Sequestration of atmospheric CO₂ in global carbon pools

Sequestering atmospheric CO₂ is necessitated by its present concentration of 385 ppm and increasing at the rate of 2 ppm y⁻¹. Increase in atmospheric emission of CO₂ with the attendant global warming and environmental degradation are driven by global energy demand. In comparison with the emission of 300 Pg C between 1850 and 2000, total emission during the 21^st century is estimated at 950 to 2195 Pg, with an annual rate of emission of 20 to 35 Pg C y⁻¹. Reduction of CO₂ atmospheric loading can be achieved by biological, chemical and technological options through either reducing or sequestering emissions. This article describes technological options of sequestering atmospheric CO₂ into other global pools. Geologic sequestration involves underground storage of industrially emitted CO₂ into the geosphere for long-term and secure storage. Liquefied CO₂ is injected about 1000 m below the ground surface either in stable porous rocks, oil wells, coal beds, or saline aquifers. Co-injecting CO₂ along with H₂S and SO₂ is also possible. Over time, the trapped CO₂ reacts with minerals to form carbonates, enhances oil recovery, or displaces coal bed methane. Deep injection of CO₂ under the ocean creates a CO₂ lake which eventually penetrates into the sediments. Iron fertilization is another technique of enhancing the C pool in marine biota, notably phytoplankton. The so-called “biological pumping” is based on the “iron hypothesis” of transferring C to the ocean floor. Terrestrial C sequestration is based on the natural process of photosynthesis. Transfer of CO₂ into the biotic pool and soil C pool via humification and formation of secondary carbonates has numerous ancillary benefits through enhancement of ecosystem services. Soil C sequestration is essential to improving soil quality, increasing use efficiency of agronomic input, and advancing world food security. It is also needed to improve water quality by filtration and denaturing of pollutants, and enhancing biodiversity by saving land for nature conservancy. Soil C sequestration is a low hanging fruit, and a bridge to the future until low-C or no-C fuel sources take effect.