Kolkata: Kolkata: Rising nighttime temperatures are robbing Kolkatans of sleep, with the city ranking as India’s third most sleep-deprived megacity, according to a new global study by Climate Central.The study found that the average Kolkatan loses 80 hours of sleep a year because of warm nights, compared with 93 hours for the average Chennai resident and 84 hours for the average Mumbaikar. Of Kolkata’s annual sleep loss, five hours are attributable to climate change, accounting for about 7% of all temperature-related sleep deprivation between 2020 and 2025.The findings assume significance for Bengal, where prolonged heatwaves, persistently warm nights and high humidity have become increasingly common.The report states poor sleep is associated with impaired cognitive performance, anxiety and depression, cardiovascular diseases, diabetes and hypertension.The study by Climate Central, a non-profit that researches effects of climate change, analysed 1,338 cities worldwide and found that temperature-related sleep-loss linked to climate change has at least doubled since the early 1970s. Between 2020 and 2025, the average person globally lost nearly 56 hours of sleep annually because of high nighttime temperatures, with more than one-tenth of that loss directly linked to climate change.Beyond Kolkata, the study paints a worrying picture for Bengal. Across the five other Bengal cities included in the analysis — Howrah, Siliguri, Barrackpore, Asansol-Durgapur and Haldia — the average resident loses 75 hours of sleep every year, with 5.6 hours directly attributable to climate change.Researchers found that densely built cities, such as Kolkata, suffer more than other places because of the urban heat island effect, in which concrete structures, asphalt roads and limited green cover trap heat during the day and release it after sunset, keeping nighttime temperatures higher than in surrounding areas.Southern India experiences between 78 and 91 hours of annual sleep loss, placing the region among the most affected globally outside West Asia. Tamil Nadu has recorded the country’s highest climate change-attributable sleep loss at nearly eight hours per person every year.Among the southern cities, Bengaluru and Hyderabad annually lose eight hours and seven hours of sleep.“The analysis reveals how climate change is translating into measurable hours of lost sleep for people around the world,” said Kristina Dahl, vice-president for science at Climate Central. “It shows the impacts of fossil fuel-driven warming extend beyond extreme weather to undermine one of the most fundamental requirements for human health.”Medical experts warn sleep disruption is no longer merely a quality-of-life issue but an emerging public health concern. “Adults need seven to nine hours of sleep every night for optimal health,” said Courtney Howard, emergency physician and chair of Global Climate and Health Alliance. “As climate change drives more frequent and intense hot nights, sleep disruption should be recognised as a growing concern.”Medical experts warn that sleep disruption is no longer merely a quality-of-life issue but an emerging public health concern. “Adults need seven to nine hours of sleep every night for optimal health,” said Courtney Howard, emergency physician and chair of Global Climate and Health Alliance. “As climate change drives more frequent and intense hot nights, sleep disruption should be recognised as a growing concern for both public health and human productivity.”For Kolkata, where warm, humid nights often persist even after the monsoon, the study adds another dimension to the city’s growing climate challenge. While discussions on climate change have largely focused on floods, cyclones, sea-level rise and heatwaves, researchers say the loss of healthy sleep represents a hidden but increasingly significant cost of a warming planet.
