The phenomenon of climate change has global implications, but there is a growing consensus that local actions can help address the 2°C global warming challenge. However, local governments in Asia-Pacific cities face a triple challenge of economic development, air pollution, and greenhouse gases (GHGs) emissions abatement and protecting citizens from extreme climate events. There are knowledge gaps that impede local action, including a lack of reliable empirical information on climate vulnerability scenarios. To address these challenges, a collaborative research network of experts has created the Integrated Climate Action Planning (ICLAP) decision-making tool for settlements with 5 million plus population in selected cities in the Asia-Pacific region. The ICLAP tool is innovative as it combines data and information for climate mitigation and adaptation, provides evidence-based recommendations, and integrates database, evaluation, and simulation features. The tool downscales global/regional climate scenarios; conducts meta-analysis of cities to forecast demographics, economy, energy, and GHGs; and conducts a systematic review of climate interventions from city case studies worldwide. This chapter provides the result of the applicational case studies in Japan (Tokyo and Osaka) of using the ICLAP tool to provide evidence-based simulation for local governments to take effective climate actions.