IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group III: Mitigation of Climate Change

11.3.5 Portfolio analysis of mitigation options

Portfolio analysis in this context is the study of the mix of actions available to reduce emissions or adapt to climate change and to business in diversifying their investments against risk.

One issue is the allocation of GHG abatement across sectors or regions. Capros and Mantzos (2000) show that, within the EU, equal percentage reductions across sectors cost more than twice as much as a least cost distribution (which can be obtained by, for example, allowing trade between sectors); see Table 11.9. The table also shows the gains through international trading both across the EU and in Annex I, confirming the benefits reported in the TAR from a wide range of previous literature.

Table 11.9: The effects of EU-wide and Annex B trading on compliance cost, savings and marginal abatement costs in 2010

 Compliance cost Savings against Reference Case Savings against Alternative Reference Case Marginal abatement cost (US$/tCO2) 
million US$ million US$ % million US$ % for sectors participating in EU-wide trading for other sectors 
No EU-wide trading 
Reference case: burden- sharing target implemented at least cost across sectors within a member state 9026 n.a. n.a. 11482 56.0 n.a. 54.3 
Alternative reference case: burden-sharing target allocated uniformly to all sectors within a member state  20508 -11482 -127.2 n.a. n.a. n.a. 125.8 
EU-wide trading 
Energy suppliers 7158 1868 20.7 13350 65.1 32.3 45.3 
Energy suppliers and energy-intensive industries 6863 2163 24.0 13645 66.5 33.3 43.3 
All sectors 5957 3069 34.0 14551 71.0 32.6 32.6 
Annex B trading: All sectors 4639 4387 48.6 15869 77.4 17.7 17.7 

Notes: A negative sign means a cost increase. A positive sign means a cost saving. It is assumed that the international allowance price would be 17.7 US$/tCO2. Compliance cost and savings are on an annual basis. Original results in € have been converted to US$ at €1 for 1US$.

The reference case assumes that the Kyoto commitment is implemented separately by domestic action in each EU member state. The alternative reference case assumes that, within a member state, the overall emission reduction target of the burden-sharing agreement applies equally to each individual sector of the economy, with allocation evidently being more expensive than the least-cost approach in the reference case.

A related issue is the allocation of CO2 emission reductions under Kyoto to sources in the EU Emissions Trading Scheme (EU ETS), as compared all non-ETS sources. Klepper and Peterson (2006), using a CGE model, conclude that ETS National Allocation Plans reduce the allowance price in the ETS below the implicit tax necessary for reaching the Kyoto targets in the non-ETS sectors, implying significant distortion. The limited use of CDM and JI to meet the allocations would result in a negative effect on welfare of close to 1% in 2012 relative to ‘business as usual’; this assumes that EU Member States do not import more than 50% of their required reductions and that they do not import ‘hot air’. Unrestricted trading in CDM and JI credits and allowances would result in an allocation where the Kyoto target can be met with hardly any welfare costs.

Jaccard et al. (2002) evaluate the cost of climate policy in Canada. They compare the costs of achieving the Canadian Kyoto target in 2010 (using the CIMS model) for equal sector targets or one national target. According to their estimates, the electricity, residential, and commercial/institutional sectors contribute more, at lower marginal costs, to reductions when there is one national target, while the industry and transportation sectors contribute less. For example, the marginal cost for the electricity sector is about 20 US$/tCO2-eq for the sector target and 80 US$/tCO2-eq for the national target, while those of industrial sector are 200 and 80 US$/tCO2-eq respectively.

Both studies illustrate a general finding that a portfolio of options which attempts to balance emission reductions across sectors with ‘equal percentage reductions’ is more costly than optimizing the policy mix for cost effectiveness.

Another aspect of mitigation options is the opportunity afforded by portfolio analysis to reduce risks and costs. Because fossil fuel prices are uncertain and variable, there are potential benefits in portfolios of energy supply sources that increase diversity so as to include, in particular, sources such as renewables and nuclear, the costs of which do not depend on fossil fuel prices. Long-standing methods from finance theory can help to quantify a new low-carbon technology’s contribution to overall risk, and to quantify costs associated with the development of a set of options for GHG mitigation and energy security. The portfolio approach differs from the traditional stand-alone cost approach in that it introduces market risk and includes inter-relationships between the costs of different technologies (Awerbuch, 2006, MITI). New technologies that diversify the generating mix and low-carbon options tend to be quantifiably more diverse than business-as-usual reliance on fossil fuels (see Stirling, 1994; 1996; Grubb et al., 2006). Moreover, in contrast to the expected year-to-year variability of fossil fuel prices (which can be estimated from historic patterns), operating costs for wind, solar, nuclear and other capital-intensive non-fossil technologies are largely uncorrelated to fossil fuel prices.

Theory, supported by application, suggests that risk-optimized generating mixes will include larger shares of wind, geothermal and other fixed-cost renewables, even where these technologies cost more than gas and coal generation. Optimal mixes will also enhance energy security while simultaneously minimizing expected generating cost and risk. Awerbuch, Stirling, Jansen and Beurskens (2006) explore the limitations of the mean-variance portfolio (MVP) approach, and compare MVP optimal generating mixes to ‘maximum diversity’ mixes that also provide protection against uncertainty, ignorance and ‘surprise’. They find that the optimal mixes in both cases contain larger shares of wind energy.

These findings suggest that portfolios of cross-sector energy options that include low-carbon technologies and products will reduce risks and costs, simply because fossil fuel prices are more volatile relative to other costs, in addition to the usual benefits from diversification.