Hot nights: USA in July sets new overnight heat record

Speaking of hot nights, America had some for the history books last month.

The continental United States set an overnight heat record in July, offering little relief from the daytime scorching heat for people, animals, plants and the power grid, meteorologists said.

The average low temperature for the lower 48 states in July was 63.6 degrees (17.6 degrees Celsius), which beat the previous record set in 2011 by a few hundredths of a degree. The mark is not just the hottest overnight average for July, but for any month in 128 years of record keeping, said National Oceanic and Atmospheric Administration climatologist Karin Gleason. July’s overnight low was more than 3 degrees (1.7 Celsius) higher than the 20th century average.

Scientists have long talked about nighttime temperatures – reflected by increasingly warm minimum readings that typically occur after sunset and before sunrise – being crucial for health.

“When you have daytime temperatures that are at or near record highs and you don’t have that overnight recovery with temperatures getting colder, that puts a lot of stress on plants, animals and humans,” Gleason said Friday. “It’s a big problem.”

In Texas, where the daily high monthly average was above 100 degrees (37.8 degrees Celsius) for the first time in July and the power grid was live, the average nighttime temperature was still 74.3 degrees ( 23.5 degrees Celsius) – 4 degrees (2.2 degrees Celsius). ) above the 20th century average.

Over the past 30 years, the nighttime low in the United States has warmed by an average of about 2.1 degrees (1.2 Celsius), while daytime high temperatures have increased by 1.9 degrees (1. 1 Celsius) at the same time. For decades, climatologists have said that global warming from burning coal, oil and natural gas will make the world warmer at night and in the northern polar regions. A study earlier this week found that the Arctic is now warming four times faster than the rest of the globe.

Nighttime heats up faster because the daytime warming allows the air to hold more moisture than that moisture helps trap heat at night, Gleason said.

“So it’s theoretically expected and it’s also something we see happening in the data,” Gleason said.

NOAA also released its global temperature data for July on Friday, showing it was on average the sixth warmest month on record with an average temperature of 61.97 degrees (16.67 degrees Celsius), or 1.57 degrees (0.87 degrees Celsius) higher than in the 20th century. medium. It was a month of heatwaves, with the UK notably breaking its all-time heat record.

“Global warming continues,” said Colorado meteorologist Bob Henson.


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