There is a temperature range the human body calls home. Across the planet, more and more people are being pushed out of it — and we counted it in people, not degrees.
A person·day is one person, one day outside the comfort band.
The official thermal comfort scale — the UTCI — draws a line. Above 26 °C the body strains against heat; below 9 °C it strains against cold. In between is where humans are simply comfortable. That narrow band is the whole story — and it is where we are losing ground.
Across 92 cities in 48 countries — 566 million residents — days of heat stress keep climbing while cold retreats. Pick a country and watch its line.
Heat doesn't follow the equator — it follows humidity and altitude. Deep in the tropics, some cities now carry heat stress every single day. Others, high in the mountains, barely feel it.
Where heat was already relentless, it can't rise much further — it's at the ceiling. So the sharpest change is happening where heat used to be rare: the temperate and northern cities that were never built for it.
Zoom from the planet to the pavement and the pattern sharpens. Within a city, the hottest ground is exactly the barest ground — the two maps mirror each other.
Across three continents, greener ground runs reliably cooler. Heat is not destiny — shade and vegetation are a public-health tool you can count, and plant.