Models are fundamental for estimating the possible costs and effectiveness of different policies for reducing greenhouse gas (GHG) emissions. There is a wide array of models to perform such analysis, differing in the level of technological detail, treatment of technological progress, spatial and sector details, and representation of the interaction of the energy sector to the overall economy and environment. These differences impact model results, including cost estimates. More fundamentally, these models differ as to how they represent fundamental processes that have a large impact on policy analysis-such as how different models represent technological learning and cost reductions that come through increasing production volumes, or how different models represent baseline conditions. Reliable estimates of the costs and potential impacts on the United States economy of various emissions reduction and other mitigation strategies are critical to the development of the federal climate change research and development portfolio. At the request of the U.S. Department of Energy (DOE), the National Academies organized a workshop, summarized in this volume, to consider some of these types of modeling issues. Table of ContentsFront Matter1 Introduction2 Uses and Abuses of Marginal Abatement Supply Curves3 Uses and Abuses of Learning, Experience, and Knowledge Curves4 Offsets - What's Assumed, What Is Known/Not Known, and WhatDifference They Make5 Story Lines, Scenarios, and the Limits of Long-TermSocio-Techno-Economic Forecasting6 Reflections on the WorkshopReferencesAppendixesAppendix A: Workshop Announcement and AgendaAppendix B: Biographical Sketches of Planning Committee Members,Speakers, and DiscussantsAppendix C: Papers Submitted by Workshop SpeakersParadigms of Energy Efficiency's Cost and Their PolicyImplications: Deja Vu All Over Again--Mark JaccardEnergy Efficiency Cost Curves: Empirical Insights forEnergy-Climate Modeling--Jayant Sathaye and Amol PhadkeThe Perils of the Learning Model For Modeling EndogenousTechnological Change--William D. NordhausUncertainties in Technology Experience Curves for Energy-EconomicModels--Sonia Yeh and Edward RubinRole of Offsets in Global and Domestic Climate Policy--Raymond J. KoppCarbon Offsets in Forest and Land Use--Brent SohngenMeasurement and Monitoring of Forests in Climate PolicyDesign--Molly K. MacauleyInternational Offsets Usage in Proposed U.S. Climate ChangeLegislation--Allen A. FawcettThe Politics and Economics of International Carbon Offsets--DavidG. VictorDeveloping Narratives for Next-Generation Scenarios Climate ChangeResearch and Assessment--Richard Moss