Dangerous humid heat days have more than doubled since 1970 due to climate change: Report

Human-caused climate change has more than doubled the number of dangerous humid heat days worldwide since the 1970s, making extreme heat increasingly hazardous to human health, according to a new analysis by Climate Central.

The report, released yesterday (24 June), found that global dangerous humid heat days increased from an average of 10 days per year in the 1970s to 23 days annually during 2016-2025.

Researchers estimated that nearly two-thirds (64%) of all dangerous humid heat days recorded since 1970 were driven by climate change. In 2025 alone, climate change accounted for 19 of the world's 23 dangerous humid heat days on average – roughly 83%.

The analysis defines dangerous humid heat as days when the maximum wet-bulb temperature, which combines heat and humidity, reaches 25°C or higher. Such conditions can significantly increase the risk of heat exhaustion, heat stroke and other heat-related illnesses.

The sharpest increases were recorded in tropical regions, including parts of South America, West Africa and Southeast Asia, although drier regions such as the Arabian Peninsula, central Australia and the southwestern United States have also experienced rising levels of dangerous humid heat.

The findings are based on climate data from 1970 to 2025 and a peer-reviewed study published in the journal Environmental Research Letters in May 2026.

According to the study, climate change has made recent humid heat events around the world substantially more likely and more intense, with peak wet-bulb temperatures becoming between 65 and 175 times more likely due to global warming.

Climate Central warned that as temperatures continue to rise, humid heat is becoming a growing threat to public health, particularly for older people, children, pregnant women and those without access to adequate cooling.