Populations in southern India among most affected by sleep loss due to climate change, says study

Rising temperatures are leading to an increase in the amount of sleep loss across populations in Tamil Nadu and India, a recent study by ‘Climate Central,’ a non-profit organisation has highlighted.

According to their analysis from 11 cities in Tamil Nadu - Chennai, Coimbatore, Erode, Kallakurichi, Madurai, Salem, Theni, Tiruchi, Tirunelveli and Tiruppur, the researchers estimate that sleep loss, caused by climate change, has increased from anywhere between 4 per cent to 7 per cent in each of the 11 cities in Tamil Nadu between 1970-1975 and 2025-2025. In Puducherry, sleep loss increased by three percent during the same comparable periods.

The research studied sleep loss caused by climate change from across 1,338 cities worldwide, including 107 cities in Puducherry, Andhra Pradesh, Kerala, Tamil Nadu, Gujarat, Telangana, Odisha, Chhattisgarh, Maharashtra, West Bengal, Bihar, Karnataka, Assam, Jharkhand, Rajasthan, Madhya Pradesh, Uttar Pradesh, Haryana, Delhi and Chandigarh being analysed in India.

In response to questions from The Hindu, Kristina Dahl, vice president for science at Climate Central, explained the methodology used by the researchers to estimate the sleep loss of people living across the world. “Minor et al. In their 2022 study on how rising temperatures erode human sleep globally built a temperature-sleep model using sleep data from a recent time period. Our analysis applies the published model to night time temperatures from 2020-2025 and 1970-1975 to estimate expected sleep loss under those temperature conditions. They estimate the effect of night time temperature on sleep duration using a fixed-effects model that compares changes within the same individuals over time while controlling for other weather, seasonal, location, and time factors. We apply that published relationship to observed and counterfactual night time temperatures. Our analysis doesn’t explain all sleep loss from all causes. It estimates the sleep loss associated with higher night time temperatures, and the climate-attributed portion reflects the difference between observed night time temperatures and night time temperatures in a world without human-caused warming,” said Dr. Dahl in an email exchange.

The researchers note that Southern India has emerged as a hotspot for sleep disruption, with Tamil Nadu, Kerala, Andhra Pradesh, Karnataka and Telangana recording the highest overall sleep loss from all factors, climate change included, with high overnight temperatures being linked to an increase in the risk of stroke, other cardiovascular conditions and mortality. “Hot nights also degrade the quality and length of sleep worldwide, which has a wide range of negative impacts on physical and mental health, cognitive functioning, and children’s brain development and learning. Short and poor-quality sleep can also shorten life expectancy and increase the risks of accidents and injuries,” they note.

Puducherry recorded the highest observed annual sleep loss per person with 92 hours, followed by Andhra Pradesh with 88.6 hours and Kerala, with 88.3 hours. However, Tamil Nadu emerged as the state with the most affected population with sleep loss linked to climate change, with the average person losing around an additional 7.9 hours of sleep annually from climate change, the highest in the country. Meanwhile, in Karnataka, the average person lost around seven hours of sleep every year due to changing weather.

Data from across India’s major cities showed that while Chennai recorded the highest observed sleep loss per person annually in the country, with 93 hours lost, climate change could account for six per cent, or five hours per person of sleep loss. However, climate change accounted for 8 hours of sleep loss per person in Bengaluru, or 12 per cent of the annual figure, the highest among India’s major cities.

Dr. Dahl said people in higher-income countries were less affected by the changing climate, which suggests that having access to better cooling could help reduce heat-related sleep loss.

“In urban areas, adaptation measures that reduce the urban heat island effect could also help, such as planting trees and painting roofs white. Those sorts of things reduce the amount of heat that gets trapped in city environments, which tends to make cities hotter than surrounding areas. Ultimately, to minimise future heat-related sleep loss, countries around the world will need to cut their heat-trapping emissions quickly and steeply, because the more the planet warms, the hotter our nights get, and the more sleep we lose,” she added.