In estimating the costs and effectiveness of policies to reduce GHG emissions, energy-economy modelers must address various uncertainties. These include (1) the real and perceived micro-economic cost differences between technological options (issues with abatement cost curves), (2) the likely evolution of technologies as policies change innovation and adoption incentives (induced technological change), (3) the likely effectiveness of different policies in terms of causing emission reductions, (4) the role of behavioral change in response to policies, and (5) general equilibrium effects of policies. Professor Jaccard will briefly survey methodological debates and research findings in these areas in expectation of stimulating a healthy dialogue following his talk.