Carbon Dioxide Removal (CDR)

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Carbon Dioxide Removal (CDR)

Carbon Dioxide Removal (CDR)

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Carbon dioxide removal, or CDR, is using technologies, practices, and approaches to remove carbon dioxide from our atmosphere through deliberate and intentional human actions.
CDR includes traditional methods like afforestation, as well as more sophisticated technologies like direct air carbon capture and storage (DACCS).
Natural processes, like the growth of a natural forest, are not CDR methods.
CDR also includes durable and efficient storage of extracted carbon dioxide in natural reservoirs like soil and vegetation, or in manufactured products like carbonated drinks.
According to IPCC, CDR methods require appropriate governance and policies as they can also cause adverse side-effects apart from the predicted benefits.

What are the different CDR methods?

Afforestation/reforestation

1. - Converting abandoned or degraded agricultural lands into forests can contribute to negative emissions. Additional plants and trees can sequester more carbon dioxide from the atmosphere into the soil.
  - According to the Intergovernmental Panel on Climate Change (IPCC), afforestation is a relatively cheaper method of CDR, costing approximately under $240 per tonne of CO2. The storage time can last from decades to centuries.

Biochar

- Biochar is the substance produced by burning organic waste from agricultural lands and forests in a controlled process called pyrolysis.
- Biochar is a stable form of carbon that cannot easily escape into the atmosphere.
- IPCC estimates biochar as a CDR method costs $10-345 per tonne of CO2. The downside of the technology includes negative impact from dust, and increased competition for biomass.

Pyrolysis involves the burning of wood chips, leaves, dead plants, etc. with very little oxygen, and the process releases a significantly small quantity of fumes.

BECCS

- Bioenergy with Carbon Capture and Storage (BECCS) is a carbon removal technology that captures CO₂ from biomass-based energy systems and stores it permanently. It builds on well-established processes—photosynthesis, combustion or fermentation, carbon capture technology, and geological storage—to create a closed-loop system that removes carbon from the atmosphere.
- According to IPCC, BECCS costs $50-200 per tonne of CO2. Growing energy crops for BECCS can also lead to increased competition for land.

From Biomass to Carbon Removal-Process

The carbon capture process begins with photosynthesis: plants absorb carbon dioxide (CO₂) from the atmosphere as they grow. This carbon is stored in plant material such as leaves, stems, roots, and trunks—referred to as biomass.
In a typical biomass-to-energy-conversion process, the biomass would be burned to generate electricity, heat, or fuel—releasing the CO₂ back into the atmosphere. BECCS interrupts this cycle. Instead of letting the biogenic CO₂ be re-emitted, the system uses Carbon Capture technology to trap it at the point of release.
This captured CO₂ is then compressed and either stored permanently in geological formations such as depleted oil and gas reservoirs or deep saline aquifers, or used in durable products, such as concrete, where it is physically bound and stabilized.
The result is net-negative emissions—more CO₂ is removed from the atmosphere than is released.

DACCS

1. - Direct air carbon capture and storage, or DACCS (also called DACS), extracts CO2 directly from the atmosphere at any location. This captured CO2 is then permanently stored in deep geological formations or used for other applications.
    - DACCS uses electricity to remove CO2 from the air. Air is drawn into the mechanism using industrial filters, and then either passed through a chemical solution that removes the gas, or exposed to a chemical agent that converts it into a compound which can be heated to release CO2 for further capture and storage.
    - The captured CO2 is then compressed under high pressure and pumped into deep geological formations. The gas can also be used in industries, like carbonated drinks.
  - DACCS is the most expensive form of CDR.
    - Atmospheric CO2 exists in a very diluted form, leading to high costs and energy needs for efficient extraction. The high-energy requirement can lead to increased competition for low-carbon energy or increased GHG emissions.

Enhanced rock weathering

1. - This CDR method involves pulverising silicate rocks to bypass the conventionally slow weathering action. The resultant product, usually a powder, has higher reactive surface area, which is then spread on agricultural lands for further chemical reactions.
  - Natural rock weathering absorbs around 0.3% of global fossil fuel emissions. Enhanced rock weathering has, therefore, been projected to absorb even more CO2 from the atmosphere.
  - Dust emissions and potential for increased GHG emissions from energy generation are a few drawbacks of the technology.

Ocean alkalinity enhancement

- Like forests and green patches on land, oceans are also vast natural sinks for carbon. Ocean alkalinity enhancement is a CDR method that involves adding alkaline substances to seawater to accelerate this natural sink.
- Alkaline substances in the ocean can convert dissolved, inorganic CO2 in water into bicarbonates and carbonates, which are stable forms of carbon with extensive lifetimes. The CO2 deficit thus created is balanced by absorbing more of the gas from the atmosphere into the water.
- However, it also comes with certain risks, like potential for increased GHG emissions from mining, transport, and deployment.
- Weathering of alkaline materials can also release byproducts like trace metals, impacting fragile marine ecosystems.

FAQs on Carbon Dioxide Removal (CDR)

1. What is Carbon Dioxide Removal (CDR)?

Carbon Dioxide Removal refers to deliberate human actions—through technologies or practices—to extract CO₂ from the atmosphere and store it in natural or artificial reservoirs.

2. How is CDR different from natural carbon absorption?

Natural carbon sinks like forests absorb CO₂ passively. In contrast, CDR involves active human intervention like afforestation, biochar production, or direct air capture.

3. What are some major CDR techniques?

Key CDR methods include Afforestation, Biochar, BECCS (Bioenergy with Carbon Capture and Storage), DACCS (Direct Air Capture), Enhanced Rock Weathering, and Ocean Alkalinity Enhancement.

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