In 1818, temperatures in the densely populated areas of newly industrialised London were recorded as being 1.3°C–3°C higher than in the surrounding rural areas. Meteorologist Luke Howard recognised the anthropogenic origins of the phenomenon, which was primarily linked to domestic coal use and poor street ventilation. Decades of urban expansion based on asphalt, concrete and steel, combined with the rapid drainage of rainwater, mass mobility and, paradoxically, air-conditioning systems themselves, have transformed urban heat islands into genuinely hazardous environments. These phenomena are particularly intense in European cities, where historic street layouts and densely built areas further amplify solar heat accumulation during the summer months. Cities such as Paris, Milan and Madrid can be, on average, 10°C–15°C warmer than their surrounding peripheral areas. Considering that only approximately 20% of the European population lives in rural areas, together with the progressive increase in global temperatures, the scale of this phenomenon is both widespread and critical. Heatwaves negatively affect the human body, causing fatigue, sleep disturbances, migraines and other symptoms. During the summer of 2022, overheating in urban areas across Europe resulted in approximately 62,000 deaths, with a particularly significant impact on women and socially vulnerable groups, including older people, infants, individuals with chronic illnesses and outdoor workers. The overheating of urban centres can essentially be addressed only through a radical reconfiguration of the physical urban fabric – including materials, volumes, green spaces, road systems and water infrastructure. This will be a slow and complex process. In the meantime, citizens can only find ways to mitigate its effects and develop strategies for co-habitation strategies. Fundamentally invisible and elusive, urban heat islands have now become an integral part of our anthropogenic geography.
