Climate Change 2001: Mitigation

2.5.2 Review of Post-SRES Mitigation Scenarios

2.5.2.1 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.

Table 2.6: Post-SRES participants and quantified scenarios (indicated by CO₂ stabilization target in ppmv)

Baseline scenarios	A1B	A1FI	A1T	A2	B1	B2

AIM (NIES and Kyoto University, Japan)	450, 550, 650	550		550	550	550
ASF (ICF Corporation, USA)				550, 750
IMAGE (RIVM, Netherlands)	550				450
LDNE (Tokyo University, Japan)	550	550	550	550	550	550
MARIA (Science University of Tokyo, Japan)	450, 550, 650		450, 550, 650		450, 550	450, 550, 650
MESSAGE-MACRO (IIASA, Austria)	450, 550, 650	450^(),550^(), 650^(), 750^()	450, 550	550, 750		550
MiniCAM (PNNL, USA)	550 ^(*)	450, 550, 650, 750		550	450, 550	550^(*)
PETRO (Statistics Norway, Norway)	450, 550, 650, 750		450, 550, 650, 750
WorldScan (CPB, Netherlands)	450^(), 550^()			450, 550^(**)	450^(**), 550	450^(**), 550

Notes: ^() High and low baselines were used; ^(*) An early action and a delayed response were quantified.

2.5.2.2 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:

The availability and dissemination of relevant knowledge on emissions and climate change;
The institutional, legal, and financial infrastructure to implement mitigation policies and measures;
Entrepreneurial and/or governmental policies for generating innovation and encouraging the penetration of new technologies; and
The mechanisms by which consumers and entrepreneurs respond to changing prices and new products and processes.

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 world’s 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 change.

In the B2 scenario actions to reduce GHG emissions are taken mainly at a local or regional scale in response to climate change impacts. Environmentally aware citizens of the B2 world will increasingly attribute damages to human-induced climate change. High-income countries, which are generally less vulnerable to climate change impacts, will increasingly see the need for climate policy action as a consequence of cost-benefit analyses. With increasing costs of damage, counter-measures challenge existing energy sector policies and institutional frameworks. Generally high educational levels promote both development and environmental protection. Resource availability, economic development, and technical change are uneven over regions. In relative terms, R&D expenditures are expected to stay constant, but they will be more targeted towards cleaner and less carbon-intensive energy technologies. Existing bilateral trade links will foster bilateral technology transfer from OECD countries to some developing countries. This is because rapidly increasing energy and, in particular, electricity demand in developing countries present business opportunities no longer available in OECD countries. Therefore, there exist a number of incentives for bilateral environmental policy co-operation between R&D intensive countries in the North and developing countries of the South. Energy trade links, first for oil and later for natural gas and methanol, will play an important seed role for new environmental bilateral co-operation, leading to a regionally heterogeneous approach to GHG reduction.

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