Parties can estimate emissions and removals using two general approaches: direct measurement or proxy data. The concept of uncertainty in direct measurements is more consistent with a statistical concept of uncertainty. The statistical issues include precision and calibration of measurement equipment, fraction of population captured, frequency of sampling, etc.

In contrast, proxy data are more typically in the form of emission factors and activity data. The proxy data approach requires assumptions as to the relationship between some activity and actual emissions.

Therefore, the uncertainty in this relationship must be considered as well as the accuracy and precision in measurements of the proxy data itself.

National statistics, which is what most Parties use for their inventories, often do not have rigorous statistical uncertainty information associated with them. In addition, many of the other variables used such as emission factors, also do not have detailed or quantitative uncertainty information associated with them. Therefore, expert judgment is often required in the development of quantified uncertainty estimates for emission and removal estimates based on proxy data.

This expert judgment, though, is inherently subjective (i.e., biased), and therefore must be interpreted cautiously. For this reason, you should not assume that an uncertainty distribution or analysis from one Party is directly applicable as an input or comparable to an analysis by another Party.

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