Phoenix is one of the hottest cities in the United States, but this month has been particularly intense: The area has seen temperatures higher than 110 Fahrenheit (43 Celsius) for several days in a row, and, even more concerning, it’s broken an overnight heat record of 90 degrees F (32 degrees C). This was the first time it was so hot at night so early in the season, the Guardian reported. That sweltering night beat the previous record for June 10 nighttime temperatures by 5 degrees F.
Both the U.S. and Europe are suffering heat waves right now, with temperatures soaring past 100 degrees in several Spanish and French cities, while dangerous temperatures are now affecting almost a third of Americans.
But while sweltering daytime temps can easily lead to deadly heat exhaustion and heat stroke, it’s the temperature at night that can have an even bigger impact.
Heat waves are silent killers, and nighttime is supposed to be a buffer from them. But when there is no respite from the heat, it not only leads to sleep deprivation and extra misery; it also means the body doesn’t get any relief before the next day’s highs. If the heat accumulated in a home or an area during the day isn’t offset with cooler night temperatures, the heat can compound, especially in dense cities that experience the heat island effect. This could make anyone sick, but chronically ill people and those without decent access to air conditioning are especially vulnerable to dehydration and heat stress.
Nighttime temperatures have risen quicker than already stifling daytime temperatures, according to the EPA. It’s an especially serious concern in Phoenix, despite the fact that the desert city is accustomed to heat. The county medical examiner is investigating 30 heat-related deaths going back in April. That’s 60% more heat deaths compared to the same time last year, the Guardian reported.
Overnight heat also screws up our ability to get a decent night’s rest. A study published last month found that, since 2010, people around the world have lost an average of more than 40 hours of sleep per year because of climate-change related elevated temperatures. Poorer countries and poorer communities are especially feeling the strain of this.
Too much heat is also related to a spike in mental health-related emergencies, a study published this past February showed. Researchers found that people who are already stressed and struggling with their mental wellness could unfortunately be tipped over the edge by uncomfortable temperatures.
The heatwave is still sweeping through the Southwest, and the National Weather Service has issued excessive heat warnings for several areas, including western Arizona. Other cities are feeling the brunt of this wave, too. Temperatures have reached a record-breaking 97 degrees Fahrenheit in Columbus, Ohio, triggering power outages in the area, Axios reported. Austin and San Antonio are both baking under 105-degree heat, and it’s only about a degree or two cooler in the shade, according to Houston Public Media. Nashville broke its June 14 record with 97 degrees Fahrenheit just yesterday, and the city is expected to continue seeing temperatures in the high 90s until the weekend.
People across the region have been warned to stay indoors as much as possible and to drink more water than usual to offset heat stress.