News release

From: Springer Nature

Heat stress intensifies worldwide

One billion more people face at least one day of extreme heat stress each year compared with the 1970s, according to a Nature Climate Change paper. The findings show that global heat stress is intensifying across events during the day, night, and during both the day and night.

Heat stress is the net heat load on an individual and is influenced by factors including temperature, humidity, wind, and radiation. It can be assessed using the Universal Thermal Climate Index (UTCI), a ‘feels-like’ temperature measure that incorporates these factors and models the human body’s response to the environment. Although heatwaves are becoming more frequent, longer and more severe, global changes in heat as experienced by people — including nocturnal heat and during both the day and night — remains poorly quantified at the global scale.

Rebecca Emerton and colleagues analysed a global dataset of human heat stress from 1950 to 2024 and found that feels-like temperatures have risen on the warmest days and nights since the 1970s. The ten warmest nights of each year have warmed faster than the ten warmest days, at a global average rate of 0.32 °C per decade compared with 0.27 °C per decade, respectively. Extreme feels-like temperatures are now more frequent on every continent. Subtropical regions, including southern North America, southern Europe, northern and southern Africa, and South America now experience up to 50 additional days per year with strong to extreme heat stress (UTCI greater than or equal to 32 °C and 46 °C, respectively) compared to the 1970s. Exposure to at least 1 day of extreme heat stress has risen from 16% to 22% of the global population, equivalent to an additional one billion people.

The authors conclude that global heat stress is increasing in frequency, severity and duration, during both the day and night. They suggest that heat-health action plans, early-warning systems, urban cooling interventions, and the integration of heat stress metrics in climate risk assessments may help to reduce vulnerability.