How Extreme Heat and Humidity Are Testing the Human Body’s Limits

The world’s two hottest days on record happened in July and 2024 is on track to be the warmest year ever. Heat waves are more frequent, have been more acute, and often arrived earlier than anticipated. Factor in humidity, and extreme weather is already testing the limits of the human body. More than 1,300 people died during the Hajj pilgrimage in Saudi Arabia in June as temperatures reached about 52C (126F), while heat-related fatalities have also been recorded this year in locations including the US, Thailand, India and Mexico. Parts of Europe — where high temperatures contributed to over 47,000 deaths in 2023 — remain on alert for more extreme conditions this summer.

There are many reasons. People are more likely to dehydrate in high temperatures, increasing the risk of heart attack and stroke. Heat can worsen breathing problems, especially in places with elevated pollution levels. Heat stress makes it harder for people to work and increases the likelihood of injuries. It’s hard to know exactly how many people die from heat each year; most go uncounted. Europe likely experienced 61,672 deaths attributable to heat in 2022, though that number potentially underestimates the actual total, according to a study led by the Barcelona Institute for Global Health. Emerging economies suffer more than developed ones, as there tends to be little respite from the sun; most people work outside and few have effective cooling at home. Concrete and asphalt in urban settings can trap the heat, increasing overnight temperatures and contributing to heat stress. Women and seniors have been found in studies to be the populations most affected by extremely hot weather.