Carbon and credits
Additionality
Additionality is the test of whether a project would have happened anyway. If it would have, the carbon it claims is not additional, and crediting it pays for something that was going to occur regardless. It is the hardest thing in carbon accounting to prove.
The difficulty is that it asks about a world that did not happen. A project has to argue it was not financially viable, not already required by law, and not standard practice, without any way to run the comparison.
It is the test most worth getting right, because it decides whether a credit represents a real change. A plantation a company would have planted anyway does not become climate action by being credited.