The number of dangerously humid hot days, when the wet-bulb temperature exceeds 25°C, has more than doubled globally over the past 50 years, according to an analysis by Climate Central released on Wednesday.
In the 1970s, there were an average of ten days per year worldwide when the wet-bulb temperature, a combination of air temperature and humidity, surpassed 25°C.
At such temperatures, sweating becomes less effective, making it harder for the human body to cool down and increasing the risk of heat-related illnesses like heat exhaustion or even potentially fatal heatstroke.
From 2016 to 2025, the global average of these humid hot days has risen to 23 per year. Of these, 19 days are linked to human-induced climate change.
The hardest-hit regions include tropical areas of South America, West Africa, and South Asia, where people experience dangerously humid and hot conditions for more than six months each year.
Since 2000, extreme heat events worldwide have claimed the lives of over 250,000 people. Older adults, children, pregnant individuals, those with existing health conditions, and people lacking access to cooling systems are the most vulnerable groups.
While humans theoretically can endure wet-bulb temperatures of up to 35°C, recent studies suggest the actual limit is significantly lower in practice.
