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As the climate warms, we can't overlook threat of nighttime heat

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David Boraks
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WFAE
Researchers at Duke University warn that nighttime heat can also be unhealthy.

Climate change has increased the number of hot days nationwide and increased the likelihood of unhealthy extreme heat. As we look for ways to cope, we usually focus on daytime heat. But researchers at Duke University say not enough attention is paid to higher temperatures overnight.

"While extreme heat in the form of daily temperatures is very serious, we're increasingly seeing a strong connection between poor health health outcomes and persistently high overnight temperatures, particularly when those overnight temperatures remain at 75 degrees or above," said Ashley Ward, a public health expert at Duke's Nicholas Institute for Environmental Policy Solutions.

Ward said we've gotten better at taking precautions for daytime heat, whether it's schools rescheduling sports practices or outdoor workers shifting their work schedules.

But high overnight temperatures can be just as harmful, especially for those who don't have access to air conditioning, she said.

"High overnight temperatures mean that those who don't have an air conditioner or can't afford to run their air conditioner or live in less energy-efficient housing are particularly vulnerable," Ward said.

That's especially true for people with health conditions or who take prescription medications for things like diabetes or high blood pressure that can impede the body's ability to process heat, she explained.

"And so when overnight temperatures remain high, what we're seeing is the body doesn't have a chance to recover from any heat exposure during the day, which starts to trigger a cascading set of events that results in heat-related illness, heat stroke, usually over a matter of days," Ward said.

She cited a National Institutes of Health study that found heat-related emergency department visits now cost North Carolinians at least $20 million a year. That doesn't include visits to urgent cares or people who are actually admitted to hospitals.

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Climate Central
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Since 1950, summer equivalent temperature - which combines heat and humidity - has increased three times more than summer air temperature on average across the contiguous U.S.

A majority of these cases are males ages 15 to 45. Health officials also worry about women who are pregnant.

Heat-related illnesses are only increasing as the planet warms, and that's taking an economic toll as well for outdoor workers, said Luke Parsons, who studies climate and air pollution impacts on human health at the Nicholas School.

"As the globe warms, and heat waves get hotter, or let's say more frequent, it gets hotter and more humid outside for these workers who are trying to work outside, and it gets harder and harder for them to safely and efficiently conduct their work," Parsons said.

He and colleagues gathered temperature data from the U.S. and studied its effects on outdoor agriculture and construction workers. They estimated that outdoor workers doing heavy manual labor lose between 50 and 100 hours of work per year.

"This roughly translates to something like a week or two of labor loss. And we're not even in the hottest part of the world, either," Parson said.

"Given how much we know agricultural and construction workers, on average, contribute to the U.S. economy, we can estimate this is something like maybe $20 (billion) to $100 billion of labor productivity losses per year in the U.S., just because people can't as efficiently and effectively do the labor anymore. They have to slow down or take breaks," Parsons said.

Parsons also said some employers and experts are increasingly looking not just at temperatures, but also humidity, the angle of the sun, and cloud cover. This measure is called the "wet bulb globe temperature" and it's another way to help plan workloads so they don't cause heat stress.

Ward and Parsons said knowing more about how heat affects public health and the economy leads to two conclusions: We need to keep up efforts to reduce greenhouse gas emissions that cause global warming and we need to continue developing tactics and policies to adapt to a problem that will only get worse.

This article originally appeared in WFAE's weekly Climate Newsletter, which is published Thursdays.

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David Boraks is a veteran journalist who covers climate change for WFAE. See more at www.wfae.org/climate-news. He also has covered housing and homelessness, energy and the environment, transportation and business.