The global community is currently facing a sharp increase in hazardous heat stress as our continued reliance on fossil fuels causes the planet to heat up. Data from the EU’s Copernicus Climate Change Service (C3S) indicates that European temperatures have risen by approximately 2.5°C compared to pre-industrial levels. Despite various global efforts to mitigate warming, Europe remains the fastest-warming continent on the planet.
To better grasp the impact on human health, researchers have shifted their focus from standard air temperature to ‘feels-like’ temperatures. Unlike traditional forecasts, these measurements account for environmental variables such as humidity and wind speed, alongside scientific models of how human bodies lose heat. A recent study published in Nature warns that extreme ‘feels-like’ conditions, frequent heat stress events, and tropical nights—where temperatures stay above 20°C—are becoming dramatically more common, even in areas that historically avoided such conditions.
Heat stress is defined as the accumulation of body heat, either from physical exertion or environmental exposure, occurring when the body cannot dissipate heat as quickly as it absorbs it. According to the C3S, this is influenced by a combination of high ambient temperatures, physical activity, humidity, and insufficient fluid intake. While the human thermoregulatory system usually balances heat through mechanisms like sweating, extreme conditions can lead to symptoms such as dizziness, nausea, rapid breathing, and elevated heart rates, potentially resulting in heat stroke or exhaustion.
Researchers categorize heat stress into three tiers: strong (32°C or above), very strong (38°C or above), and extreme (46°C or above). In nations like Greece, Italy, Turkey, and southern Spain, some regions are now experiencing nearly a month of additional strong heat stress days compared to the 1970s. Lead study author Rebecca Emerton notes that the footprint of heat stress is expanding into regions where it was once rare.
Other global regions, including parts of Central America, Mexico, and countries across Southern and Eastern Africa like Namibia, Angola, Kenya, Tanzania, and Uganda, may see roughly 50 more days of strong heat stress annually compared to previous decades. Furthermore, the study highlights that nighttime temperatures are rising faster than daytime ones at a rate of 0.32°C per decade. These high temperatures prevent the body from recovering overnight, which Ruth Engel of the World Resources Institute notes is a critical public health concern, especially in Europe where air conditioning is less prevalent and mortality rates among the elderly and vulnerable are known to rise during such events.
