He noticed the light-headedness first.
Then there was stifling heat, which made everything seem to be moving in slow motion.
And by the time Oscar Rodriguez, a bricklayer from Cypress, Texas, was able to find shelter under an air conditioner during a triple-digit degree day last summer, he realized that he may have just escaped a brush with a serious heat-related illness.
“I felt dizzy and fell on the grass,” said Rodriguez, who is 56 and a native of Mexico. “I was in the sun all day and I was drinking water, but I think it was one of the hottest days. I lost consciousness.”
For those who work outdoors like Rodriguez, an announcement by NASA officials that 2023 was the hottest year on record likely came as little surprise. Nor was the latest data from Texas officials showing that more than 300 people died from excessive heat in 2023, the most since they began counting those deaths in 1989.
In recent years it has become clear that our warming planet has begun to exact a heavy death toll. In 2021, a study found that nearly 40 percent of heat-related fatalities could be linked to climate change.
In 2022, nearly 1,700 people died of heat-related causes—a sharp increase from the roughly 950 deaths in 2018, according to figures from the CDC. And experts say that trend has shown few signs of abating. For those who have consistently followed global temperature changes over the last decade—the hottest on record—it is no surprise that scientists predict 2024 will be even hotter than its predecessor.
Now, spurred by ever-increasing temperatures, many who work at the intersection of health and climate change are placing an increased emphasis on answering questions about the myriad effects of heat on the human body—many of which are not well understood—as well as questions related to the disproportionate toll heat takes on the elderly and people of color.
A Heightened Risk of Death and Illness
A team of researchers from the University of California, Berkeley noted in a paper published in 2022 that there were pronounced racial disparities in climate-change related health effects across the country.
“The recent literature overwhelmingly confirms earlier studies suggesting rising temperatures will lead to higher mortality and illness among adults of color than white adults,” the paper’s authors wrote. “Risk of dying associated with higher temperatures and extreme heat events was elevated among Black, Latinx, and Native American individuals compared to Whites in studies across the USA, with even higher risk among non-U.S. citizens.”
The researchers noted that heat-related illnesses related to global warming are an environmental justice issue that threatens to “exacerbate existing social and economic inequalities and worsen racialized health disparities among both children and adults.”
Alique G. Berberian, the paper’s lead author, noted that many heat-related illnesses among people of color can be traced to jobs that require them to work outside.
“Some of those outcomes were related to occupational exposures,” Berberian said. “Studies show that workers of color might be exposed to higher temperatures because of their workplace, their inability to protect themselves because they’re working outside as farmworkers or as construction workers.”
Some health experts say that they place a particular emphasis on cautioning Black and brown people about protection from extreme heat.
Jerry Abraham, president of the Los Angeles County Medical Association, pushed to remove barriers preventing Black and brown people from getting immunization shots during the COVID-19 vaccine rollout in 2021. But now he worries about another threat: heat.
“Studies show that workers of color might be exposed to higher temperatures because of their workplace, their inability to protect themselves because they’re working outside as farmworkers or as construction workers.”
Last week, the Board of Supervisors for Los Angeles County voted to have staff begin work on a new legal requirement that would establish a maximum allowable temperature in rental units, which could affect about a million county residents.
“Heat affects us in so many different ways depending on humidity within your community, depending on how close you live to a highway or if you live close to a landfill,” said Abraham, who is a family medicine physician at a mobile clinic in South Los Angeles. “We need to make sure that society understands that it”—heat—“has a direct implication on you. Look at the stats. You are at risk. You potentially could be one of the one of 100 that experiences a very severe complication from this exposure.”
Abraham, who is biracial, said he is constantly thinking about his patients and staff who work outdoors, especially members of his community who are people of color.
Abraham said that he suspected long before NASA’s recent announcement that 2023 was a record-breaking year, but his focus is on hurdles that lie ahead, and addressing the “lack of health literacy, medical literacy within our culture.”
“If we can’t interpret these numbers and statistics, if we don’t really understand exposure and disease and the complications and why prevention and public health matters, we’re really starting at an extreme disadvantage that we didn’t need to be—we weren’t prepared for this moment,” added Abraham.
“And that’s where we find ourselves in a perfect storm of heat,” he said.
Understanding “When it Becomes Dangerous”
Scientists have long been aware of the distinctive effects of prolonged heat exposure. While researchers have long warned of the increased risk from heat faced by adults with existing illnesses, a new study has found that healthy older adults are seriously threatened by ever-increasing temperatures, too.
