As India experiences longer summers, more frequent heatwaves and warmer nights, climate change is beginning to affect something most people rarely connect with: sleep. While daytime heat is uncomfortable, it is the rising temperatures after sunset that may be silently taking a toll on people’s health.
A new report by Climate Central has found that India is among the global hotspots for climate-related sleep loss. According to the analysis, people in many parts of southern India are losing between 78 and 91 hours of sleep every year because of hot nights. Of this, eight to nine hours annually can be directly linked to climate change, making India one of the countries most affected by warming-driven sleep disruption.
The findings add to growing evidence that climate change is not only causing extreme weather events but is also affecting everyday aspects of life, including how well people sleep. Health experts say poor sleep is linked to a wide range of health problems, from heart disease and diabetes to weakened immunity and poor mental health.
INDIA AMONG THE WORST AFFECTED
The report analysed temperature data and sleep research from 1,338 major cities worldwide, including 107 cities in India. Researchers found that across all cities studied, climate change has at least doubled heat-related sleep loss since the early 1970s.
Globally, an average person lost nearly 56 hours of sleep every year because of nighttime heat between 2020 and 2025. Around six of those lost hours were directly linked to climate change, accounting for just over 10 per cent of the total sleep loss.
However, the impact is much greater in places where nights are already very warm, including several parts of India.
TAMIL NADU RECORDS THE HIGHEST CLIMATE-RELATED SLEEP LOSS
Among Indian states, Tamil Nadu recorded the highest climate change-driven sleep loss, with residents losing an estimated 7.9 additional hours of sleep per person each year due to climate change.
Among major cities:
- Chennai recorded the highest overall sleep loss at 93 hours per year.
- Mumbai followed with 84 hours.
- Kolkata recorded 80 hours annually.
- Bengaluru showed the strongest climate change signal, with around eight hours of sleep loss every year directly linked to climate change.
The report also highlighted state-wise estimates:
- Maharashtra: Around 76.3 hours of sleep lost annually, including 5.8 hours due to climate change.
- Uttar Pradesh: Around 69 hours lost each year, with 4.9 hours attributed to climate change.
Medical experts say adults generally need seven to nine hours of sleep each night for good physical and mental health.
According to Dr Courtney Howard, Emergency Physician and Chair of the Global Climate and Health Alliance, rising nighttime temperatures are particularly harmful for people living in lower-income countries, older adults and women.
WHY DO HOT NIGHTS AFFECT SLEEP?
The human body naturally lowers its core temperature before and during sleep. Cooler nighttime temperatures help this process and allow the body to enter deeper, more restorative stages of sleep.
When nights remain hot, the body struggles to cool itself. This makes it harder to fall asleep, increases the chances of waking up during the night and reduces the amount of deep sleep a person gets. Even if someone spends enough time in bed, the quality of sleep may be poor.
Unlike daytime heat, nighttime heat often goes unnoticed because people are indoors. However, experts say it may have long-term health consequences.
CLIMATE CHANGE HAS DOUBLED HEAT-RELATED SLEEP LOSS
Kristina Dahl, Vice-President for Science at Climate Central, said the report demonstrates another hidden cost of global warming.
She said the analysis shows that climate change is translating into measurable hours of lost sleep by combining climate attribution science with research on how heat affects sleep. According to Dahl, climate change has at least doubled temperature-related sleep loss across more than 1,300 cities since the early 1970s, highlighting that the effects of fossil fuel-driven warming extend beyond extreme weather and affect one of the most basic human needs.
The report says hotter nights are becoming more common as climate change continues to warm the planet. While extreme heat often receives attention because of heatwaves and record-breaking daytime temperatures, rising nighttime temperatures could become an equally important public health challenge.
Unlike many other effects of climate change, sleep loss affects millions of people every night. Over months and years, even small reductions in sleep can build up, affecting health, work performance and overall quality of life.
As cities continue to warm, experts say protecting people from nighttime heat through better urban planning, cooler buildings, more green spaces and stronger climate action will become increasingly important for both public health and productivity.
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