Carbon credits are often described as if every unit were interchangeable: one credit, one tonne of carbon dioxide equivalent. The arithmetic is simple. The integrity test is not.
A credible credit must represent a climate benefit that would not otherwise have happened, endure for the period claimed, and be counted only once. These tests are known as additionality, permanence and no double counting. They do not guarantee that every project is good, but a credit that fails any one of them can overstate its climate value.
Additionality asks: would the reduction have happened anyway?
A project is additional when carbon-credit revenue changes the outcome. The Integrity Council for the Voluntary Carbon Market defines additional reductions or removals as those that would not occur without the incentive created by credit revenue.
This is harder to prove than showing that a project exists. A solar plant may reduce fossil generation, but if it was already required by law, fully financed and commercially inevitable, selling credits may not have caused the reduction. A forest project may protect land, but the baseline must show a credible risk of loss rather than an exaggerated counterfactual.
Questions that reveal the baseline
- What would have happened without credit revenue?
- Which law, subsidy or commercial trend is included in that baseline?
- When was the investment decision made relative to the credit application?
- How sensitive are credited reductions to a different baseline?
A strong methodology makes these assumptions visible and uses conservative estimates. Independent validation helps, but it does not replace scrutiny of the baseline itself.
Permanence asks: how long will the benefit last?
Fossil carbon released into the atmosphere has long-lived effects. Biological storage can be reversed by fire, drought, disease, harvesting or land-use change. The permanence question is therefore especially important for forestry and other land-based removals.
Programs may use monitoring periods, pooled buffer reserves or replacement obligations to manage reversal risk. These tools reduce risk; they do not make it disappear. Buyers should look for who is responsible if stored carbon is later released, how long monitoring lasts and whether the buffer is large enough for correlated risks such as regional wildfire.
This is one reason a credit should not be treated as permission to delay direct emissions cuts. Our guide to checking corporate transition plans explains why near-term operational reductions need their own milestones and budgets.
No double counting asks: who gets to claim the tonne?
Double counting can occur through double issuance, double use or double claiming. The Core Carbon Principles assessment framework distinguishes all three:
- Double issuance: more than one credit exists for the same reduction or removal.
- Double use: the same credit is retired or presented more than once.
- Double claiming: two entities count the same underlying outcome toward their targets.
Registries, unique serial numbers, transparent retirement records and clear accounting boundaries are essential. A marketing statement should identify what was retired, in which registry, for which period and for whose claim.
A practical buyer checklist
- Read the methodology, not only the project description.
- Check the baseline and the date of the investment decision.
- Identify reversal risks and the mechanism used to address them.
- Confirm serial numbers and retirement in a public registry.
- Look for overlapping schemes or claims.
- Keep credits separate from the company’s gross emissions inventory and direct-reduction progress.
Carbon credits can channel finance toward mitigation, but the unit is only as credible as its rules, data and claims. Treat additionality, permanence and double counting as three separate questions. A convincing answer to one does not repair a weak answer to another.
For the accounting foundation beneath these claims, see our explainer on why emissions factors can produce different carbon numbers.
Featured image: AI-generated editorial illustration by ClimateCrisis Editorial. It does not depict a specific place, project or event.