Permanence refers to the longevity of a carbon pool. Under most carbon standards, an increased carbon stock or avoided loss of carbon stock as a result of a project activity must be maintained for a long period (usually at least for 100 years), and its reversal must be avoided. Permanence is important when emission reductions or removals are used as offsets – if the underlying carbon stock disappears, this is considered a “reversal”. Most carbon methodologies require a buffer pool to ensure against some projects having a reversal, such as could occur due to wildfire or illegal logging. (TNC)