The effect of different historical emissions datasets on emission targets of the sectoral mitigation approach Triptych

The Triptych approach differentiates emission reduction targets under a future international climate agreement based on technological considerations at the sector level. The advantage of such a sectoral approach is that it allows for discussions on worldwide competing sectors and on the role of emission reduction contributions of developing countries. The disadvantage is that the reduction targets are influenced by countries' historical emissions data at the sectoral level, which are, especially for developing countries, uncertain. A major drawback of the analyses of the Triptych approach is that they lack a sensitivity analysis of the effect of using different historical emissions datasets on the allocation of emission allowances. The present article addresses this by analysing and comparing the differences in future emissions allowances under the Triptych approach, using two different historical emissions datasets. For some countries, the differences in historical emissions data are large. This leads to big differences in emission allocations: for 18 of the 32 countries considered, reduction targets in 2020 relative to the 2005 levels differ by more than 5 percentage points. This highlights the need for reliable, uniform sectoral emissions registrations at the country level for allocating emissions to sectors, especially for more sophisticated sectoral approaches than Triptych.