Analysis: Climate change is increasing dangerous nighttime temperatures across the globe

Summary

The purpose of this analysis is to assess the extent to which human-caused climate change has increased the number of uncomfortably hot summer nights (December-February in the Southern Hemisphere, June-August in the Northern Hemisphere).

To do this, we calculated the number of days where the nighttime minimum temperature exceeded 18°C, 20°C, and 25°C. We also used the Climate Shift Index daily attribution system to quantify how climate change has influenced the number of uncomfortably hot nights.

This analysis is an update on the recent Climate Central report, Sleepless Nights, which focuses on how climate change has driven up nighttime temperatures in India, the U.S., and the U.K. The current report provides a detailed global analysis, examining the impacts of heat at night on regions, countries, and cities across the globe.

Key findings

• Climate change - caused by burning fossil fuels like oil, coal, and gas - is causing a significant increase in dangerously hot nights across the globe.
• Due to human-caused climate change, 2.4 billion people experienced an average of at least 2 additional weeks per year where nighttime temperatures exceeded 25°C. Over 1 billion people experienced an average of at least 2 additional weeks per year of nights above 20°C and 18°C.
• High nighttime temperatures are detrimental to human health. These temperatures prevent the body from recovering from daytime heat, increase the risk of illness and mortality, and disrupt sleep. Short and poor quality sleep has a range of negative impacts on physical and mental health, cognitive function, and life expectancy.