Concept and Rationale
Carbon sequestration refers to the process of capturing and storing atmospheric carbon dioxide (CO₂) in a way that prevents it from being released into the atmosphere for a long period. It is considered a key strategy for mitigating climate change by reducing the concentration of CO₂ (the most significant anthropogenic greenhouse gas) in the atmosphere.
The buildup of atmospheric CO₂ from burning fossil fuels, deforestation, and other human activities is the primary driver of global warming. Carbon sequestration aims to remove CO₂ from the atmosphere or capture it at its source and store it in long-term reservoirs (sinks). This can help to slow down the rate of climate change and provide more time for transitioning to a low-carbon economy.
Types of Carbon Sequestration
Natural Carbon Sequestration (Biological Sequestration)
Utilizes natural processes to absorb and store carbon.
Forests (Afforestation & Reforestation)
Trees absorb CO₂ via photosynthesis, storing carbon in biomass and soils. Afforestation (new forests) and Reforestation (replanting) are key.
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REDD+: An international framework (Reducing Emissions from Deforestation and Forest Degradation, plus conservation, sustainable management of forests, and enhancement of forest carbon stocks) to incentivize developing countries.
Significance: Forests are major carbon sinks. Protecting existing forests (avoided deforestation) and increasing forest cover are crucial.
Soil Carbon Sequestration
Soils naturally store organic carbon. Sustainable agricultural practices (no-till, cover cropping, crop rotation, organic amendments, agroforestry) enhance this storage.
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Improved grassland management (e.g., rotational grazing) also enhances soil carbon.
Oceans (Natural Processes)
Largest active carbon sink. CO₂ dissolves (Physical Pump) and marine life absorbs it (Biological Pump), sinking carbon to the deep ocean.
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Coastal Blue Carbon Ecosystems: Mangroves, salt marshes, seagrass beds are highly effective at sequestering carbon in biomass and sediments. Protecting and restoring these is vital.
Wetlands (Peatlands)
Peatlands are crucial carbon stores, accumulating partially decomposed organic matter (peat) over millennia. Draining or degrading them releases significant carbon.
Artificial (Technological/Geological) Carbon Sequestration (CCS)
Involves capturing CO₂ emissions from large point sources or directly from air, then transporting and storing it in geological formations or other long-term sites.
Carbon Capture Technologies
- Post-Combustion Capture: CO₂ separated from flue gases after combustion (e.g., solvents, membranes). Most mature, retrofittable.
- Pre-Combustion Capture: Fuel reacted to syngas (CO, H₂), CO converted to CO₂, then separated. H₂ used as fuel.
- Oxy-Fuel Combustion: Fuel burned in pure oxygen, flue gas is mainly CO₂ and water vapor, easing separation.
- Direct Air Capture (DAC): Captures CO₂ from ambient air. Energy-intensive, expensive, early stage.
Carbon Transport
Captured CO₂ (usually compressed into a supercritical fluid) is transported via pipelines, ships, or tankers to storage sites.
Carbon Storage (Geological Sequestration)
- Deep Saline Aquifers: Porous rock formations (>800m) filled with brine. Largest potential. CO₂ trapped structurally, residually, dissolved, or mineralized.
- Depleted Oil and Gas Reservoirs: Existing structures and infrastructure can be used. Can aid Enhanced Oil Recovery (EOR).
- Unmineable Coal Seams: CO₂ adsorbs to coal, potentially displacing methane (ECBM).
- Basalt Formations: CO₂ reacts with minerals to form stable carbonates (mineral carbonation).
(Ocean Storage - direct injection - largely abandoned due to acidification/ecosystem impact concerns).
Carbon Utilization (CCUS/CCU)
Captured CO₂ can be used as feedstock for valuable products:
- Fuels (e.g., synthetic methane, methanol).
- Chemicals (e.g., polymers, carbonates, urea).
- Building materials (e.g., concrete curing, aggregates).
- Enhanced Oil Recovery (EOR).
Utilization provides economic incentives but scale is small and some uses only delay CO₂ release.
Simplified CCS Process
Historical Context and Development
Billions of Years Ago
Natural sequestration processes (photosynthesis, ocean absorption) begin, shaping Earth's carbon balance.
Latter Half, 20th Century
Ideas for geological storage of CO₂ emerge as understanding of anthropogenic climate change grows.
1970s
Early Enhanced Oil Recovery (EOR) projects using CO₂ begin, primarily for economic rather than climate reasons.
1990s - 2000s
Large-scale dedicated CCS projects for climate mitigation demonstrated (e.g., Sleipner - Norway, Weyburn - Canada).
