Bengaluru and Chennai losing hours of sleep every year, and climate change is to blame, study finds

The temperature-related sleep loss linked to climate change has at least doubled since the early 1970s, a new study conducted across all 1,338 major global cities has found

The analysis by Climate Central also shows that over the last five years, the average person globally lost nearly 56 hours of sleep due to high temperatures. More than 10 per cent of that sleep loss was attributed to climate change, primarily caused by burning fossil fuels like coal, oil, and gas, and cutting down forests.

Climate Central is an independent group of scientists and communicators that researches and reports the facts about our changing climate and how it affects people’s lives.

This is the first analysis to directly quantify the number of hours of sleep lost due to climate change, combining cutting-edge research on the effects of temperature on sleep with the latest attribution science.

Climate change driving sleep loss across India

India emerges as a global hotspot for climate-related sleep loss. Cities in southern India experience 78–91 hours of annual sleep loss, with 8–9 hours directly attributable to climate change, placing them among the most affected globally outside the Middle East, the report revealed.

According to the report, poor sleep is associated with a range of health impacts, including impaired cognitive performance, poorer mental health, weakened immunity, cardiovascular diseases, and reduced productivity. These risks are likely to be particularly severe in India, where millions of people live in densely populated urban areas affected by the urban heat island effect, which traps heat and keeps cities warmer after sunset.

The burden also falls disproportionately on vulnerable populations, including older adults, women, low-income households, and those without access to adequate cooling.

Major impact in Southern states

Southern states such as Tamil Nadu, Kerala and Andhra Pradesh record the highest overall temperature-related sleep loss, while Tamil Nadu and Karnataka show the strongest climate change signal. This suggests that persistently hot and humid nights are not only reducing sleep but that climate change is increasingly amplifying these losses across some of India's hottest regions.

Tamil Nadu stands out as the state most affected by climate change, with an average of 7.9 additional hours of sleep loss per person annually, the highest in the country. Karnataka (7.8 hours) and Rajasthan (7.0 hours) also record high climate change-attributable sleep loss, despite lower overall sleep loss than southern coastal states.

Puducherry has recorded the highest observed annual sleep loss at 92 hours per person, followed by Andhra Pradesh (88.6 hours) and Kerala (88.3 hours).

Chennai records highest overall sleep loss

India's largest metros are losing between 65 and 93 hours of sleep each year because of high nighttime temperatures, the report said.

While Chennai, Mumbai, and Kolkata experience the greatest overall sleep loss, Bengaluru and Hyderabad show the strongest climate change signal, indicating that rising temperatures are increasingly disrupting sleep, even in cities with comparatively milder climates.

Chennai records the highest overall sleep loss among India's major metros, with residents losing an average of 93 hours of sleep annually, of which 5 hours are directly attributable to climate change. Mumbai (84 hours) and Kolkata (80 hours) also rank among the highest for overall sleep loss, reflecting persistently warm and humid nights.

Bengaluru stands out

Bengaluru stands out for having the strongest climate change signal, with 8 additional hours of sleep loss annually—the highest among India's major metros. Nearly 12 per cent of all temperature-related sleep loss in the city is attributable to climate change.

Hyderabad follows with 7 additional hours of climate-driven sleep loss each year, while Ahmedabad and Pune each record 6 hours. Although Delhi records the lowest overall sleep loss among the eight metros (66 hours/year), residents still lose an estimated 5 additional hours of sleep annually because of climate change.

“This analysis reveals how climate change is translating into measurable hours of lost sleep for people around the world. By combining the latest climate attribution science with research on how heat affects sleep, we can now quantify a hidden but growing consequence of rising temperatures," Dr Kristina Dahl, Climate Central’s Vice President for Science, said in the report.