|Working Group III: Mitigation|
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2.5.2 Review of Post-SRES Mitigation Scenarios
126.96.36.199 Background and Outline of Post-SRES Analysis
The review of general mitigation scenarios shows that mitigation scenarios and policies are strongly related to their baselines, and that there has been no systematic comparison of the relationship between baseline and mitigation scenarios. Modellers participating in the SRES process recognized the need to analyze and compare mitigation scenarios using as their baselines the new IPCC scenarios, which quantify a wide range of future worlds. Consequently, they participated (on a voluntary basis) in a special comparison programme to quantify SRES-based mitigation scenarios (Morita et al., 2000a; 2000b). These SRES-based scenarios are called Post-SRES Mitigation Scenarios.
The process of the post-SRES analysis was started by a public invitation to modellers. A Call for Scenarios was sent to more than one hundred researchers in March 1999 by the Co-ordinating Lead Authors of this chapter and the SRES to facilitate an assessment of the potential implications of mitigation scenarios based on the SRES cases, which report was developed in support of the Third Assessment Report. Modellers from around the world were invited to prepare quantified stabilization scenarios for two or more concentrations of atmospheric CO2, based on one or more of the six SRES scenarios. Concentration ceilings include 450, 550 (minimum requirement), 650, and 750ppmv, and harmonization with the SRES scenarios was required by tuning reference cases to SRES values for GDP, population, and final energy demand.
Nine modelling teams participated in the comparison programme, including six SRES modelling teams and three other teams: AIM team (Jiang et al., 2000), ASF team (Sankovski et al., 2000), IMAGE team, LDNE team (Yamaji et al., 2000), MESSAGE-MACRO team (Riahi & Roehrl, 2000), MARIA team (Mori, 2000), MiniCAM team (Pitcher, 2000), PETRO team (Kverndokk et al., 2000) and WorldScan team (Bollen et al., 2000). Table 2.6 shows all the modelling teams and the stabilized concentration levels which were adopted as stabilization targets by each one. Most of the modelling teams covered more than two SRES baseline scenarios, and half of them developed multiple stabilization cases for at least one baseline, so that a systematic review can be conducted to clarify the relationship between baseline scenarios and mitigation policies and/or technologies.
While all baselines were analyzed, the A1B baseline was most frequently used. Across baselines, the stabilization target of 550ppmv seemed to be the most popular. Because of time constraints involved in quantifying the stabilization scenarios, the modelling teams mostly focused their analyses on energy-related CO2 emissions. However, about half of the modelling teams, notably the AIM, IMAGE, MARIA, and MiniCAM teams, have quantified mitigation scenarios in non-energy CO2 emissions as well as in non-CO2 emissions. The modelling teams that did not estimate non-energy CO2 emissions introduced scenarios of them from outside of their models for estimating atmospheric concentrations of CO2.
In order to check the performance of CO2 concentration stabilization for each post-SRES mitigation scenario, a special generator (Matsuoka, 2000) was used by the modelling teams to convert the CO2 emissions into CO2 concentration trajectories. In addition, the generator was used by them to estimate the eventual level of atmospheric CO2 concentration by 2300, based on the 1990 to 2100 CO2 emissions trajectories from the scenarios. This generator is based on the Bern Carbon Cycle Model (Joos et al., 1996), which was used in the IPCC SAR (IPCC, 1996) and TAR (IPCC, 2001). Using this generator, each modelling team adjusted their mitigation scenarios so that the interpolated CO2 concentration reached one of the alternative fixed target levels at the year 2150 within a 5% error. The year 2150 was selected based on Enting et al. (1994) who gave a basis for stabilization scenarios of the IPCC SAR (IPCC, 1996).13 A further constraint imposed was that the interpolated emission curve should be smooth after 2100, the end of the time-horizon of the scenarios. This adjustment played an important role in the post-SRES analyses for harmonizing emissions concentrations levels across the stabilization scenarios. The key driving forces of emissions such as population, GDP, and final energy consumption were harmonized in baseline assumptions specified by the six SRES scenarios.
