Global Courant
Summers are getting hotter than ever, breaking all records for high temperatures, straining the energy grid and damaging critical infrastructure.
Heat waves are also going to include another increasingly dangerous element: nighttime temperatures which do not cool enough to provide adequate respite from oppressive heat, especially for those without access to air conditioning.
“Most people don’t realize that in recent decades, high nighttime temperatures have outpaced daytime temperature increases in most populated regions around the world,” Kelton Minor, a postdoctoral researcher at Columbia University’s Data Science Institute, told CNN.
Hotter nights are a result of the climate crisis, scientists warn. In most of the United States, nights warm faster than days on average National Climate Report 2018 found it.
“We think it’s because as the days get warmer, there’s more moisture in the air that traps the heat,” said the Medical Society Consortium on Climate and Healths executive director, Lisa Patel, told CNN. “During the day, that moisture reflects the heat, but at night it traps the heat.”
Increasing night heat is even more common in cities due to the urban heat island effectin which metropolitan areas are significantly hotter than their surroundings.
Places with a lot of asphalt, concrete, buildings and highways absorb more solar heat than areas with many parks, rivers and tree-lined streets. At night, when temperatures should cool, the retained heat is released back into the air, said University of Washington climate and health expert Kristie Ebi.
Areas with lots of greenery — with grass and trees that reflect sunlight and create shade — are cooler on the hottest summer days, she said.
“Many cities are putting together cooling shelters, but people need to know where they are, how to get there and what hours they work,” Ebi told CNN, noting that city officials need to rethink city planning to consider climate change.
“Trees will take time to grow, but we need tree-planting programs that target places that are particularly vulnerable, to ensure that urban planning takes into account the fact that we are heading into a much warmer future.”
The night should be when our bodies get a break from the heat, Patel said. But with the climate crisis, it is becoming less and less likely. Heat-related deaths could sixfold by the end of the century due to warmer nighttime temperatures unless planet-warming pollution is significantly curbed, a 2022 study in the Lancet Planetary Health found.
The climate crisis is already affecting people’s ability to sleep, says Minor, co-author of a study that found that people living in warmer climates lose more sleep for every degree of temperature rise. It was published in May in One Earth magazine.
“We all know what it’s like to try to fall asleep on a hot night — it’s uncomfortable,” Patel said. “We often sleep late. It is estimated that by the end of the century we could lose about two days of sleep per year, and it will be even worse for people without access to air conditioning.”
In the most extreme case, when a human body doesn’t get a chance to recover — usually overnight — heat stress can develop into heat stroke, which is accompanied by confusion, dizziness, and fainting, Patel explains.
People around the world are already losing an average of about 44 hours of sleep per year due to warm nighttime temperatures in the early part of the 21st century, Minor’s study estimated. He calls this “sleep erosion,” noting that each person could lose up to 58 hours of sleep by the end of the century.
“People in our study didn’t seem to make up for lost sleep during warmer nights by napping during the day or sleeping more during the days or weeks after,” Minor said. “In fact, they lost extra sleep during these periods due to a delayed temperature effect, possibly due to ambient heat being trapped indoors.”
And as with other social issues, the impact isn’t even across communities, he said.
“For every degree of nighttime temperature increase, we found that elderly people lost more than twice as much sleep as middle-aged adults, women lost slightly more sleep than men, and crucially, residents of low-middle-income countries lost three times as much sleep as adults.” sleep the same amount compared to people living in higher-income countries,” Minor said.
Heat waves that last for several days are often associated with more deaths because the body can no longer keep itself cool, Patel said.
And unless global warming-induced pollution is curbed, the climate crisis will increase exposure to dangerous heat index levels by 50% to 100% in large parts of the tropics and up to 10 times in large parts of the world, according to a Study from 2022 published in Communication Earth & Environment.
“Endurance of a heat wave during the day can be like running a race,” said Patel. “We need a cool break to recover and recuperate, and if nighttime temperatures don’t drop, we don’t get the critical time we need to relieve the stress on our bodies from overheating during the day.”
