Summers are getting hotter than ever, shattering all-time high temperature records, straining the energy grid and damaging critical infrastructure.
Heat waves also are coming to include another increasingly dangerous element: that don鈥檛 cool down enough to offer sufficient reprieve from oppressive heat, particularly for people without access to air conditioning.
鈥淢ost people don鈥檛 realize that hot night-time temperatures have been outpacing daytime temperature increases across most populated regions worldwide in recent decades,鈥� Columbia University鈥檚 Data Science Institute postdoctoral research scientist Kelton Minor told CNN.
Hotter nights are a consequence of the climate crisis, scientists have warned. On average, nights are warming faster than days in most of the United States, the found.
鈥淲e think it鈥檚 because as the days grow warmer, there is more moisture in the air that traps the heat,鈥� the executive director, Lisa Patel, told CNN. 鈥淒uring the day, that moisture reflects the heat, but at night, it traps the heat in.鈥�
Increasing night-time heat is even more common in cities because of the , in which metro areas are significantly hotter than their surroundings.
Places with a lot of asphalt, concrete, buildings and freeways absorb more of the sun鈥檚 heat than areas with ample parks, rivers and tree-lined streets. At night, when temperatures are supposed to cool down, the retained heat is released back into the air, said University of Washington climate and health expert Kristie Ebi.
Areas with a lot of green space 鈥� with grass and trees that reflect sunlight and create shade 鈥� are cooler on summer鈥檚 hottest days, she said.
鈥淢any cities put together cooling shelters, but people have to know where they are, how to get to them and what hours they operate,鈥� Ebi told CNN, noting city officials must rethink urban planning to consider climate change.
鈥淚t鈥檚 going to take a while for trees to grow, but we need tree-planting programs focusing on places that are particularly vulnerable, making sure that city planning takes into account that we鈥檙e heading into a much warmer future.鈥�
Night-time should be when our bodies get a break from the heat, Patel said. But with the climate crisis, it鈥檚 becoming less likely to happen. Heat-related deaths couldby the end of the century due to warmer night-time temperatures, unless planet-warming pollution is significantly curbed, a 2022 study in the Lancet Planetary Health found.
The climate crisis is already affecting people鈥檚 ability to sleep, said Minor, co-author of a that found people living in warmer climates lose more sleep for each degree of temperature increase. It was published in May in the journal One Earth.
鈥淲e all know what it鈥檚 like to try to fall asleep on a hot night 鈥� it鈥檚 uncomfortable,鈥� Patel said. 鈥淲e often lose sleep. It is estimated that by the end of the century, we could lose about two days of sleep per year, and it will be worse for people without access to air conditioning.鈥�
At its most extreme, when a human body does not get the chance to recover 鈥� typically at night 鈥� heat stress can progress to heat stroke, which is associated with confusion, dizziness and passing out, Patel explained.
People around the world are already losing roughly 44 hours of sleep every year on average due to warm night-time temperatures during just the first part of the 21st century, Minor鈥檚 study estimated. He calls this 鈥渟leep erosion,鈥� noting each person may lose up to 58 hours of sleep by the end of the century.
鈥淧eople in our study did not appear to make up for lost sleep on hotter nights by napping during the day or by sleeping more during the days or weeks after,鈥� Minor said. 鈥淚n fact, they lost additional sleep over these periods due to a delayed temperature effect, possibly due to ambient heat being trapped indoors.鈥�
And much like other social issues, the impacts don鈥檛 fall equally across communities, he said.
鈥淔or every degree of night-time temperature rise, we found that the elderly lost over twice as much sleep as middle-aged adults, females lost slightly more sleep than males, and critically, residents of lower-middle-income countries lost three times as much sleep compared to people living in higher income countries,鈥� Minor said.
Heat waves that go on for several days tend to be associated with more deaths as the body can no longer keep itself cool, Patel said.
And unless planet-warming pollution is curbed, the climate crisis is set to increase exposure to dangerous heat index levels by 50% to 100% in much of the tropics and by up to 10 times across much of the globe, according to a published in Communications Earth & Environment.
鈥淟iving through a heat wave during the day can be like running a race,鈥� Patel said. 鈥淲e need a cool break to recover and recuperate, and when night-time temperatures don鈥檛 drop, we don鈥檛 get that critical time we need to relieve the stress on our bodies from being overheated during the day.鈥�
