Dangerous Humid Heat Days have more than Doubled Globally since 1970: Report

This brutal summer has been deadly for the world, and especially in Europe, where 1,300 excess deaths have been reported since June 21 as temperatures cross 40°C, according to the World Health Organisation. A new report by Climate Central found that such occurrences will become more commonplace. 

According to the report, climate change is making the planet significantly hotter, humid, and more dangerous to human health. The report revealed that the frequency of dangerous humid heat days has more than doubled globally over the past five decades, shifting climate change from a minor contributor to the primary driver of these conditions. 

The report is based on data from 1970-2025, globally. It found that dangerous humid heat days, globally, have increased from an average of 10 per year in the 1970s to 23 days per year in the past decade (2016-2025).

It defines a ‘dangerous humid heat day’ as one where the daily maximum wet-bulb temperature—a metric combining heat and humidity—reaches 25°C or higher. At this threshold, the human body’s primary cooling mechanism—sweating—begins to break down. As humidity nears saturation, sweat cannot evaporate efficiently, trapping heat inside the body and drastically elevating the risks of dehydration, heat exhaustion, and potentially fatal heat stroke. 

Extreme heat has already claimed more than a quarter-million lives globally since 2000, disproportionately affecting vulnerable groups like older adults, children, pregnant individuals, and those lacking cooling access.

Rising dangerous heat

According to the report, the acceleration of humid heat is directly tied to the burning of fossil fuels. Nearly two-thirds (64%) of all global dangerous humid heat days recorded since 1970 are directly attributable to human-caused climate change.

Mathematically, climate change is now responsible for six times as many dangerous humid heat days annually, compared to the 1970s.

In 2025, amid the planet's third-hottest year on record, the global average reached 23 dangerous humid heat days—and an astonishing 19 of those days (83%) were entirely added by climate change, found the report.

Escalating risks in Global South 

The report pointed out that tropical humid regions, primarily based in the Global South countries, are bearing the brunt of this shift, as their baseline wet-bulb temperatures sit closest to the danger zone. Portions of tropical South America, coastal West Africa, and Southeast Asia now endure at least six months of dangerous humid heat on average each year.

However, the phenomenon is not limited to the tropics. Arid sectors of the planet, including the Arabian Peninsula, central Australia, and the southwestern United States, are also experiencing noticeably more dangerous humid heat days than they did 50 years ago, according to the report.

“These findings show how profoundly climate change is reshaping our world. Dangerous humid heat has gone from being an uncommon event to a defining feature of daily life in some regions, pushing conditions closer to the limits of what the human body can safely endure,” said Kaitlyn Trudeau, Applied Climate Scientist at Climate Central.