Carbon Sequestration or carbon-dioxide removal (CDR) is the process of systematically capturing and storing carbon dioxide from the atmosphere. It is an endeavour to minimize the amount of carbon dioxide in the atmosphere to reduce global climate change. Carbon dioxide is the most commonly produced greenhouse gas and has to heavily contribute to the ozone layer depletion and other environmental hazards. Atmospheric carbon dioxide comes from two primary sources – natural and human activities. Natural sources of carbon dioxide include most animals that exhale carbon dioxide as a waste product. Human activities that lead to carbon dioxide emissions come primarily from energy production, including burning coal, oil, or natural gas. Carbon Sequestration describes long term storage of carbon dioxide or other forms of carbon to either resolve or defers global warming and deter hazardous climatic catastrophe. It has been proposed as a way to slow the atmosphere and marine accumulation of greenhouse gases, which are released by burning fossil fuels.
The underlying idea of carbon Sequestration is to stabilize carbon in solid and dissolved forms so that it does not cause the atmosphere to warm. The process shows tremendous promise for reducing the human carbon footprint. There are two main types of carbon sequestration: biological and geological. The rationale for carbon capture and storage is to enable the use of fossil fuels while reducing the emissions of carbon dioxide into the atmosphere and thereby mitigating global climate change. The storage period should exceed the estimated peak periods of fossil fuel exploitation so that if carbon dioxide reemerges into the atmosphere, it should occur after the predicted peak in atmospheric carbon concentration. Removing carbon dioxide from the atmosphere by increasing its update in soils and vegetation or in the ocean, a form of carbon sequestration sometimes referred to as enhancing natural sinks and eventually provides for a decrease in the amount of carbon footprint in the atmosphere. Depending on the source of emissions, different techniques and methodologies have been adopted by the scientific community to combat the increased carbon production due to power generation and other industrial activities.
Types of Carbon Sequestration
There are many technologies under investigation for sequestering carbon from the atmosphere. Primarily there are three main categories which are discussed below:
Carbon stored in oceans through direct injection or fertilization.
Natural pore spaces in geologic formations serve as reservoirs for long term carbon dioxide storage.
A large amount of carbon is stored in soils and vegetation, which are our natural carbon sinks. Increasing carbon fixation through photosynthesis, slowing down or reducing decomposition of organic matter, and changing land-use practices can enhance carbon uptake in these natural sinks.
Ways to Sequestration Carbon to Avoid Climate Catastrophe
Bioenergy with Carbon Capture and Sequestration
Extraction of energy from biomass by oxidizing and in site capturing of the produced carbon-dioxide is called as bioenergy with carbon capture and Sequestration (BECGS). Biomass, which assimilates the atmosphere carbon via photosynthesis, is the main source of BECGS. This is eventually used to produce energy at the expense of liberating Carbon dioxide and water vapor. Biomass can also be used to get biofuels such as ethanol, methanol, hydrogen, which will not cause net Sequestration of carbon but will involve in the production of energy and subsequent emission of carbon dioxide back to the atmosphere.
Soil Carbon Sequestration
Soil carbon content is expected to fail down by 25-50% after a period of 30-50 years from now due to intensive soil cultivation. The soil carbon content can be improved by growing cover crops, leaving the residues to decay in the fields, applying compost manures, and double cropping and other land management techniques to increase the soil structure and organic matter inputs. Biochar is an impeccable technique, targeted to fix the carbon content of the soil. Biochar is a unique process where the biomass is pyrolyzed to become a product that is more resistant to decomposition, which, when added to the soil, can store the embedded carbon and, in some cases, enhance fertility as well.
