Maarg Manthan · Topic 16.3

Climate Change Mitigation: Carbon Sequestration and Carbon Sinks

Environment & Ecology › Climate Change Impacts and Mitigation · Topic 16.3

Climate change mitigation means cutting greenhouse gas emissions or enhancing their removal from the atmosphere. Carbon sequestration is the capture and long-term storage of carbon, and a carbon sink is any reservoir that absorbs more carbon than it releases. Natural sinks are forests, soils, wetlands and peatlands, grasslands, oceans and blue carbon ecosystems such as mangroves, seagrass and salt marshes; land and oceans together absorb roughly half of human CO2 emissions. Biological sequestration includes afforestation, reforestation, agroforestry, restoring wetlands, improved soil management and biochar. Technological sequestration includes carbon capture and storage (CCS) or capture, utilisation and storage (CCUS), in which CO2 is captured from power plants and industries and injected into deep geological formations such as depleted oil and gas fields, saline aquifers and unmineable coal seams, as at the Sleipner field in Norway since 1996; bioenergy with carbon capture and storage (BECCS); and direct air capture (DAC). Ocean fertilisation and enhanced rock weathering are proposed but uncertain. India's climate pledge aims to create an additional carbon sink of 2.5 to 3 billion tonnes of CO2 equivalent through forest and tree cover by 2030.

5 min read · UPSC Prelims · Environment & Ecology · Climate Change Impacts and Mitigation

At a Glance

Natural sinks Forests, soils, oceans, wetlands
Tech options CCS, BECCS, DAC
Blue carbon Mangroves, seagrass
India goal 2.5 to 3 Gt CO2e sink by 2030
First CCS site Sleipner, 1996
Exam link UPSC Prelims, Environment & Ecology: Climate Change Impacts and Mitigation

Where Does It Fit?

This topic follows the impacts and health effects of climate change and opens the discussion of mitigation. It leads to carbon credits and carbon tax, the economic tools of mitigation. Previous topic: Global Warming and Human Health: Mosquito-Borne Diseases, Ozone Depletion Effects. Next topic: Carbon Credit and Carbon Tax.

What Are Carbon Sinks and Sequestration Methods?

Sink or method	How it works
Forests	Trees absorb CO2 by photosynthesis and store it in wood, roots and soil; afforestation and reforestation increase the sink
Soils	Hold more carbon than the atmosphere and vegetation together; increased by cover crops, less tillage and organic manure
Wetlands and peatlands	Store very large amounts of carbon in waterlogged organic soil; drained peat releases it
Oceans	Absorb about a quarter of human CO2 through dissolving and biological pumps, but become more acidic
Blue carbon ecosystems	Mangroves, seagrass and salt marshes bury carbon in sediments for centuries
CCS and CCUS	Capture CO2 from flue gas, compress and inject it deep underground, or use it in products
BECCS and DAC	BECCS burns biomass with CCS to give net removal; DAC captures CO2 directly from air with chemicals

What Are the Benefits, Limits and Indian Plans?

Net zero need: most pathways to 1.5 C use removals to balance hard-to-abate emissions
Forest sinks: cheap with co-benefits for biodiversity and water, but risk of fire and reversal
CCS cost: high energy cost and cost, few large projects
Storage safety: risk of leakage and need for monitoring
Land competition: BECCS needs vast land
Not a substitute: sinks cannot replace deep emission cuts
India: NDC target of an extra 2.5 to 3 billion tonnes of CO2e sink by 2030 through forests and trees
CCUS policy: NITI Aayog roadmap and a National Mission on CCUS under discussion, with pilots by industry; check latest

What Else Should You Remember?

Carbon pool: a reservoir that stores carbon, such as forests or the ocean
Source and sink: source releases more carbon than it takes up; sink does the opposite
Land and ocean sink: absorbs roughly half of annual fossil emissions
Forest carbon in India: ISFR reports forest carbon stock of about 7 billion tonnes of carbon, with a rising trend; check the latest report
Green India Mission: aims to raise forest and tree cover and carbon stock
Compensatory afforestation: adds to the sink but quality varies
Agroforestry: stores carbon in trees on farms
Soil organic carbon: many Indian soils are low in it, so there is a large potential
Biochar: charred biomass added to soil, locking in carbon and improving fertility
Blue carbon: coastal vegetation stores carbon per hectare at rates higher than many forests
Peatlands: cover about 3 percent of land but hold about twice the carbon of all forests
Sleipner: Norwegian offshore gas field that has stored CO2 in a saline aquifer since 1996
Boundary Dam: a Canadian power plant with CCS
Enhanced oil recovery: use of captured CO2 to extract more oil, a debated use
Direct air capture: plants such as Orca in Iceland capture CO2 from air at high cost
Carbon dioxide removal: CDR, a set of methods to take CO2 out of the air
Net zero: balance of emissions and removals
Ocean iron fertilisation: proposed to boost plankton growth; ecological risks
Enhanced weathering: spreading crushed rock to absorb CO2
Permanence: how long carbon remains stored, longer in geology than in trees
Link to previous: see Global Warming and Human Health: Mosquito-Borne Diseases, Ozone Depletion Effects
Link to next: see Carbon Credit and Carbon Tax
Link to mangroves: see Mangroves: Definition, Distribution in India, Importance and Threats
Caution: carbon stock and CCUS project data change quickly, so check current reports
Exam hint: separate natural from technological sequestration with an example each

