Rising Nighttime Temperatures Threaten Global Sleep Health, Scientists Warn

How Does Nighttime Warming Affect Sleep Quality?

Human sleep is tightly regulated by core body temperature. To fall asleep, the body needs to drop its core temperature by roughly 1°C, a process facilitated by cool ambient conditions. When nighttime temperatures remain elevated, the body struggles to dissipate heat effectively, delaying sleep onset and fragmenting sleep architecture. Research published in One Earth in 2022 by Kelton Minor and colleagues, using data from sleep-tracking wristbands across 68 countries, found that warmer-than-average nights shortened sleep duration and that the effect was most pronounced in lower-income countries and among older adults.

Deep slow-wave sleep and REM sleep — the stages most critical for memory consolidation, immune function, and emotional regulation — are particularly vulnerable to thermal disruption. The body's thermoregulatory mechanisms compete with the need to maintain sleep continuity, often resulting in more frequent awakenings and lighter sleep overall. As global temperatures continue to rise, sleep scientists warn that these effects will compound, creating a chronic sleep deficit across entire populations.

What Are the Health Risks of Heat-Disrupted Sleep?

Sleep deprivation is already recognized by the World Health Organization as a significant public health concern. When nighttime warming chronically reduces sleep quality, the downstream health effects are substantial. Studies have consistently shown that insufficient sleep raises levels of cortisol and inflammatory markers, contributing to hypertension, insulin resistance, and weight gain. The CDC estimates that roughly one in three American adults already gets less than the recommended seven hours of sleep, and rising temperatures threaten to make this worse.

Mental health is equally affected. Poor sleep is one of the strongest modifiable risk factors for depression and anxiety, and research suggests that even modest reductions in sleep quality can impair emotional regulation and decision-making. Vulnerable populations — including the elderly, outdoor workers, people with pre-existing conditions, and those without access to air conditioning — face disproportionate risk. Sleep scientists are now calling for nighttime temperature to be integrated into public health planning and climate adaptation strategies, including urban design that reduces heat islands and improved access to cooling infrastructure.

What Can Individuals and Communities Do to Protect Sleep in a Warming World?

At the individual level, sleep hygiene in a warming climate includes keeping bedroom temperatures as close to 18°C (65°F) as possible, using breathable bedding and sleepwear, and staying well hydrated in the evening. Cross-ventilation, fans, and — where available — air conditioning can help, though energy costs and environmental impact create their own challenges. Some research suggests that cool showers before bed can assist the body's natural temperature drop.

At the community and policy level, experts recommend expanding green spaces and tree canopy to reduce urban heat islands, improving building insulation standards, and creating public cooling centers. The sleep science community is also calling for nighttime temperature monitoring to be included in climate health surveillance systems. Given that approximately 3.5 billion people live in areas highly vulnerable to climate change according to the IPCC, protecting sleep is increasingly being recognized not as a lifestyle issue but as a fundamental public health priority.