Jul 9, 2021 - Science

Nights are warming faster than days in the U.S.

People walking through a fountain at dusk in Hobroken, New Jersey, on June 29.

People walking through a fountain at dusk in Hobroken, New Jersey, on June 29. Photo: Gary Hershorn/Getty Images

Nights on average are heating up faster than days in most parts of the United States — a trend caused by climate change, according to the 2018 National Climate Assessment Report, newly cited by the New York Times.

Why it matters: Last month was the hottest June on record for the U.S., and more than 1,500 areas of the country logged new record-high overnight temperatures toward the end of the month.

Abnormally high nighttime temperatures can increase the risk of heat-related hospitalizations and deaths because prolonged stretches of hot weather prevent people from cooling off from the day’s heat.

  • They can also worsen wildfire conditions because fires typically die down overnight when temperatures dip, the air cools and humidity increases.

What they're saying: “[I]t’s really important that people have an opportunity to bring their core body temperature down,” Kristie Ebi, an environmental health scientist at the University of Washington, told the Times.

  • “When it’s really hot at night, you don’t have that relief and it puts more physiological strain on your body," Ebi added.

How it works: Meteorologists and other scientists believe nights are heating up as temperatures rise throughout the day and the air is able to hold more moisture.

  • They theorize that the increased moisture in the air traps heat close to the ground’s surface, producing warmth that can persist throughout the night.

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