image: Changes in feels-like temperatures (UTCI), heat stress days and tropical nights over time. Maps show the difference between the 1970s and the last 10 years (2015–2024), based on decadal averages of: the 10 highest daily maximum UTCI values per year (°C), the 10 highest daily minimum UTCI values per year (°C), the annual number of days with at least very strong heat stress (UTCI ≥ 38°C) and the annual number of tropical nights (minimum temperature ≥ 20°C). Line charts show the global average for each indicator, for each year from 1950 to 2024, with trends per decade since the 1970s shown above each chart. Data: ERA5-HEAT. Source: Emerton et al., 2026: Global heat stress intensification and its expanding footprint on the human population, Nature Climate Change, https://doi.org/10.1038/s41558-026-02670-5
Credit: ECMWF
Under Embargo until 16:00 BST 22 June 2026
Sharp rises in the intensity of global heat stress are exposing more people to hazardous heat, a ground-breaking new study reports. The results, published in the journal Nature Climate Change (22 June 2026) reveal how the frequency, severity, and duration of heat stress have accelerated and intensified across the globe since around 1970, impacting health and livelihoods around the world.
Heat stress is the leading cause of weather-related deaths and involves the build-up of body heat due to exposure to high temperatures, often combined with other factors such as high humidity.
Heat can exacerbate underlying cardiovascular, respiratory and mental health conditions, especially affecting, for example, vulnerable people, outdoor workers and urban residents.
New research by scientists at the European Centre for Medium-Range Weather Forecasts (ECMWF) provides a first comprehensive global scale analysis of heat stress with climate change, offering novel insights for public health, climate adaptation strategies and policy planning.
Lead author, and Senior Scientist at ECMWF, Rebecca Emerton, said:
“Our research shows a clear, climate-driven intensification of heat stress across the globe. Compared to the 1970s, heat stress is now more severe, more frequent and longer-lasting. As a result, more people worldwide are exposed to hazardous heat, driven not only by population growth but by our changing climate. These findings highlight the need to both limit future warming and integrate heat stress into climate risk assessments, early warning systems and policy and planning to protect human health.”
Using the Universal Thermal Climate Index (UTCI), this research provides the first simultaneous global tracking of not only daytime extremes, but also nighttime heat and compound daytime-nighttime events.
The paper compares heat stress conditions in our current climate (2015–2024) with the 1970s and illustrates how every continent is now affected by more frequent ‘very strong’ and ‘extreme’ heat stress, with the footprint expanding into previously unaffected regions. Daily maximum UTCI is rising, and heat stress seasons are lengthening, with more frequent, severe, and prolonged compound events. Pronounced trends are observed across the globe, with some of the largest changes seen in Europe, Africa, the Arabian Peninsula and North America, amongst other regions.
In southern Europe, and parts of northern Africa and the Arabian Peninsula, for example, the maximum UTCI on the ten warmest days of the year is up to 4°C warmer in our current climate than in the 1970s, and in parts of southwestern Europe, up to 5°C warmer. Elsewhere, increases fall mainly between 2–3°C. In Europe, extreme heat stress, while still rare, now occurs 2.5 times more frequently, while subtropical regions – including southern North America, southern Europe, Africa and South America – are now experiencing up to 50 more days per year with at least strong heat stress.
Taking the study beyond standard air temperature measurements, UTCI is used to capture the physiological impact of the environment. Expressed in °C, it represents a "feels-like" temperature accounting for air temperature, humidity, wind, and radiation, while modelling how the human body responds to the environment. Considering factors beyond temperature is important, as, for example, a high humidity and low wind environment may be more hazardous to health than the same temperature at a lower humidity and with a breeze or cloud cover. As such, the UTCI can differ substantially from the measured air temperature.
Claudia Di Napoli, Scientist at ECMWF and one of the co-authors of the paper, explains why it is critical to look beyond air temperature:
“The Universal Thermal Climate Index (UTCI) can differ substantially from air temperature. During the recent May 2026 heatwave in Europe for instance, the UTCI often reached values 4°C higher than air temperature at their daytime peak. This highlights the importance of considering other factors, such as humidity and radiation.”
Umberto Modigliani, Acting Director of Forecasts, concluded:
“This study provides compelling evidence that heat stress is no longer an emerging risk but a defining feature of today’s climate. By capturing how it is experienced by people across both day and night, this research shows a clear intensification that is already affecting societies worldwide. This reinforces the critical role of reliable and trusted weather and climate information in helping communities anticipate, adapt, and protect lives and livelihoods.”
Journal
Nature Climate Change