As India continues to suffer a severe heatwave, a latest study shows that climate change added approximately 50 to 80 nights each year where the temperature exceeded 25°C, with serious impacts on sleep and health. Climate change is leading to a rise in nighttime warming, which is impacting sleep quality and human health in India and across the globe, according to a new analysis by Climate Central and Climate Trends reported Indian Express.
The analysis shows that approximately 50 to 80 days each year were added above this threshold by climate change in cities across Kerala, Karnataka, Maharashtra, Tamil Nadu, Punjab, Jammu and Kashmir, and Andhra Pradesh, between 2018 and 2023. Among the Metro cities, Mumbai has seen the highest changes in the nighttime temperatures, with the city experiencing an additional 65 days of warmer nights due to global warming. West Bengal and Assam are the regions that have been most impacted, with cities like Jalpaiguri, Guwahati, Silchar, Dibrugarh and Siliguri experiencing between 80 and 86 additional days each year above the 25°C threshold due to climate change, on average.
Several cities across India saw between 15 and 50 additional days where the minimum temperatures exceeded 25°C due to the influence of climate change, including Jaipur, with an additional 19 hot nights attributable to climate change as per the report.
Meanwhile, in both observations and in the counterfactual climate, the nighttime summer temperatures across India often exceeded 20°C over the entire summer period.
The cities that had the largest number of days where the minimum temperature exceeded 20°C due to climate change are Gangtok, Darjeeling, Shimla, and Mysore, with an average of 54, 31, 30, and 26 days added by climate change, respectively.
These findings come during a week that saw new records for nighttime warming in several Indian cities. On June 19, Delhi shattered the all-time high minimum temperature record, with the mercury reaching 35.2°C overnight. Delhi recorded almost four number of additional nights over 25°C due to climate change between 2018 and 2023, according to the Climate Central analysis.
On June 18, Alwar in Rajasthan had a minimum temperature of 37°C, the highest-ever nighttime temperature since records began in 1969. Alwar experienced almost nine additional nights that crossed 25°C that are attributable to climate change, between 2018 and 2023. In Uttar Pradesh, Lakhimpur Khiri, Shahjahanpur and Varanasi also witnessed their highest recorded minimum temperatures at 33°C, 33°C and 33.6°C respectively this week. Varanasi saw 4 additional nights over 25°C due to climate change from 2018 to 2023.
These increasingly frequent extreme nighttime temperatures are contributing to heat stress, exhaustion and heat-related deaths. The analysis looks at the number of times the minimum nighttime temperature exceeded 20° and 25°C in summers over the last 10 years (2014-2023) and where this is attributable to climate change, focusing on India, the United States, and the United Kingdom. These temperature thresholds were used due to evidence that sleep and human health are negatively impacted above these temperatures.
An average person on earth experienced 4.8 additional days above 20°C as a result of higher nighttime temperatures induced by climate change between 2018 and 2023. Meanwhile, over this time period, the average person experienced an additional 11.5 days each year above 25°C, according to the report.
Aarti Khosla, director, Climate Trends, said in the report that “Like day temperatures, night temperatures have also shown constant and steady rise over the last few years. Warm nights have been punishing this summer with several cities shattering five decades of records. It’s evident that cities will bear the highest brunt which will get worse due to urban heat island effect.”
The methodology
In India, annual number of days above each threshold were calculated in cities with a population over 1 lakh. An analysis of observed temperature patterns in India, the United States, and the United Kingdom was done using ERA5 reanalysis temperature data. The data is available at a resolution of 0.25° (31 km). Additionally, the analysis utilized counterfactual temperatures or the temperature that would have occurred in a world without human-induced climate change. This is estimated using Climate Central’s Climate Shift Index (CSI) system.
The system is grounded in the latest peer-reviewed attribution science, quantifying the influence of climate change on daily temperatures around the world.
For the global analysis, the extracted data corresponded to each hemisphere’s summer season: June, July, August for the Northern Hemisphere, and December, January, February for the Southern Hemisphere. They then counted the number of days in each month where the minimum temperature exceeded 20°C and 25°C over the ERA5 and counterfactual temperatures from 2014-2023. Thereafter, summing the annual count for each year in both scenarios and found the difference to assess how climate change has impacted nighttime temperatures reported Indian Express.
