The duration of extreme weather events, particularly days characterized by "dangerous" levels of humid heat, has more than doubled globally since the 1970s, with Southeast Asia among the most affected regions, according to recent climate analyses. These heightened conditions pose significant health risks as they push human physiological limits.

A report by Climate Central highlights that the global average of extreme weather days, defined by wet-bulb temperatures— which capture the combined effect of heat and humidity—reached 23 days per year, up from 10 days in the 1970s. Wet-bulb temperatures of 25 degrees Celsius or higher, considered "dangerous," strain the body’s ability to cool itself, raising the risk of heat-related illnesses.

Southeast Asia, along with parts of South America and coastal West Africa, now experiences at least six months annually of such perilous humid heat days. Tropical humid regions, where wet-bulb temperatures have increased most significantly, are particularly vulnerable due to the compounding effects of high humidity.

Climate scientist Zack Labe of Climate Central explained that humidity intensifies heatwave impacts by impairing the body’s primary cooling mechanism, forcing the cardiovascular system to work harder to regulate temperature. He cited Hong Kong as an example, where there have been an average of 144 dangerous humid heat days per year over the past decade, approximately 33 of which are linked to human-induced climate change.

Recent heatwaves across northern and central Vietnam and Thailand underscore the region’s vulnerability. Some districts in Thailand, such as Bangna, have recorded heat index values—measures of "feels like" temperatures—reaching as high as 54 degrees Celsius. Similar trends are observed in South Asia; parts of India saw temperatures surpass 45 degrees Celsius in May, with nights remaining dangerously warm. The Indian Meteorological Department recently reported maximum temperatures of 40 to 44.2 degrees Celsius across northern and central states, including Uttar Pradesh, Haryana, Rajasthan, Madhya Pradesh, and Bihar.

Rising temperatures have led to increased electricity demand and strained healthcare systems due to heat-related illnesses. Outdoor workers are particularly at risk, given their exposure to heat, humidity, direct sunlight, and physically demanding tasks. A recent McKinsey Global Institute report noted Southeast Asia’s heightened vulnerability to climate hazards, highlighting reliance on outdoor labor in agriculture, which makes up 8 to 15 percent of the economies of Cambodia, Indonesia, and Thailand—significantly above the global average of 4 percent.

The region faces multiple climate hazards, with nearly half its land area and population exposed to at least one risk. Ten percent of Southeast Asia’s land faces riverine flooding, while 15 percent encounters heat stress conditions. Adaptation measures, including air conditioning, irrigation, stormwater systems, and early warning networks, currently amount to roughly $12 billion annually across 20 initiatives, but required investments to meet standards comparable to developed countries could extend to $37 billion per year.

Experts stress that mitigating heat-related illness risks requires not only infrastructure investment but also improved workplace training, increased awareness, regular access to hydration, rest, and shade, as well as acclimatization protocols for workers.

Kaitlyn Trudeau, an applied climate scientist with Climate Central, emphasized the global scale of the issue, noting that what were once rare events have become defining features in affected regions, pushing conditions closer to human physiological limits.

The impact of climate change on heatwaves is increasingly evident worldwide. A recent report from World Weather Attribution linked the ongoing European heatwave to anthropogenic climate change, with nearly half of 854 surveyed cities across 30 countries breaking or anticipated to break wet-bulb temperature records in late June.

Theodore Keeping, an extreme weather researcher at Imperial College London, affirmed the established scientific consensus that climate change is worsening heatwave severity. "Continued fossil-fuel emissions are directly responsible for the disruption people are experiencing this week in their homes, schools and workplaces," he said, underscoring the urgency of addressing global emissions to mitigate further risks.