Why Does It Matter for the Exam?

Natural sinks: Forests, oceans, soils
Tech options: CCS, DAC
India goal: 2.5 to 3 Gt
Current affairs link: CCUS mission
Common errors: treating sinks as a substitute for emission cuts

As an analytical point, sinks buy time but cannot replace emission cuts, because forests burn, soils lose carbon when disturbed, and technological capture is costly. A sound approach protects existing carbon-rich ecosystems first and uses engineered removals only for hard-to-abate emissions.

Why Is This Topic Important?

Natural Cheap, fragile
Tech Costly
Role Complement cuts

What Came Next?

The next topic covers carbon credit and carbon tax. Next topic: Carbon Credit and Carbon Tax.

Key People and Terms

Carbon sink Net absorber of carbon
CCS Carbon capture and storage
BECCS Bioenergy with CCS
DAC Direct air capture
Blue carbon Coastal ecosystem carbon
CDR Carbon dioxide removal

Exam Corner

Points to Remember

Land and ocean absorb about half of emissions.
Blue carbon: mangroves, seagrass.
Sleipner since 1996.
India sink goal 2.5 to 3 Gt.
Sinks complement cuts.

Do Not Confuse With

Carbon sink and carbon source Net absorber versus net emitter
CCS and CCUS Storage versus capture with use
BECCS and DAC Biomass-based versus air-capture removal

Memory Hook

Trees, soils and seas soak up; capture and store the rest; cut first.

Mains Angle

Questions ask for sinks and technologies. These points help.

Sinks Natural
Tech CCS, DAC
Role Complement

A Question You May Face

An original practice question, not a past paper question.

“Discuss carbon sequestration and the role of natural and technological carbon sinks in climate change mitigation.”

How to Answer

Define Sink, sequestration.
Natural Forests, oceans.
Tech CCS, DAC.
Limits Not a substitute.

GS Relevance

Prelims: sinks, CCUS, BECCS, DAC. GS Paper 3: mitigation technologies.

Frequently Asked Questions

What is carbon sequestration?

Carbon sequestration is the capture and long-term storage of carbon dioxide or other forms of carbon so that it is kept out of the atmosphere. It can be natural, as when trees and soils store carbon, or technological, as when CO2 is captured from power plants and injected underground. It is used to reduce the build-up of greenhouse gases.

What is a carbon sink?

A carbon sink is any natural or artificial reservoir that absorbs and stores more carbon than it releases. The main natural sinks are forests, soils, wetlands, grasslands and the oceans, and blue carbon ecosystems like mangroves and seagrass. Together, land and ocean sinks absorb roughly half of the carbon dioxide emitted by humans each year.

What is carbon capture and storage?

Carbon capture and storage is a technology that captures CO2 from the exhaust of power plants and industries such as cement and steel, compresses it and transports it to a site where it is injected deep underground into formations such as depleted oil and gas fields or saline aquifers. When the captured gas is used, the process is called CCUS.

What is blue carbon?

Blue carbon is the carbon captured and stored by coastal and marine ecosystems, especially mangroves, seagrass meadows and salt marshes. Much of it is buried in waterlogged sediments for centuries. Protecting and restoring these ecosystems conserves carbon stocks and also protects coasts and fisheries.

What is India's carbon sink target?

India's updated Nationally Determined Contribution commits to creating an additional carbon sink of 2.5 to 3 billion tonnes of carbon dioxide equivalent through additional forest and tree cover by 2030. The India State of Forest Report tracks forest carbon stock, and programmes such as the Green India Mission support the goal.

PYQ Practice — Statement Analysis

1 Mangroves are blue carbon ecosystems.

True

They store carbon in sediments.

2 Carbon sinks can fully replace emission cuts.

False

They only complement cuts.

3 Sleipner is a CCS site in Norway.