongside, focus needs to be on enhancing the scope decentralized activities such as afforestation, renewable energy resources and eco-friendly habits for containing the CO2 emission below 400ppm.