- Recent research finds that limitations to people’s daily lives imposed by climate change are already widespread and likely to continue growing as global temperatures rise. Older people are the most impacted.
- The researchers used a “physiologically grounded” heat model to analyze 75 years of global climate data.
- The global average number of hours per year that people are exposed to heat that severely limits their activity was found to have doubled for younger adults since the 1950s, while for older adults, it went from about 600 hours per year to about 900 hours.
- Parts of Southwest and South Asia, South America and Australia already experience what the study researchers call “extreme livability limitations,” which is even true for younger adults.
As a grueling March heat wave batters the U.S. West with dangerous temperatures, and the world girds itself for what could be another sizzling record-smashing Super El Niño, a team of researchers has published a study looking at how global warming is already impairing people’s regular daily activities.
Using 75 years of data stretching from 1950 to 2024, the scientists identified a clear trend and concluded that climate change is already placing serious limitations on people’s daily lives, with those impacts now widespread and very likely to worsen as temperatures continue to rise. Older adults, and people in the tropics, are especially being affected.
The research team found that the global average number of hours per year people are exposed to heat that severely limits their activity has doubled for younger adults since the 1950s, while for older adults it went from about 600 hours per year to about 900 hours.
However, these impacts aren’t evenly distributed: Parts of Southwest and South Asia, South America and Australia already experience what the researchers call “extreme livability limitations” even for younger adults.
The research team behind the study, led by Luke Parsons, an applied climate modeling scientist at The Nature Conservancy, said he used a “physiologically grounded” heat model to analyze 75 years of global climate data to fill in what the researchers perceive as a gap in our understanding of ongoing and projected heat impacts on people’s daily lives.
“There’s all these different heat metrics out there,” Parsons told Mongabay. “They’re very useful tools, but they carry these hidden assumptions about who’s being exposed. They oftentimes don’t distinguish between younger and older people,” for example. They’re also often focused more on when it’s too hot to work outdoors or when extreme heat is a threat to human survival.
Parsons continued: “We wanted to take what we call a physiologically grounded approach here to think about, ‘Can a person do [typical] day-to-day activities? How does extreme heat outside impact or limit our day-to-day lives?’” In other words: “Is this place livable?”
Rather than use a traditional heat index to answer these questions, Parsons and his team utilized the human/environmental adaptation and threshold limit model (HEAT-Lim model), developed by study co-author Jeni Vanos and her lab at Arizona State University. That model was first applied by Vanos et al. in a paper published in Nature Communications in 2023.
Combining the HEAT-Lim model’s output with global climate data for the past 75 years allowed the researchers to determine what level of activity humans could sustain without an uncontrolled rise in body temperature threatening their well-being.
“We looked at how hot it was, and how humid it was, from 1950 all the way up to the end of 2024,” Parsons said. “And we asked, for every hour of the day, if you were a younger adult who can sweat [efficiently] or an older adult who can’t cool themselves as easily, when would it be dangerously hot for you to participate in basic day-to-day activities?” Younger adults as defined in the study are those 18-40 years old, while older adults are those 65 and older.
The team found that there are already places on Earth where it gets so hot and humid at times as to make it unsafe for either younger or older adults to do more than lie down or sit outdoors. There are parts of Southwest and South Asia, South America and Australia where even younger adults already experience what the scientists call “extreme livability limitations.”
For older adults, the team found extreme limitations that make human life “unlivable,” where it’s impossible for the human body to naturally compensate for environmental heat loads, in parts of southwestern and eastern North America; tropical South America; western Saharan Africa; Southwest, South and Eastern Asia; and Australia. They write: “Temperature and humidity severely limit livability for older adults across large swaths of tropical and subtropical areas.”
The researchers also looked at the global average number of hours per year that heat and humidity severely limit people’s activity and found that it has “doubled for younger adults since the 1950s up to the recent couple decades,” Parsons said. “And for older adults, it went from about 600 hours in the year to about 900 hours in the year.”
That estimate of 900 hours annually of livability limitations for older people is a global average, Parsons noted, averaging together colder places and hotter places. In some parts of the globe, limitations are much worse.
“We looked at places in the Persian Gulf or sub-Saharan West Africa or South Asia or Southeast Asia, and some of these places, [see] roughly 2,000 to maybe almost 3,000 hours out of the year [that] are so hot and humid that older adults can’t really safely go about their day-to-day lives if they don’t have access to air conditioning and can’t go inside out of the heat.”
The data indicate that a large fraction of humanity is already being impacted by global warming, Parsons explained. “About … 35% of the current global population lives in areas where peak annual heat already really severely limits what younger adults can safely do outdoors. And for older adults, that number grows to about 78%, [impacting] almost four in five older adults. When it’s the hottest hours of the year, [they] are going to be really heat limited in what they can do outside.”
Parsons was particularly struck by the fact that, even when considering younger adults, about 1% of the global population already lives in locations where it’s hot enough in the hottest hours of the year to make it unsafe to do any outside activity. “And that number grows to almost 25%, or one in four, older adults. That is roughly 2 billion people.”
Drew Shindell, a professor of Earth sciences at Duke University who was not involved in the present study, said the research shows just how “potentially damaging” the global rise in temperatures that’s already occurred could turn out to be. “I say potentially,” he noted, “as the types of changes we’ve seen thus far can mostly be adapted to, at least in well-functioning countries.”
But, he added, “adaptation has its limits, and as warming continues, it will become more and more difficult to adapt and also more and more risky, as we’ll become highly reliant on artificial cooling.”
It’s not difficult to imagine conditions becoming so hot that overtaxed electrical grids in very hot climates fail, Shindell posited, meaning people will lose their cooling systems and hence their ability to adapt to the “unlivable” conditions to which they’re being subjected.
“That’s not only a risk for poorer tropical countries, but even for places like Texas or Arizona, where the grid could fail under the stress of a very hot summer’s high AC demand,” he said. “So adaptation carries risk of failure that may be small but [could] still have potentially enormous consequences.”
Research like the present study is important because it can help nations, local governments and communities determine where vulnerable people are most exposed to extreme heat in order that adaptation resources might be directed to them, according to Cascade Tuholske, an assistant professor of human-environment geography at Montana State University, who was not involved in the study.
“While numerous studies have documented how climate change is driving a rapid increase in extreme heat globally, this study expands our understanding of how the actual livability of locations is changing for different demographics because of increased outdoor heat stress,” Tuholske said.
He continued: “This is really important because it showcases where actual outdoor activities, like farming or construction, should be limited due to increasing heat exposure, and which populations live in these warming regions. Middle Eastern countries, [for example] where there are large numbers of migrant workers who work outside, really stand out as places of concern.”
Banner image: Research finds that there are already places on Earth where it gets so hot and humid at times during the year that it’s unsafe for either younger or older adults to do more than lie down or sit outdoors. Photo by NOAA.
Citations:
Parsons, L. A., Baldwin, J. W., Guzman-Echavarria, G., Jay, O., Kalmus, P., Staudmyer, H., … & Wolff, N. H. (2026). Intensifying global heat threatens livability for younger and older adults. Environmental Research: Health, 4(1), 015013. doi:10.1088/2752-5309/ae3c3a
Vanos, J., Guzman-Echavarria, G., Baldwin, J. W., Bongers, C., Ebi, K. L., & Jay, O. (2023). A physiological approach for assessing human survivability and liveability to heat in a changing climate. Nature Communications, 14(1), 7653. doi:10.1038/s41467-023-43121-5
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