The optimization of energy consumption in response to global warming scenarios presents fundamental challenges in the built environment, particularly in Mediterranean climates, where comfort and energy efficiency require priority-based adaptation. This study examines the effectiveness of passive energy retrofit strategies applied to an educational building in Granada, Spain, accommodating both teaching and residential uses. The research uses advanced climatic data based on Shared Socioeconomic Pathways (SSPs), incorporating precise projections of climate evolution. Using simulations conducted in DesignBuilder, it evaluates three intervention packages for the building envelope—window replacement, facade insulation, and roof insulation—across three temporal scenarios: 2024, 2050, and 2080. The results indicate that passive measures could reduce heating demand by up to 90% in future scenarios, while cooling demand is projected to increase by more than 80% by the end of the century. Additionally, climate projections under the SSP scenarios show up to an 83% increase in energy demand, emphasizing the need for integrated passive and active strategies. The research includes a sensitivity analysis of the interaction between passive strategies and advanced climate scenarios. It offers decision-making models for energy retrofitting and provides replicable key insights to support energy retrofitting policies and climate resilience in the Mediterranean region.