New research indicates countries like Mexico, Kenya, and Italy are experiencing increased heat stress, extending by one to two months compared to several decades ago. Areas previously unaffected by heat stress are also experiencing challenges as global temperatures rise. This escalating heat is attributed to fossil fuel combustion, increasing the frequency and severity of extreme temperatures, heat stress days, and tropical nights over the past 60 years.
The study, published in Nature Climate Change, considers more than just temperature by evaluating feels-like temperatures, which offer greater insight into human impacts. Researchers used the Universal Thermal Climate Index, which factors in temperature, humidity, wind speed, and other elements to assess heat stress on individuals.
“The combina tion of heat and humidity is hazardous,” researchers point out, noting how humidity affects sweat evaporation, a vital cooling process. Humid heat waves pose more danger than dry ones due to their impact on the human body’s ability to cool down effectively.
Past studies often focused on climate-change-induced temperature increases. This study notes people worldwide experienced an average of 41 extra days of dangerous heat as of 2024. By century’s end, the number of extremely hot days could nearly double yearly, research suggests.
In places like Southern Africa, Eastern Africa, and parts of Mexico and Central America, regions might see 50 more days annually of strong heat stress compared to the 1970s. Southern Europe regions, such as Spain, Italy, Greece, and Turkey, experience up to 40 additional strong heat stress days. In the U.S., states such as Texas and Florida experience up to 25 more days of very strong heat stress.
This heat stress expansion extends into previously unaffected regions, observed Rebecca Emerton, lead author and senior scientist at the European Centre for Medium-Range Weather Forecasts. Increasing heat stress in regions historically immune reveals an expanding footprint of global warming.
Temperature increases on the warmest nights have accelerated faster than on the hottest days, affecting nighttime recovery from daytime heat. The number of people facing at least one extreme heat stress day annually has risen by one billion since the 1970s.
Jennifer Francis, a climate scientist at the Woodwell Climate Research Center, emphasizes the dual threat of rising temperatures and humidity. She highlights how increased humidity compromises the body’s cooling system, posing heightened risks.
Lead researcher Emerton underscores the urgent necessity for future warming mitigation, adaptation strategies, heat health action plans, early warning systems, and climate risk assessments to combat these growing challenges.
Alexa St. John, an Associated Press climate reporter, contributed to this report. Follow her on X: @alexa_stjohn or contact her at [email protected]
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