Human-induced climate change is significantly increasing the number of hot nights for nearly one in three people around the world, a global analysis said on Aug 8.
High night-time temperatures can become dangerous if they prevent the human body from cooling off and recovering from daytime heat.
The World Health Organisation (WHO) recommends keeping room temperature at or below 24 degrees C during the night – a threshold above which sleep can be uncomfortable.
This is especially important for vulnerable people, such as babies, the elderly and people with chronic health conditions, according to the WHO.
But burning coal, oil and gas releases climate-warming emissions into the atmosphere, fuelling a rise in nights above 25 degrees C, according to Climate Central, an independent group of scientists and climate communicators.
Around 2.4 billion people experienced at least two additional weeks on average per year over the past decade when the thermometer did not fall below 25 degrees C at night, it found.
“Warmer night-time temperatures, particularly during hot times of the year, can harm sleep and can reduce physical recovery from hot daytime temperatures, both of which can have cascading impacts on health outcomes,” Dr Nick Obradovich, a chief scientist at the Laureate Institute for Brain Research, told AFP.
The year 2024 has seen heat records tumble, with extreme temperatures gripping vast swathes of the world from India to Saudi Arabia and Mexico, often staying high at night.
The analysis compared the annual average of hot nights between 2014 and 2023 with a counterfactual world absent of human-caused climate change, based on a peer-reviewed methodology using models that incorporate historical data.
Long-term historical data being patchy or missing for many countries, researchers decided to compare their findings with an imaginary world where the only thing that changed was the amount of carbon in the atmosphere.
The Caribbean nation of Trinidad and Tobago experienced the largest increase of any country, with an extra 47 nights per year above 25 degrees C. The Indian city of Mumbai endured an additional two months of hot nights.
The 25 deg C threshold “isn’t some hard-and-fast number below which health is fine and above which health is harmed”, Dr Obradovich, who was not involved in the analysis, explained.
“Hotter night-time temperatures, on average, are worse for health,” he said, but the impacts on people vary.
But when heat is coupled with high humidity levels, the consequences can turn deadly.
Several studies have shown that nocturnal temperatures above 25 degrees C deteriorate the quality and length of sleep – which is vital for humans to function – and increase the risks of strokes, cardiovascular conditions and mortality.
The elderly and lower-income groups are disproportionally affected, researchers previously found. AFP
