Aging Americans face deadly risk due to wide temperature swings, study warns

People over age 65 face a higher risk of dying when exposed to temperatures that swing far outside the seasonal average, findings that underscore an “urgent” need to mitigate climate change, according to new research.

The study, published this month in Environmental Health Perspectives, examined how seasonal variations in temperature impacted mortality rates among older Americans. The authors include researchers from the Harvard T.H. Chan School of Public Health, and the Emory Rollins School of Public Health.

The study concludes that the modulated temperature variability that is accompanying a changing climate “must be considered as a considerable threat to life” for people over 65 years old.

Specifically, the study determined that for every 1°C increase in temperature variability, the annual death rate increased by 1.54% in the warmer half of the year and by 0.69% in the cooler half, based on an analysis of government data on more than 72 million Medicare recipients from 2000 to 2016.

As the climate crisis grows, the world is observing more extreme temperatures, though they come with “a lot more variability and nuance,” said James Healy, a climate change epidemiologist and a lead author of the study. “That nuance, while not seeming immediately life-threatening, still has these pronounced health effects and is killing older Americans.”

A “real health risk”

Older people tend to be less able to cope with large temperature fluctuations due to physiological changes in core body temperatures that come with the aging process. Even relatively healthy older adults have a reduced ability to sweat and sense heat. Exposure to an unusual temperature, such as an 80-degree day in early spring in the Northeast, for instance, can lead to a stroke or other health impairments.

“This is a real health risk, and it’s actively shortening the lifespans of [older] Americans all over the country,” Healy said. He believes government and public health agencies must do a better job of communicating the risk posed by highly variable temperatures, not just with heatwaves in summer but year-round.

“We need nursing homes to understand that older residents cannot go outside in full winter clothes if it’s 70 or 80 degrees out, even if it’s a fairly nice day in spring,” Healy said.

While summer heatwaves like the one currently baking large swaths of the US tend to grab attention and media headlines, the public health researchers authoring the new study say that this focus risks overlooking the dangers of longer-term or seasonal swings in temperature.

“Fixating on heat waves misses an important part of the problem. Providing cooling shelters for a few days of heat waves will not ameliorate the effects of summers (or winters) where the temperature fluctuates a lot,” said Joel Schwartz, a professor of environmental epidemiology at the Harvard TH Chan School of Public Health.

He explained that temperature variability is more difficult to adapt to, both behaviorally and physiologically, and therefore this variability “is more important than temperature itself.”

Katrin Burkhart, assistant professor at the Institute of Health Metrics and Evaluation at the University of Washington, said the study “indicates that we need to go beyond absolute temperatures and consider variability as well,” and that this is where most adaptation efforts fall short.

“That makes [climate] mitigation more urgent,” Schwartz said.

Rupert Stuart-Smith, research associate in climate science and the law at the University of Oxford’s Sustainable Law Programme, agreed.

“Studies that demonstrate the humanitarian consequences of climate change play a crucial role in demonstrating the urgent action required if we are to prevent the human rights impacts of climate change from worsening,” he said.

More research needed

Climate change, driven primarily by the burning of fossil fuels, is not only warming the planet but also generating more volatile and extreme weather events, scientists say. Still, there are complexities in temperature variability and it remains understudied in the context of climate change.

“Different regions over the globe respond differently to climate change, and their response is also different between seasons,” said Talia Tamarin-Brodsky, a climate scientist at the Massachusetts Institute of Technology who has studied temperature variability changes in the Northern hemisphere.  

She said Northern hemisphere winters are likely to see a reduction in temperature variability, but regions like Europe might see an increase in fluctuating temperatures during summers.

Regardless of the seasonal nuances, Healy said, it is important to be aware of varying temperatures all year round.

“If there is an unusual temperature no matter what month it is, people have to act accordingly,” he said.

While Healy acknowledges a need for more research into temperature variability, including studies examining how it may be attributable to climate change, he said it is clear that this variability “is going to be around in some form or another.”