Carbon sequestration is the process of capture of CO2 from the atmosphere, and its long-term storage in plants (through photosynthesis), soil, geologic formations (as calcium carbonate), and ocean. This process can be physical, chemical, or biological (biosequestration) in nature.
Oceans are the largest sink for atmospheric carbon. Carbon dioxide from the atmosphere dissolves into surface water of ocean, where it is utilised by marine plants (phytoplanktons) that turn it into organic matter through the process of photosynthesis. Many organisms in ocean convert CO2 into calcium carbonate – which becomes the building material for their shells and skeletons.
Soil is the second largest sink for carbon. Wetland soil is an important carbon sink. With only about 6% of the world land area, wetland soil accounts for around 15% of total soil carbon. Peatlands, a type of wetland, are very efficient at carbon sequestration. They store large stock of partially decomposed organic matter. Their mis-management or destruction can release huge amounts of carbon dioxide into the atmosphere.
To promote the conservation of peatlands, the UNEP (United Nations Environment Programme) launched the Global Peatlands Initiative at the Global Landscapes Forum in Marrakesh in 2016.
In 2018, a historic agreement (The Brazzaville Declaration 2018) was signed between Democratic Republic of Congo, Republic of the Congo, and Indonesia to promote conservation of the world’s largest peatlands basin – the Cuvette Centrale Region.
Dry soil holds much less carbon than wet soil as natural process of decay, which releases CO2 into atmosphere, is faster in dry soil due to better aeration. Modern agriculture has reduced the soil’s carbon content due to removal of plant material from the soil. Some of this reduction in soil carbon can be offset by using good soil management practices such as – not tilling soil to more depth than required, adopting organic farming practices, leaving post-harvest residue on the field, etc.
Negative Emission Technologies
Negative Emission Technologies, also called Carbon Capture technologies, are technologies that can be used to reduce the concentration of greenhouse gases (primarily carbon dioxide) from the atmosphere. They include:
- BECCS – Bio Energy with Carbon Capture and Storage
- BECCS involve creating bio-energy (from biomass or waste) and capturing CO2 emissions in some form (like Biochar). By turning waste into energy, the technology can reduce energy our dependence on fossil fuels.
- The Intergovernmental Panel on Climate Change (IPCC), in a report, has indicated BECCS as a key technology for reaching the low atmospheric carbon dioxide concentration targets created by countries under the Paris Agreement.
- Ocean Fertilisation
- It involves ocean nourishment (with iron) for increased photosynthesis, by increasing phytoplankton activity, to convert more CO2 into organic matter and calcium carbonate.
- It is the charcoal made by thermal decomposition of organic waste in the absence of oxygen and air (pyrolysis), thereby avoiding natural decomposition – which otherwise results in huge CO2 emissions.
- Biochar can be used as a soil conditioner and can store carbon for thousands of years (like coal).
- Enhanced Weathering
- Also called mineral carbonation, it involves dissolution of natural or artificial minerals that combine with dissolved CO2 to form new minerals, i.e. CO2 converts from bicarbonate (HCO3–) or other dissolved forms to create new minerals like CaCO3.
- Direct Air Capture using carbon scrubber – which separates CO2 from atmosphere through adsorption and/or absorbtion.
These negative emission technologies are under development, some of them at very early stages of development. Innovative methods need to be developed to deal with climate change in a cost-effective manner. One such innovation was shown by ONGC (Oil and Natural Gas Corporation Ltd.) in 2018, when it planned to use an unconventional technology – carbon dioxide injection – in Gandhar field for crude oil extraction. The pressure of CO2 pushes out crude oil from a porous reservoir, while the CO2 gets captured in the voids vacated by the oil.