Smart Cities are increasingly cited as a solution to decrease CO2 emissions within cities. However, the technology that supports Smart City systems may in turn cause direct, indirect and rebound environmental impacts, including greenhouse gas emissions. Recent studies assessing the positive environmental impact of Information and Communication Technology (ICT) tend to focus on direct effects, thus giving little attention to indirect and especially rebound effects. The goal of our thesis is to propose an evaluation methodology to assist Smart City systems designers in assessing all possible environmental impacts of candidate Smart City systems designs. To design and validate the proposed methodology, the research scope will be narrowed on a subcategory of Smart City systems, chosen according to its relevance in terms of risk to produce rebound effects. The research process will follow the guidelines defined by Wieringa for conducting design science in ICT.