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 21st 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.