Working Group III: Mitigation

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2.3.3 Summary of General Mitigation Scenario Review

Many mitigation as well as stabilization scenarios have already been quantified and published. Most assume very simple policy options for their mitigation scenarios, and only some of them have detailed policy packages. These policy options have a very wide range in their level, which is apparently caused by the divergent baseline scenarios and GHG reduction targets, with other factors such as differences in models and reduction time-paths also acting to increase the range. Allocations of emission reductions between OECD and non-OECD countries also vary widely, and are affected by policy assumptions and model structures.

The mitigation scenarios under review were quantified based on a wide range of baselines that reflect a diversity of assumptions, mainly with respect to economic growth and low-carbon energy supply. The range of future trends shows greater divergence in scenarios that focus on developing countries than in scenarios that consider developed nations. There is little consensus with respect to future directions among the existing disaggregated scenarios in developing regions.

Some general conclusions about the relationships between baseline scenarios and mitigation policies are suggested by this review: an assumption of high economic growth in the baseline tends to be associated with more technological progress; the additional improvement of energy efficiency in mitigation scenarios tends to be lower when the energy efficiency improvement is high in the base case; and baseline scenarios with high carbon intensity reductions lead to mitigation scenarios with relatively more carbon intensity reduction. The counterintuitive nature of some of these conclusions suggests that the relationship between economic growth and the macroeconomic cost of emission reduction is very complicated.

Most generally, it is clear that mitigation scenarios and mitigation policies are strongly related to their baseline scenarios, but no systematic analysis has been published on the relationship between mitigation and baseline scenarios.

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