Study Finds Global Share Facing Extreme Heat Stress Rose From 16% to 22% Since 1970s

A study published Monday found that one billion more people now experience at least one day of extreme heat stress each year compared with the 1970s. The research, which appeared in Nature Climate Change, examined global data from 1950 to 2024 using the Universal Thermal Climate Index that incorporates temperature, humidity, wind speed and solar radiation.

Exposure to at least one day of extreme heat stress rose from 16 percent to 22 percent of the world population, according to the paper.

Subtropical areas including southern North America, southern Europe and parts of Africa recorded up to 50 additional days per year of strong to extreme heat stress. The frequency of such conditions increased 2.5 times in Europe and South America, twice in North America, 1.8 times in Africa, 1.7 times in Oceania and 1.2 times in Asia.

Nighttime temperatures have warmed faster than daytime temperatures, rising at a global average rate of 0.58 degrees Fahrenheit for the ten warmest nights of each year.

Rebecca Emerton, senior scientist at the European Centre for Medium-Range Weather Forecasts and lead author, said nighttime heat prevents the body from recovering from daytime conditions. Emerton stated that the rise in heat stress is a direct result of climate change.

The study noted that heat stress remains the leading cause of weather-related deaths and worsens cardiovascular disease, diabetes, mental health conditions and asthma.

The authors said action plans for heat health, early-warning systems, urban cooling measures and inclusion of heat stress metrics in climate assessments will be needed to protect populations. "We hope this helps people across the world understand the changes that are happening, and we hope that information can support decision-making on how to plan and adapt for the future," Emerton said.