Sleepless Nights in India: Climate Change leading to hotter nights in many cities

As global temperatures continue to rise, India is experiencing an increasingly severe impact on its climate, particularly regarding night temperatures. A recent study by Climate Central and Climate Trends has revealed that climate change has significantly contributed to the rise in night temperatures, adding approximately 50 to 80 nights each year where temperatures exceed 25°C. This warming trend is adversely affecting sleep quality and overall health across the country.

The study calculated the number of nights where temperatures exceeded thresholds of 20°C and 25°C, and used the Climate Shift Index to estimate the additional hot nights attributable to climate change. 

Indian cities with major increases

From 2018 to 2023, cities across Kerala, Karnataka, Maharashtra, Tamil Nadu, Punjab, Jammu and Kashmir, and Andhra Pradesh experienced an additional 50 to 80 days per year with temperatures above 25°C. 

Mumbai recorded the most significant increase among major cities, with 65 additional warm nights annually. West Bengal and Assam were the most affected regions, with cities like Jalpaiguri, Guwahati, Silchar, Dibrugarh, and Siliguri experiencing 80 to 86 extra hot nights each year on average.

Many Indian cities saw an increase of 15 to 50 nights annually where temperatures surpassed 25°C. For example, Jaipur experienced 19 more hot nights each year due to climate change.

Observations and counterfactual climate scenarios showed that night summer temperatures in India often exceeded 20°C throughout the entire summer period. Cities with the highest increases in days where temperatures stayed above 20°C due to climate change included Gangtok, Darjeeling, Shimla, and Mysore, with an average of 54, 31, 30, and 26 additional hot nights, respectively.

Record-breaking night temperatures across India

Several Indian cities have broken records for nighttime temperatures recently. 

On June 19, Delhi recorded a minimum temperature of 35.2°C, the highest ever, with almost four additional hot nights attributed to climate change from 2018 to 2023.

On June 18, Alwar saw a record minimum temperature of 37°C, the highest since 1969, with nine additional hot nights due to climate change over the same period.

Cities like Lakhimpur Khiri, Shahjahanpur, and Varanasi reported record high minimum temperatures around 33°C, with Varanasi experiencing four additional nights above 25°C due to climate change between 2018 and 2023.

Global analysis of night temperatures

As part of the study, the researchers also did an analysis of night temperatures over the past decade (2014-2023) highlighting the global scope of this issue. The study calculated the number of nights where temperatures exceeded thresholds of 18°C, 20°C, and 25°C, and utilised the Climate Shift Index to estimate the additional hot nights attributable to climate change. 

Between 5 and 25 additional nights above 20°C were observed across the eastern U.S., southern Australia, southern South America, and parts of Asia. Regions like southern Africa and Spain experienced between 25 and 40 additional hot nights. Notably, the southwestern U.S. and Brazil saw increases of 40 or more nights.

Cities in California such as Merced, Clovis, and Fresno experienced the most significant increases in nights above 20°C, with climate change adding between 45 and 58 nights annually. The trend extends to cooler states, with cities in Wisconsin and Michigan observing over 10 additional hot nights.

England saw the highest increase in nights above 18°C, with an average of two additional nights per year due to climate change. Specific cities like Clacton-on-Sea and Margate experienced up to 16 additional hot nights annually.

Why is it happening?

The phenomenon of faster nighttime warming compared to daytime temperatures is influenced by several factors, including urban heat islands, which retain heat absorbed during the day, and increased greenhouse gas concentrations that trap heat. This persistent night heat prevents adequate recovery from daytime heat stress, leading to a host of health issues.

Health impacts 

Increased nighttime temperatures disrupt sleep patterns, resulting in various health problems. Poor sleep quality has been linked to physical and mental health issues, impaired cognitive function, and developmental challenges in children. Additionally, hot nights are associated with higher mortality risks, with studies indicating that the mortality risk can be significantly higher on days with hot nights compared to those with cooler nights. Vulnerable populations, including the elderly, children, and those without access to air conditioning, are particularly at risk.

The rapid rise in night temperatures due to climate change is significantly impacting sleep quality across India, with wide-ranging health implications. Addressing this issue requires a multifaceted approach, combining climate mitigation efforts with targeted adaptation strategies to protect the most vulnerable populations and ensure a healthier future for all.

References:

https://csi.climatecentral.org

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