188.8.131.52 Storylines of Post-SRES Mitigation Scenarios
The procedure for creating post-SRES mitigation scenarios was similar to the SRES process, even though the period for the post-SRES work was much shorter than that for the SRES and, in contrast to the SRES process, the exercise was voluntary and not mandated by the IPCC. The storyline approach of SRES indicates that different future worlds will have different mitigative capacities (cf. Section 1.5.1). Hence, the first step of the post-SRES scenario work was to create storylines for the mitigation scenarios.
In general, mitigation scenarios are defined relative to a baseline scenario.
If mitigation strategies are formulated and implemented in any of the future
worlds as described within SRES, a variety of aspects of that world will determine
the capacity to formulate and implement carbon reduction policies, for instance:
In the post-SRES process, it was difficult for the modelling teams to consider all of these aspects with relation to the SRES future worlds, because of their inherent complexity and the amount of time available for the work. However, some aspects were considered by some modelling teams and these were reflected in the quantification assumptions. The rest of this section illustrates these major points in the form of storylines for each of the six SRES scenarios, which describe the relationship between the kind of future world on the one hand and the capacity for mitigation on the other.
The A1 world is well equipped to formulate and implement mitigation strategies in view of its high-tech, high-growth orientation and its willingness to co-operate at a global scale, provided the major actors acknowledge the need for mitigation. There will be good monitoring and reporting on emissions and climate change, and possible signs of climate change will be detected early and become part of the international agenda. Market-oriented policies and measures will be the preferred response. Least-cost options will be searched for and implemented through international negotiation and mechanisms with the support of governments and multinational companies. New emission reduction technologies from developed countries will enable developing countries to respond more rapidly and effectively if barriers to technology transfer can be overcome. In this high-growth world, the economic costs associated with the response to climate change are likely to be bearable. In the A1B scenario, where mitigation strategies may hit the limits of renewable energy supply, and in the A1FI scenario, carbon removal and storage as well as higher end-use energy efficiency will become major emission reduction options. In the A1T scenario, technology developments are such that mitigation policies and measures only require limited additional efforts.
Developing and implementing climate change mitigation measures and policies in the A2 world can be quite complicated. This is a result of several features embedded in the scenario storyline: rapid population growth, relatively slow GDP per capita growth, slow technological progress, and a regional and partially isolationist approach in national and international politics. Because of all these serious challenges, the abatement of GHG emissions in the A2 world becomes plausible only in the situation when the negative effects of climate change become imminent and the associated losses outweigh the costs of mitigation. The same features that make the A2 world non-receptive to worldwide mitigation policies may exacerbate the climate change effects and prompt nations to act. Measures such as a rapid shift towards high-tech renewable energy or deep-sea carbon storage will be highly improbable in the A2 world as a consequence of technology limitations. Instead, such relatively low-tech measures as limiting energy consumption, and capturing and using methane from natural gas systems, coal mining, and landfills better fit the A2 worlds economic and technological profile. The lack of global co-operation may cause rather large regional variations in the feasibility and cost of mitigation policies and measures.
The B1 world is also well equipped to formulate and implement mitigation strategies,
in view of its high economic growth and willingness to co-operate at a global
scale. In comparison with the A1 world, however, it will be confronted with
higher marginal abatement costs, although total costs are much lower than in
A1B or A1FI. This is because baseline carbon emissions are lower in the B1 world
compared to the A1 world, a consequence of the emphasis on sustainable development
in B1. There will be intense monitoring and reporting of emissions and climate
change. The precautionary principle informs international agenda setting and
policy formulation, with governments taking responsibility for climate change-related
preventive and adaptive action. Tightening international standards generates
incentives for further innovation towards energy-efficiency and low- and zero-carbon
options. Educational campaigns are another important instrument. Developed regions
support the less developed regions in a variety of ways, including transfer
of energy-efficiency and renewable-energy related technologies. Carbon taxes
are introduced; an elaborate phase-in mechanism for less developed regions is
negotiated and implemented. A part of the carbon tax revenue is used to compensate
some fossil-fuel exporters and for a fund to compensate those affected by climate
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