Public data, not opinion

How much of humanity lives outside the livable band.

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.

cold stressheat stress
How we count this →

A person·day is one person, one day outside the comfort band.

person·days = stress days in the year × city population
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The comfort line

Nine to twenty-six.

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.

It's rising

The line is moving the wrong way.

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.

Global
heatcold
It isn't latitude

Two cities, one parallel, opposite fates.

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.

Manaus · Amazon lowland
0
days a year with heat stress. The ceiling — there are no more days to give.
Bogotá · 2,600 m
0
days a year. Same tropics, but altitude keeps the body inside the line.
See every country on the globe →
Two worlds

The tropics are full. The north is catching fire.

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.

At the ceiling

9 countries at ~365 days
In DR Congo, Indonesia, Malaysia, Singapore, Lagos and more, essentially every day of the year already carries heat stress.

The temperate shock

+133%
Sweden's rise in heat-stress person·days over 40 years. Berlin went from 34 to 68 days a year; Stockholm from 11 to 27.
Down to your street

Heat and green are the same map, inverted.

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.

Open the atlas, city by city →
The lever
−0.85

Green cools. Measurably.

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.

Public data, not opinion

Every number here is traceable.

No modelling of our own, no estimates. Just the official record, counted in people.

How robust is the number?
−9% / +7%
is all the headline moves if we slide the comfort line ±2 °C.
1.3 T
person·days remain even if we count only severe heat, above 32 °C.
+4 → +9%
the rise, from the comfort line to severe-heat-only — it never reverses, only steepens.
The curve The globe The atlas
The author

An independent study by Artur Scartazzini — a curious outsider who doesn't work in climate science, just someone who couldn't stop asking the question.

This needs a co-author and a home.

heatline is one person's honest calculation from public data. To become an official indicator it needs a climate scientist to co-sign the method and an institution to host it. If that could be you — a researcher, an agency, a lab — put yourself forward.

Put yourself forward →