Cities are especially vulnerable to extreme heat — and increasingly experience days when the sidewalks seem to cook like a stove and it's a struggle to sleep at night. Densely built urban areas, with their paved roads, impermeable surfaces and limited green spaces, are heat islands that can be 10 to 15 degrees Celsius (up to 30 degrees Fahrenheit) hotter than surrounding rural areas. That extra heat strains crucial city infrastructure and harms public health . Nearly half a million people die