Bangladesh is emerging as one of the countries most severely affected by intensifying global heat-a combination of rising temperatures, high humidity and dense population makes the country particularly vulnerable to heat stress as the climate warms, which scientists describe as increasingly "unlivable", a study said.
A new international study published on Tuesday in the journal Environmental Research Health finds that older adults in Bangladesh now face more than 2,500 hours of extreme heat each year, during which safe outdoor activity becomes nearly impossible.
In the mid-20th century, that figure was about 2,180 hours, indicating a sharp increase in life-limiting heat exposure over the past several decades, it disclosed.
The study, led by researchers from The Nature Conservancy with contributions from several international institutions, analyzed more than 70 years of climate data from 1950 to 2024. The researchers used a physiological model to assess how the human body responds to heat under different environmental conditions and age groups.
"Climate change isn't just making heat more intense - it's shrinking the amount of time people can safely go about their daily lives," said Luke Parsons, the study's lead author and a climate scientist.
However, the findings show that about 35 percent of the global population now lives in regions where extreme heat severely limits safe physical activity during the hottest periods of the year, even for younger adults.
He warned that in some regions, even minimal physical activity in the shade could push the human body beyond its ability to cool itself.
The study notes that in Bangladesh, Cambodia and Thailand, older adults now experience between 2,000 and 2,800 hours each year when heat severely limits safe physical activity-hundreds of hours more than in the 1950s. In Bangladesh alone, this represents an additional 390 hours of severely life-limiting heat annually compared with historical levels.
In practical terms, the findings suggest that for nearly one-third of the year, elderly people in Bangladesh cannot safely engage in activities beyond slow walking or light household tasks due to the risk of heat-related illness. The growing number of older adults in the country further increases the risk, as aging bodies are less capable of regulating heat.
Scientists warn that under such conditions, routine activities such as climbing stairs, doing household chores or walking outdoors can become dangerous, particularly for older people.
'Unlivable' conditions emerging
Researchers also identified areas where extreme combinations of heat and humidity can create what they describe as "unlivable" conditions, meaning that even resting in shaded and ventilated environments could pose serious health risks.
Currently, about 24.5 percent of the global population lives in areas that experience such conditions for older adults during the hottest hours of the year.
The risks are particularly severe across the Indo-Gangetic Plain, which includes large parts of Bangladesh and eastern India.
Low elevation, high humidity and dense populations in the region amplify the health impacts of extreme heat.
Heat risks rising worldwide
Globally, younger adults experienced an average of 25 hours per year of severe heat-related activity restrictions in the 1950s; now the figure has doubled to around 50 hours annually.
The situation is significantly worse for people aged 65 and older. The study found that older adults worldwide now face roughly 900 hours each year when heat severely restricts safe physical activity, compared with about 600 hours in the 1950s.
Population exposure amplifies risks
Although some wealthy Gulf countries experience higher absolute numbers of extreme heat hours, scientists say the human impact is greater in South Asia because of large populations and limited access to cooling infrastructure.
When researchers measured "people-hours" of exposure-the number of people affected multiplied by hours of extreme heat-India, Bangladesh and Pakistan ranked among the most exposed countries globally.
Experts say the key difference between wealthier and poorer countries lies not in the intensity of the heat but in their capacity to adapt, including access to air conditioning, cooling centers, workplace protections and public health systems.
A rapidly warming planet
The study comes as global temperatures have already risen by nearly 1.5°C above pre-industrial levels, with 2024 recorded as the hottest year on record.
During that year alone, more than 43 percent of younger adults and nearly 80 percent of older adults worldwide experienced periods when heat and humidity severely limited daily activity.
"Unless we stop burning fossil fuels, the constraints on livability caused by extreme heat will only become more common and widespread," Parsons said.
Researchers say practical measures such as public cooling centers, heatwave early-warning systems, adjusted working hours and improved urban planning can help reduce risks.
