- Carbon sequestration stores CO2 in forests, oceans, soils, and rock formations.
- Natural sinks absorb only about half of human CO2 emissions annually.
- Direct air capture works but costs over $1,000 per tonne at current scale.
Carbon sequestration is the process of capturing atmospheric carbon dioxide and storing it in long-term reservoirs, including forests, soils, oceans, and underground geological formations.
Why It Matters
Key figure
2,200 Gt
Carbon stored in Earth's vegetation, soils, and detritus
The atmosphere currently holds roughly 760 gigatons of carbon. Earth's oceans hold more, around 920 gigatons, and terrestrial ecosystems (vegetation, soils, detritus) store an estimated 2,200 gigatons, according to the Encyclopaedia Britannica. Carbon sequestration works because these natural reservoirs already absorb enormous quantities of CO2 without human intervention.
The problem is one of balance. Human activities release approximately 37 gigatons of CO2 per year, and natural sinks absorb only about half of that. Roughly 45% of emitted carbon stays in the atmosphere, 30% dissolves into oceans, and the remainder enters terrestrial ecosystems.
Closing the gap between emissions and absorption is why carbon sequestration has become central to climate policy.
The Keeling Curve, the continuous measurement of atmospheric CO2 begun by Charles David Keeling at Mauna Loa Observatory in 1958, provides the clearest visual record of this imbalance. Each year the curve climbs higher.
How It Works
Carbon sequestration falls into two broad categories: biological and geological.
Biological sequestration relies on photosynthesis. Forests, grasslands, wetlands, and oceans all capture CO2 through natural processes. The U.S. Department of Energy classifies soil organic carbon as a particularly significant reservoir, noting that cold environments like Arctic permafrost and waterlogged marshlands store carbon effectively because low temperatures and limited oxygen slow decomposition.
Key figure
36,000 t/yr
CO2 captured by Climeworks' Mammoth plant in Iceland
Geological sequestration involves injecting compressed CO2 into porous rock formations deep underground. The DOE explains that once injected, the gas becomes physically trapped in pore spaces, dissolves in subsurface fluids, and eventually reacts with minerals to form stable carbonates. In 2013, the U.S. Geological Survey published the first comprehensive national assessment of geological storage capacity, estimating a mean potential of 3,000 metric gigatons of CO2.
Direct air capture (DAC) is a newer technological approach. DAC systems use chemical processes to extract CO2 directly from ambient air, rather than from point sources like power plants.
The largest operational DAC facility as of 2025 is Climeworks' Mammoth plant in Iceland, which captures up to 36,000 tonnes of CO2 per year. Current costs for small-scale DAC plants exceed $1,000 per tonne, though projections for commercial-scale facilities (1 million tonnes per year capacity) estimate costs between $97 and $168 per tonne.
Key Context
The Kyoto Protocol (1997) was the first international agreement to recognize carbon sequestration as a legitimate climate mitigation strategy, allowing countries to claim credits for land-use and forestry activities that store carbon.
Natural carbon sequestration may be weakening. A 2025 study published in the journal Weather found that terrestrial CO2 absorption peaked in 2008 and has since declined by approximately 0.25% per year. If this trend continues, the gap between emissions and natural absorption will widen, increasing the pressure on engineered solutions.
FAQ
What is the difference between carbon capture and carbon sequestration?
Carbon capture refers specifically to the act of separating CO2 from emission sources or ambient air. Carbon sequestration refers to the long-term storage of that captured carbon. In practice, the two are often combined under the umbrella term carbon capture and storage (CCS).
Can trees alone solve climate change?
No. Forests are powerful carbon sinks, but they cannot absorb enough to offset current global emissions. If scaled to their maximum potential, nature-based solutions could sequester roughly 10 gigatons of CO2 per year by 2050, compared to annual emissions of approximately 37 gigatons. Forests are a necessary part of the solution, not the whole answer.
How long does geological carbon storage last?
The IPCC estimates a 66 to 90% probability that properly managed geological formations will retain 99% of injected CO2 for more than 1,000 years. The key variable is site selection: porous rock sealed by impermeable cap rock provides the most reliable containment.
Is direct air capture commercially viable?
Not yet at the scale needed. The technology works, but current costs ($1,000+ per tonne at small-scale facilities) are far above the threshold for widespread deployment. The U.S. 45Q tax credit offers up to $180 per tonne for DAC-captured CO2 stored permanently, helping to close the gap.
Sources
- Primary References:
- Carbon sequestration (Encyclopaedia Britannica)
- DOE Explains Carbon Sequestration (U.S. Department of Energy)
- What is carbon sequestration? (U.S. Geological Survey)
- Additional Context:
- Natural sequestration of CO2 is in decline (Curran, 2025, Weather)
- Direct Air Capture cost analysis (IDTechEx, 2025)
Fact Check: Claim-by-Claim Verification Verified
All major claims verified against authoritative sources including Britannica, U.S. DOE, USGS, and IPCC data. Carbon reservoir figures, DAC costs, and geological storage estimates all confirmed.
Sources used for verification
- Carbon sequestration - britannica.com
- DOE Explains Carbon Sequestration - energy.gov
- What is carbon sequestration? - usgs.gov
- Natural sequestration of CO2 is in decline - Weather journal
- Direct Air Capture cost analysis - IDTechEx
