Additionality: the extent to which greenhouse gas emission reductions or removals would have occurred in the absence of the associated policy intervention or activity.
An additionality test is applied in carbon credit programs to ensure that credits are not awarded for mitigation that would have occurred in the absence of the carbon credit revenue.
In other words, additionality evaluates the degree to which an intervention – for example, a CDR project – causes a climate benefit above and beyond what would have happened in a no-intervention baseline scenario. By definition, this counterfactual baseline scenario cannot be directly observed (because it did not happen), so can only be estimated or inferred based on contextual information. Additionality can be assessed at the level of individual projects or protocols that define categories of projects. In policy regimes such as cap-and-trade programs, where emissions are permitted in exchange for reduction or storage elsewhere, failures of additionality result in increased emissions.
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