Southeast Asia is among the most vulnerable regions grappling with growing risks from heatwaves and high humidity, while the period of extreme weather has more than doubled globally over the past five decades.

The duration of extreme weather has increased worldwide to an average of 23 days per year from 10 in the 1970s, according to a report by non-profit news organisation Climate Central.

Parts of Southeast Asia, South America and coastal West Africa are among the regions that now experience at least six months of “dangerous” humid heat days annually, the report released on Wednesday shows.

The largest increases have occurred in tropical humid regions, where wet-bulb temperatures, which measure the combined effect of heat and humidity, are typically higher.

Zack Labe, a climate scientist with Climate Central, said in written responses to queries by This Week in Asia that the term “dangerous” humid heatwaves referred to days with a wet-bulb temperature of 25 degrees Celsius or higher – a threshold at which the body’s ability to cool itself becomes increasingly strained with higher risk of heat-related illnesses.

The report said human-caused climate change was the primary driver of dangerous humid heat, contributing to nearly two-thirds of such days worldwide, endangering millions.