Sunset at Scripps Pier - La Jolla, California
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How Hotter Nights Hurt Your Health

Nicole Gregory

It's not your imagination: Even nighttime is warmer now. A San Francisco State professor explains how the rise in temperature could affect us.

Sunset at Scripps Pier - La Jolla, California

Between 2000 and 2011, 622 Californians died as a result of excessive heat, according to the California Environmental Health Tracking Program. From 2000 to 2012, nearly 7,000 residents were hospitalized because of heat. 


After this summer's recording-breaking heat118°F in Riverside, 109°F in Long Beach, 114°F in Burbankand massive wildfires, California residents are definitely ready for the cooler temperatures of autumn.

But more than just keeping us comfortable, cool temperatures are critical to our health, says Lara Cushing, Ph.D., assistant professor of environmental epidemiology in the department of health education at San Francisco State University. (Environmental epidemiology is the study the environmental determinants of health in populations, such as pollution and climate change.)

And though daytime temperatures have been on the rise, nighttime temperatures are increasing even faster, according to a recent article in Scientific American—and this has health consequences.

"From studying extreme heat events, we know that health effects are worse if heat persists overnight," says Dr. Cushing. "The body tries to maintain a relatively constant temperature within a range, and being exposed to heat for prolonged periods makes that difficult." 

She explains that continued days of high temperatures can cause heat stress, heat exhaustion and heat stroke. "Cool temperatures at night give the body a little respite," she says.

Without that break, people suffer. "We worry about night temperatures during heat waves because we see a rise in deaths as well as hospital admissions for types of conditions sensitive to heat," she says. "Anyone healthy or sick can be vulnerable to heat stress during an extreme heat event. People with certain preexisting illnesses such as a heart condition or kidney issues are even more vulnerable. And the elderly who live alone and pregnant women are vulnerable—their thermoregulatory systems are often not as able to cool the body."

Heat accounts for more U.S. fatalities than any other type of weather-related hazard, according to the National Weather Service."

People who work or live outside, such as farm workers, athletes and the homeless, are particularly at risk when temperatures spike. 

"Interestingly, several studies show that African Americans also fair worse during extreme heat events," Cushing notes. "We don't know exactly why; one factor may be housing and lack of access to air conditioning." 

Her research has shown that people of color also live in neighborhoods that are less green, "meaning there are fewer trees and more heat-trapping surfaces like cement and asphalt that can contribute to hotter microclimates," she explains.

Will temperatures this fall disappoint those of us craving cool weather? Possibly.

A recent study reported in Nature magazine predicts that 2018–2022 will be a warmer-than-normal period, with an increased likelihood of intense to extreme temperatures. 

Reversing the trend requires action. "As individuals we can reduce our carbon footprint," says Cushing, "but ultimately we need to act as a whole and let people in power know that climate change is important. California has some ambitious climate goals, but California can't change the climate on its own—we need a coordinated international effort, and right now the U.S. is hindering that effort." 

To learn more about the CSU's commitment to sustainability and the work we're doing, read "Sustainability in the California State  University" (PDF)