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Negative-emissions technologies remove carbon dioxide (CO₂) from the atmosphere and store it; they do not simply prevent emissions from reaching the air. They can help lower net emissions, balance some emissions that remain difficult to eliminate, and—if removals exceed those residual emissions—produce net-negative emissions. They complement deep emissions cuts; they are not a substitute for them.
What counts as negative emissions?
The key distinction is where the CO₂ comes from. Carbon dioxide removal (CDR) takes CO₂ already in the atmosphere and stores it in geological, terrestrial, ocean, or product reservoirs. Capturing CO₂ from a fossil-fuel power plant or industrial process before it enters the atmosphere can reduce emissions, but that capture alone is not atmospheric removal.
A project also needs to deliver net removal, not merely capture a gross quantity of CO₂. Its full emissions—including those from energy, materials, land use, processing, and transport where relevant—must be accounted for, as must whether the stored carbon remains out of the atmosphere. A pathway is net-negative only when its removals exceed its associated emissions.
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Why do climate pathways include carbon removal?
The IPCC identifies three roles for CDR in ambitious mitigation strategies. Removal can lower net emissions in the near term; counterbalance residual emissions that are hard to eliminate as countries and sectors approach net zero; and, if annual removal exceeds residual emissions, achieve net-negative emissions over the longer term. The IPCC says that limiting warming to well below 2°C and reaching net zero CO₂ or greenhouse-gas emissions will require anthropogenic CO₂ removal.
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This does not mean that future removal can safely replace emissions cuts now. The IPCC frames removal as complementary to emissions abatement. Relying on large future volumes is uncertain: pathways differ in their assumptions, and modeled quantities are not commitments or proof that the capacity will be built.
Which methods remove CO₂, and how do they differ?
There is no single negative-emissions technology. The options differ in how they take up CO₂, where it is stored, how easily that storage could be reversed, and what resources and safeguards they require.
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| Approach | How it works and where carbon is stored | Main constraints and risks |
|---|---|---|
| Afforestation and reforestation | Establishing forests or restoring forest cover draws CO₂ into vegetation and soils. | Fire, pests, drought, later land-use change, or poor project design can reverse storage. Land choices matter: tree planting is not automatically additional removal and can harm biodiversity or compete with other land uses. |
| Soil carbon and ecosystem restoration | Land-management practices can increase or protect soil carbon; restoring wetlands, peatlands, and coastal ecosystems can protect or rebuild ecosystem carbon stocks. | Results depend on local conditions and management. Measurement and permanence are challenging, and interventions can have ecological or land-use trade-offs. |
| Bioenergy with carbon capture and storage (BECCS) | Biomass is grown and converted or burned for energy; some resulting CO₂ is captured and stored, generally in geological storage. | Net removal depends on sustainable feedstock, land-use effects, the conversion pathway, and full lifecycle accounting. Bioenergy can either increase or reduce emissions depending on how and where it is produced. |
| Direct air carbon capture and storage (DACCS) | Chemical sorbents or solvents capture CO₂ directly from ambient air; the separated CO₂ is stored underground or mineralised. | It requires substantial energy and water, and low-carbon energy is important to net performance. Cost and the energy needed to process dilute atmospheric CO₂ constrain deployment. |
| Biochar | Biomass is converted into a carbon-rich material, some of which can remain stored when the material is used or placed in suitable conditions. | Outcomes depend on feedstock, production process, and end use. Carbon storage and net removal need project-specific evidence rather than a general guarantee. |
| Enhanced weathering | Reactive minerals are crushed or otherwise used to speed up natural weathering, which consumes CO₂ and can store carbon in dissolved forms or minerals. | The IPCC assessed this as low in technology readiness in its 2022 assessment. Scaling requires suitable minerals and handling, and net effects need to be measured. |
| Ocean-based approaches | Methods include ocean alkalinity enhancement and biological approaches such as fertilisation, intended to increase ocean uptake or storage of carbon. | Feasibility remains uncertain, and marine side effects are possible. These approaches require careful monitoring and governance; they are an active research area, not a settled large-scale solution. |
The IPCC identifies afforestation and reforestation among widely practiced CDR approaches. In its AR6 discussion, DACCS is more mature than enhanced weathering and ocean-based methods, but that relative maturity does not remove DACCS’s energy, water, cost, or scale constraints. Maturity, operating scale, and the quality of evidence should be assessed method by method rather than inferred from the label “carbon removal.”
How much removal do climate models assume?
In IPCC-assessed scenarios limiting warming to 2°C with greater than 67% likelihood, or below, the modeled cumulative removals for 2020–2100 span wide ranges. These are scenario results, not forecasts or guaranteed future capacity.
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| Method or category | Cumulative removal, 2020–2100 | Annual removal in 2050 |
|---|---|---|
| BECCS | 328 GtCO₂ (range: 168–763 GtCO₂) | 2.75 GtCO₂ per year (range: 0.52–9.45) |
| AFOLU removal, mainly afforestation and reforestation | 252 GtCO₂ (range: 20–418 GtCO₂) | 2.98 GtCO₂ per year (range: 0.23–6.38) |
| DACCS | 29 GtCO₂ (range: 0–339 GtCO₂) | 0.02 GtCO₂ per year (range: 0–1.74) |
All figures in the table are IPCC 2022 assessed scenario ranges for pathways limiting warming to 2°C (>67%) or below; the cumulative figures cover 2020–2100, and annual figures are for 2050. AFOLU means agriculture, forestry, and other land use. The breadth of the ranges reflects differing modeled pathways and assumptions, not a promise that any particular amount will be delivered. These figures should not be read as current deployment totals.
How should a removal claim be evaluated?
A headline tonne or price cannot establish that a project has delivered durable net removal. The relevant questions span the entire pathway, from CO₂ uptake through storage and monitoring.
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- Atmospheric removal: Does the process remove CO₂ already in the air, or does it capture a point-source emission or avoid an emission?
- Net quantity: What lifecycle emissions arise from energy, materials, transport, land-use change, and processing, and how are they deducted from gross capture?
- Storage and reversal: Where is the carbon stored, for how long is storage expected to last, and what could release it again?
- Readiness and scale: Is the method operating, demonstrated, or still at an early stage? What evidence supports claims about practical capacity?
- Resources and costs: What energy, water, land, biomass, or mineral inputs are required, and what constraints follow from those requirements?
- Effects beyond carbon: How could the activity affect biodiversity, food production, communities, or marine ecosystems?
- Verification and governance: How are removal, lifecycle emissions, storage, and possible reversals monitored, reported, and independently checked?
For BECCS in particular, the IEA cautions that results depend on feedstock sustainability, changes in land management, and the scope and timing of emissions and removals. For biological approaches, the possibility of reversal means that storage claims need a credible account of duration and risk. Geological storage can offer longer-duration storage, but it still requires sound accounting and governance.
What is the practical conclusion?
CDR is a portfolio of approaches, not a single device or guaranteed backstop. Land-based methods can store carbon in ecosystems but face permanence and land-use questions; engineered and biomass-based routes require careful lifecycle accounting; and some mineral and ocean approaches remain less mature or uncertain. Their contribution depends on credible net-removal measurements, durable storage, available resources, and safeguards against environmental and social harm. The central climate strategy remains to cut emissions deeply and use removal for the roles it can responsibly serve.
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