Double Counting
When the same tonne of emissions reduction is claimed more than once, whether by two buyers, by two registries, or by a buyer and the host country. Serial numbers, single-registry issuance, and corresponding adjustments exist to prevent it.
Why double counting matters for carbon credit buyers
Double counting undermines the arithmetic the whole market rests on, because a tonne counted twice leaves a tonne of real emissions unaddressed. It takes three main forms: double issuance, where two programmes credit the same activity; double use, where one credit is applied to two claims; and double claiming, where the host country also counts the reduction towards its national target. Unique serial numbers and issuance through a single registry handle the first two. The third is exactly what corresponding adjustments under the Paris Agreement were designed to resolve.