Concept

Carbon sequestration

Capturing and storing atmospheric carbon dioxide in long-term carbon pools — soil, vegetation, ocean, geological formations. Distinct from 'reducing emissions' (which means putting less new CO₂ into the atmosphere); sequestration removes CO₂ from atmosphere into longer-term storage. Natural pathways include forest growth, soil organic matter, ocean uptake (at the cost of acidification), wetland accumulation, agricultural soil-building. Engineered pathways (direct air capture, BECCS, geological injection) are nascent and expensive. Most credible analyses suggest the climate response requires both substantial emission reductions and substantial sequestration.

Pathways

Natural / nature-based:

Forests — temperate, tropical, boreal; the largest land-based sink. Trees take up CO₂ during growth; mature forests continue sequestering at slower rates.
Soil — organic matter accumulation in agricultural and natural soils. See [[soil-carbon-sequestration]].
Wetlands — particularly mangroves, salt marshes, seagrass beds (collectively “[[blue-carbon|blue carbon]]”); among the most-rapid per-area sequestration. See [[blue-carbon]].
Ocean — surface waters absorb atmospheric CO₂; mixing into deep ocean stores carbon centuries-to-millennia, but at the cost of [[ocean-acidification|ocean acidification]].
Peatlands and bogs — slowly-accumulating organic matter under anaerobic waterlogged conditions; storing carbon for thousands of years.

Engineered:

Direct air capture (DAC) — chemical scrubbers pulling CO₂ from ambient air; energy-intensive; very expensive currently
Bioenergy with Carbon Capture and Storage (BECCS) — burning biomass and capturing CO₂ from emissions; geologically injecting; complex life-cycle analysis
Geological injection — saline aquifers, depleted oil/gas fields, basalt formations
Mineral carbonation — accelerating natural rock-weathering; magnesium and calcium silicates react with CO₂ to form stable carbonates
Ocean alkalinity enhancement — adding alkaline materials to seawater; increases ocean CO₂ uptake; ecological effects under study

Scale and feasibility

Current global emissions — ~37 billion tons CO₂ per year
Necessary scale of sequestration — debated; IPCC scenarios assume 5-15 billion tons per year of negative emissions by 2050 in many pathways
Land-based potential — substantial but bounded by land availability and competing uses
Engineered potential — currently very small (megatons), needs to scale dramatically and quickly

Persistence — how long does carbon stay sequestered?

Atmosphere — CO₂ residence time ~100s of years (effective time)
Vegetation — decades to centuries
[[soil-organic-matter|Soil organic matter]] — decades to centuries (most); millennia for stabilized humus and biochar
Wetland peat — centuries to millennia
Ocean surface — decades
Deep ocean — centuries to millennia
Geological formations — millennia to permanently
Mineralized carbonate — permanent

Why this matters

The IPCC’s 1.5°C and 2°C climate scenarios depend not just on emission reductions but also on substantial carbon-removal at scale. The technical feasibility of this scale of removal — particularly through engineered means — is uncertain. Nature-based sequestration (forests, soils, wetlands) is the most-mature pathway but bounded by land availability.

Sources

IPCC AR6 Working Group III
Drawdown, Paul Hawken ed. (Penguin, 2017)
IEA Energy Technology Perspectives

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Scientific

shares approach with

Blue carbon blue carbon is a major component of total ocean and ocean-margin carbon sequestration
Drawdown drawdown by definition requires sequestration alongside emission reductions
Nature-based solutions nature-based solutions are the substantial natural-pathway component of carbon-sequestration strategy

subset of

Soil carbon sequestration soil carbon is one of the largest and most-tractable carbon-sequestration pathways

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