As carbon dioxide removal attracts more attention, the number of concepts used across projects, policy, standards, and carbon markets is also growing. For readers who are becoming more familiar with CDR, building fluency in this language can significantly accelerate learning and make the field easier to navigate.
This issue brings together a selection of core terms that appear frequently in CDR discussions. By grouping related concepts together, we aim to make the logic of the field easier to follow and to show how different parts of the CDR ecosystem connect to one another. For each term, we briefly explain what it means and why it matters.
Defining the removal itself
Carbon removal credit
A carbon removal credit represents a verified quantity of CO₂ that has been removed from the atmosphere and stored. It is usually issued in units of one tonne of CO₂.
This is one of the main ways removals are quantified, transacted, and claimed in carbon markets.
Engineered/Novel CDR
Engineered/Novel CDR refers to human-designed systems that remove CO₂ from the atmosphere and store it through physical, chemical, or engineered biological pathways. Examples include direct air capture, biochar, and mineralization-based approaches.
This category is central to discussions about durability, measurement quality, and long-term scaling.
Nature-based CDR
Nature-based CDR refers to approaches that increase carbon stored in ecosystems such as forests, soils, wetlands, and coastal systems.
These approaches often offer important co-benefits, but they also raise key questions around permanence, reversal risk, and land use.
Net-negativity
Net-negativity describes a situation in which more CO₂ is removed from the atmosphere than is emitted overall.
It is a critical concept for understanding how the world moves beyond net zero and begins lowering atmospheric CO₂ concentrations.
Neutralization
Neutralization refers to the use of carbon removals to counterbalance residual emissions that remain after deep decarbonization.
It sits at the heart of many net-zero frameworks and helps define the role removals should play in credible climate strategies.
Residual emissions
Residual emissions are the emissions that remain after all feasible efforts to reduce them have been made.
They are the reason removals remain necessary even in a deeply decarbonized economy.
Scalability
Scalability refers to the ability of a CDR pathway to grow in volume without running into prohibitive constraints.
A removal pathway may work well at pilot scale, but climate relevance depends on whether it can expand responsibly and materially.
Storage and durability
Durability (often also referred to under permanence; there are important distinctions, but we will not unpack them in detail here)
Durability refers to how long removed carbon is expected to stay out of the atmosphere.
Different CDR pathways store carbon for very different lengths of time, and that affects how they should be valued and used.
Reversal
A reversal occurs when carbon that was previously removed and stored is released back into the atmosphere.
Reversal risk affects the reliability of a project and the confidence buyers can place in a removal claim.
Reservoir
A reservoir is the place where carbon is stored after removal. This can include soils, biomass, rocks, oceans, products, or deep geological formations.
Where carbon is stored strongly shapes durability, monitoring needs, and long-term risk.
Storage
Storage refers to the process or state of keeping removed carbon out of the atmosphere after capture.
A removal is only as credible as its storage pathway, so this concept is fundamental to the field.
Tonne-year accounting
Tonne-year accounting is a way of valuing carbon storage based on how much carbon is stored and for how long.
It appears in debates about how to compare temporary and long-lived storage, especially across very different CDR approaches.
Measuring, checking, and proving quality
Monitoring
Monitoring is the ongoing collection of data to track how much CO₂ is being removed and how securely it is stored.
Without monitoring, it is impossible to understand whether a project is performing as intended.
Validation
Validation is the assessment of a project design before implementation or credit issuance to check whether the methodology and assumptions are sound.
It helps ensure that a project is structured credibly from the beginning.
Verification
Verification is the independent assessment of whether a project has actually delivered the removals it claims.
It is one of the main mechanisms used to build trust in carbon removal outcomes.
MRV
MRV stands for Monitoring, Reporting, and Verification. It describes the overall system used to measure removals and confirm results.
MRV is one of the core foundations of quality, comparability, and trust in CDR.
Methodology
A methodology is the formal framework used to define how a CDR project should be measured, assessed, and credited.
Methodologies shape what counts as a removal, how performance is calculated, and how conservative the rules are.
Baseline
A baseline describes the scenario against which a project’s impact is measured.
It is essential for judging whether the removal is truly additional and whether credited impact is real.
Additionality, system effects, and net climate value
Additionality
Additionality asks whether a carbon removal would have happened without the project, incentive, or carbon finance attached to it.
It is one of the most important tests of whether a credited removal is genuinely creating extra climate value.
Leakage (also called market-leakage)
Leakage refers to unintended emissions increases outside the project boundary that happen because of the project.
A project may appear effective on paper while causing emissions elsewhere, so leakage must be understood and managed.
Trade-offs
Trade-offs are the compromises that arise when a project delivers benefits in one area while creating pressure in another, such as land, water, biodiversity, energy, or cost.
CDR scaling requires honest recognition of trade-offs, not just headline benefits.
Co-benefits
Co-benefits are the positive side effects a project may create beyond carbon removal, such as soil improvement, biodiversity support, rural income, or waste reduction.
They can strengthen the broader value of a project, especially when they are real, material, and well evidenced.
Delivery, market process, and claims
Delivery
Delivery refers to the actual fulfillment of a promised carbon removal.
In carbon markets, the difference between a promise and a delivered removal is critical.
Issuance
Issuance is the formal creation of a carbon removal credit after the required checks have been completed.
It is the point at which a removal becomes an official tradable unit.
Retirement
Retirement is the process of taking a credit out of circulation after it has been used.
It prevents the same credit from being used more than once and is essential for credible claims.
Offsetting
Offsetting refers to the use of carbon credits to compensate for emissions occurring outside the boundary of the project or activity generating the credit.
It is one of the most widely known uses of carbon markets, but in CDR it also raises important questions around claims, integrity, and how removals should be matched to ongoing emissions.
Insetting
Insetting refers to the use of carbon interventions within a company’s own value chain to reduce or remove emissions connected to its operations, suppliers, or products.
It is often discussed as a closer-to-home alternative to offsetting, especially when companies are trying to generate climate impact within the systems they directly influence.
Like-for-like principle
The like-for-like principle suggests that emissions should be balanced with removals that match their carbon-cycle characteristics and durability as closely as possible. In practice, this often means that fossil CO₂ emissions are best matched with high-durability or permanent removals, while shorter-cycle emissions may in some cases be paired with less durable pathways.
This matters because not all tonnes behave the same way over time, and more credible matching can lead to more credible net-zero claims.
Risk, responsibility, and project governance
Buffer pool
A buffer pool is a reserve of credits set aside to cover potential future reversals or underperformance.
It is one of the main tools used to manage uncertainty, especially in projects with higher reversal risk.
Chain of custody
Chain of custody refers to the traceable record of where carbon-containing material comes from, where it goes, and how it is handled along the way.
It is especially important in biomass-based pathways, where project credibility depends on tracking material flows carefully.
Liability
Liability refers to who is responsible if a project fails, underdelivers, or experiences a reversal.
Clear responsibility is essential for market confidence and long-term accountability.
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As the field continues to evolve, these concepts will keep showing up across project design, standards, claims, and investment decisions. Building familiarity with them is a simple but important step toward engaging with CDR more confidently and more critically. The clearer this shared language becomes, the stronger the foundation for credible scale-up will be.
