Nature-based Solutions (NbS) have gained increasing attention as strategies to mitigate urban heat, reduce building energy demand, and support climate adaptation in cities. However, existing evidence on their energy and carbon benefits remains fragmented, often focusing on individual NbS types or relying on heterogeneous methods and indicators. This study aims to systematically assess and compare the impacts of green roofs, green walls, and urban trees on building energy consumption and CO₂ emissions through a combined literature review and district-scale case study. First, a systematic literature review was conducted to synthesize quantitative evidence on the energy and carbon impacts of NbS. Reported results were standardized using relative (%) and absolute (kWh/m²·year) indicators, distinguishing between cooling, heating, and total energy demand, as well as direct and indirect CO₂ reduction pathways.