In the Heat of the Night

Hot nights lead to lots of hospitalizations. There are ways to keep your cool

- LYDIA DENWORTH

IF THE SUMMER OF 2025 is anything like last year's, get ready to sweat. July and August of 2024 were among the hottest months on record in the U.S. Phoenix, Ariz., saw daytime temperatures higher than 100 degrees Fahrenheit for more than 100 days. But now temperatures are staying high at night, too, which increases health dangers. When it stays hot after the sun goes down, more people die than typically would. Emergency room visits and hospital admissions go up. Premature births increase. Sleep and mental health suffer. But there are simple and practical methods you can use to stay cooler and healthier, beyond cranking up your expensive air conditioner.

“Most heat exposure is chronic,” says Ashley Ward, director of the Heat Policy Innovation Hub at Duke University’s Nicholas Institute. She and others are increasingly focused on the cumulative effect of warmer nights following warmer days. Nighttime temperatures are rising twice as fast as daytime temperatures because increasing cloud cover at night, created by the greenhouse effect, traps heat and sends it back to the ground. In parts of the Southeast, for example, there are now more than 30 days a year when the temperature stays above 75 degrees F at night, Ward says. Urban heat islands, which are parts of cities with lots of concrete and few shade trees, trap warmth and add to the effect, but rural areas are also suffering.