It's the urban heat island effect: concrete and asphalt soak up heat by day and release it at night, there is less vegetation to cool the air, and air conditioners and engines pump out heat of their own. The gap with nearby countryside is often a few degrees, and larger at night and during heatwaves. Trees, light-coloured roofs and green spaces are among the most effective fixes.
That's the estimate from a WHO-led study published in The Lancet in 2024, covering the half-century since the Expanded Programme on Immunization was launched in 1974. It works out to about six lives saved every minute, mostly infants. The measles vaccine alone accounts for around 60% of those lives.
According to the World Gold Council, about 216,000 tonnes of gold have been mined in all of human history. Because gold is so dense (19.3 tonnes per cubic metre), it would fit in a cube about 22 metres on each side, roughly the height of a seven-storey building. Strikingly, about two-thirds of it has been mined since 1950.