Why the same heat kills more in some places

There are two ways to read the trace left by a heat wave: one is the relentless rise of mercury in the thermometer, the other the silent sorrow of death registers. In the shadow of the climate crisis, the fate of cities is determined by how prepared they are for the gap between these two realities.

In August 2003, when Paris's famously romantic summer evenings gave way to a suffocating disaster, France recorded about 14,800 more deaths than expected in the first twenty days of the month. This was a surge of around 60 percent, and most of the victims were elderly people who breathed their last alone at home.1source 1 The tragedy proved that public health is not merely a medical issue, but an administrative one. France woke from its slumber and drew up a national action plan: alerts issued by area, lists of isolated older people kept by town halls, and special instructions for care homes and hospitals.1source 1

The city of Ahmedabad in western India learned the same lesson in the scorching May of 2010, when it buried 1,344 of its residents. Its response in 2013 was a heat action plan: early warnings, the mobilisation of health workers, drinking water and shade in public places, and later a "cool roofs" programme that lowers indoor temperatures in poor neighbourhoods – an effort credited with preventing nearly 2,300 premature deaths.2source 2 Japan, on the other hand, seeks its answer in technical precision, relying on a single number. When an index that melts heat, humidity and sunlight into one figure is forecast to reach 33, nationwide alerts go out; in 2024 a stronger alert was added for days when the index is forecast to reach 35 or above. There were 613 alerts in the first year and 1,722 in 2024.3source 3 4source 4

A study estimated that 61,672 people died from the heat across 35 European countries in the summer of 2022, with women dying at a markedly higher rate than men.5source 5 6source 6 That figure whispers how far an entire continent still lags in its test against nature.