Unliveable Earth: Daily Life Is Becoming More Dangerous as Planet Heats Up

Extreme heat is no longer just uncomfortable—in many parts of the world, it is increasingly making everyday life physically unsafe, according to a new global study led by scientists from The Nature Conservancy and published in the journal Environmental Research: Health.

Combining more than 70 years of global climate data (1950–2024) with a physiological heat balance model that accounts for how the body responds to conditions at different ages, the study finds that around 35% of the global population now lives in areas where heat severely limits safe activity, even for younger adults during the hottest parts of the year.

Intense outdoor labour has always been dangerous in the heat. However, even light physical activity—like climbing stairs or household chores—can become dangerous in certain conditions. Rising temperatures and humidity are increasingly restricting how much physical activity people can safely do outdoors—even in the shade.

The impacts are most severe for older adults. On average, people over 65 now experience around 900 hours each year—more than a month of daytime hours—when heat severely limits safe outdoor activity, compared with 600 hours in 1950. For younger adults, that figure has risen from 25 to 50 hours over the same timeframe. In some tropical and subtropical regions, heat restricts outdoor activity for older adults for between one-quarter and one-third of the year.

Unlike commonly used heat indices, this study—co-authored by researchers from University of Sydney, University of California (Irvine), Arizona State University (ASU), NASA Jet Propulsion Laboratory/Caltech, UCLA and Duke University—considers how the human body responds to heat during physical activity and how that response changes with age. By combining climate data with human physiology models, the study identifies when heat doesn’t just feel dangerous but physically overwhelms the body’s ability to stay cool.

“Climate change isn’t just making heat more intense—it’s shrinking the amount of time people can safely go about their daily lives,” said lead author Luke Parsons, a climate scientist at The Nature Conservancy. “In some places, we’re already seeing conditions where even minimal activity can push the human body beyond its limits.”

While extreme heat is often associated with poorer regions, the study finds that some of the most severe constraints already afflict relatively wealthy countries, particularly in parts of South and Southwest Asia including the Gulf states. The key difference is not the heat itself but people’s ability to cope with it. Access to cooling, infrastructure and workplace protections can reduce risk, but these protections are unevenly distributed—even within high-income countries.

These findings come as global temperatures have already risen by almost 1.5°C from preindustrial levels. The researchers warn that as the climate heats and the global population ages, the parts of the world where everyday life is physically constrained by heat will continue to expand.

However, rapid cuts to the use of oil, coal and gas, along with technological and behavioural adaptations to rising temperatures, can help to manage unliveable heat. This research can identify those areas of extreme heat and vulnerable populations (e.g., older and/or low-income) where investments in public health measures would make the greatest difference.

“Our study highlights just one of many reasons to act on climate,” said co-author Haley Staudmyer, a climate scientist at the University of California, Irvine. “Cutting greenhouse gas emissions and investing in public health will prevent all kinds of tragedies—not just heat-related deaths.”

Practical measures to mitigate these risks include municipal “cooling stations” where vulnerable people can access air conditioning; public education campaigns about how to deal with heatwaves; and shifts in working hours—although there are limits to our ability to adapt, underlining the urgency of eliminating emissions at source.

Adding further context, co-author Gisel Guzman Echavarria from ASU said: “Our findings imply we are facing lifestyle changes at a planetary level, but strategies to prevent harm and make a positive impact start at the individual and community level. In addition, we can learn from successful cases in which entire communities have coped with heat for years in more sustainable and socially cohesive ways, while overheating is reduced or reversed.”

Parsons L.A., Baldwin J.W., Guzman Echavarria G., Jay O., Kalmus P., Staudmyer H., Vanos J.K., Wolff N.H. Intensifying global heat threatens livability for younger and older adults. Environmental Research Health. 

https://doi.org/10.1088/2752-5309/ae3c3a