How Heat Waves Work
On 23 October 2026 researchers at Imperial College London and the London School of Hygiene & Tropical Medicine estimated that summer heat caused more than 50,000 deaths in 854 European urban areas, about two-thirds of them because of climate change. This film explains what lies behind such a number: why there is no single definition of a heat wave, how a stalled high-pressure 'heat dome' warms sinking air and clears the sky, how dry soil and cities add heat, how the body sheds heat by blood flow and sweat, why humid heat is so dangerous and what wet-bulb temperature measures, how heat exhaustion differs from heatstroke, who is most at risk, why heat deaths are estimated as excess mortality, and how scientists show that climate change is making heat waves more frequent and more intense.
The weather that kills quietly
How heat waves form, and what they do to us.
What counts as hot
There is no single line for the whole world.
The heat dome
Air that sinks, and warms as it falls.
Ground and city
The surface underneath can make it worse.
The body
A furnace that must keep cool.
Humid heat
When sweat can no longer evaporate.
Counting the toll
The deaths that should not have happened.
A warming world
A small shift in the average, a big change at the edge.
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