As Climate Hazards Converge, Health Risks Increase in California

State health officials know that extreme heat can cost lives and send people to the hospital, as can smoke from wildfires. Now, new research finds that when people are exposed to both dangers simultaneously (as is increasingly the case in California), cardiac and respiratory crises exceed the expected sum of hospitalizations compared to when the conditions occur separately.

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In a study published Friday in the journal Science Advances, researchers determined that wildfire smoke and extreme heat together create a previously unrecognized “synergistic effect,” or additional burden on people's health, increasing the risk of hospitalization for cardiorespiratory causes by 7%.

The researchers also concluded that this excess harm is disproportionately borne by the most vulnerable Californians and falls more heavily in areas with lower incomes, denser housing, and less access to health insurance than in wealthier regions.

“This additional burden is not random,” said Tarik Benmarhnia, study author and climate change epidemiologist at the Scripps Institution of Oceanography at the University of California, San Diego. “This is concentrated in very, very specific communities, and these communities are systematically less advantaged, with fewer resources, and with more racial and ethnic minorities.”

Researchers from Scripps and the UCLA Fielding School of Public Health reached these conclusions after examining satellite images of wildfire smoke, temperature records, hospital admissions and demographic data from 2006 to 2019 for nearly 1,000 ZIP codes across California, a sample that covers two thirds of the state's population.

The areas that experienced the greatest exposure to heat and smoke were the state's northern mountains and the Central Valley, and included swaths of Siskiyou, Shasta, Fresno and Kern counties, the study authors found.

Map of California showing areas of low to high health risk by ZIP code due to exposure to heat and smoke from wildfires.

The findings have troubling implications for a state already struggling to adapt to a changing climate. Global temperature changes Driven by fossil fuel emissions, they are causing days of more extreme heat as well as drier conditions that intensify the risk of wildfires in California, according to the study.

An orange haze of smoke settles over a pontoon marina.

Both outcomes can be deadly, with an estimated 360,000 global deaths attributed to high temperatures in 2019, and up to 680,000 global deaths annually attributed to fine particles from wildfire smoke.

But the chances of hospitalization are higher when there is heat and smoke, said Noam Rosenthal, who worked on the study as part of his doctoral research at UCLA. “The relative risk increases for both so that the probability is greater than the sum of its parts.”

A lone figure paddleboards on a smoke-covered lake.

The study highlights the need for a more collaborative response to such challenges, or even a fundamental rethinking of public policies. For example, the National Weather Service typically issues heat advisories, while local air quality districts issue smoke advisories, resulting in isolated information that does not always convey the full extent of the risk.

“There is some discrepancy between local hazards as we know them, and how they impact people, and how they are classified by the state and federal government,” said Marta Segura, heating director for the city of Los Angeles.

The risk is only expected to increase in California and the West, where both wildfires and heat waves have increased in duration, intensity and geographic area in recent years. During the 2020 wildfire season, the state's worst on record, about 68% of California was exposed to both extreme heat and smoke particles at the same time, according to the study.

It found that communities most at risk include those with lower incomes, lower health insurance coverage, lower levels of education, lower proportions of car ownership, lower tree canopy cover, higher population density, and higher proportions of racial and ethnic minorities. ethnic.

The reasons for this are myriad: many of these populations often have underlying health problems, such as cardiovascular disease and diabetes, which can be exacerbated by heat and smoke. Lifestyle and behavioral factors, such as the need to commute to work or work outdoors, can also worsen your exposure.

Similarly, the built environment can contribute to this baseline through existing air pollution problems or housing features that allow for increased infiltration of heat and smoke. These problems already affect places like the Central Valley, which suffers from some of the worst air quality in the country, among other climate hazards.

But historical discrimination and structural racism have also played a role, leaving many of these communities less able to adapt, according to the study.

“Many of these minority populations reside in these communities because of racism,” said Karen Lincoln, a UC Irvine social scientist and director of the UCI Environmental Health Disparities Research Center in Public Health Program, who was not involved in the study. study. .

“It is not random that low-income, Black, Brown, Indigenous, some Asian and migrant populations are located in these areas,” Lincoln said. “The reason is that these areas had already been considered unhealthy, dangerous and uninhabitable.”

The study adds to a growing body of research on the intersection of different climate risks. Last month, the California-based think tank Pacific Institute released a report on how converging hazards — including wildfires, droughts, floods, sea level rise and increasingly intense storms — are harming access to the drinking water and sanitation in California and other parts of the world. . The deadly 2018 Camp Fire in Butte County affected approximately 2,438 private wells, according to the report.

These intersections only add to “the many layers of complexity that climate change really brings,” said Morgan Shimabuku, a senior researcher at the Pacific Institute.

Although the latest paper focused on heat and smoke from wildfires, other researchers said they would expect a similar amplifying effect between heat and air pollution from other sources, such as traffic, diesel trucks, industry and oil refineries.

“It's not a phenomenon unique to wildfire smoke,” said Rima Habre, associate professor of environmental health and space sciences at USC.

Rosenthal said researchers decided to focus on the intersection of heat and smoke because of their apparent correlation. Previous studies have shown that wildfires and extreme heat occur simultaneously with high frequency, and that people's physiological responses to hazards are related, she said.

In addition to recommending better alert systems, Rosenthal said the study highlights the need for stricter regulations. The California Division of Occupational Safety and Health requires heat protections for outdoor workers, but has no such protections for indoor workers. The agency has some guidelines on wildfire smoke, but none on the combination of smoke and heat.

In Los Angeles, officials are now in the process of developing a vulnerability map to identify communities most at risk from the effects of extreme heat and an altered climate, so that interventions and investments can be targeted to the areas most in need, according to Segura, who is also the city's director of Climate Emergency Mobilization.

Cracked and faded paint covers a traffic sign.

Meanwhile, officials at the state and county level are pushing for indoor cooling standards in residential units. The Los Angeles County Board of Supervisors recently directed its staff to draft an ordinance that would set a maximum indoor temperature for rental units, with a potential limit of around 82 degrees.

The move could make a significant difference, as the study found lower impacts from both extreme heat and wildfire smoke in areas with a higher prevalence of air conditioners.

“If we do it right as a city, we will be able to tell the state and federal government precisely what we need on a more granular level,” Segura said. “And we hope they listen to us.”

Scripps' Benmarhnia said he was not aware of any state or nation that has yet implemented the type of joint task force or comprehensive hazard warning system the study calls for. But while those efforts are important, he added that it's equally important to focus first on the communities that are most at risk.

“We need to prioritize these communities, because we are not all the same,” he said.

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