Approach To Developing The Guidelines

The 2006IPCC Guidelines are an evolutionary development starting from the 1996IPCC Guidelines, GPG2000 and GPG-LULUCF. A fundamental shift in methodological approach would pose difficulties with time series consistency in emissions and removals estimation, and incur additional costs, since countries and the international community have made significant investments in inventory systems. An evolutionary approach helps ensure continuity, and allows for the incorporation of experiences with the existing guidelines, new scientific information, and the results of the UNFCCC review process. The most significant changes occur in Volume 4, which consolidates the approach to Land Use, Land-Use Change and Forestry (LULUCF) in GPG-LULUCF and the Agriculture sector in GPG2000 into a single Agriculture, Forestry and Other Land Use (AFOLU) Volume. This, and other important developments and changes, are summarised in Section 5 below.

The 2006 IPCC Guidelines retain the definition of good practice that was introduced with GPG2000. This definition has gained general acceptance amongst countries as the basis for inventory development. According to this definition, national inventories of anthropogenic greenhouse gas emissions and removals consistent with good practice are those, which contain neither over- nor under-estimates so far as can be judged, and in which uncertainties are reduced as far as practicable.

These requirements are intended to ensure that estimates of emissions by sources and removals by sinks, even if uncertain, are bona fide estimates, in the sense of not containing any biases that could have been identified and eliminated, and that uncertainties have been reduced as far as practicable, given national circumstances. Estimates of this type are presumably the best attainable, given current scientific knowledge and available resources.

The 2006 IPCC Guidelines generally provide advice on estimation methods at three levels of detail, from tier 1 (the default method) to tier 3 (the most detailed method). The advice consists of mathematical specification of the methods, information on emission factors or other parameters to use in generating the estimates, and sources of activity data to estimate the overall level of net emissions (emission by sources minus removals by sinks). Properly implemented, all tiers are intended to provide unbiased estimates, and accuracy and precision should, in general, improve from tier 1 to tier 3. The provision of different tiers enables inventory compilers to use methods consistent with their resources and to focus their efforts on those categories of emissions and removals that contribute most significantly to national emission totals and trends.

The 2006 IPCC Guidelines apply the tiered approach by means of decision trees (see the example in Figure 2). A decision tree guides selection of the tier to use for estimating the category under consideration, given national circumstances. National circumstances include the availability of required data, and contribution made by the category to total national emissions and removals and to their trend over time. The most important categories, in terms of total national emissions and the trend, are called key categories12. Decision trees generally require tier 2 or tier 3 methods for key categories. The 2006 IPCC Guidelines provide for exceptions to this, where evidence demonstrates that the expense of data collection would significantly jeopardize the resources available for estimating other key categories.

The 2006 IPCC Guidelines also provide advice on; i) ensuring data collection is representative and time series are consistent, ii) estimation of uncertainties at the category level, and for the inventory as a whole, iii) guidance on quality assurance and quality control procedures to provide cross-checks during inventory compilation, and iv) information to be documented, archived and reported to facilitate review and assessment of inventory estimates. Reporting tables and worksheets for tier 1 methods are provided. The use of tiered methodologies and decision trees and the cross cutting advice ensure that the finite resources available for inventory development and updating are deployed most effectively, and that the inventory is checked and reported in a transparent manner.

12 In the GPG2000 and GPG-LULUCF these were called key sources, or key categories where there could be removals.

Figure 2 Example Decision Tree (for CH4 and N2O from Road Transport)

Figure 2 Example Decision Tree (for CH4 and N2O from Road Transport)

Box 3: Tier 1

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