New research highlights that humans have certain limitations: they cannot cope with the effects of extreme heat combined with a certain level of humidity.
A new interdisciplinary study led by researchers at the Penn State College of Science and Purdue University College of Sciences has just shed light on the potentially devastating impact of extreme heat due to climate change.
According to this work published in the Proceedings of the National Academy of Science, if global temperatures rise at least 1°C above current levels, billions of people could be exposed to levels of heat and humidity beyond their tolerance limits.
Experts note that extreme heat waves combined with higher humidity can be extremely dangerous because the air cannot absorb excess moisture, limiting the evaporation of sweat from the human body and the humidity in certain infrastructure, such as evaporative coolers. In other words, man can no longer naturally cool his body and he then lives in conditions that are no longer favorable to the species.
An example is given by the researchers: the limit for a young and physically fit person is around 31°C at a level of 100% humidity, according to work published last year by Penn State researchers . Besides temperature and humidity, the specific threshold for each individual also depends on their level of exertion and other environmental factors, including wind speed and solar radiation.
In human history, temperatures and humidity beyond human limits have been recorded only a limited number of times – and only for a few hours at a time – in the Middle East and South Asia. Is, according to researchers.
The study modeled warming scenarios ranging from 1°C to 4°C to identify regions where heat and humidity levels would exceed human tolerance. If warming reaches 2°C, billions of people in India, China and sub-Saharan Africa would face prolonged periods of intolerable heat, mainly in the form of humid heatwaves, making air conditioning and mitigation measures heat inaccessible to many populations living in low- and middle-income countries.
The scenario of 2°C compared to today may correspond to the “pessimistic” scenario of the IPCC by 2100, but the trajectory is regularly reassessed with indicators which do not encourage optimism.
At 3°C ??of warming, regions such as the east coast and central United States, South America, and Australia would also experience extreme heat of this magnitude, although the United States would not exceed the limits of human tolerance as frequently as other regions.
The researchers pointed out that these models do not account for extreme and unusual weather events, such as the 2021 heat wave in Oregon or record temperatures in London last summer.
The research emphasizes that governments and policy makers should respond very quickly. “Across the world, official weather adaptation strategies focus only on temperature,” said Qinquin Kong, who participated in the work. “But this research shows that moist heat poses a much greater threat than dry heat. Governments and policymakers must re-evaluate the effectiveness of heat mitigation strategies in order to invest in programs that will address the most great dangers that people will face.
The study also emphasizes that middle- and low-income countries will be particularly vulnerable, but rich countries will not be spared.
