Energy efficiency has been proposed as one of the most effective instruments for mitigating greenhouse gas emissions. However, the methodologies to estimate the impact of energy savings on these emissions are generally aggregated and simplified. This study presents an approach for evaluating the emissions avoided by energy-efficiency programs; decomposing the energy savings in the national electrical system load curve and correlating it with the emission factor observed in different periods of this curve. This methodology was applied to the three main programs that promote the rational use of electricity in Brazil: National Electric Energy Conservation Program (PROCEL), Energy Efficiency Law and Energy Efficiency Program (PEE) coordinated by National Agency of Electric Energy (ANEEL). A specific mitigation effect ranging from 0,329 to 0,332 tCO(2avoided)/MWh(saved) is found, which is above the value currently assumed in governmental estimates. The basis for this difference is the fact that energy saved occurs mainly in uses such as lighting, which happen at the load curve peak (or near it) when the thermal power plants are dispatched. The proposed methodology presents more consistent results than those obtained by conventional approaches, endorsing the energy-efficiency role as an instrument for climate change mitigation. (C) 2017 Elsevier Ltd. All rights reserved.