Paris, London and New York are more often associated with culture, finance and history than with dangerous heat. Yet each summer all three are increasingly exposed to extreme temperatures they were never designed to withstand. Like many dense urban areas, they amplify heat through what is known as the “urban heat island effect”. This reflects the way that warmth is trapped in concrete, asphalt and glass, turning hot days into hazardous ones. With skyscrapers made of glass and steel, roadways enc