Carbon Sequestration (Land Removals) — Definition and GHG Accounting Context
Every year a growing forest quietly does what no industrial machine yet does at scale: it pulls carbon dioxide out of the air and locks it into wood and soil. A hectare of recovering tropical forest can remove around eleven tonnes of CO₂-equivalent annually, for free, powered by sunlight. This is the one lever in climate accounting that produces a genuinely negative number.
That process is carbon sequestration. Carbon sequestration is the capture and storage of atmospheric CO₂ in a reservoir such as forest biomass or soil — and, in the land sector, it is counted as a removal: a negative emission.
Carbon sequestration is the process by which CO₂ is captured from the atmosphere and stored in a carbon reservoir. In the land sector this is biological — photosynthesis builds carbon into biomass, and soils accumulate organic carbon — so growing forests and improving soils act as sinks. In accounting it becomes a land removal, a negative emission reported separately from gross emissions. It is the mirror image of land-use-change emissions.
Definition — Capturing Carbon in a Reservoir
Carbon sequestration is the process by which carbon dioxide is captured from the atmosphere and held in a carbon reservoir, or “pool”. In the land sector — the focus of this definition — sequestration is biological: through photosynthesis, plants fix atmospheric CO₂ into living biomass, and as leaves and roots die, carbon accumulates in the soil as organic matter. A forest that is growing, a wetland that is accreting, or a field whose soil carbon is building all act as carbon sinks, drawing CO₂ down out of the air.
The carbon is stored across several pools: above-ground biomass (trunks, branches, leaves), below-ground biomass (roots), dead organic matter, and soil organic carbon. Coastal ecosystems — mangroves, seagrass, saltmarsh — sequester carbon especially densely, a category often called “blue carbon”. Because the carbon originates in the atmosphere and passes through living things, sequestered land carbon is biogenic, and converting a stored mass of carbon to CO₂ uses the same molecular ratio as any other — 3.667 (44⁄12).
Sequestration is the exact reverse of land-use change: where clearing land releases stored carbon, growing land rebuilds it. That symmetry — and a crucial asymmetry in speed — is what makes land removals both valuable and fragile.
Definition at a glance
| What it is | Capture and storage of atmospheric CO₂ in a carbon reservoir |
|---|---|
| Land-sector mechanism | Biological — photosynthesis into biomass; carbon build-up in soils |
| Carbon pools | Above/below-ground biomass, dead organic matter, soil organic carbon |
| In accounting | A removal — a negative emission, reported separately from gross |
| The catch | Reversible — fire, harvest, or conversion can release it again |
| Relationship | The mirror image of land-use-change emissions |
Process, Removal, Storage: Three Words Often Confused
Three closely related terms get used interchangeably but mean different things, and precision matters in accounting:
| Term | What it refers to |
|---|---|
| Sequestration | The process — the ongoing flux of carbon into the reservoir (a rate, e.g. tonnes per hectare per year) |
| Removal | The accounting outcome — how that flux is counted in a greenhouse-gas inventory: a negative emission |
| Storage | The stock — the carbon already held in the reservoir at a point in time |
So sequestration is what a forest does, storage is what it holds, and a removal is how the doing is recorded. Carbon sequestration is one route to carbon dioxide removal (CDR) — the nature-based route — alongside engineered approaches such as direct air capture. What unites all removals is that they must be counted as negative emissions and, under the GHG Protocol Land Sector and Removals Guidance, reported on a separate line from gross emissions.
How Much Land Sequesters: Live Rates
Sequestration rates are expressed per hectare per year, and — because they are removals — they carry a negative sign. The live IPCC AR6 aggregates show how much biomass and soil pathways draw down, and how much they differ:
| Ecosystem / practice | Net flux kg CO₂e / ha / year | Pool |
|---|---|---|
| Tropical forest (growing) | -11000 | Biomass |
| Temperate broadleaf forest | -5800 | Biomass |
| Temperate conifer forest | -4900 | Biomass |
| Boreal forest | -2200 | Biomass |
| Improved grassland | -500 | Soil |
| Cover cropping | -300 | Soil |
Forests sequester far faster than soil practices, and warm, fast-growing tropical forest fastest of all. The forest pathways compared by magnitude:
Annual removal per hectare, kg CO₂e (IPCC AR6, live). Bar width is magnitude; the labels keep the negative sign because a removal is a negative emission. Soil practices (improved grassland -500, cover cropping -300) sequester an order of magnitude less than forest, and both slow as the reservoir saturates.
The Release–Uptake Asymmetry
Land carbon is easy to lose and slow to rebuild. Clearing a hectare of tropical forest releases a one-time pulse of about 165000 kg CO₂e (a land-use-change emission); regrowing forest on that hectare removes only around 11,000 kg CO₂e per year. The arithmetic is sobering: recovering what was lost in a single clearing takes roughly 15 years of uninterrupted regrowth.
