Is climate change found in indoors temperatures?

Urban outdoor air temperatures have increased as a consequence of climate change, resulting in adverse health effects to urban dwellers and increased energy cooling demand. However little is known whether, and to what extent, summertime indoor temperatures have increased due to climate change. This study presents modelled summertime indoor temperatures for 80 houses in Amsterdam for the period 1951-2025, and for future projections. A physics-inspired statistical model was driven with ERA5 and local automatic weather station data (KNMI-AWS) to model indoor temperatures. The model accounts for solar radiation, outdoor air temperature, thermal radiation and wind speed as drivers. We find that the summer-mean living room temperature has significantly increased by on average 0.36 °C per 10 summers (1951-2025). Moreover, we find an acceleration of indoor temperature rise after 1988 (0.54 °C per 10 summers). In addition, we find that daily mean living room temperatures start to exceed 26 °C for more than six days per summer in the 21th century. Also we find analogue indoor temperature trends if the model is ran for northerly (Groningen, Den Helder) and more southerly (Eindhoven, Maastricht) cities. Finally we use KNMI 2023 climate scenarios, to explore the evolution of indoor summertime temperatures in the future. This appears to be 5.1 °C increase on average for living room temperature for the Hd (high emission, dry climate) scenario for 2100. Across the entire study, we find equivalent results between bedroom and living room temperatures. This study concludes that climate change has reached indoors over the past 75 years.