Stand on a street corner in a big city on a hot day and have a look around at the towers of concrete, glass and steel. If the temperature is in the 30s, there’s a good chance it’ll feel substantially hotter.
That’s the urban heat island effect warming you up.
All that steel and concrete absorbs heat. Higher outdoor temperatures pose a threat to human health leading to an increase in heat-related illnesses, particularly for vulnerable populations, such as the elderly and young children. In some places, it can be a killer.