[WORLD] As global temperatures rise, so too do disruptions to one of our most vital health functions: sleep. Scientists warn that increasingly hot nights, driven by climate change and urbanisation, are interfering with sleep quality, with growing concern about long-term health consequences.
The human brain is acutely sensitive to heat. Warmer environments elevate the body’s internal thermostat and activate physiological stress responses, making restful sleep more difficult to achieve.
Recent research shows that the effects of heat-related sleep disturbances are not evenly felt. Older adults, low-income households, and residents of densely built urban "heat islands"—where concrete and asphalt surfaces trap warmth—are particularly vulnerable. Many of these communities also lack reliable access to air conditioning, deepening the inequity. Public health experts caution that without targeted mitigation strategies, these disparities will only grow as the climate continues to warm.
In response, scientists are ramping up efforts to understand how the human body might adapt to hotter nights, and what interventions could protect sleep and health.
“Rising temperatures induced by climate change and urbanisation pose a planetary threat to human sleep and, therefore, to health, performance and wellbeing,” warned a comprehensive review published in Sleep Medicine last year.
A 2022 study in the journal One Earth found that people lost an average of 44 hours of sleep annually during the first two decades of this century, a decline linked to increasing nighttime heat. The study also revealed a stark contrast between rich and poor: residents of lower-income nations lost nearly three times more sleep than those in wealthier regions—highlighting the importance of infrastructure in shielding people from climate impacts.
While some populations in historically warmer regions appeared to exhibit slight resilience, researchers say it's uncertain whether acclimatisation alone can keep up with extreme future warming.
One projection, led by Kelton Minor at the University of Copenhagen, suggests the average person could lose between 50 and 58 hours of sleep per year by the end of the century. This forecast, based on sleep data from over 47,000 people across 68 countries, underscores the urgency of addressing sleep health in climate adaptation plans.
“Interventional studies and field experiments are now urgently needed to safeguard the essential restorative role of sleep in a hotter world,” Minor and colleagues concluded.
In some cities, innovative solutions are being trialled: reflective rooftops, cool pavements, and the expansion of green urban spaces are being used to combat nighttime heat retention. Pilot programmes in cities like Melbourne and Los Angeles have shown modest improvements, though experts stress that these efforts must be coupled with broader climate action to tackle the underlying issue.
Lowering the body’s internal temperature is essential for good sleep, but adapting comes with physical costs. “We sweat more and faster and require more hydration,” said Fabien Sauvet, a researcher at Paris Cité University. “So during heatwaves, we must adjust our behaviours—our activities, schedules, and even our clothing.”
Still, Sauvet believes that humans can tolerate more heat than often assumed. Research suggests that good sleep is still possible in rooms up to 28°C, challenging the common belief that ideal bedroom temperatures must fall between 18°C and 20°C. Wearing light clothing, using just a sheet, and ensuring proper ventilation can all help the body adjust.
“If we always sleep with air conditioning, we will never acclimatise,” he added.
The Enemies of Sleep
However, sleep becomes “much more complicated” when room temperatures rise above 28°C, said neuroscientist Armelle Rancillac of the Centre for Interdisciplinary Research in Biology.
Sleep deprivation, even in the short term, impairs recovery and alertness—leading to fatigue, daytime drowsiness, and increased risk of workplace and driving accidents.
New research is also drawing attention to the psychological toll. A 2023 study in Nature Human Behaviour linked poor sleep during heatwaves to heightened irritability and reduced mental performance, especially in tasks demanding focus. Employers are now being encouraged to adapt work schedules and improve rest areas during extreme heat events to maintain safety and productivity.
Long-term sleep deficits contribute to a growing list of health risks, including weight gain, diabetes, cardiovascular issues, and neurodegenerative diseases such as Alzheimer’s, Rancillac noted. Chronic sleep loss can also lower stress tolerance and impact mental wellbeing.
To improve sleep in hotter conditions, both Rancillac and Sauvet recommend identifying and eliminating common “sleep enemies.” That includes avoiding caffeine and alcohol close to bedtime, skipping hot tubs post-exercise, and taking cool—but not cold—showers to help regulate body temperature.
Napping during the hottest part of the day can also help. Short naps—ideally between 30 and 40 minutes, and before 2 p.m.—can offset sleep deficits without disrupting nighttime rest.
As the planet warms, scientists agree that rethinking how we sleep—and how to protect that rest—is becoming a critical part of climate resilience.
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