There is a revival in the nuclear debate observed in the literature. Several analyses have shown that nuclear technologies may represent very attractive options for greenhouse gas (GHG) emission reductions, especially in countries with high growth projections for energy demand. Our objective is to analyze the role of nuclear energy in long-term climate scenarios using the World-TIMES (The Integrated MARKAL-EFOM System) bottom-up model. World-TIMES is a global model that optimizes the energy system of 15 regions over a 100-year horizon (2000-2100). We present energy and emission results for climate scenarios for two levels of CO2 concentration (450 and 550 ppmv by 2100). We analyze the penetration level of nuclear energy under various sets of assumptions on technology parameters and exogenous constraints on nuclear development to reflect social perceptions. Nuclear energy technologies satisfy a large portion of electricity production in many regions. Most regions experience an energy transition based on advanced oil and gas technologies and hydropower. Other renewable technologies might play a more important role but need further cost reductions or new regulations to penetrate the market in substantial proportions. Carbon sequestration and endogenous demand reductions for energy services are also significantly contributing to reach environmental target. (C) 2008 Elsevier Ltd. All rights reserved.