Sleepless In India: New Study Says How Nights Are Getting Hotter Amid Climate Change, Posing Health Risks
Study finds a surge in India's nighttime temperatures, with cities experiencing 50-80 extra nights above 25°C annually. This increase exacerbates health problems, particularly for vulnerable groups.
New Delhi: India is experiencing a dramatic increase in nighttime temperatures due to climate change, with significant implications for public health, a new analysis reveals. The study, conducted by Climate Central, shows that the country has been subjected to an additional 50 to 80 nights per year where temperatures exceed 25°C, affecting sleep and exacerbating health problems.
Impact of Rising Nighttime Temperatures
Global mean temperatures have risen by over 1.3°C since 1850, hitting a new peak in 2023. This warming is primarily driven by increased carbon dioxide levels from burning fossil fuels such as coal, oil, and natural gas. The analysis highlights that nighttime temperatures are rising more quickly than daytime temperatures, posing severe health risks.
Increased nighttime temperatures make it difficult for people to recover from the heat of the day, leading to a range of health issues. Poor sleep due to hot nights is linked to higher risks of physical and mental health problems, impaired cognitive function, and greater chances of workplace accidents.
Mortality risks are also heightened, with relative mortality risk on hot nights being 50% higher than on cooler nights, says the analysis by Climate Central, an independent group of researchers comprising scientists and communicators.
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Nighttime Warming In India
The analysis focuses on nighttime temperatures in India, particularly in cities with populations over 100,000. Over the last decade, minimum nighttime temperatures often exceeded 20°C throughout the summer, with significant increases attributed to climate change. The analysis used the Climate Shift Index daily attribution system to quantify how climate change has affected the number of uncomfortably hot nights.
The study noted that the threshold of 20 degrees was chosen "due to the potential health and sleep impacts of nighttime temperatures exceeding this threshold". The researchers did additional analysis at the 25 degrees threshold to factor in countries that record higher night-time temperatures, and because several previous studies have shown that the quality of sleep deteriorates when nighttime temperatures breach this threshold.
Cities such as Gangtok, Darjeeling, Shimla, and Mysore have experienced an increase in nights where temperatures exceeded 20°C, with an average of 54, 31, 30, and 26 additional nights, respectively, the Climate Central study found.
The impact of climate change on temperatures above 25°C has been even more pronounced. Cities in West Bengal and Assam, including Jalpaiguri, Guwahati, Silchar, Dibrugarh, and Siliguri, saw an average of 80 to 86 additional hot nights each year.
Recent records illustrate the severity of the situation. On June 19, Delhi set a new record for the highest minimum temperature, reaching 35.2°C. Between 2018 and 2023, according to the analysis, Delhi recorded almost four additional nights when the 25°C threshold was crossed.
On June 18, Alwar in Rajasthan also recorded its highest ever nighttime temperature of 37°C. Between 2018 and 2023, there were almost 9 additional nights when over 25°C was recorded in the town.
The study found these extreme temperatures "attributable to climate change", as it quoted studies by World Weather Attribution and ClimaMeter to say climate change has "more likely" made the current heatwave in India hotter and frequent.
Significant increase in hot nights has been observed across the country.
In Uttar Pradesh, Lakhimpur Khiri, Shahjahanpur and Varanasi witnessed their highest recorded minimum temperatures at 33°C, 33°C and 33.6°C, respectively this week. Varanasi experienced 4 additional nights with over 25°C temperature between 2018 and 2023.
The study covered cities with a population of over 1 lakh.
Stating that higher night temperatures made this year’s heatwave in India even deadlier, Michelle Young, Climate Impacts Research Associate at Climate Central, said there would be more of these sleepless nights "until the world stops burning fossil fuels like coal, oil and gas and cutting down forests”.
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Health Implications Of Hotters Nights
The Climate Central analysis said these "increasingly frequent extreme nighttime temperatures" were causing exhaustion, heat stress, and heat-related deaths. Higher nighttime temperatures prevent the body from cooling down, increasing the risk of heat-related health problems such as heat strokes and cardiovascular diseases. The rise in nighttime temperatures also disrupts sleep, leading to long-term health consequences. Vulnerable populations, including the elderly and those without access to air conditioning, are particularly at risk.