Late 20th - 21st Century
Afforestation/Reforestation gain prominence (e.g., CDM, REDD+). Growing focus on soil and blue carbon. DAC research intensifies.
Advantages & Challenges
Advantages
Natural Sequestration
- Co-benefits (biodiversity, soil health, water quality).
- Relatively low cost for some methods.
- Utilizes existing natural processes.
Artificial Sequestration (CCS/CCUS)
- Large CO₂ capture from point sources.
- Pathway for "negative emissions" (BECCS, DAC).
- CCUS can create economic value.
Challenges & Limitations
Natural Sequestration
- Saturation: Finite capacity.
- Permanence/Reversibility: Risk of release (wildfires, deforestation).
- MRV Challenges: Quantifying and verifying.
- Land Competition: Food production vs. afforestation.
- Timescale: Can be slow.
Artificial Sequestration (CCS/CCUS)
- High Cost: Expensive to build and operate.
- Energy Penalty: Reduces net energy output.
- Storage Security: Risk of leaks, long-term liability.
- Public Acceptance: NIMBY, safety concerns.
- Limited Deployment: Still not widespread.
- Moral Hazard: May delay fossil fuel phase-out.
- DAC Challenges: Very expensive, energy-intensive.
Carbon Sequestration in India
India is actively pursuing various carbon sequestration strategies as part of its climate action plan.
Forests & NDCs
India's forests are a significant sink. The National Green India Mission aims to increase cover. NDC Target: Additional 2.5-3 billion tonnes CO₂e sink by 2030 via forest/tree cover.
Soil Carbon
Promoting sustainable agricultural practices (e.g., no-till, organic farming) to enhance soil organic carbon, crucial for both climate mitigation and food security.
Blue Carbon
Significant mangrove and seagrass ecosystems offer substantial blue carbon sequestration potential. Conservation and restoration efforts are underway.
CCS/CCUS Exploration
India is exploring CCS/CCUS for hard-to-abate sectors (cement, steel, power). Research and pilot projects ongoing, but large-scale deployment faces hurdles.
Case Study: CAMPA, India
Compensatory Afforestation Fund Management and Planning Authority (CAMPA): Established under the Forest (Conservation) Act, 1980.
Objective: Manages funds from project proponents diverting forest land for non-forest use. These funds support compensatory afforestation, regeneration, wildlife protection, contributing to carbon sequestration.
Challenges: Ensuring ecological quality, survival rates of plantations, and genuine effectiveness as a long-term carbon sink remain areas of focus and improvement.
Policy & Economic Considerations
Mechanisms like carbon taxes or emissions trading schemes (ETS) can incentivize investment in sequestration projects by making emissions costlier.
Subsidies, R&D funding, and clear regulatory frameworks are crucial for developing and deploying new sequestration technologies, especially CCS.
Climate finance, technology transfer, and collaborative research (e.g., for DAC, large-scale storage) are vital for global success.
Robust MRV systems are paramount for accurate carbon accounting, ensuring credibility of sequestration efforts, and enabling carbon markets or credits. This is particularly challenging for natural sinks due to their variability and permanence risks.
Conclusion on Carbon Sequestration
Carbon sequestration, encompassing both natural and artificial methods, is an important component in the portfolio of solutions to address climate change.
Natural sequestration offers significant co-benefits but faces limitations in scale, permanence, and verifiability. Technological solutions like CCS/CCUS hold potential for deep emission reductions from industrial sources but grapple with high costs, energy demands, and storage security challenges.
A balanced approach is crucial: prioritizing aggressive decarbonization and rapid emission reductions, enhancing natural carbon sinks, and cautiously developing technological sequestration where it is viable, safe, and genuinely contributes to net-zero goals. Sequestration should complement, not substitute, the fundamental shift away from fossil fuels.
UPSC Civil Services Exam Relevance
Understanding carbon sequestration is crucial for Environment, Science & Technology, and current affairs segments of the UPSC exam.
- Definition and types (Natural vs. Artificial).
- Specific methods: Afforestation, Reforestation, Soil Carbon, Blue Carbon, CCS technologies (Post, Pre, Oxy-fuel, DAC), Geological Storage options.
- Key terms: REDD+, Carbon Sinks.
- Context of CO₂ as a Greenhouse Gas.
- Comprehensive questions on methods, potential, and challenges (with India context).
- Critical examination of CCS/CCUS viability and limitations.
- Role of forests and sustainable land management.
- Linkages to India's NDCs, climate policies, and international agreements.
- Ethical considerations and the "moral hazard" debate.
Example PYQs (Conceptual): Questions on UN-REDD+, Blue Carbon, emissions from thermal plants (context for CCS), and carbon-related S&T often appear.