Phytoplankton’s and microscopic plants are some of nature’s gift which can consume the carbon dioxide from the ocean surface and convert them to organic matters which can be consumed by other marine habitats, or its will settle at the deep of the ocean. The success of this approach will depend on a number of nutrients present on the ocean surface, and the rare nutrients can be absorbed by phytoplankton. So fertilizing the ocean surface with nutrients containing nitrate and phosphates will increase the growth of phytoplankton and consequently will sequester the carbon dioxide under the ocean bed. The reason for the organic matter in the planktons has a lower ratio of carbon to nitrogenous phosphorous than the ratio of carbon to iron.
Direct Air Capture and Sequestration (DACS)
DAC is a chemical method wherein synthetic sorbents are used to capture atmospheric carbon dioxide directly. It is an endeavour to reduce the amount of carbon footprint in the atmosphere. The sorbents are in the form of amines, alkali/alkaline earth metal oxides, polymers, etc. which will be regenerated. It is a process in which the atmospheric carbon dioxide is directly removed by using scrubbers and produces concentrated carbon dioxide as the end product, which will be sequestered or used for other purposes. There are two different approaches for the scrubbing process, namely, adsorption and absorption, and sometimes both or through the membrane. DACS tends to separate carbon dioxide from a very separate dilute atmospheric source. The dilution requires more energy for the separation process, which will be around 2-10 times higher than the point source capture. For this reason, the DACS process is a slightly expensive affair than the CCS process.
Afforestation and reforestation
Worldwide forests currently sequester on the order of 2 Gt carbon dioxide per year. Concerted efforts to plant trees in new places and replant deforested acreage could increase this by a gigaton or more, depending on the species, growth, patterns, economics, politics, and other variables. Forest management practices emphasizing carbon storage and genetic modification of trees and other forest plants to improve their ability to take up and store carbon could push these numbers higher. Another way to help enhance trees’ ability to store carbon is to make long-lasting products from them-wood frame buildings, books, and so on. Using carbon-rich wood for construction, for example, could extend trees storage capacity beyond forests’ borders, with wood storage and afforestation combining for a potential 1.3- 14 Gt carbon dioxide per year possible.
Carbon dioxide is naturally removed from the atmosphere every day through reactions between rainwater and ricks. Some scientists advocate the improvement of this process and so increasing carbon-dioxide removal from the atmosphere through artificial measures such as crushing rocks and exposing them to carbon dioxide in a reaction chamber or spreading them over large areas of land or ocean, increasing the surface area in which the reactions can occur. Some require extensive land use, and so have the potential to compete with other needs such as food production and biodiversity protection. Researchers are looking at ways to use mine waste and otherwise refine the strategy to reduce costs and increase efficiency.
Most farming is intended to produce something that’s harvested from the land. Carbon farming is essentially the reciprocal of that idea. It uses plants to trap carbon dioxide and then strategically use practices such as reducing tilling, planting longer rooted crops and incorporating organic materials into the soil to encourage the trapped carbon to move into and stay in the soil. Managing vegetative cover in ways that enhance the capacity of soil to sequester and store large volumes of atmospheric carbon in a stable form offers a practical almost immediate solution to some of the most challenging issues currently facing humankind. It is established by scientists that the capacity of farmland to store carbon dioxide can be drastically increased by involving trees with deep roots in the entire process. Generally, trees that have the most carbon storage, often two to ten times more carbon per hectare, are mostly incorporated in the farming endeavour.
Enhanced weathering involves grinding and spreading rocks to increase their surface area so that it absorbs carbon dioxide more rapidly and efficiently. The ground rock can be spread on land or on the ocean to absorb atmospheric Carbon dioxide. Accelerating or inducing the active solid rock materials to remove atmospheric carbon dioxide is a new approach to enhanced weathering. The carbon dioxide released in the atmosphere gets converted to bicarbonate ions hen it dissolves in the ocean, which settles at the bottom of the seafloor. This natural process can be utilized successfully for the carbon dioxide removal process by accelerating the reactions by bringing carbon dioxide in contact with a natural rock formation, where the carbonate will be formed. All these weathering processes occur over a timescale of a few seconds to millennia.