An is a claim that an somewhere has been cancelled by a reduction somewhere else.
The claim is only true if the reduction would not have happened anyway, a property called .
Additionality is a statement about a world that does not exist and therefore cannot be measured.
It can only be estimated by modelling what the project developer would have done without the money.
The developer supplies the information from which that model is built, and is paid according to its conclusion.
This is not an accusation of fraud; it is a description of the facing an honest person.
Audits of forest protection schemes have repeatedly found that most credited were never at risk.
The forests were protected, the payments were made, and the s elsewhere continued.
A defence sometimes offered is that the money still did good, which is true and is a different claim.
An is not a donation; it is a licence to emit, and its value depends entirely on the cancellation.
Where the cancellation did not occur, the transaction has increased s relative to doing nothing.
That conclusion is uncomfortable and follows directly from the definition.
Some categories of avoid the problem because the is not in doubt.
Destroying an industrial gas that has no other use and costs money to destroy is additional by construction.
Such projects are a small share of the market because they are a small share of the opportunities.
The market has grown by expanding into categories where is arguable rather than .
Buyers have accepted this because an arguable and a one look identical on a .
Until they are priced differently, the market will continue to supply whichever is cheaper to produce.