Mexico, Kenya, Italy and other nations around the world are experiencing one to two more months of heat stress per year than they did several decades ago, according to new research published Monday in the journal Nature Climate Change. The study found that extreme “feels-like” temperatures, heat stress days and tropical nights have all surged in frequency, duration and severity over the past six decades.
Researchers moved beyond measuring air temperature alone, which is the standard metric in climate studies, and instead assessed the combined effect of temperature, humidity, wind speed and solar radiation on the human body. They used an analytical tool called the Universal Thermal Climate Index to model how the environment stresses an individual’s ability to stay cool.
The combination of heat and humidity poses a particular danger, the study noted, because humidity impairs the evaporation of sweat — the body’s chief cooling mechanism. Humid heat waves can be more fatal than dry heat waves, as humans cannot cool down as easily.
The authors — who include lead researcher Rebecca Emerton — linked the rising heat stress directly to planetary warming driven by the burning of fossil fuels: coal, oil and gas. Regions previously untouched by heat stress are now beginning to feel it, according to the paper, as the planet’s warming intensifies over time.
The findings come amid a string of climate research published in recent weeks, including MSI’s own reporting on how heat waves drive wildfire burn area in the Western United States and how marine heatwaves have more than tripled since the early 1990s.