Global Rise in Heat Stress and Its Impacts

Countries such as Mexico, Kenya, and Italy are experiencing an increase in heat stress lasting one to two months longer compared to decades ago. This phenomenon, affecting even regions previously untouched by such stress, highlights the intensification of extreme temperatures worldwide. The findings published in the journal Nature Climate Change underscore how the burning of fossil fuels like coal, oil, and gas contributes to this warming trend.

Researchers assessed heat stress based on feels-like temperatures, taking into account variables like temperature, humidity, and wind speed. The Universal Thermal Climate Index was employed to model how humans respond to their environment. Humidity can hinder sweat evaporation, a crucial cooling mechanism, making humid heat waves even more dangerous than dry ones.

The study examined heat stress at different levels: strong, very strong, and extreme. Regions such as Southern Africa, Eastern Africa, Mexico, and Central America are experiencing 50 more days of strong heat stress than in the 1970s. Southern Europe, including Spain, Italy, Greece, and Turkey, is seeing an increase of nearly a month in strong heat stress days. In the U.S., areas like Texas and Florida endure close to 25 or more days of very strong heat stress. Heat stress seasons are also extending.

Rebecca Emerton, the study’s lead author, remarks on the expansion of heat stress into regions historically not affected. The data indicate that feels-like temperatures during the ten warmest nights per year have increased faster than during the ten warmest days. Tropical nights now present minimum temperatures of 20 degrees Celsius, potentially impacting post-daytime heat recovery.

A billion more people face at least a day of extreme heat stress annually compared to the 1970s. The study emphasizes the urgent need for adaptation strategies like climate risk assessments and heat health action plans. The world must address the emission of heat-trapping gases through fossil fuel combustion and deforestation.

Climate scientist Jennifer Francis notes that increasing humidity compounds the dangers of rising temperatures. She highlights the struggle of human cooling mechanisms such as sweating, stressing the importance of mitigating future warming.

Emerton advocates for action to reduce future warming impacts. Implementing strategies like early warning systems and climate risk assessments is crucial to dealing with the expanding footprint of heat stress.