Heat Deaths Jump in Southwest United States, Puzzling Officials

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WASHINGTON — Heat-related deaths have increased sharply since 2014 in Nevada and Arizona, raising concerns that the hottest parts of the country are struggling to protect their most vulnerable residents from global warming.

In Arizona, the annual number of deaths attributed to heat exposure more than tripled, from 76 deaths in 2014 to 235 in 2017, according to figures obtained from the U.S. Centers for Disease Control and Prevention. Heat-related deaths in Nevada rose almost fivefold during the same period, from 29 to 139.

Most of those deaths were in the Phoenix and Las Vegas areas, according to state records.

The long-term health effects of rising temperatures and heat waves are expected to be one of the most dangerous consequences of climate change, causing “tens of thousands of additional premature deaths per year across the United States by the end of this century,” according to the federal government’s Global Change Research Program. The effect could be even more severe in other parts of the world, potentially making parts of North Africa and the Middle East “uninhabitable.”

Still, the fact that deaths have already increased so rapidly in Nevada and Arizona is surprising, according to David Hondula, a professor at the School of Geographical Sciences and Urban Planning at Arizona State University. He said heat deaths have generally been declining in the United States, thanks to changes like better health care, more air-conditioning and improved weather forecasting.

The latest data — which the C.D.C. has compiled for all 50 states — suggests that climate change could be starting to outweigh those advances in the Southwest, at least for some parts of the population. Other states haven’t yet shown such significant spikes, but Dr. Hondula warned they might eventually see more deaths as temperatures keep rising.

“Phoenix and other cities of the Southwest are the canary in the coal mine,” Dr. Hondula said. “We really need to figure out what piece or pieces of the system are lacking.”

Afternoon highs in Phoenix last summer averaged 106 degrees Fahrenheit, almost 3 degrees hotter than the average for the second half of the 20th century, according to data from the National Oceanic and Atmospheric Administration. Las Vegas recorded its hottest summer to date, with average daily highs reaching 105 degrees, more than 5 degrees above the 1950-2000 mean.

Nighttime lows have warmed up, too, giving residents less chance to recover from the heat.

Nights Are Warming Faster Than Days. Here’s Why That’s Dangerous.

Nationwide, summer evening temperatures have risen at nearly twice the rate of daytime temperatures, putting older people, the sick, and young children at greater risk during heatwaves.

“There’s only so much our bodies can take,” said Rupa Basu, chief of the air and climate epidemiological section for the Office of Environmental Health Hazard Assessment in California, where the number of heat-related deaths doubled between 2015 and 2017. As heat waves become more severe, she said, “I think we’re going beyond that temperature threshold.”

The increase in deaths also illustrates how climate change can exacerbate other challenges. Experts say the death toll is likely to reflect the growing ranks of vulnerable groups, and the failure to protect those groups from global warming.

A particularly vulnerable group, experts say, are the homeless, especially in Maricopa County, which includes Phoenix. “The unsheltered homeless population in Maricopa County has risen every year by about 25 percent since 2014,” said Lisa Glow, chief executive officer of Central Arizona Shelter Services. “We have been turning away hundreds monthly who need shelter.”

She said that reflects rising housing costs as the county’s population grows, as well as a reduction in the number of emergency shelter beds.

As Phoenix Heats Up, the Night Comes Alive

In one of the hottest and fastest-warming American cities, residents adapt their summer schedules to find times when temperatures are more tolerable.

Data compiled by the county’s public health department show that the homeless represent a fast-growing share of heat deaths. In 2014, the county recorded seven homeless people who had died from heat-related causes. By last year, that number had increased to 61 deaths, more than one-third of the total.

Cara Christ, director of Arizona’s Department of Health Services, said she didn’t know why heat-related deaths were rising. She said her office had been focusing on increasing public awareness about the risks of extreme heat. “We take this issue very seriously,” she said.

In Nevada, public health officials were similarly unable to explain the jump in deaths. “We’re trying to figure out what it is that needs to be done,” said Rebecca Cruz-Nanez, a health educator with the Southern Nevada Health District’s Office of Epidemiology and Disease Surveillance.

Data suggest the number of homeless people in Las Vegas has fallen since 2014. A better explanation for the increase in heat-related deaths may be the rising number of older residents, according to Erick Bandala, a professor of environmental science at the Desert Research Institute in Las Vegas.

Not only are older adults more susceptible to the physical effects of heat, they’re also more likely to live alone with no one to check on them.

In a paper published this year, Dr. Bandala examined the ages of all 437 people who were determined to have died from heat-related causes in Clark County, which includes Las Vegas, between 2007 and 2016. He found that 76 percent of those who had died were older than 50.

“I would put my money on the increase of retirees coming to live in town in the last eight to 10 years,” Dr. Bandala said, but added that more demographic information is still needed.

Others worried that the problem might be worse than it seems. “Heat-related deaths are just very underreported,” said Dr. Basu, the California official, because coroners often mark a death as heat-related only if no other cause of death is suspected. But that can miss cases in which heat contributed to a death from another cause.

What’s clear so far is that governments need to do a better job protecting people from extreme heat before conditions get worse. “Our strategies are insufficient for the current climate,” Dr. Hondula said, “let alone what might be coming.”

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