The poster presents information about the heating and cooling gap in Southern European cities and its implications for climate mitigation. It highlights that people spend a significant amount of time indoors, and in the European Union, many low-income households cannot ensure indoor thermal comfort due to poor building construction and high energy costs. This can impact people's health and ability to function. Heatwaves put vulnerable populations at risk, and climate change scenarios predict an increase in the frequency and intensity of heatwaves in the region. Portugal is identified as a good case study due to its aging building stock, low energy performance, and high levels of energy poverty. The potential increase in energy consumption for adequate indoor thermal comfort poses a problem for climate mitigation goals, and the poster recommends increasing energy efficiency in buildings and equipment, using passive measures, and investing in local renewable energy sources to prevent impacts on CO2 emissions. The results can be used to track vulnerable consumers and support energy efficiency policies and instruments.