In a peer-reviewed paper published in December in the journal Nature, researchers at Pennsylvania State University found that healthy older adults were more vulnerable to heat compared to younger adults.
“Their core temperature begins to rise at lower combinations of temperature and humidity,” said Rachel Cottle, one of the authors of the study. “So there’s a smaller range of environments that they would be safe in compared to younger adults at the same exercise intensity.”
In an October study published in the Proceedings of the National Academy of Sciences, researchers at Penn State and Purdue Universities used a model to predict future heat stress risk and found that humans are more vulnerable to moist heat stress and that humanity is at risk as heatwaves become more frequent, intense and longer-lasting from climate change.
Humidity is dangerous to the human body. When temperatures and humidity levels are high, sweat dissipates more slowly than usual. As a result, the cooling benefits of perspiration are diminished. And when that occurs, people’s bodies have a difficult time controlling internal temperatures, which can lead to heat stroke and other conditions.
“Heat is the leading type of weather fatality in the United States and one of the largest causes of weather-related deaths worldwide,” researchers wrote in the study. “It increases the risk of both morbidity and mortality in vulnerable groups such as the elderly, children, outdoor workers, and those with comorbidities or those taking medication that causes diminished thermoregulatory capabilities.”
“Heatwaves are associated with increased hospitalization and death for cardiovascular, respiratory, and renal ailments as well as diabetes,” they wrote. “These specific outcomes are not solely due to the body becoming too hot, but rather are compounded by the physiological strain extreme heat puts on the body and the body having to compensate to cool itself. Direct heat-related death (i.e., heat stroke) occurs when the core (internal) temperature of the body becomes too high due to the fact that it no longer has the capability to cool itself and biological functions cease.”
In the lab at Penn State, called the Human Thermoregulation Laboratory run by W. Larry Kenney, a professor at the university who examines environmental and exercise physiology, researchers are running a series of tests on adults ranging in age from 65 to 92 in a controllable environment chamber. Participants in the chamber are sitting at rest or on a recumbent bicycle as the temperature or humidity gradually increases, just like it would in the real world during a heat wave.
Cottle said that researchers are looking for the point where the core temperature of participants continuously rises.
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Donate NowCottle said when study subjects are in the chamber and the temperature and humidity is low enough that they are able to sweat, and that sweat is able to evaporate, it helps their bodies cool. And she said increasing blood flow towards our skin also helps lower core temperature.
“So when those two mechanisms are efficient, and you can lose heat at the same rate that you’re gaining heat from the environment, you have a relatively stable core temperature,” said Cottle.
But when researchers start increasing temperature and humidity to greater values, then the heat stress becomes too much. “So now you’re gaining heat faster than you can lose it,” Cottle said. “That’s what causes your core temperature to rise continuously. That’s when it becomes dangerous.”
Amid Surging Deaths, a Model for Heat Response
The Centers for Disease Control and Prevention warns that exposure to extreme temperatures can lead to heat stroke—when the body’s temperature rises and cannot be cooled down, or heat exhaustion—dizziness, nausea and extreme sweating. Those at particular risk for heat-related illnesses include older people and outdoor workers.
The official count of how many Americans died from a heat-related illness in 2023 has not yet been released by federal authorities, but places like Maricopa County in Arizona, which includes Phoenix, are keeping close watch—and many experts say that their work could be a model for other municipalities around the country.
The county has created a team that monitors temperatures, publishes social media alerts about harmful conditions, and informs residents about cooling centers. Last summer, Phoenix set a record for 31 straight days of temperatures of 110 degrees or more. The city requires landlords to provide sufficient air conditioning to keep all rental units no hotter than 82 degrees.
In 2022, Maricopa County officials said, there were 425 heat-associated deaths in Maricopa—a 25 percent increase from the prior year. Although officials are still compiling the figures for 2023, officials have confirmed at least 600 heat-associated deaths, which would put the county on track for a 30 percent increase, said Rebecca Sunenshine, medical director for the county’s Department of Public Health.
Besides increased temperatures, Sunenshine said, other factors also contribute to extreme heat exposures and related illnesses.
“While the temperature is the primary contributor, there are other things that contribute particularly to heat-related deaths, and that is the rising population of individuals experiencing homelessness,” Sunenshine said. “Difficulty finding housing and energy insecurity. Challenges with paying energy bills, all of those things contribute. And so it really will take a village to improve our heat relief both here and in other states and counties.”
