America had some hot nights last month.
The continental United States in July set a record for overnight warmth, providing little relief from the day’s sizzling heat for people, animals, plants and the electric grid, meteorologists said.
In July, the lowest temperature recorded in the Lower 48 States was 63.6° (17.6 Celsius), beating the record of 2011 by only a few hundredths. Karin Gleason (National Oceanic and Atmospheric Administration) said that the July record was not just for the hottest night, but also for any month of 128 years’ worth of records. July’s nighttime low was more than 3 degrees (1.7 Celsius) warmer than the 20th century average.
Scientists have long talked about nighttime temperatures—reflected in increasingly hotter minimum readings that usually occur after sunset and before sunrise—being crucial to health.
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“When you have daytime temperatures that are at or near record high temperatures and you don’t have that recovery overnight with temperatures cooling off, it does place a lot of stress on plants, on animals and on humans,” Gleason said Friday. “It’s a big deal.”
In Texas, where the monthly daytime average high was over 100 degrees (37.8 Celsius) for the first time in July and the electrical grid was stressed, the average nighttime temperature was a still toasty 74.3 degrees (23.5 Celsius)—4 degrees (2.2 Celsius) above the 20th century average.
The average nighttime temperature in the U.S. over the last 30 year has increased by about 2.1 degrees (1.2 Celsius), and the daytime highs have increased by about 1.9 degrees (1 Celsius). Since the 1970s, climate scientists have believed that the warming of the planet from burning coal, oil, and natural gas would cause it to heat faster in northern polar areas and at night. An earlier study found that the Arctic has been warming faster than any other region of the world.
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Gleason explained that nighttime is warmer because the humidity in the air increases with daytime warmth. Then, the moisture traps heat inside at night.
“So it is in theory expected and it’s also something we’re seeing happen in the data,” Gleason said.
NOAA also published its July global temperature data on Friday. It showed it to be the sixth hottest month in recorded history with an average temperature at 61.97°C (16.67°C), 1.57° (0.87°C) above the 20th-century average. There were heat waves throughout the month, with even the United Kingdom surpassing its record for heat.
“Global warming is continuing on pace,” Colorado meteorologist Bob Henson said.
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