Carbon sequestration capture and store carbon either through biological means or in geological formations. This process, currently used on a small scale, hopes to reduce carbon dioxide (CO2) levels in Earth's atmosphere.
Carbon sequestration is the process of capturing and storing carbon in a "carbon pool," thus removing it from the atmosphere. Although carbon dioxide is necessary for life, excess can have the opposite effect.
CO2 is a greenhouse gas. It's created by factors including industry, forest fires, volcanoes, microbes, older motor vehicles, large vehicles like SUVs, coal burning, commercial and private jets.
According to NASA, CO2 causes about 20% of Earth’s greenhouse effect; water vapor accounts for 50%; and clouds 25%. The rest is made of small particles (aerosols) and minor greenhouse gases like methane.
The greenhouse effect itself is natural. It keeps the planet from turning into a block of ice. Problems proliferate when too much heat is trapped and contributes to rising global temperatures.
The objective of carbon sequestration is to securely store carbon in what is known as a carbon pool. Forests, soils, oceans, or deep underground geological formations supply the storage.
The two main types of carbon sequestration include:
Biological Carbon Sequestration: This method uses natural processes involving plants and soil to absorb CO2 from the atmosphere and store it within biomass and soil.
Geological Carbon Sequestration: This method captures carbon emissions from sources such as power plants and injects them deep underground into rock formations for long-term storage.
Biological Sequestration
Biologic sequestration is the natural ability of plants, soil, and water to absorb and store carbon.
Forests
Through photosynthesis, trees and other plants absorb CO2 and convert it into biomass like trunks, branches, leaves and roots. Actively growing forests are best at collecting and containing CO2.
An example of a large-scale reforestation effort is the Great Green Wall in Africa. The project hopes to combat desertification and sequester carbon across the Sahel region.
Since 2007 it's restored an area the size of the Philippines, or 30% of goal. Organizers expect the effort to overshoot its initially projected conclusion date of 2030 but it's making progress.
The Amazon rainforest absorbs about 2 billion tons or 1.8 billion metric tons of CO2 each year. In 2023, China releases 11.9 billion metric tons of CO2 into the atmosphere, the greatest amount of any country.
The rainforest holds 56.8 billion metric tons of above-ground carbon. Destruction by fires and deforestation contribute to a swift turnaround and the Amazon rainforest now emits more CO2 than it absorbs.
Soil
Healthy soil absorbing and retains carbon as organic matter. Agricultural practices like no-till farming, cover cropping, and the use of organic fertilizers significantly enhance soil's carbon sequestration potential.
Tilling is often recommended to aerate and improve soil. No-till farming minimizes soil disturbance, preventing release of stored carbon and promoting accumulation of organic matter.
Oceanic Carbon Sinks
The ocean is the largest natural carbon sink. It absorbs CO2 directly from the atmosphere and through the process of photosynthesis by marine plants, like phytoplankton and kelp forests.
Concepts to enhance ocean sequestration include kelp forest restoration, and conservation of mangrove coast, seagrass and salt marshes. Ideas include iron fertilization to promote phytoplankton in specific regions.
Oceanic carbon sequestration is undergoing research. Iron fertilization can lead to algal blooms which can deplete oxygen levels in the water, killing marine life. Some algal blooms are toxic in the right circumstances.
Mangroves, commonly found along tropical coasts, can store up to five times more carbon per hectare than terrestrial forests. Mangroves are being replanted in countries such as Kenya, Cambodia, India and Nigeria.
Geologic Sequestration
Geologic sequestration starts with capturing CO2 from industrial sources like power plants and cement factories. It's then injected deep underground into geological formations for long-term storage.
Formations for storage include:
Depleted Oil and Gas Reservoirs: Repositories with existing infrastructure.
Deep Saline Aquifers: Porous rock formations saturated with salty water.
Unmineable Coal Seams: CO2 injected into seams improves methane recovery while storing carbon.
In the North Sea, the Sleipner gas field project is a successful example of geologic CO2 storage. Since 1996, it's been injecting a million tons of CO2 per year into a saline aquifer 1000 m (0.6 mi) under the seabed.
The Sleipner CO2 gas processing and capture unit is built in order to evade the 1991 Norwegian CO2 tax. Sleipner obtains CO2 credit for the injected CO2 and does not pay the tax.
This project shows the possibility of large-scale geologic sequestration and provides data on long-term storage. However for this to work, companies must be willing to change.
Enhanced Oil Recovery (EOR)
Injecting CO2 into depleted oil wells enhances oil recovery, making companies richer. However, the climate benefits depend on the overall carbon footprint of the EOR process and the fate of extracted oil.
Problems of Carbon Sequestration
Permanence: Long-term stability of carbon storage is a strong factor. Forests can be lost to wildfires or deforestation, while geological storage sites need monitoring to prevent leakage.
Scale: Scaling up both biologic and geologic sequestration to meet the demand requires significant investment, tech advancements and policy support.
Environmental Impacts: Certain sequestration methods, like ocean fertilization, can have unintended ecological consequences.
Cost: The cost of carbon capture and storage technologies remains relatively high. Companies might be more motivated if more countries follow the Norwegian example.
Continuous monitoring is essential after the CO2 is injected to ensure it doesn't leak into the atmosphere or contaminate groundwater. The process includes seismic surveys, pressure tracking, and chemical analyses.
Current Use of Carbon Sequestration
Carbon sequestration is presently use on a limited scale, with several large-scale carbon capture and storage (CCS) facilities already functioning worldwide. Participating countries include Canada, the UK and Australia.
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