Completeness refers to an accounting of all applicable sources and sinks. In the context of a Kyoto Protocol accounting system, the sources and sinks that are "applicable" would be defined by the provisions of the Protocol.
Accuracy refers to the general validity of the reported numbers from an accounting system. Accurate estimates are unbiased in that they do not systematically under- or overstate the true number. A related issue is precision. Precise estimates have small standard errors. Accuracy and precision can be independent. A system can be accurate (unbiased) but produce estimates of limited precision. On the other hand, extremely precise estimates can be biased if the system is not well designed.
The accounting system should enable a third party to verify the reported numbers. Verifiability requires that the accounting system is built on proper data collection, measurement, and reporting procedures. For instance, claims that relevant LULUCF activities sequestered a given quantity of carbon over a certain period of time should be based on substantiated data, models, and methods. The location and extent of the land on which the claimed carbon sequestration took place should also be clearly identified, preferably using a consistent geographic information system that would facilitate identification of possible double-counting and the overlay of information used for verification (e.g., remote-sensing data). In short, claims should be able to withstand reasonable scrutiny.
An accounting system is not free. Systems that are more accurate, precise, and verifiable may be more expensive to develop and operate. An efficient accounting system operates at the point where the marginal costs of increased accuracy, precision, and verifiability just equal the marginal benefits of achieving the improvements. When resources are not available to obtain an efficient system, the objective should be to obtain the most effective system given the available resources.
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