11.3.1.1 Problems in aggregating emissions

In compiling estimates of this kind, various issues must be considered:

Comparability: There is no common, standardized approach in the underlying literature that is used systematically for assessing the mitigation potential. The comparability of data is therefore far from perfect. The comparability problem was addressed by using a common format to bring together the variety of data found in the literature (as shown below in section 11.3.1.3 and Table 11.3), acknowledging that any aberrations due to a lack of a common methodological base may in part cancel each other out in the aggregation process. Some extrapolations were necessary, for example in the residential sector where the literature mostly refers to 2020. The final result can be considered the best result that is possible and it is accurate within the uncertainty ranges provided.

Coverage: Chapters 4 to 10 together cover virtually all sources of greenhouse gas emissions. However, for parts of some sectors, it was not possible to derive emission reduction potentials from the literature. Furthermore, no quantified emission reduction potentials were available for some options. This leads to a certain under-estimation of the emission reduction potential as discussed in Section 11.3.1.3. The under-estimation of the total mitigation potential is limited, but not negligible.

Baselines: Ideally, emission reduction potentials should adopt a common baseline. Some emission scenarios, such as those developed for the Special Report on Emission Scenarios (IPCC, 2000), are suitable for worldwide, sectoral and multi-gas coverage. However, for a number of sectors, such baselines are not detailed enough to serve as a basis for making bottom-up emission reduction calculations. The baselines used are described and discussed further in Section 11.3.1.2.

Aggregation: The aggregation of mitigation potentials for various sectors is complicated by the fact that mitigation action in one sector may affect mitigation potential in another. There is a risk of double counting of potentials. The problem and the procedures used to overcome this risk are explained in Section 11.3.1.3. In addition the baselines differ to some extent.