Chapter 5: Time Series Consistency

The time series is a central component of the greenhouse gas inventory because it provides information on historical emissions trends and tracks the effects of strategies to reduce emissions at the national level. As is the case with estimates for individual years, emission trends should be neither over nor underestimated as far as can be judged. All emissions estimates in a time series should be estimated consistently, which means that as far as possible, the time series should be calculated using the same method and data sources in all years. Using different methods and data in a time series could introduce bias because the estimated emission trend will reflect not only real changes in emissions or removals but also the pattern of methodological refinements.
 

This chapter describes good practice in ensuring time series consistency. Section 5.2 provides guidance on common situations in which time series consistency could be difficult to achieve: carrying out recalculations, on adding new categories, and on accounting for technological change. Section 5.3 describes techniques for combining or “splicing” different methods or data sets to compensate for incomplete or missing data. Additional guidance on reporting and documentation and QA/QC of time series consistency is given in Sections 5.4 and 5.5.