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.