Fast release, slow uptake means removals cannot simply cancel emissions in the same year, and it is a core reason land removals are reported separately from gross emissions rather than netted. A tonne emitted today and a tonne sequestered over the next fifteen years are not equivalent on the timescale that matters for climate targets. The forestry & removals calculator estimates sequestration by forest type and age; the land-use-change side handles the release.
What Makes a Removal Count
A sequestration rate on paper is not automatically a creditable removal. Four conditions decide whether it holds up in accounting or a carbon market:
- Additionality — the carbon must be sequestered beyond what would have happened anyway. A forest that was growing regardless does not generate an additional removal.
- Permanence — the storage must be durable. Sequestered carbon is reversible: a fire, a harvest, a drought, or reconversion can release it straight back.
- Measurement & monitoring (MRV) — the removal must be quantified and tracked over time, not assumed.
- Saturation — reservoirs fill up. A maturing forest and an improving soil both sequester ever more slowly as they approach equilibrium, so a rate is not perpetual.
These conditions are why land removals are governed carefully — by the GHG Protocol Land Sector and Removals Guidance for corporate inventories, and by crediting standards such as the Woodland Carbon Code for woodland-creation units — and why sequestration is counted toward a company’s FLAG removal target only when it is additional, durable, and verified.
Common Confusions
- Using “sequestration”, “removal”, and “storage” interchangeably. Sequestration is the process (a rate), a removal is the accounting outcome (a negative emission), and storage is the stock already held.
- Netting removals against emissions. Land removals are reported separately from gross emissions, never quietly subtracted — the release–uptake asymmetry is one reason why.
- Treating sequestration as permanent. It is reversible: sequestered carbon can return to the atmosphere through fire, harvest, drought, or land conversion. Durability is a condition, not a given — see permanence.
- Assuming the rate lasts forever. Forests and soils saturate; sequestration slows as the reservoir matures and eventually approaches equilibrium.
- Confusing biological sequestration with fossil carbon capture. Capturing CO₂ at a smokestack (CCS) stores fossil carbon to avoid an emission; sequestration draws atmospheric carbon into a reservoir. Only the latter is a removal of carbon already in the air.
Frequently Asked Questions
Carbon sequestration is the process by which carbon dioxide is captured from the atmosphere and stored in a carbon reservoir. In the land sector it is biological: plants fix atmospheric CO₂ into biomass through photosynthesis, and carbon accumulates in soils as organic matter, so growing forests, restored wetlands, and improving soils act as carbon sinks. In greenhouse-gas accounting the resulting flux is a land removal — a negative emission — reported separately from gross emissions. It is the mirror image of land-use-change emissions, which release stored land carbon.
They describe three different things. Sequestration is the process — the ongoing flux of carbon into a reservoir, expressed as a rate such as tonnes of CO₂ per hectare per year. A removal is the accounting outcome — how that flux is recorded in a greenhouse-gas inventory, namely as a negative emission. Storage is the stock — the carbon already held in the reservoir at a given moment. In short: sequestration is what a forest does, storage is what it holds, and a removal is how the doing is recorded. Keeping them distinct matters because only a durable, additional, verified process produces a removal that counts.
It depends heavily on the forest type. Using the live IPCC AR6 aggregates, a growing tropical forest removes about -11000 kg CO₂e per hectare per year, temperate broadleaf forest about -5800 kg, temperate conifer about -4900 kg, and boreal forest about -2200 kg. The values are negative because a removal is a negative emission. Soil practices sequester far less — improved grassland around -500 kg and cover cropping around -300 kg per hectare per year — and all of these rates slow as the forest or soil matures and its carbon reservoir saturates.
No — land-based sequestration is reversible, which is one of its most important limitations. Carbon stored in trees and soils can be released back to the atmosphere by wildfire, harvesting, drought, pests, or converting the land to another use. That is why permanence is one of the conditions a removal must meet to count, alongside additionality (the carbon must be sequestered beyond what would have happened anyway), measurement and monitoring, and an allowance for saturation as the reservoir fills. Corporate accounting under the GHG Protocol Land Sector and Removals Guidance and crediting standards such as the Woodland Carbon Code build in reversal risk explicitly.
Because a tonne emitted and a tonne sequestered are not equivalent in the same year. Sequestration is slow: recovering the one-time pulse from clearing a hectare of tropical forest — about 165000 kg CO₂e — takes roughly 15 years of regrowth at around 11,000 kg per year. Netting a fast release against a slow, reversible uptake would hide that mismatch and make a rising emissions figure look controlled. So both AFOLU/FLAG and the GHG Protocol require gross emissions and removals to be reported as separate lines, with removals shown as their own negative figure rather than blended into the gross total.