The findings underscore the urgent need for climate resilience initiatives and equitable access to cooling solutions in India. Nighttime temperatures are projected to continue rising, exacerbating health risks and making recovery from daytime heat more difficult.
“Our analysis shows that over the last decade the average person on Earth experienced almost five more nights that were uncomfortably or even dangerously hot due to climate change," said Michelle Young, adding that these hot nights disrupt people’s sleep, which has "a range of serious knock-on effects on physical and mental health".
Global Context
The global analysis of nighttime temperatures shows that, between 2018 and 2023, individuals experienced 4.8 additional nights per year on an average with temperatures above 20°C, and 11.5 more nights above 25°C, due to climate change.
It said every region covered by the study recorded net warming during their respective summer season. On average (2018-2023), there were 5 to 25 additional days above 20°C across the eastern US, the southern portion of South America, southern Australia, and western and eastern Asia.
Southern Africa, northern Mexico, and Spain had 25 to 40 additional days when over 20°C temperature was recorded. The southwestern US and Brazil added 40 days or more.
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Serious Threat To Urban Populations From Rising Minimum Temperatures: Experts
Climate experts expressed significant concern over the rising nighttime temperatures caused by the urban heat island effect, where cities, with their dense infrastructure of buildings and roads, absorb and retain heat, making them considerably warmer than rural areas.
“The urban heat island effect is most visible in the night-time temperatures. Cities turn into urban heat islands when buildings, roads, and other infrastructure absorb and re-emit heat, causing cities to be several degrees hotter than surrounding rural areas," explained Dr Roxy Mathew Koll, climate scientist at the Indian Institute of Tropical Meteorology, Pune.
He added: "During the day, the sun’s rays reach as shortwave radiation and heats the Earth’s surface. At night, the heat escapes as longwave radiation... The high-rise buildings and concrete setup in the cities do not let the excess heat to escape during the night. As the temperatures do not cool down, the heatwave continues into the night."
Blaming "haphazard city planning, poor architecture and unsustainable construction" for the creation of urban heat islands, Koll said
Indian cities need natural environment with trees, or open green spaces, to help release the heat faster at night.
Aarti Khosla, Director, Climate Trends, said: “Warm nights have been punishing this summer with several cities shattering 5 decades of records. It’s evident that cities will bear the highest brunt which will get worse due to urban heat island effect."
Batting for "very large reductions in fossil fuel burning", Khosla said studies have established that night-time temperatures would not fall below 25 degrees in some places during hot weather otherwise. "If we do not act now, nights would continue to be hotter, longer and sleepless, especially for the vulnerable,” she said.
“Climate change has a big role to play as constant rise in global temperatures have also increased air temperature impacting both day and night temperatures,” said Mahesh Palawat, Vice President – Meteorology and Climate Change, Skymet Weather.
Prof Anjal Prakash, - Clinical Associate Professor (Research) and Research Director, Bharti Institute of Public Policy, Indian School of Business, said vulnerable populations, especially in metropolitan areas like Mumbai, faced an increased threat from the rise in nighttime temperatures. "As global warming adds an additional 50 to 80 warm nights annually in states such as Kerala, Karnataka, Maharashtra, Tamil Nadu, Punjab, Jammu and Kashmir, and Andhra Pradesh, the impact on those without access to proper cooling mechanisms is profound."
He said this added climate stress can be devastating for marginalised communities already facing hardships.
Dr Akshay Deoras, research scientist at the National Centre for Atmospheric Science, University of Reading, UK, said the impact of high nighttime temperatures often got overlooked in tropical countries such as India. "This is concerning since the population density in many areas is high and not everyone can afford cooling devices. In such cases, the room temperature can be a lot more than the outside air temperature, and if it is accompanied by high relative humidity, the human body finds it very difficult to cool down."
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