Climate change may impact the energy sector directly and indirectly. The objective of this study is to develop a systematic approach for assessing impacts of climate change and adaptation response as well as the growing population on energy economy and greenhouse gas emissions. Such an approach was based on regional energy systems characterization,climate change scenario analysis, vulnerability assessment, energy systems modeling, and climate change policy analysis. The developed methodology is then applied to the Toronto-Niagara Region, Canada. The results suggested that, through modeling energy demand sensitivity to temperature variations within an energy systems management framework, the approach can effectively reflect the impacts from climate change and adaptation response, not only on energy demands and supplies but also on various energy-related technologies and greenhouse gas emissions. It can reflect the system's interactive and dynamic complexities quantitatively; thus, it could provide robust decision bases for supporting effective energy systems management and sustainable energy development under changing climatic conditions.