Americans most at risk from more frequent and intense heat waves tend to misjudge the deadly dangers hot spells can pose to their health, scientists said on Tuesday.

People’s vulnerability to heat waves is growing as cooler states become hotter, in part because air conditioning and other ways to cool down are less common there, according to a study in the Proceedings of the National Academy of Sciences of the United States of America.

Right now, people in cooler areas “don’t experience hotter weather as frequently,” said co-author Peter Howe from Utah State University. That means “they have less of that experience… to handle those hot days.”

Global temperatures are on course for a 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) rise this century, overshooting a global target of limiting the increase to 2C (3.6F) or less, the U.N. World Meteorological Organization has said.

In the United States, hot years are projected to soon become more common as annual average temperatures — already a degree higher than in 1901 — continue to rise, according to the National Climate Assessment, a U.S. government report.

After surveying more than 9,000 people in all 50 states, researchers carrying out the heat wave study discovered that people in northern states, including in the northern Midwest, had fewer health concerns about extreme heat than those living in the country’s south.

Residents of the normally temperate Rocky Mountains and Appalachians were among the least concerned by extreme heat, the study said, while those in sweltering Hawaii, Texas and Louisiana were most worried.

But previous research has shown that as climate change pushes temperatures up, residents of the northeastern United States and those living in high elevations are at particularly high risk of heat-related complications, the researchers said.

That’s because they often lack air conditioning and other means of combatting extreme heat, and are less acclimatized to potentially dangerous temperatures.

Heat can exacerbate existing health conditions and contribute to heat strokes, dehydration and heat exhaustion, Howe said.

Elderly people also were often oblivious to the risks of extreme heat to their health, even though they constitute one of the highest risk groups, the findings showed.

“People generally, if they are older, they don’t consider themselves to be elderly,” he said — and so don’t see themselves as particularly at risk.

Heat in 2017 killed more people than any other weather-related disaster except floods, according to the National Weather Service. Over the last 30 years heat has been the biggest cause of weather-related deaths.

A 2014 study published in the journal Environmental Health Perspectives said a 5 degree Fahrenheit increase in average temperature would lead an extra 1,900 deaths per summer across 105 U.S. cities.
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