Introduction to EMF 24.

• Author: Fawcett, Allen A.

This special issue of the Energy Journal documents the main findings of Energy Modeling Forum Model Inter-comparison Project (MIP) number 24 (EMF 24) entitled "The EMF24 Study on U.S. Technology and Climate Policy Strategies." This study focused on the development and cross model comparison of results from a new generation of comprehensive U.S. climate policy intervention scenarios focusing on technology strategies for achieving climate policy objectives. These scenarios enabled the community to exercise enhanced modeling capabilities that were focused on in previous EMF studies on the international trade implications of climate policies; the representation of technological change; and the incorporation of multi-gas mitigation and land use emissions and mitigation policy alternatives.

This introduction has four objectives: (1) describe the motivation for the EMF 24 study, (2) put this study in the context of other past and current IAM inter-model comparison projects, (3) describe the structure of this special issue of the Energy Journal, and (4) give a brief overview of the insights developed in the papers produced by the individual modeling teams that are included in this special issue.

EMF 24 focused on the interactions between climate policy architectures and advanced energy technology availabilities in the U.S.. It followed on previous EMF climate change oriented Model Inter-comparison Projects (MIPs): EMF 12 on carbon emission limits (Gaskins and Weyant, 1993; Weyant, 1993), EMF 14 on carbon concentration limits (EMF 14, 1996; Haites, et al., 1997), EMF 16 on the costs and energy system impacts of the Kyoto Protocol (Weyant, 1999), EMF 19 on carbon constraints and advanced energy technologies (Weyant, 2002), EMF 21 on non-C[O.sub.2] Kyoto gas mitigation (de la Chesnaye and Weyant, 2006), and EMF 22 on climate control scenarios (focusing on phased participation in a climate mitigation coalitions and the possibility overshooting long run climate targets (Clarke, et al, 2009). As such, this study was able to take advantage of all the significant model extensions and enhancements that have taken place over the last twenty years.

EMF 24 itself was the outgrowth of a study started in April 2010 and was set up to include three parallel model comparison exercises at the global, US and European Union (EU) levels as had been the case in the EMF 22 study. As the work progressed, however, that study became too large, including too many people, models, (over forty models across the three domains) and interests to deal with efficiently in one large project and so the original project was split into three separate studies on constructing and interpreting the results of climate policy and technology scenarios at the global (EMF 27, Kriegler, Weyant, et al., 2013b), US (EMF 24, this volume) and EU levels (EMF 28, Knopf, et al., 2013). At the same time there was great interest in doing a new model comparison study on the international trade dimensions of climate policy (following on an earlier attempt in EMF 18, 2002) using a largely different set of (trade oriented) global models than those included in EMF 27, and a MIP focused on energy infra-structure transitions in Europe tied into the EMF 28 study. The trade interest lead to another working group which produced a trade oriented global model inter-comparison on leakage effects and border carbon adjustments (Boehringer, et al., 2012), and the latter lead to an extension of the EMF 28 scenario analysis focusing on infrastructure constraints and opportunities (von Hirchhausen et al., 2014). Thus, the reporting on this collective work is being communicated through five separate journal special issues.

Over the last ten years, there has also been a steady and extremely valuable increase in model comparison studies organized within the European Union and other parts of the world as well as a broadening of the types of exercises being conducted in the U.S. In fact, this trend, lead, in part, to the formation of the Integrated Assessment Modeling Consortium (IAMC, 2014) six years ago to coordinate this work and make the studies truly global in scope and participation. The IAMC has now matured to the point that it has formal charter, a scientific steering committee, an annual research conference, and a world wide web site (IAMC, 2014).

Early EU sponsored inter-model comparison studies included "The Innovation Modeling Comparison Project" (IMCP, Edenhofer, et al, 2006) which noted that in the first generations of global energy-economy modeling applied to climate change, emerging from the late 1980s roughly up until the mid 1990s, technology entered through a series of exogenous assumptions. In true 'top-down' models, supply side technologies were reflected in assumptions about the elasticity of substitution between generic carbon and non-carbon sources (if any), whilst an "autonomous energy efficiency improvement" (AEEI) parameter was often used to reflect an assumed degree of decoupling between GDP and energy consumption--a single, fixed parameter encompassing both structural change in the relationship between economy and energy and the development and diffusion of demand-side technologies. Another early EU model inter-comparison study was "The Economics of Low Stabilization Project" (Edenhofer, et al. 2010) explored the economics of very low targets for stabilization of atmospheric concentrations of GHGs in the atmosphere. The objective of the United Nations Framework Convention on Climate Change (UNFCCC) is "stabilization of greenhouse gas (GHG) concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system" (UNFCCC 1992, Article 2). Reaching the target of climate stabilization at no more than 2[degrees]C above pre-industrial levels by the end of this century--which is how the European Union (EU)...