Heatwaves have grown hotter and stronger as the planet has warmed, making what doctors call a “silent killer” even more dangerous. How worried should we be about heat – and how can we stay safe as the climate changes?Guardian Ajit Niranjan 27 June 2025 Heatwaves have grown hotter and stronger as the planet has warmed, making what doctors call a “silent killer” even more dangerous. How worried should we be about heat – and how can we stay safe as the climate changes?
How many people die from heat?
Hot weather kills an estimated half a million people each year. The average annual death toll is greater than that from wars or terrorism, but smaller than that from cars or air pollution.
Despite this, heat is rarely listed as the cause of death. That’s because extreme temperatures are largely indirect killers. Most heat victims die early from illnesses – such as heart, lung and kidney disease – that are made worse in warm weather.
How do heatwaves hurt your health?
High heat stresses the human body. When days are too hot to function and nights are not cool enough to recover, the heart and kidneys go into overdrive working to keep the body cool.
There are also secondary health effects from high heat. Heatwaves lead to more accidents, dirtier air, bigger wildfires and more frequent blackouts, all of which can increase the burden on health systems.
Who is most at risk from extreme heat?
People who are forced to be outdoors in scorching weather – builders, farmers, rough sleepers – are most likely to suffer from heat exhaustion and the heatstroke that can follow.
But older people, and particularly those with underlying illnesses, make up the bulk of heat-related deaths. Women are more likely to die from heat-related causes than men. Poorer people – who are less likely to have air conditioning, well-insulated homes, or access to green spaces – are also at greater risk.